Skip to main content
NCBI home page
NIHPA Author Manuscripts logoLink to NIHPA Author Manuscripts
. Author manuscript; available in PMC: 2021 Jan 23.
Published in final edited form as: Adv Synth Catal. 2019 Nov 19;362(2):404–416. doi: 10.1002/adsc.201901289

Pyridine(diimine) Iron Diene Complexes Relevant to Catalytic [2+2]-Cycloaddition Reactions

C Rose Kennedy a, Hongyu Zhong a, Matthew V Joannou a, Paul J Chirik a,*
PMCID: PMC7236768  NIHMSID: NIHMS1061032  PMID: 32431586

Abstract

The synthesis, characterization, and catalytic activity of pyridine(diimine) iron piperylene and isoprene complexes are described. These diene complexes are competent precatalysts for (i) the selective cross-[2+2]-cycloaddition of butadiene or (E)-piperylene with ethylene and α-olefins and (ii) the 1,4-hydrovinylation of isoprene with ethylene. In the former case, kinetic analysis implicates the diamagnetic η4-piperylene complex as the resting state prior to rate-determining oxidative cyclization. Variable temperature 1H NMR and EXSY experiments established that diene exchange from the diamagnetic, 18e− complexes occurs rapidly in solution at ambient temperature through a dissociative mechanism. The solid-state structure of (Me(Et)PDI)Fe(η4-piperylene) (Me(Et)PDI = 2,6-(2,6-Me2-C6H3N═CEt)2C5H3N), was determined by single-crystal X-ray diffraction and confirmed the s-trans coordination of the monosubstituted 1,3-diene. Possible relationships between ligand-controlled diene coordination geometry, metallacycle denticity, and chemoselectivity of iron-mediated cycloaddition reactions are discussed.

Keywords: cycloaddition, diene ligands, iron, metallacycles

Graphical Abstract

graphic file with name nihms-1061032-f0001.jpg

Introduction

Olefins are among the most versatile and widely used building blocks for the syntheses of both small molecules and polymers.[1–3] Conjugated dienes are particularly valuable as they offer multiple sites for elaboration through either 1,2- or 1,4-functionalizations and cycloadditions.[4] Furthermore, many conjugated dienes are readily available as petrochemical or biomass-derived feedstocks.[1,4–6] Transition metal catalysis has proven to be enabling for selective transformations of 1,3-dienes,[7–12] and metal complexes of 1,3-diene substrates are frequently implicated as catalytic intermediates.[8–13] While significant structural work has enabled the detailed characterization of diene complexes of both early transition metals and noble metals,[13–16] less is known about diene complexes with the late 3d elements (e.g. Fe, Co, Ni, Cu) that are increasingly applied for catalysis.[17]

Functionalized cyclobutanes are valuable, conformationally constrained molecules and important building blocks in the synthesis of natural products and industrially relevant small molecules including pharmaceutical candidates.[18] In 2011, our research group reported that reduced iron complexes supported by pyridine-2,6-diimine (PDI) ligands catalyze the cross-selective [2+2]-cycloaddition of butadiene and ethylene (Scheme 1A).[17g] Diene and metallacyclopentane complexes ([(MePDI)Fe(η4-butadiene)] and [(MePDI)Fe(η1,η3-C6H10)] where MePDI = 2,6-(2,6-Me2-C6H3N═CMe)2C5H3N) were isolated, characterized, and implicated as catalytically relevant species.[17g,h] Notably, the butadiene complex exhibited an s-trans coordination geometry, in contrast to the more commonly observed s-cis configuration.[13–17,19] Exposure of isoprene and ethylene to the conditions identified for butadiene–ethylene [2+2]-cycloaddition instead resulted in diene hydrovinylation (Scheme 1B); however, subsequent modification of the iron precatalyst enabled cross-selective [2+2]-cycloaddition of numerous 2-substituted-1,3-dienes and α-olefins to generate value-added 1,3-disubstituted cyclobutanes.[20] Nonetheless, the effects of substrate modifications on catalyst speciation and diene coordination, along with their relationship to reaction chemoselectivity, remained unknown.

Scheme 1.

Scheme 1.

Open in a new tab

Substrate-dependent (PDI)Fe-catalyzed cross-reactions between 1,3-dienes and ethylene. [a] Ref. 17g

Here we describe the synthesis, dynamics, and reactivity of a family of [(PDI)Fe] complexes of isoprene and (E)-piperylene (Scheme 1C). The piperylene complex (MePDI)Fe(η4-piperylene) was identified as the catalyst resting state in cross-[2+2]-cycloadditions between (E)-piperylene and various α-olefins. The combination of X-ray crystallographic data, NMR experiments, and kinetic measurements suggest that both (MePDI)Fe(η4-piperylene) and the coordinatively saturated complexes isolated previously[17g] are off-cycle species. These findings highlight the interplay of ligand and substrate substituent effects in accessing the metallacyclopentane intermediate required for productive [2+2]-cycloaddition.

Results and Discussion

Our studies commenced with re-examination of the effects of diene substitution on the selectivity of non-canonical cycloaddition reactions catalyzed by [(MePDI)Fe(N2)]2(μ2-N2). As reported previously, [17g] exposure of a benzene-d6 solution containing an equimolar mixture of ethylene and isoprene to the iron precatalyst afforded exclusively hydrovinylation product 5 (Scheme 1B, top). By contrast, exposure of an equimolar ratio of ethylene and (E)-piperylene (either as the pure (E) isomer or as a mixture with (Z)-piperylene and cyclopentene) to the same reaction conditions resulted in clean conversion to propenylcyclobutane (6) in 89% yield (Scheme 1B, bottom).[21,22] Similarly high chemoselectivity for cross-[2+2]-cycloaddition was observed for an array of α-olefin coupling partners, albeit with low diastereoselectivity (Scheme 2). These results highlighted that the specialized ligand identified for [2+2]-cycloadditions with 2-substituted-1,3-dienes[20,23] is not necessary to achieve high selectivities with the feedstock 4-substituted-1,3-diene, piperylene. This finding is attractive due to the straightforward, single-step preparation of MePDI from commercial materials. Moreover, the differences in the reaction outcomes observed with isoprene and piperylene indicate a non-obvious interplay between substrate and ligand substitution patterns and highlight opportunities to learn about the potential roles of the corresponding iron diene and iron metallacycle complexes in determining reaction outcomes.

Scheme 2.

Scheme 2.

Open in a new tab

Iron-catalyzed cross-[2+2]-cycloadditions between (E)-piperylene and α-olefins. Combined isolated yields of diastereomeric [2+2]-cycloadducts listed for reactions performed on 1 or 3 mmol scale unless noted otherwise. [a] 2.0 M in benzene-d6 [b] with 1.25 mol% [(Me(Et)PDI)Fe(N2)]2(μ2-N2) [c] yield determined by integration of diagnostic 1H NMR signals relative to an internal standard [d] with 0.5 mol% [(Me(Et)PDI)Fe(N2)]2(μ2-N2) [e] with 5 mol% (Me(Et)PDI)Fe(η4-butadiene) [f] with 2.5 mol% [(Me(Et)PDI)Fe(N2)]2(μ2-N2) [g] with 2.5 mol% [(MePDI)Fe(N2)]2(μ2-N2) [h] product 8h was not separated from remaining tributyl(vinyl)stannane (7h); conversion (40%) determined from the relative integration of 1H NMR signals diagnostic of 8h and 7h.

With the goal of elucidating the coordination mode(s) of a substituted 1,3-diene with pyridine(diimine) iron, isoprene was added to a benzene-d6 solution of [(MePDI)Fe(N2)]2(μ2-N2) at ambient temperature (~23 °C; Scheme 3A) resulting in a slight deepening of its red-brown hue. The reaction was monitored by 1H NMR spectroscopy, and the final spectroscopic features were consistent with those expected for the diamagnetic, C1 symmetric complex (MePDI)Fe(η4-isoprene) (>95% conversion after two hours).[17g] However, isolation of the diene complex was precluded by its instability to vacuum; numerous attempts instead returned [(MePDI)Fe(N2)]2(μ2-N2). Attempts at recrystallization to remove excess diene were unsuccessful, likely due to the high solubility of the complex.

Scheme 3.

Scheme 3.

Open in a new tab

Synthesis of (MePDI)Fe(diene) complexes.

As observed with isoprene, treatment of a benzene-d6 solution of [(MePDI)Fe(N2)]2(μ2-N2) with (E)-piperylene resulted in a rapid color change from red-brown to vibrant red-pink and formation of the iron diene complex (MePDI)Fe(η4-piperylene) (>98% conversion in <15 minutes; Scheme 3B, top). Notably, upon exposure of [(MePDI)Fe(N2)]2(μ2-N2) to a mixture of (E)- and (Z)-piperylene, only coordination of the (E) isomer was observed. The ambient temperature benzene-d6 1H NMR spectrum of (MePDI)Fe(η4-piperylene) was consistent with that of a diamagnetic iron complex. While six upfield-shifted resonances corresponding to chemically inequivalent piperylene protons were observed (3.0–5.0 ppm for olefinic protons; 0.3 ppm for allylic protons), the six additional resolved PDI ligand resonances were consistent with an effectively C2v symmetric molecule. The pyridine 3,5-CH, imine CH3, and benzylic CH3 resonances were broadened at ambient temperature, consistent with a dynamic process accounting for the observed, higher-than-anticipated symmetry.

