Skip to main content
NCBI home page
ACS AuthorChoice logoLink to ACS AuthorChoice
. 2023 Dec 12;145(51):27922–27932. doi: 10.1021/jacs.3c10491

A Cooperative Cobalt-Driven System for One-Carbon Extension in the Synthesis of (Z)-Silyl Enol Ethers from Aldehydes: Unlocking Regio- and Stereoselectivity

Soumyashree Jena †,‡, Lars Frenzen †, Vishal Chugh †,‡, Jiajun Wu †, Thomas Weyhermüller †, Alexander A Auer §, Christophe Werlé †,‡,*
PMCID: PMC10755702  PMID: 38086018

Abstract

graphic file with name ja3c10491_0009.jpg

The research presented herein explores a cobalt-based catalytic system, distinctively featuring a cooperative boron-centric element within its intricate ligand architecture. This system is strategically engineered to enable the integration of a singular carbon atom into aldehydes, a process culminating in the production of (Z)-silyl enol ethers. Beyond offering an efficient one-pot synthesis route, this method adeptly overcomes challenges inherent to conventional techniques, such as the need for large amounts of additives, restrictive functional group tolerance, and extreme reaction temperatures. Initial mechanistic studies suggest the potential role of a cobalt–carbene complex as a catalytically significant species and underscore the importance of the borane segment. Collectively, these observations highlight the potential of this system in advancing complex bond activation pursuits.

Naturally occurring catalysts exhibit remarkable precision in controlling chemical bond dynamics, using synergistic interactions within their structures to selectively activate and transform substrates.1 Scientists have replicated these phenomena in laboratory settings, enabling the activation and transformation of traditionally unreactive small molecules.2,3

The focal point of our research program encompasses the advancement of dynamic and adaptive molecular systems capable of facilitating complex bond activations.4 Such systems are particularly salient in the domain of chemical energy conversion, where obstacles arise due to variable energy supplies and inconsistent feedstock quality. Through modulation of the reactivity, these dynamic catalyst systems target efficient resource allocation and optimization.

Leveraging our previous advancements, we have now concentrated our efforts on the formation of carbon–carbon bonds,5 specifically the incorporation of a single carbon atom into aldehydes to produce silyl enol ethers, a standing challenge in bond activation.

Silyl enol ethers are pivotal intermediates in many synthetic transformations.6 While traditional synthesis methods have proven insightful and in certain instances exceptionally elegant, they come with limitations.7,8 These include the need for excessive amounts of base, functional group sensitivity, potential over-reductions, and strict reaction conditions (Scheme 1A).9

Scheme 1. Development of a Cooperative Catalytic System for Selective (Z)-Silyl Enol Ether Synthesis from Aldehydes.

Scheme 1

Open in a new tab

(A) Current methods.8 (B) Syntheses using rhodium complexes.13b,13c (C) Guiding principle for our approach. (D) Concept validation.

In the pursuit of aligning the synthesis processes with environmentally conscious methodologies advancing the principles of Green Chemistry,10 researchers have been directed toward employing transition metals.11

However, in the prevailing research landscape, a substantial number of studies preferentially focus on noble metals12,8q and significantly emphasize the usage of ketones as starting materials (Scheme 1B).13,12b In contrast, protocols that explore the addition of a single carbon atom to aldehydes, culminating in the synthesis of silyl enol ethers, especially when utilizing base metal catalysts, have been exceedingly limited.

In our quest to navigate the complexities specific to this area of research, we devised a strategy tailored to the unique demands of the target substrate. Central to our approach is a catalytic system, integrating a cobalt center synergistically paired with a boron site in its secondary coordination sphere.14,15 This configuration is engineered to proficiently engage in simultaneous activation: targeting the carbonyl unit at the boron site and (trimethylsilyl)diazomethane (Me3SiCHN2) at the cobalt site. We propose that this cooperative dual-activation mode not only enables the pivotal carbon atom transfer necessary for C–C bond genesis but also orchestrates the delivery of the −SiMe3 group to the nascent alcohol functionality, all while expelling nitrogen as the sole byproduct (Scheme 1C).16

Considering the specified parameters, a procedure is proposed for one-carbon extension in the synthesis of (Z)-silyl enol ethers derived from aldehydes, utilizing a Co-based catalytic system (Scheme 1D). This catalytic framework demonstrates exceptional versatility, accommodating a broad spectrum of substrates without the necessity of specific functional groups. Importantly, this system operates efficiently under comparatively mild conditions, thereby obviating the need for stringent temperature controls and ensuring the preservation of other potentially susceptible functional groups.