Treatment of [(MePDI)Fe(N2)]2(μ2-N2) with an excess of (E)-piperylene (5 equiv; in a mixture with (Z)-piperylene and cyclopentene) in pentane for one hour, followed by removal of the volatiles in vacuo afforded (MePDI)Fe(η4-piperylene) as a red powder in >90% purity (Scheme 3B, bottom). While small amounts of analytically pure material (up to 39% isolated yield) were obtained by repeated recrystallizations from diethyl ether at −35 °C, crystals suitable for X-ray diffraction analysis were not obtained.

To aid in isolation, purification, and solid-state structure determination of a (PDI)Fe(piperylene) complex, a modified ligand bearing ethyl groups on the diimine backbone was evaluated. In previous studies, introduction of ethyl substituents improved the crystallinity of resulting iron, cobalt, and vanadium complexes.[20,24] Treatment of a pentane solution of [(Me(Et)PDI)Fe(N2)]2(μ2-N2) with (E)-or (E/Z)-piperylene produced the same rapid color change. Following recrystallization from diethyl ether/pentane at −35 °C, (Me(Et)PDI)Fe(η4-piperylene) was obtained in 63% yield (Scheme 4). The zero-field 57Fe Mößbauer spectrum (solid-state, 80 K, Figure 1) of the bulk material exhibited a quadrupole doublet, consistent with a single iron-containing product, with parameters (δ = 0.38 mm/s, |ΔEQ| = 0.78 mm/s) in good agreement with those measured for (MePDI)Fe(η4-butadiene) (δ = 0.38 mm/s, |ΔEQ| = 0.50 mm/s).

Scheme 4.

Scheme 4.

Open in a new tab

Synthesis and solid-state structure of (Me(Et)PDI)Fe(η4-piperylene), depicted with 30% probability ellipsoids (CCDC #1956377). Hydrogen atoms are omitted for clarity. C = gray, N = blue, Fe = red-orange. Selected bond distances (Å) and angles (deg): Fe1–N1 1.978(4), Fe1–N2 1.844(4), Fe1–N3 1.976(4), Fe1–C28 2.20(3), Fe1–C29 2.082(9), Fe1–C30 2.058(12), Fe1–C31 2.17(4), N1–C9 1.329(6), C9–C12 1.423(6), C12–N2 1.382(6), N2–C16 1.385(6), C16–C17 1.417(7), C17–N3 1.335(6), N1–Fe1–N3 151.99(15), N1–Fe1–N2 78.89(15), N3–Fe1–N2 79.21(16), N1–Fe1–C31 105.7(6), N2–Fe31–C31 101.6(8), N3–Fe1–C31 95.7(8)

Figure 1.

Figure 1.

Open in a new tab

Zero-field 57Fe Mößbauer spectra of (A.) (MePDI)Fe(η4-butadiene) and (B.) (Me(Et)PDI)Fe(η4-piperylene) recorded at 80 K in the solid state. Simulated spectra with the listed parameters are plotted in red.

A second recrystallization of bulk (Me(Et)PDI)Fe(η4-piperylene) afforded single crystals suitable for X-ray diffraction. The overall molecular geometry is best described as square pyramidal with the 4-substituted diene carbon occupying the apical position. The bond lengths of the pyridine(diimine) are consistent with significant contributions from a closed-shell, two-electron reduced description of the redox-non-innocent ligand.[17f,25] Although the piperylene fragment exhibited positional disorder in the unit cell (half-occupancy in either of two orientations), the structure provided unambiguous support for an s-trans coordination geometry. As such, (Me(Et)PDI)Fe(η4-piperylene), like the parent butadiene complex, is one of few known s-trans diene complexes, especially with 3d metals.[13,15j,15k,17e–g,19] Full-molecule density functional theory using the M06-L functional[26,27] reproduced the experimentally observed preference for s-trans butadiene and piperylene coordination. Comparison of the lowest energy s-cis and s-trans structures (Figure 2) suggested that the s-trans isomers were lower in energy by >7 kcal/mol (ΔG = 8.9 kcal/mol for butadiene, ΔG = 7.1 kcal/mol for piperylene, at 298 K). Evaluation of the lowest-energy s-cis and s-trans isomers predicted for (MePDI)Fe(η4-isoprene) suggested a similar preference favoring the s-trans coordination geometry; however, significant distortion induced by projection of the 2-substituent toward the flanking aryl groups resulted in a smaller energy difference between the isomers (ΔG = 4.3 kcal/mol at 298 K).

Figure 2.

Figure 2.

Open in a new tab

Lowest-energy optimized structures for the s-trans (A–C.) and s-cis (D–F.) isomers of (MePDI)Fe(η4-diene) complexes, computed using the M06-L level of density functional theory with the ZORA-def2-TZVP(-f) basis set augmented by SARC/J terms for Fe, N, and C atoms in the primary coordination sphere, and the ZORA-def2-SVP basis set augmented with SARC/J terms for all other atoms. [26,27] Images rendered using CYLview.[28] Relative free energies listed in kcal/mol calculated at 298 K; relative electronic energies listed in parentheses. Hydrogen atoms, except those on the diene ligand, omitted for clarity. H = white, C = gray, N = blue, Fe = red-orange.

As observed for (MePDI)Fe(η4-piperylene), the 1H NMR spectra of (Me(Et)PDI)Fe(η4-piperylene) in benzene-d6 or toluene-d8 at 23 °C were consistent with diene exchange resulting in an observed C2v symmetric molecule in solution.[29] The origin of this behavior was evaluated by variable temperature (VT) 1H NMR spectroscopy in toluene-d8 over a 130 °C range (−93 to 38 °C; Figure 3A). At temperatures at or below −20 °C, the resonances sharpened, and clear separation of two (C3 and C5) pyridine CH, two imine backbone CH3, and four benzylic CH3 signals was observed, consistent with the idealized Cs symmetry observed in the solid state. At 40 °C the resonances also sharpened due to rapid exchange on the NMR timescale. The rates of diene exchange leading to this coalescence were extracted from total lineshape analysis at each temperature evaluated over this range,[30] and Eyring analysis afforded activation parameters of ΔH‡ = + 27.7 kcal mol−1 and ΔS‡ = + 48.3 cal mol−1 K−1 (Figure 3B).[31] These results, particularly the large positive entropy of activation, suggest that diene exchange occurs through a dissociative mechanism. However, these data cannot distinguish between mechanisms involving rate-determining partial or full diene dissociation, to form [(Me(Et)PDI)Fe(η2-piperylene)] or [(Me(Et)PDI)Fe + piperylene], respectively, prior to coordination of another molecule of piperylene.

Figure 3.

Figure 3.

Open in a new tab

Variable temperature 1H NMR measurements established exchange of inequivalent sites on the NMR timescale. (A.) Temperature dependence of representative NMR signals for (Me(Et)PDI)Fe(η4-piperylene) collected in toluene-d8. Rate constants (k) for exchange extracted from lineshape analysis. (B.) Eyring plot of VT NMR rate data. Dotted line indicates the fit to the linear regression shown to afford the activation parameters for diene exchange.

In order to gain deeper understanding of the mechanism of diene exchange, a series of 1H–1H EXSY (EXchange SpectroscopY) experiments was conducted on (Me(Et)PDI)Fe(η4-piperylene) at 23 °C.[32] A solution of (Me(Et)PDI)Fe(η4-piperylene) in benzene-d6 was treated with an equimolar quantity of free (E)-piperylene. The resonances corresponding to free and coordinated piperylene (6 each) were resolved by Δδ = 1.3–1.8 ppm in the 1D 1H NMR spectrum, and in-phase cross-peaks indicative of exchange between them were readily apparent in the 2D EXSY spectrum (Figure 4A).[33] The rate of exchange was extracted from the normalized area under the EXSY cross-peaks observed as a function of added piperylene concentration (1–5 equiv, 0.04–0.15 M). An inverse relationship was observed between the first-order rate constant for exchange (kobs) and the concentration of free (E)-piperylene ([4b]; Figure 4B). A plausible mechanism for diene exchange, accounting for both the calculated activation parameters and the inhibitory effect of excess diene, is presented in Figure 4C. The reversible formation of (Me(Et)PDI)Fe(η2-piperylene)2 competitive with rate-determining diene dissociation accounts for the observed inhibition; however, alternative possibilities were not ruled out.

Figure 4.

Figure 4.

Open in a new tab

1H–1H EXSY titrations reveal that diene exchange is inhibited by excess diene. (A.) Excerpt of the 2D EXSY spectrum obtained in the absence of exogenous piperylene. Circles highlight the in-phase cross-peaks indicative of exchange between coordinated and free (E)-piperylene. (B.) Observed first-order rate constant for diene exchange as a function of added (E)-piperylene. (C.) Plausible mechanism for diene exchange accounting for the inhibitory effect of excess diene.

Given the observed lability of both isoprene and piperylene ligands in pyridine(diimine) iron complexes, this feature was exploited to quantitate the relative coordination affinities of the dienes. The equilibrium ratios of free and coordinated diene were measured by 1H NMR spectroscopy of pairwise combinations of either (MePDI)Fe(diene) or (Me(Et)PDI)Fe(diene) and a second, distinct diene in benzene-d6 at 23 °C (Scheme 5). The relative diene coordination affinities were determined as: butadiene > piperylene > isoprene. The relative binding affinities measured experimentally were in reasonable agreement with those calculated for the isodesmic reactions using DFT (ΔGbutadiene-piperylene = 2.1 kcal/mol, ΔGbutadiene-isoprene = 4.9 kcal/mol, ΔGpiperylene-isoprene = 2.8 kcal/mol at 298 K). The poor coordination ability of isoprene relative to butadiene and piperylene is consistent with the vacuum instability that precluded isolation of the compound (vide supra).

Scheme 5.

Scheme 5.

Open in a new tab

Relative coordination affinities of diene ligands to pyridine(diimine) iron complexes determined from isodesmic reaction equilibria. Experimental values determined from relative 1H NMR integrations for equilibrium mixtures in benzene-d6 at 23 °C. Computational values calculated at 298 K for isodesmic reactions of (MePDI)Fe(η4-diene) and butadiene, isoprene, or (E)-piperylene optimized in the gas phase. [26,27]

To better understand the role that the diene complexes played in the mechanism of catalytic [2+2]-cycloaddition, a series of stoichiometric experiments was performed. Exposure of (Me(Et)PDI)Fe(η4-piperylene) in benzene-d6 to excess ethylene (5 equiv) at ambient temperature caused the characteristic resonances in the 1H NMR spectrum to broaden, suggestive of the formation of a new unidentified species. The volatile reaction components were collected after 40 hours, and 1H NMR analysis supported the assignment of cyclobutane and 1,5-heptadiene in ≲5% yield; propenylcyclobutane (6) was not detected (Scheme 6A). The residue remaining after the reaction was reconstituted in benzene-d6, and the resulting 1H NMR spectrum supported that (Me(Et)PDI)Fe(η4-piperylene) remained the single, major identifiable iron compound. By contrast, exposure of the diene complex to a mixture of both piperylene and ethylene resulted in clean formation of propenylcyclobutane (Scheme 6B). The requirement for additional equivalents of diene to induce C–C bond-forming reductive elimination is consistent with the observed reactivity in the butadiene–ethylene [2+2]-cycloaddition.[17g] However, in this parent case, the metallacycle formed through stoichiometric reactions (Scheme 1A) persisted until a strong-field ligand such as butadiene or carbon monoxide was added. Such a diamagnetic metallacycle was not detected in the experiments with (Me(Et)PDI)Fe(η4-piperylene).

Scheme 6.

Scheme 6.

Open in a new tab

Stoichiometric activity of (Me(Et)PDI)Fe(η4-piperylene) toward cross-[2+2]-cycloaddition.

To elucidate the origins of these similarities and differences, stoichiometric experiments were supplemented by reaction progress kinetic analysis under catalytically relevant conditions[34] using [(MePDI)Fe(N2)]2(μ2-N2) or (MePDI)Fe(η4-butadiene) as the precatalyst. The disappearance of diene (either butadiene[35] or piperylene) and the formation of the corresponding [2+2]-cycloadduct (either vinylcyclobutane (3) or propenylcyclobutane (6)) could be monitored readily over the entire course of the reaction through 1H NMR spectroscopy. In both cases, runs initiated at different concentrations of diene but with the same excess concentration of ethylene[36] afforded concentration vs. time data that overlaid graphically, indicating that no catalyst decomposition or product inhibition occurred over the course of the reactions (Figure 5).

Figure 5.

Figure 5.

Open in a new tab

Time-shifted reaction profiles for trials conducted with the ‘same excess’ of diene and the same catalyst concentration ([Fe]tot = 10.0 mM) but different [ethylene]0 and [diene]0 (open markers vs. filled markers). Overlay indicates that neither catalyst death nor product inhibition occurred during the iron-catalyzed cross-[2+2] cycloaddition of ethylene with (A.) butadiene and (B.) (E)-piperylene. Grey arrows indicate where values were time-shifted and/or concentration-shifted to correct for the differing initial concentrations.

Despite the catalyst fidelity in both case studies examined, the catalyst resting states differed. Metallacycle (MePDI)Fe(η1,η3-C6H10) was clearly resolved by 1H NMR as the major (PDI)Fe-containing species at intermediate conversion during catalysis of the cross-[2+2]-cycloaddition of butadiene and ethylene. By contrast, diene complex (MePDI)Fe(η4-piperylene) was detected as the major (PDI)Fe-containing species at intermediate conversion during catalysis of the cross-[2+2]-cycloaddition of piperylene and ethylene. The differences in catalyst resting state were further reflected in kinetic profiles of the reactions. The linearity of the [butadiene] versus time plot (Figure 5A) indicated that the reaction obeys a zero-order rate dependence up to >80% conversion. Conversely, the [piperylene] versus time plot exhibited a clear exponential decay consistent with a first-order rate dependence overall (Figure 5B). Trials conducted with a different excess in the initial concentration of ethylene relative to piperylene also resulted in kinetic profiles that overlaid, indicating a first-order rate dependence on the concentration of ethylene and no rate dependence on the concentration of piperylene (Figure 6). Trials conducted with either pure (E)-piperylene or (E)-piperylene in a mixture with (Z)-piperylene and cyclopentene afforded comparable results, establishing that (Z)-piperylene and cyclopentene are kinetically innocent and unchanged over the course of the reaction with (E)-piperylene. Taken together, these findings are consistent with competing kinetic manifolds in a common mechanism involving oxidative cyclization, C–C reductive elimination, and intramolecular isomerization steps (Scheme 7). In particular, the zero-order dependence in the cross-cycloaddition of ethylene and butadiene suggests that an intramolecular event is rate determining. Given that the resting-state metallacycle (MePDI)Fe(η1,η3-C6H10) is coordinatively saturated, isomerization to an on-cycle coordinatively unsaturated metallacyclopentane (MePDI)Fe(η1,η1-C 6H10) is hypothesized to be rate-determining prior to a ligand-induced C–C bond-forming reductive elimination.[37] Conversely, the first-order dependence on ethylene in its cross-[2+2]-cycloaddition with piperylene is most consistent with a mechanism in which ethylene coordination or oxidative cyclization is rate-determining. Given the steric penalty that would be associated with accessing η3-coordination of the substituted metallacycle, on-cycle (MePDI)Fe(η1,η1-s-trans-C7H12) metallacyclopentane is posited to be the major intermediate sampled en route to C–C reductive elimination.

Figure 6.

Figure 6.

Open in a new tab

Rate profiles for trials conducted with a ‘different excess’ of ethylene (open markers vs. filled markers) but the same catalyst concentration ([Fe]tot = 10.0 mM) and [piperylene]0. Overlay of the linear rate vs. [ethylene] curves indicates that the reaction is zero-order in [piperylene] and first-order in [ethylene].

Scheme 7.

Scheme 7.

Open in a new tab

Proposed catalytic cycle for iron-catalyzed cross-[2+2]-cycloadditions with ethylene.

Given these insights into the reactivity differences between butadiene and piperylene, the placement of diene substituents in an incipient metallacycle is likely the origin of the chemoselectivity differences observed in the cross-reaction of ethylene and isoprene (Scheme 8). Because the substitution pattern of isoprene would also disfavor η3-coordination analogous to that observed in (MePDI)Fe(η1,η3-C6H10), reaction through the s-cis diene conformation to access the (MePDI)Fe(η1,η1-s-cis-C7H12) metallacycloheptene would become kinetically accessible. As such, the flexibility of the larger metallacycle would enable facile β-H elimination,[38] thereby providing a kinetically accessible pathway to C–H reductive elimination and the formation of the observed hydrovinylation product 5.

Scheme 8.

Scheme 8.

Open in a new tab

Proposed mechanistic basis for diene-controlled divergent chemoselectivity in iron-catalyzed cross-reactions with ethylene.

Conclusion

The structures and reactivity of pyridine(diimine) iron diene complexes implicated in non-canonical cycloaddition reactions were studied. These complexes exhibited an unusual s-trans coordination geometry, and the ligand dynamics and lability were examined by VT 1H NMR and EXSY experiments. These iron complexes supported by the readily prepared (MePDI) ligand were found to be competent for the selective cross-[2+2] cycloaddition of (E)-piperylene and α-olefins. Stoichiometric experiments and kinetic analyses suggested that isolable, coordinatively saturated diene and metallacyclic complexes are off-cycle, but that rapid dissociation and/or isomerization enable productive C–C bond-forming oxidative cyclization and reductive elimination, respectively. This study underscores that nuanced consideration of the interplay of ligand and substrate substituent effects is necessary in understanding the relationships between ligand-controlled diene coordination geometry, metallacycle denticity, and the chemoselectivity of iron-mediated cycloaddition reactions. Further work in our laboratory is directed toward exploiting this understanding to design new transformations that upgrade abundant hydrocarbon building blocks using iron catalysis.