Results and Discussion

To assess the viability of the proposed strategy, the initial step involved the synthesis of cobalt complex 1 (Scheme 2). This complex encompasses a triazine-based PNtzn-B ligand (A).4d The ligand structure was designed to merge an electron-withdrawing triazine core with an electron-donating phosphine. A boron component was incorporated into the secondary coordination sphere, specifically to mediate substrate capture and activation during the reaction sequence. The targeted Co(III) complex was synthesized from the precursor [Cp*Co(CH3CN)3](SbF6)2 (7).17 A detailed protocol for synthesis and complex characterization, which supports the illustrated binding scenario in Scheme 2, is further elaborated in the Supporting Information (SI).18

Scheme 2. (A) Synthesis of Complex 1; (B) 40% Probability Thermal Ellipsoid of 1•CH3CN with Partial Atom Numbering.

Scheme 2

Open in a new tab

SbF6 anions, protons, and extra solvents were omitted for clarity.

To evaluate the protocol’s broad applicability, standard reaction conditions were established using 4-methyl benzaldehyde. The optimized method, detailed in Table 1, emerged from a comprehensive screening of the various conditions. Initial trials utilized catalyst 1 in acetonitrile at 40 °C with 1 equiv of Me3SiCHN2, yielding (Z)-silyl enol ether 3b (76%) and (E)-silyl enol ether 4b (14%).19 Further optimization explored various solvents. Nonpolar options like toluene and mesitylene lowered selectivity (Table 1, entry 2; Table S1, entries 4–6), while dichloromethane yielded the best performance (Table 1, entry 4). Temperature studies indicated that variations from 25 °C had minimal effect on selectivity (Table 1, entries 5–6). Modifying catalyst loading and shortening reaction time to 1 h fine-tuned the protocol, leading to an 87% yield of (Z)-silyl enol ether 3b (Table 1, entry 9). A control experiment without a catalyst showed no aldehyde conversion (Table 1, entry 10).

Table 1. Reaction Optimization.

graphic file with name ja3c10491_0007.jpg

graphic file with name ja3c10491_0008.jpg

Open in a new tab
a

Yield (%) is based on 1H NMR relative to mesitylene (0.2 mmol) as an internal standard.

The protocol’s versatility was assessed through a broad substrate scope (Scheme 3). Many substrates, despite varied functionalities, reacted efficiently, highlighting the protocol’s robustness. Alkyl-substituted aryl aldehydes showed strong selectivity for (Z)-silyl enol ether synthesis (3b–f). Biphenyl (2h) and polyaromatic aldehydes (2i–l) also converted well, with moderate to satisfactory yields. Halogenated (2m–o) and electron-rich (2p–x) substrates showed similar selectivity, the latter reducing the level of unwanted compound 5 formation. The protocol effectively handled heterocyclic (2y, 2z, 2aa–ab) and base-sensitive substrates like hydroxyl (2u), alkyne (2g), and Boc-protected amines (2w). Dual aldehyde substrates (2ac–ad) mostly yielded (Z)-silyl enol ethers. However, substrates featuring electron-withdrawing groups such as cyano (2ae), nitro (2af), and trifluoromethyl (2ah) also led to the formation of internal silyl enol ether (5ae, 5af, and 5ah). This behavior could potentially be attributed to the limited migration capabilities of these aryl groups, which seem to favor hydride migration over that of their aryl counterparts.20

Scheme 3.

Scheme 3

Open in a new tab

Conversion and selectivity based on 1H NMR with mesitylene (0.2 mmol) standard.

Isolated yield of (Z)-silyl enol ethers.

Used 2 equiv of Me3SiCHN2.

To understand the catalyst’s mechanics, action mode, and comparative performance, we conducted control experiments. These focused on the impact of the structural elements on the reaction efficiency. Initial tests compared its efficacy with analogous systems and traditional Lewis acid catalysts (Scheme 4). Results showed that, under optimized conditions, none outperformed our principal catalyst.21

Scheme 4. (A) Catalyst Systems Compared under Optimized Conditions; (B) Graph Illustrating Differences in Catalytic Performance.

Scheme 4

Open in a new tab

To isolate the impact of the peripheral boron center, we created complex 6 without a boron arm and analyzed its catalytic behavior. Under standard conditions, catalyst 6 showed reduced yield and selectivity, 3b (62%) and 4b (11%), compared to 1.