Experimental Section

General Considerations:

All air- and moisture-sensitive manipulations were carried out using standard Schlenk techniques on a high vacuum line or in an M. Braun glovebox containing an atmosphere of purified N2. Reagents were purchased in reagent grade from commercial suppliers and used without further purification unless described otherwise. Pure (E)-piperylene and (E/Z)-piperylene were purchased from TCI, but crude (E/Z)-piperylene (also containing cyclopentene) was provided by Firmenich. Ethylene (2) and propylene (7a) were stored over activated 4 Å molecular sieves in a thick-walled glass pressure vessel for >24 hours prior to use. Butadiene (1) and 3-methyl-1-butene (7g) were stored over calcium hydride in a thick-walled glass pressure vessel for >24 hours then degassed prior to use. Isoprene (4a), piperylene (4b), allyl benzene (7f), and tributyl(vinyl)stannane (7h) were stirred over calcium hydride for >48 hours, degassed, and distilled under high vacuum. 1-Nonene (7b), 1-decene (7c), 4,4-dimethyl-1-pentene (7d), and 4-methyl-1-pentene (7e) were stirred over lithium aluminum hydride for >48 hours, degassed, and distilled under high vacuum. The liquid reagents were then either passed through a plug of activated alumina and/or stored over activated 4 Å molecular sieves in the glovebox. Solvents (diethyl ether, dichloromethane, n-hexane, n-pentane, tetrahydrofuran, and toluene) used for air- and moisture-sensitive manipulations were dried and deoxygenated by passage through an activated alumina column.[39] Deuterated solvents for NMR spectroscopy of air- and moisture-sensitive species (benzene-d6, cyclohexane-d12, or toluene-d8) were distilled from sodium metal under an atmosphere of argon and stored over 4 Å molecular sieves. Deuterated chloroform (CDCl3) was stored over anhydrous potassium carbonate. The iron complexes Me [(MePDI)Fe(N2)]2(μ2-N2), [((Et)PDI)Fe(N2)]2(μ2-N2), and [(MePDI)Fe(η4-butadiene)] were prepared as reported previously.[17g,40] NMR spectroscopy experiments were performed at the Princeton University Nuclear Magnetic Resonance Facility. Mass spectrometric data were obtained at the Princeton University Mass Spectrometry Facility. All DFT calculations were performed using ORCA[27a,b] on the Princeton Della Research Computing Cluster. Computed structures were rendered using CYLview.[28] CCDC-1956377 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Additional considerations are described in the Supporting Information.

Representative Procedure for Cross-[2+2]-Cycloaddition with Gaseous Alkenes:

In a glovebox filled with an inert atmosphere of purified N2, a J. Young NMR tube was charged with [(Me(Et)PDI)Fe(N2)]2(μ2-N2) (0.012 g, 0.0125 mmol dimer, 0.025 mmol [Fe], 2.5 mol%) as a solution in C6D6 (0.5 mL). Piperylene (52 wt% (E)-piperylene, 27 wt% (Z)-piperylene in a mixture with cyclopentene and cyclopentane; 193 μL, 1.0 mmol (E)-piperylene, 1.0 equiv) was added via microliter syringe. The tube was sealed, removed from the glovebox and frozen in liquid N2. The headspace was evacuated, and then propylene (7a, 1.2 mmol, 1.2 equiv) was added by vacuum transfer via a calibrated gas bulb. The tube was sealed under static vacuum, and gradually warmed to ambient temperature (23 °C). Reaction progress was monitored by 1H NMR analysis. Upon consumption of the substrates, the volatiles were transferred by way of a vacuum transfer tube to another J. Young NMR tube for analysis. Product 8a was obtained in 86% yield (95% [2+2], 77:23 d.r.) after 63 hours. Analogous procedures were followed for reactions with ethylene (2) and 3-methyl-1-butene (7g). Organic product characterization data are provided in the Supporting Information.

Representative Procedure for Cross-[2+2]-Cycloaddition with Liquid Alkenes:

In a glovebox filled with an inert atmosphere of purified N2, a 1.5 mL vial was charged with allylbenzene (7f, 0.355 g, 3.0 mmol, 1.2 equiv) and piperylene (52 wt% (E)-piperylene, 27 wt% (Z)-piperylene in a mixture with cyclopentene and cyclopentane; 482 μL, 2.5 mmol (E)-piperylene, 1.0 equiv). Precatalyst [(Me(Et)PDI)Fe(N2)]2(μ2-N2) (0.012 g, 0.0125 mmol dimer, 0.025 mmol [Fe], 1.0 mol%) was added as a solid to initiate the reaction. A PTFE-coated magnetic stir bar was added, and the vial was sealed. The vial was maintained with stirring at ambient temperature (~23 °C). Reaction progress was monitored by GC analysis of aliquots removed from the reaction mixture. Upon consumption of the substrates, the vial was removed from the glovebox. The contents were exposed to air, and the product mixture was filtered through a plug of silica, eluting with pentane (5 × 2 mL). The filtrate was concentrated under reduced pressure to afford 8f as a colorless oil in 92% yield (≥98% [2+2], 62:38 d.r.) after 26 hours. Analogous procedures were followed for reactions with 1-nonene (7b), 1-decene (7c), 4,4-dimethyl-1-pentene (7d), 4-methyl-1-pentene (7e), and tributyl(vinyl)stannane (7h). Organic product characterization data are provided in the Supporting Information.

Synthesis of (MePDI)Fe(η4-isoprene):

In a glovebox filled with an atmosphere of purified N2, a J. Young NMR tube was charged with [(MePDI)Fe(N2)]2(μ2-N2) (20.0 mg, 0.0214 mmol dimer, 0.043 mmol [Fe], 1.0 equiv) and 600 μL of benzene-d6. Isoprene (5 μL 0.05 mmol, 1 equiv per [Fe]) was added via microliter syringe, and the tube was sealed and removed from the glovebox. After mixing by repeated inversion at ambient temperature for 2 hours, the reaction mixture was analyzed by 1H NMR spectroscopy to reveal (MePDI)Fe(η4-isoprene) as the single major species. No remaining [(MePDI)Fe(N2)]2(μ2-N2) was observed. The complex persisted in solution at ambient temperature with a half-life of ~ 3 hours. NMR parameters for (MePDI)Fe(η4-isoprene) have been reported previously.[17g] 1H NMR (300 MHz, C6D6) δ 8.00 (d, J = 7.6 Hz, 1H), 7.89 (d, J = 7.7 Hz, 1H), 7.38 (t, J = 7.3 Hz, 1H), 7.10 – 6.70 (m, 5H), 6.55 (d, J = 7.3 Hz, 1H), 4.65 (s, 1H), 4.15 (s, 1H), 3.52 (d, J = 8.8 Hz, 1H), 2.59 (q, J = 7.3 Hz, 1H), 2.35 (d, J = 8.9 Hz, 2H), 1.98 (s, 3H), 1.79 (s, 3H), 1.72 (s, 3H), 1.64 (s, 3H), 1.26 (s, 3H), 0.90 (s, 3H), −0.05 (d, J = 6.1 Hz, 3H)

Synthesis of (MePDI)Fe(η4-piperylene):

In a glovebox filled with an atmosphere of purified N2, a 20-mL scintillation vial was charged with [(MePDI)Fe(N2)]2(μ2-N2) (0.100 g, 0.12 mmol dimer, 0.24 mmol [Fe], 1.0 equiv), pentane (4.8 mL, 0.05 M), and a PTFE-coated magnetic stir bar. Piperylene (52 wt% (E)-piperylene, 27 wt% (Z)-piperylene in a mixture with cyclopentene and cyclopentane; 230 μL, 1.2 mmol (E)-piperylene, 5.0 equiv) was added via microliter syringe. The vial was sealed, and the reaction was maintained at ambient temperature with gentle stirring. After 1 hour, the volatiles were removed in vacuo to afford a deep raspberry red solid. The solid was resuspended in pentane, stored at −35 °C overnight, then dried in vacuo. A sample of the crude solid was analyzed by 1H NMR spectroscopy to reveal (MePDI)Fe(η4-piperylene) as the single major species with minor organic impurities. No remaining [(MePDI)Fe(N2)]2(μ2-N2) was observed. The crude solid was recrystallized from diethyl ether (~1 mL) at −35 °C over two weeks to afford a pure sample of (MePDI)Fe(η4-piperylene) (0.040 g, 0.09 mmol, 39% yield) for further analysis. Additional crude material was collected from the supernatant. 1H NMR (400 MHz, C6D6) δ 8.10 (br. s, 2H), 7.46 (t, J = 7.6 Hz, 1H), 6.90 (t, J = 7.4 Hz, 2H), 6.86 – 6.79 (m, 4H), 4.75 (dd, J = 12.3, 9.0 Hz, 1H), 4.47 (dt, J = 13.2, 8.2 Hz, 1H), 3.85 (dq, J = 12.9, 6.5 Hz, 1H), 3.38 (d, J = 13.1 Hz, 1H), 3.13 (d, J = 7.2 Hz, 1H), 1.65 (s, 6H), 1.61 (br. s, 12H), 0.34 (d, J = 6.5 Hz, 3H). 13C NMR (101 MHz, C6D6) δ 150.97, 150.25, 125.04, 117.12, 100.43, 98.38, 75.64, 65.96, 19.37, 17.01, 13.98, four resonances not detected. Elemental analysis calculated for C30H35FeN3: 73.02 %C, 7.15 %H, 8.52 %N; found: 72.79 %C, 6.76 %H, 8.07 %N.

Synthesis of (Me(Et)PDI)Fe(η4-piperylene):

In a glovebox filled with an atmosphere of purified N2, a 20-mL scintillation vial was charged with [(Me(Et)PDI)Fe(N2)]2(μ2-N2) (0.200 g, 0.23 mmol dimer, 0.46 mmol [Fe], 1.0 equiv), pentane (10 mL, 0.05 M), and a PTFE-coated magnetic stir bar. Piperylene (52 wt% (E)-piperylene, 27 wt% (Z)-piperylene in a mixture with cyclopentene and cyclopentane; 450 μL, 2.3 mmol (E)-piperylene, 5.0 equiv) was added via microliter syringe. The vial was sealed, and the reaction was maintained at ambient temperature with gentle stirring. After 1 hour, the volatiles were removed in vacuo to afford a deep raspberry red solid. The crude solid was recrystallized from ~1:1 diethyl ether/pentane at −35 °C overnight to afford a pure sample of (Me(Et)PDI)Fe(η4-piperylene) (0.150 g, 0.29 mmol, 63% yield). Additional crude material was collected from the supernatant. 1H NMR (400 MHz, C6D6) δ 8.04 (br. s, 2H), 7.47 (t, J = 7.7 Hz, 1H), 6.90 (t, J = 7.3 Hz, 2H), 7.02–6.66 (m, 4H), 4.73 (dd, J = 12.2, 9.1 Hz, 1H), 4.48 (td, J = 13.1, 9.1, 7.2 Hz, 1H), 3.67 (dq, J = 12.2, 6.5 Hz, 1H), 3.31 (d, J = 13.1 Hz, 1H), 3.15 (d, J = 7.2 Hz, 1H), 2.35 (br. s, 4H), 1.67 (br. s, 12H), 0.86 (t, J = 7.5 Hz, 6H), 0.23 (d, J = 6.5 Hz, 3H). 13C NMR (126 MHz, C6D6) δ 149.55, 128.35, 125.04, 118.01, 101.09, 97.31, 75.55, 68.12, 24.28, 22.74, 19.69, 14.29, 13.31, 12.18, four resonances not detected. Elemental analysis calculated for C32H39FeN3: 73.70 %C, 7.54 %H, 8.06 %N; found: 73.28 %C, 7.38 %H, 7.95 %N

Supplementary Material

SI

Acknowledgements

C.R.K. thanks the NIH for a Ruth L. Kirschstein National Research Service Award (F32 GM126640). Financial support and a gift of piperylene were provided by Firmenich. We thank Dr. Megan Mohadjer Beromi (Princeton University) and Andreu Tortajada Navarro (Institute of Chemical Research of Catalonia) for helpful discussion and Dr. István Pelczer and Kenith Conover (Princeton University) for assistance with NMR experiments.

Footnotes

Dedicated to Professor Eric N. Jacobsen on the occasion of his 60th birthday.

References

  • [1].Schmidt R, Griesbaum K, Behr A, Biedenkapp D, Voges H-W, Garbe D, Paetz C, Collin G, Mayer D, Höke H, Hydrocarbons In Ullmann’s Encyclopedia of Industrial Chemistry; Wiley: Chichester, U.K., 2014. [Google Scholar]
  • [2].Corey EJ, Cheng X-M. In The Logic of Chemical Synthesis, Wiley, New York, 1989. [Google Scholar]
  • [3].Chain Polymerization of Vinyl Monomers; a) , In Polymer Science: A Comprehensive Reference, Vol. 3 (Eds: Matyjaszewski K, Möller M), Elsevier, 2012, 1–954; [Google Scholar]; b) Claverie JP, Schaper F, MRS Bull. 2013, 38, 213–218; [Google Scholar]; c) Domski GJ, Rose JM, Coates GW, Bolig AD, Brookhart M, Prog. Polym. Sci 2007, 32, 30–92. [Google Scholar]
  • [4].a) Grub J, Löser E. Butadiene, In Ullmann’s Encyclopedia of Industrial Chemistry; Wiley: Chichester, U.K., 2012, 381–396; [Google Scholar]; b) Weitz HM, Löser E. Isoprene, In Ullmann’s Encyclopedia of Industrial Chemistry; Wiley: Chichester, U.K., 2012, 83–101. [Google Scholar]
  • [5].Matar S, Hatch LF, Chemistry of Petrochemical Processes, 2nd ed; Gulf Professional: Boston, 1991. [Google Scholar]
  • [6].a) Behr A, Johnen L, Chem. Sus. Chem 2009, 2, 1072–1095; [DOI] [PubMed] [Google Scholar]; b) Morais ARC, Dworakowska S, Reis A, Gouveia L, Matos CT, Bogdał D, Bogel-Łukasik R, Catal. Today, 2015, 239, 38–43; [Google Scholar]; c) Sun R, Zheng M, Li X, Pang J, Wang A, Wang X, Zhang T, Green Chem. 2017, 19, 638–642. [Google Scholar]
  • [7].For select reviews:; a) RajanBabu TV, In Comprehensive Asymmetric Catalysis (Eds. Jacobsen EN, Pfaltz A, Yamamto H), Springer, Berlin, 1999, 417–427; [Google Scholar]; b) RajanBabu TV, Synlett, 2009, 853–885; [DOI] [PMC free article] [PubMed] [Google Scholar]; c) Hilt G, Eur. J. Org. Chem 2012, 4441–4451; [Google Scholar]; d) McNeill E, Ritter T. Acc. Chem. Res 2015, 48, 2330–2343; [DOI] [PubMed] [Google Scholar]; e) Röse P, Hilt G, Synthesis, 2016; 48, 463–492; [Google Scholar]; f) Holmes M, Schwartz LA, Krische MJ, Chem. Rev 2018, 118, 6026–6052; [DOI] [PMC free article] [PubMed] [Google Scholar]; g) Hirano M, ACS Catal. 2019, 9, 1408–1430; [Google Scholar]; h) Doerksen RS, Meyer CC, Krische MJ, Angew. Chem. Int. Ed 2019, 58, 2–12. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [8].For select recent examples of [Fe] catalysis:; a) Moreau B, Wu JY, Ritter T, Org. Lett 2009, 11, 337–339; [DOI] [PubMed] [Google Scholar]; b) Wu JY; Moreau B, Ritter T, J. Am. Chem. Soc 2009, 131, 12915–12917; [DOI] [PubMed] [Google Scholar]; c) Wu JY, Stanzl BN, Ritter T, J. Am. Chem. Soc 2010, 132, 13214–13216; [DOI] [PubMed] [Google Scholar]; d) Raynaud J, Wu JY, Ritter T, Angew. Chem. Int. Ed 2012, 51, 11805–11808; [DOI] [PubMed] [Google Scholar]; e) Lee H, Campbell MG, Hernández Sánchez R, Börgel J, Raynaud J, Parker SE, Ritter T, Organometallics, 2016, 35, 2923–2929; [Google Scholar]; f) Schmidt VA, Kennedy CR, Bezdek MJ, Chirik PJ, J. Am. Chem. Soc 2018, 140, 3443–3453; [DOI] [PMC free article] [PubMed] [Google Scholar]; g) Kennedy CR, Zhong H, Macaulay RL, Chirik JPJ. Am. Chem. Soc 2019, 141, 8557–8573. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [9].For select recent examples of [Co] catalysis:; a) Hilt G, Treutwein J, Chem. Commun 2009, 1395–1397; [DOI] [PubMed] [Google Scholar]; b) Hilt G, Janikowski J, Org. Lett 2009, 11, 773–776; [DOI] [PubMed] [Google Scholar]; c) Hilt G, Danz M, Treutwein J, Org. Lett 2009, 11, 3322–3325; [DOI] [PubMed] [Google Scholar]; d) Hilt G, Arndt M, Weske DF, Synthesis, 2010, 1321–1324; [Google Scholar]; e) Arndt M, Reinhold A, Hilt G, J. Org. Chem 2010, 75, 5203–5210; [DOI] [PubMed] [Google Scholar]; f) Sharma RK, RajanBabu TV, J. Am. Chem. Soc 2010, 132, 3295–3297; [DOI] [PMC free article] [PubMed] [Google Scholar]; g) Hilt G, Roesner S, Synthesis, 2011, 662–668; [Google Scholar]; h) Bohn MA, Schmidt A, Hilt G, Dindaroğlu M, Schmalz H, Angew. Chem. Int. Ed 2011, 50, 9689–9693; [DOI] [PubMed] [Google Scholar]; i) Erver F, G. Hilt. Org. Lett 2011, 13, 5700–5703; [DOI] [PubMed] [Google Scholar]; j) Arndt M, Dindaroğlu M, Schmalz H-G, Hilt G, Org. Lett 2011, 13, 6236–6239; [DOI] [PubMed] [Google Scholar]; k) Kersten L, Hilt G, Adv. Synth. Catal 2012, 354, 863–869; [Google Scholar]; l) Arndt M, Dindaroğlu M, Schmalz H-G, Hilt G, Synthesis, 2012; 44, 3534–3542; [Google Scholar]; m) Pünner F, Hilt G, Chem. Commun 2012, 48, 3617–3619; [DOI] [PubMed] [Google Scholar]; n) Erver F, Kuttner JR, Hilt G, J. Org. Chem 2012, 77, 8375–8385; [DOI] [PubMed] [Google Scholar]; o) Schmidt A, Hilt G, Org. Lett 2013, 15, 2708–2711; [DOI] [PubMed] [Google Scholar]; p) Schmidt A, Maiterth E, Hilt G, Synthesis, 2014, 46, 2040–2044; [Google Scholar]; q) Kuttner JR, Hilt G, Macromolecules, 2014, 47, 5532–5541; [Google Scholar]; r) Chen Q-A, Kim DK, Dong VM, J. Am. Chem. Soc 2014, 136, 3772–3775; [DOI] [PMC free article] [PubMed] [Google Scholar]; s) Möckel R, Hilt G, Org. Lett 2015, 17, 1644–1647; [DOI] [PubMed] [Google Scholar]; t) Timsina YN, Sharma RK, RajanBabu TV, Chem. Sci 2015, 6, 3994–4008; [DOI] [PMC free article] [PubMed] [Google Scholar]; u) Raya B, Jing S, Balasanthiran V, RajanBabu TV, ACS Catal. 2017, 7, 2275–2283; [DOI] [PMC free article] [PubMed] [Google Scholar]; v) Jing SM, Balasanthiran V, Pagar V, Gallucci JC, RajanBabu TV, J. Am. Chem. Soc 2017, 139, 18034–18043; [DOI] [PMC free article] [PubMed] [Google Scholar]; w) Thullen SM, Rovis T, J. Am. Chem. Soc 2017, 139, 15504–15508; [DOI] [PubMed] [Google Scholar]; x) Pagar VV, RajanBabu TV. Science, 2018, 361, 68–72; [DOI] [PMC free article] [PubMed] [Google Scholar]; y) Parsutkar MM, Pagar VV, RajanBabu TV. J. Am. Chem. Soc 2019, 141, 15367–15377. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [10].For select recent examples of [Ni] catalysis:; a) Saito N, Kobayashi A, Sato Y, Angew. Chem. Int. Ed 2012, 51, 1228–1231; [DOI] [PubMed] [Google Scholar]; b) Biswas S, Zhang A, Raya B, RajanBabu TV, Adv. Synth. Catal 2014, 356, 2281–2292; [DOI] [PMC free article] [PubMed] [Google Scholar]; c) Lian X, Chen W, Dang L, Li Y, Ho C-Y. Angew. Chem. Int. Ed 2017, 56, 9048–9052; [DOI] [PubMed] [Google Scholar]; d) Tortajada A, Ninokata R, Martin R, J. Am. Chem. Soc 2018, 140, 2050–2053; [DOI] [PubMed] [Google Scholar]; e) Tran G, Shao W, Mazet C, J. Am. Chem. Soc 2019, 141, 14814–14822. [DOI] [PubMed] [Google Scholar]
  • [11].For select recent examples of [Cu] catalysis:; a) Smith KB, Brown MK, J. Am. Chem. Soc 2017, 139, 7721–7724; [DOI] [PMC free article] [PubMed] [Google Scholar]; b) Sardini SR; Brown MK, J. Am. Chem. Soc 2017, 139, 9823–9826; [DOI] [PMC free article] [PubMed] [Google Scholar]; c) Gui Y-Y, Hu N, Chen X-W, Liao L−L, Ju T, Ye J-H, Zhang Z, Li J, Yu D-G, J. Am. Chem. Soc 2017, 139, 17011–17014; [DOI] [PubMed] [Google Scholar]; d) Smith KB, Huang Y, Brown MK, Angew. Chem. Int. Ed 2018, 57, 6146–6149; [DOI] [PMC free article] [PubMed] [Google Scholar]; e) Jia T, He Q, Ruscoe RE, Pulis AP, Procter DJ, Angew. Chem. Int. Ed 2018, 57, 11305–11309; [DOI] [PubMed] [Google Scholar]; f) Liu Y, Fiorito D, Mazet C, Chem. Sci 2018, 9, 5284–5288; [DOI] [PMC free article] [PubMed] [Google Scholar]; g) Jia T, Smith MJ, Pulis AP, Perry GJP, Procter DJ, ACS Catal. 2019, 9, 6744–6750; [Google Scholar]; h) Bergmann AM, Sardini SR, Smith KB, Brown MK, Isr. J. Chem 2019, DOI: 10.1002/ijch.201900060; [DOI] [PMC free article] [PubMed] [Google Scholar]; i) Li C, Shin K, Liu R, Buchwald S, Angew. Chem. Int. Ed 2019, 58, 17074–17080. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [12].For select recent examples of [Ru], [Rh], [Pd], and [Ir] catalysis:; a) Zbieg JR, Yamaguchi E, McInturff EL, Krische MJ, Science, 2012, 336, 324–327; [DOI] [PMC free article] [PubMed] [Google Scholar]; b) Goldfogel MJ, Roberts CC, Meek SJ, J. Am. Chem. Soc 2014, 136, 6227–6230; [DOI] [PubMed] [Google Scholar]; c) Roberts CC, Matías DM, Goldfogel MJ, Meek SJ, J. Am. Chem. Soc 2015, 137, 6488–6491; [DOI] [PubMed] [Google Scholar]; d) Chen T-Y, Tsutsumi R, Montgomery TP, Volchkov I, Krische MJ, J. Am. Chem. Soc 2015, 137, 1798–1801; [DOI] [PubMed] [Google Scholar]; e) McCammant MS, Sigman MS, Chem. Sci 2015, 6, 1355–1361; [DOI] [PMC free article] [PubMed] [Google Scholar]; f) Goldfogel MJ, Meek SJ, Chem. Sci 2016, 7, 4079–4084; [DOI] [PMC free article] [PubMed] [Google Scholar]; g) Oda S, Franke J, Krische MJ, Chem. Sci 2016, 7, 136–141; [DOI] [PMC free article] [PubMed] [Google Scholar]; h) Nguyen KD, Herkommer D, Krische MJ, J. Am. Chem. Soc 2016, 138, 14210–14213; [DOI] [PMC free article] [PubMed] [Google Scholar]; i) Goldfogel MJ, Roberts CC, Manan RS, Meek SJ, Org. Lett 2017, 19, 90–93; [DOI] [PubMed] [Google Scholar]; j) Marcum JS, Roberts CC, Manan RS, Cervarich TN, Meek SJ, J. Am. Chem. Soc 2017, 139, 15580–15583; [DOI] [PubMed] [Google Scholar]; k) Yang X-H; Dong VM, J. Am. Chem. Soc 2017, 139, 1774–1777; [DOI] [PMC free article] [PubMed] [Google Scholar]; l) Yang X-H, Lu A, Dong VM, J. Am. Chem. Soc 2017, 139, 14049–14052; [DOI] [PMC free article] [PubMed] [Google Scholar]; m) Sato H, Fukaya K, Poudel BS, Krische MJ, Angew. Chem. Int. Ed 2017, 56, 14667–14671; [DOI] [PMC free article] [PubMed] [Google Scholar]; n) Yang X-H, Davison RT, Dong VM, J. Am. Chem. Soc 2018, 140, 10443–10446; [DOI] [PMC free article] [PubMed] [Google Scholar]; o) Nie S-Z, Davison RT, Dong VM, J. Am. Chem. Soc 2018, 140, 16450–16454; [DOI] [PMC free article] [PubMed] [Google Scholar]; p) Trost BM, Huang Z, Murhade GM, Science, 2018, 362, 564–568. [DOI] [PubMed] [Google Scholar]; q) Yang X-H, Davison RT, Nie S-Z, Cruz FA, McGinnis TM, Dong VM, J. Am. Chem. Soc 2019, 141, 3006–3013; [DOI] [PMC free article] [PubMed] [Google Scholar]; r) Marcum JS, Cervarich TN, Manan RS, Roberts CC, Meek SJ, ACS Catal. 2019, 9, 5881–5889; [Google Scholar]; s) Fiorito D, Mazet C, ACS Catal. 2018, 8, 9382–9387; [Google Scholar]; t) Zhang Q, Yu H, Shen L, Tang T, Dong D, Chai W, Zi W, J. Am. Chem. Soc 2019, 141, 14554–14559. [DOI] [PubMed] [Google Scholar]
  • [13].a) Solan GA, Reactions of Transition Metal π-Complexes of Alkenes, Alkynes and Dienes, In Organometallic Chemistry, Vol. 32 (Ed. Green M), RSC, 2005, pp. 342–347; [Google Scholar]; b) Crabtree RH, In The Organometallic Chemistry of the Transition Metals, 5th ed, Wiley, Hoboken, 2009, pp. 132–134; [Google Scholar]; c) Hartwig JF, In Organotransition Metal Chemistry, University Science Books, United States, 2010, pp 439–442. [Google Scholar]
  • [14].Select diene complexes of early transition metals:; a) Erker G, Wicher J, Engel K, Rosenfeldt F, Dietrich W, Krüger C, J. Am. Chem. Soc 1980, 102, 6344–6346; [Google Scholar]; b) Erker G, Wicher J, Engel K, Krüger C, Chem. Ber 1982, 115, 3300–3309; [Google Scholar]; c) Yasuda H, Kajihara Y, Mashima K, Nagasuna K, Lee K, Nakamura A, Organometallics, 1982, 1, 388–396; [Google Scholar]; d) Hunter AD, Legzdins P, Nurse CR, Einstein FWB, Willis AC, J. Am. Chem. Soc 1985, 107, 1791–1792; [Google Scholar]; e) Hunter AD, Legzdins P, Nurse CR, Einstein FWB, Willis AC, Bursten BE, Gatter MG, J. Am. Chem. Soc 1986, 108, 3843–3844; [Google Scholar]; f) Christensen NJ, Hunter AD, Legzdins P, Organometallics, 1989, 8, 930–940; [Google Scholar]; g) Benyunes SA, Green M, Grimshire MJ, Organometallics, 1989, 8, 2268–2270; [Google Scholar]; h) Vong W-J, Peng S-M, Liu R-S, Organometallics, 1990, 9, 2187–2189; [Google Scholar]; i) Christensen NJ, Legzdins P, Einstein FWB, Jones RH, Organometallics, 1991, 10, 3070–3080; [Google Scholar]; j) Debad JD, Legzdins P, Young MA, Batchelor RJ, Einstein FWB, J. Am. Chem. Soc 1993, 115, 2051–2052; [Google Scholar]; k) Wang L-S, Fettinger JC, Poli R, J. Am. Chem. Soc 1997, 119, 4453–4464; [Google Scholar]; l) Poli R, Wang L-S, J. Am. Chem. Soc 1998, 120, 2831–2842; [Google Scholar]; m) Beddows CJ, Box MR, Butters C, Carr N, Green M, Kursawe M, Mahon MF, J. Organomet. Chem 1998, 550, 267–282; [Google Scholar]; n) Wang L-S, Fettinger JC, Poli R, Meunier-Prest R, Organometallics, 1998, 17, 2692–2701; [Google Scholar]; o) Ng SHK, Adams CS, Hayton TW, Legzdins P, Patrick BO, J. Am. Chem. Soc 2003, 125, 15210–15223; [DOI] [PubMed] [Google Scholar]; p) Erker G, Kehr G, Frölich R, J. Organomet. Chem 2004, 689, 4305–4318; [Google Scholar]; q) Nakamura A, Mashima K, J. Organomet. Chem 2004, 689, 4552–4563; [Google Scholar]; r) Erker G, Kehr G, Frölich R, Adv. Organomet. Chem 2004, 51, 109–162; [Google Scholar]; s) Joannou MV, Bezdek MJ, Al-Bahily K, Korobkov I, Chirik PJ, Organometallics, 2017, 36, 4215–4223. [Google Scholar]
  • [15].Select diene complexes of [Cr]:; a) Koerner von Gustorf EA, Jaenicke O, Polansky OE, Angew. Chem. Int. Ed 1972, 11, 532–533; [Google Scholar]; b) Koerner von Gustorf EA, Jaenicke O, Wolfbeis O, Eady CR, Angew. Chem. Int. Ed 1975, 14, 278–286; [Google Scholar]; c) Fischler I, Budzwait M, Koerner von Gustorf EA, J. Organomet. Chem 1976, 105, 325–330; [Google Scholar]; d) Kreiter CG, Özkar S, J. Organomet. Chem 1978, 152, C13–C18; [Google Scholar]; e) Kotzian M, Kreiter CG, Özkar S, J. Organomet. Chem 1982, 229, 29–42; [Google Scholar]; f) Kreiter CG, Kotzian M, J. Organomet. Chem 1985, 289, 295–308; [Google Scholar]; g) Wang NF, Wink DJ, Dewan JC, Organometallics, 1990, 9, 335–340; [Google Scholar]; h) Betz P, Döhring A, Emrich R, Goddard R, Jolly PW, Krüger C, Romão C, Schönfelder KU, Tsay Y-H, Polyhedron, 1993, 12, 2651–2662; [Google Scholar]; i) Döhring A, Göhre J, Jolly PW, Kryger B, Rust J, Verhovnik GPJ, Organometallics, 2000, 19, 388–402; [Google Scholar]; j) Norman DW, Ferguson MJ, McDonald R, Stryker JM, Organometallics, 2006, 25, 2705–2708; [Google Scholar]; k) Monillas WH, Young JF, Yap GPA, Theopold KH, Dalton Trans. 2013, 42, 9198–9210. [DOI] [PubMed] [Google Scholar]
  • [16].Select diene complexes of late 4d and 5d metals:; a) Melendez E, Ilarraza R, Yap GPA, Rheingold AL, J. Organomet. Chem 1996, 522, 1–7; [Google Scholar]; b) Gemel C, Mereiter K, Schmid R, Kirchner K, Organometallics, 1997, 16, 2623–2626; [Google Scholar]; c) Fukumoto H, Mashima K, Organometallics, 2005, 24, 3932–3938; [Google Scholar]; d) Fukumoto H, Mashima K, Eur. J. Inorg. Chem 2006, 5006–5011; [Google Scholar]; e) Hirano M, Sakate Y, Inoue H, Arai Y, Komine N, Komiya S, Wang X.-q., Bennett MA, J. Organomet. Chem 2012, 708–709, 46–57. [Google Scholar]
  • [17].Select diene complexes of [Fe]:; a) Knölker H-J, Chem. Rev 2000, 100, 2941–2962; [DOI] [PubMed] [Google Scholar]; b) Reihlen H, Gruhl A, Hessling G. v., Pfrengle O, Liebigs Ann. Chem 1930, 482, 161–182; [Google Scholar]; c) Hallam BF, Pauson PL, J. Chem. Soc 1958, 642–645; [Google Scholar]; d) Bachler V, Grevels F-W, Kerpen K, Olbrich G, Schaffner K, Organometallics, 2003, 22, 1696–1711; [Google Scholar]; e) Bouwkamp MW, Bowman AC, Lobkovsky E, Chirik PJ, J. Am. Chem. Soc 2006, 128, 13340–13341; [DOI] [PubMed] [Google Scholar]; f) Russell SK, Milsmann C, Lobkovsky E, Weyhermüller T, Chirik PJ, Inorg. Chem 2011, 50, 3159–3169; [DOI] [PubMed] [Google Scholar]; g) Russell SK, Lobkovsky E, Chirik PJ. J. Am. Chem. Soc 2011, 133, 8858–8861; [DOI] [PubMed] [Google Scholar]; h) Hu L, Chen H, J. Am. Chem. Soc 2017, 139, 15564–15567. [DOI] [PubMed] [Google Scholar]
  • [18].a) Rappoport Z, Liebman JF, In The Chemistry of Cyclobutanes, Wiley, Chichester, UK, 2005, pp. 281–355; [Google Scholar]; b) Xu Y, Conner ML, Brown MK, Angew. Chem. Int. Ed 2015, 54, 11918–11928; [DOI] [PubMed] [Google Scholar]; c) Secci F, Frongia A, Piras PP, Molecules, 2013, 18, 15541–15572; [DOI] [PMC free article] [PubMed] [Google Scholar]; d) Winkler JD, Bowen CM, Liotta F, Chem. Rev 1995, 95, 2003–2020; [Google Scholar]; e) Lee-Ruff E, Mladenova G, Chem. Rev 2003, 103, 1449–1484; [DOI] [PubMed] [Google Scholar]; f) Dembitsky VM Phytomedicine, 2014, 21, 1559–1581; [DOI] [PubMed] [Google Scholar]; g) Carreira EM, Fessard TC, Chem. Rev 2014, 114, 8257–8322; [DOI] [PubMed] [Google Scholar]; h) Wager TT, Pettersen BA, Schmidt AW, Spracklin DK, Mente S, Butler TW, Howard H, Lettiere DJ, Rubitski DM, Wong DF, Nedza FM, Nelson FR, Rollema H, Raggon JW, Aubrecht J, Freeman JK, Marcek JM, Cianfrogna J, Cook KW, James LC, Chatman LA, Iredale PA, Banker MJ, Homiski ML, Munzner JB, Chandrasekaran RY, J. Med. Chem 2011, 54, 7602–7620; [DOI] [PubMed] [Google Scholar]; i) Blakemore DC, Bryans JS, Carnell P, Carr CL, Chessum NEA, Field MJ, Kinsella N, Osborne SA, Warren AN, Williams SC, Bioorg. Med. Chem. Lett 2010, 20, 461–464; [DOI] [PubMed] [Google Scholar]; j) Slade J, Bajwa J, Liu H, Parker D, Vivelo J, Chen G-P, Calienni J, Villhauer E, Prasad K, Repič O, Blacklock TJ, Org. Process Res. Dev 2007, 11, 825–835; [Google Scholar]; k) Singh J, Bisacchi GS, Ahmad S, Godfrey JD, Kissick TP, Mitt T, Kocy O, Vu T, Papaioannou CG, Wong MK, Heikes JE, Zahler R, Mueller RH, Org. Process Res. Dev 1998, 2, 393–399. [Google Scholar]
  • [19].Mashima K, Nakamura A, J. Organomet. Chem 2002, 663, 5–12. [Google Scholar]
  • [20].Hoyt JM, Schmidt VA, Tondreau AM, Chirik PJ, Science, 2015, 349, 960–963. [DOI] [PubMed] [Google Scholar]
  • [21].Trace amounts of cyclobutane, (Z)-propenylcyclobutane, and a linear product tentatively assigned as 1,5-heptadiene were also observed.
  • [22].Formation of mixed [2+2]-cycloadducts from the combination of (E)-piperylene and ethylene using a titanium catalyst has been observed previously:; Cannell LG, J. Am. Chem. Soc 1972, 94, 6867–6869. [Google Scholar]
  • [23].a) Appukuttan VK, Liu Y, Son BC, Ha C-S, Suh H, Kim I, Organometallics, 2011, 30, 2285–2294; [Google Scholar]; b) Hoyt JM, Sylvester KT, Semproni SP, Chirik PJ, J. Am. Chem. Soc 2013, 135, 4862–4877. [DOI] [PubMed] [Google Scholar]
  • [24].a) McTavish S, Britovsek GJP, Smit TM, Gibson VC, White AJP, Williams DJ, J. Mol. Cat. A, 2007, 261, 293–300; [Google Scholar]; b) Perry MR, Allan LEN, Decken A, Shaver MP, Dalton Trans. 2013, 42, 9157–9165; [DOI] [PubMed] [Google Scholar]; c) Schmidt VA, Hoyt JM, Margulieux GW, Chirik PJ, J. Am. Chem. Soc 2015, 137, 7903–7914. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [25].a) Römelt C, Weyhermüller T, Wieghardt K, Coord. Chem. Rev 2019, 380, 287–317; [Google Scholar]; b) Bart SC, Chlopek K, Bill E, Bouwkamp MW, Lobkovsky E, Neese F, Wieghardt K, Chirik PJ, J. Am. Chem. Soc 2006, 128, 13901–13912; [DOI] [PubMed] [Google Scholar]; c) Bart SC, Lobkovsky E, Bill E, Wieghardt K, Chirik PJ, Inorg. Chem 2007, 46, 7055–7063. [DOI] [PubMed] [Google Scholar]
  • [26].a) Zhao Y, Truhlar DG, Theor. Chem. Account, 2008, 120, 215–241; [Google Scholar]; b) Wang Y, Jin X, Yu HS, Truhlar DG, He X, Proc. Nat. Acad. Sci. U.S.A 2017, 114, 8487–8492. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [27].Calculations were performed with the ZORA-def2-TZVP(-f) basis set augmented by SARC/J terms for Fe, N, and C atoms in the primary coordination sphere, and the ZORA-def2-SVP basis set augmented with SARC/J terms for all other atoms:; a) Neese F, WIREs Comput. Mol. Sci 2012, 2, 73–78; [Google Scholar]; b) Neese F, WIREs Comput. Mol. Sci 2018, 8, e1327; [Google Scholar]; c) Pople JA, Gill PMW, Handy NC, Int. J. Quantum Chem 1995, 56, 303–305; [Google Scholar]; d) Weigend F, Ahlrichs R, Phys. Chem. Chem. Phys 2005, 7, 3297–3305; [DOI] [PubMed] [Google Scholar]; e) Weigend F, Phys. Chem. Chem. Phys 2006, 8, 1057–1065; [DOI] [PubMed] [Google Scholar]; f) Ekstrom U, Visscher L, Bast R, Thorvaldsen AJ, Ruud K, Chem J. Theory Comput. 2010, 6, 1971–1980; [DOI] [PubMed] [Google Scholar]; g) van Wüllen C, J. Chem. Phys 1998, 109, 392–399; [Google Scholar]; h) Pantazis DA, Chen X-Y, Landis CR, Neese F, Chem J. Theory Comput. 2008, 4, 908–919. [DOI] [PubMed] [Google Scholar]
  • [28].CYLview, 1.0b; Legault CY, Université de Sherbrooke, 2009. (http://www.cylview.org)
  • [29].The dynamic behavior was recapitulated both under an atmosphere of N2 and following three freeze-pump-thaw cycles. This observation suggests that the mechanism for exchange does not involve N2.
  • [30].The spectrum recorded at −93 °C exhibited globally broadened resonances due to the increased viscosity of the toluene solvent at this temperature. As such, data at this temperature were not included in the Eyring analysis.
  • [31].a) Anet FAL, Bourn AJR, J. Am. Chem. Soc 1967, 89, 760–768; [Google Scholar]; b) Brookhart M, Hauptman E, Lincoln D, J. Am. Chem. Soc 1992, 114, 10394–10401; [Google Scholar]; c) Gasparro FP; Kolodny NH, J. Chem. Ed 1977, 54, 258–261; [Google Scholar]; d) Diaz A, Radzewich C, Wicholas M, J. Chem. Ed 1995, 72, 937–938. [Google Scholar]
  • [32].Perrin CL, Dwyer TJ, Chem. Rev 1990, 90, 935–967. [Google Scholar]
  • [33].A second 2D EXSY spectrum was recorded for a sample of (Me(Et)PDI)Fe(η4-piperylene) with no added piperylene; nonetheless, the same cross-peaks were observed.
  • [34].a) Blackmond DG, Angew. Chem. Int. Ed 2005, 44, 4302–4320; [DOI] [PubMed] [Google Scholar]; b) Blackmond DG, J. Am. Chem. Soc 2015, 137, 10852–10866; [DOI] [PubMed] [Google Scholar]; c) Nielsen CD-T, Burés J, Chem. Sci 2019, 10, 348–353. [DOI] [PMC free article] [PubMed] [Google Scholar]
  • [35].While butadiene is a gas at ambient temperature and pressure, its high solubility coefficient in hydrocarbon solvents renders its vapor pressure negligible under the conditions examined. See:; Hayduk W, Minhas BS. J. Chem. Eng. Data, 1987, 32, 285–290. [Google Scholar]
  • [36].The presence of ethylene in solution was also readily detected under these reaction conditions. Due to the extremely long relaxation time of the C2H4 resonance, as well as its spectral overlap with propenylcyclobutane CH resonances, reliable quantitation under the reaction conditions proved challenging. However, approximate ethylene concentrations estimated from peak fitting deconvoution were in reasonable agreement with values expected from the absolute amount of ethylene added in the reaction head space (see Supporting Information). Taken together, these observations suggest that reaction rates are not limited by diffusion of ethylene into solution. See also:; a) Zhuze TP, Zhurba AS. Russ. Chem. Bull 1960, 9, 335–337; [Google Scholar]; b) Sahgal A, Hayduk W. J. Chem. Eng. Data, 1979, 24, 222–227. [Google Scholar]
  • [37].However, an alternative mechanism, wherein reductive coupling is rate-determining and is followed by diene coordination prior to or concomitant with product dissociation, cannot be excluded on the basis of the data available.
  • [38].a) Briggs JR. J. Chem. Soc. Chem. Commun 1989, 674–675; [Google Scholar]; b) Dixon JT, Green MJ, Hess FM, Morgan DH, J. Organomet. Chem 2004, 689, 3641–3668; [Google Scholar]; c) McGuinness DS. Chem. Rev 2011, 111, 2321–2341; [DOI] [PubMed] [Google Scholar]; d) Rummelt SM, Zhong H, Korobkov I, Chirik PJ, J. Am. Chem. Soc 2018, 140, 11589–11593. [DOI] [PubMed] [Google Scholar]
  • [39].Pangborn AB, Giardello MA, Grubbs RH, Rosen RK, Timmers FJ, Organometallics, 1996, 15, 1518–1520. [Google Scholar]
  • [40].a) Russell SK, Darmon JM, Lobkovsky E, Chirik PJ, Inorg. Chem 2010, 49, 2782–2792; [DOI] [PubMed] [Google Scholar]; b) Russell SK, Hoyt JM, Bart SC, Milsmann C, Stieber SCE, Semproni SP, DeBeer S, Chirik PJ. Chem. Sci 2014, 5, 1168–1174. … [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

SI
NIHMS1061032-supplement-SI.pdf (2.5MB, pdf)

RESOURCES