To expand our understanding, several intermolecular variants of compound 1 were synthesized by reacting complex 6 with exogenous boron-based additives, culminating in systems 9–11. While these modifications resulted in enhanced reactivity compared to 6, they did not reach the yield and selectivity demonstrated by 1.

Boron’s impact on catalysis was studied using boron-binding additives like NEt3 and MeOH. These additives lowered the conversion and yield of 3b compared to 1 (Scheme 5A).15a11B NMR studies supported boron’s ability to interact with, bind with, and potentially activate substrates. This was evidenced by the observed new chemical shifts in the presence of MeOH or NEt3 (Scheme 5B).23,22e,4d Importantly, in a CD2Cl2 solution with compound 1 and 4-methyl benzaldehyde, a unique 11B resonance at δ 57.6 ppm appeared, similar to the signal observed at δ 57.5 ppm when the aldehyde was combined with 9-HBBN, suggesting carbonyl activation at the boron site. Incorporating Me3SiCHN2 into the mixture containing 1 eliminated the original resonance and unveiled (Z)-silyl enol ether signals in the 1H NMR spectrum.24

Scheme 5. Empirical Mechanism Studies.

Scheme 5

Open in a new tab

(A) Boron’s impact on catalysis. (B) Presents a comparison of adducts as characterized by 11B NMR spectroscopy alongside referenced literature values.22 (C) Activation mechanism of Me3SiCHN2. (D) Probing radicals with TEMPO. (E) Examination of alkenyl migration and 1,2-Brook rearrangement.

Subsequent investigations were directed toward unraveling the fundamental mechanism at play. Historically, studies into one-carbon homologation processes have hinted at the formation of a metal–carbene complex post-N2 extrusion25 or, as an alternative, the generation of metal-bound diazo complexes.26 An observation of particular note was the instantaneous release of nitrogen gas upon the stepwise addition of Me3SiCHN2 to complex 1. Remarkably, this phenomenon was consistent even at profoundly low temperatures, such as −80 °C. Motivated by this finding, an array of studies was undertaken to delve into the solution’s internal dynamics and to pinpoint possible intermediates of the metal catalyst. The methodology involved executing several reactions between catalyst 1 and the diazoalkane under both ambient and reduced temperatures.27 Subsequent 1H NMR analysis evidenced the complete depletion of Me3SiCHN2, unmasking organic derivatives such as the homocoupled alkene, azine, and various compounds enriched with nitrogen and silicon (Scheme 5C1). While these derivatives do not conclusively point toward metal carbene synthesis, their properties are suggestive of carbene-mimetic reactivity.28

Attempts to fully characterize any carbene-related intermediate via NMR spectroscopy largely proved futile given the highly reactive nature of the metal-based species generated. Nevertheless, the nearest structural approximation at this stage was derived from the stoichiometric reaction between compounds 1 and Me3SiCHN2, culminating in the identification of a novel species, denoted as 1″ (Scheme 5C2–C3; see the SI for details).29 These observations were in accordance with existing literature, indicating the potential for the −CHSiMe3 fragment from diazomethane to integrate into the B–C bonds of the 9-BBN ring.30a,16a,30b

The most compelling evidence of metal–carbene formation was gleaned when a −60 °C sample, a mixture of complex 1 and diazoalkane incorporated shortly prior to the procedure, was swiftly introduced into a mass spectrometer. This analysis revealed a high-resolution molecular mass consistent with the anticipated cobalt carbene (Scheme 5C4). Further, when juxtaposing the molecular structure of complex 1 with other cobalt complexes from the literature, it becomes clear that complex 1, characterized by its higher oxidation state (+III), lacks the charge transfer capability observed in previously described low-coordinate, low-valent systems.26 This discrepancy makes the system more prone to generating carbene intermediates after nitrogen release.31 As a result, an end-on binding scenario, characterized by a considerable overlap between high-lying, filled metal d-orbitals and diazoalkane π*-orbitals, which would theoretically lead to charge accumulation on the diazoalkane and strengthening of metal–nitrogen and carbon–nitrogen bonds to prevent nitrogen loss, appears less probable.

Pivoting to another facet, we investigated the potential involvement of free or carbenoid radicals in the reaction pathway (Scheme 5D).32,25d The method chosen was a radical trapping experiment employing the radical scavenger 2,2,6,6-tetramethylpiperidinyloxyl (TEMPO). Notably, product formation was not affected by the presence of TEMPO, which discarded this hypothesis.

In an effort to delve deeper into the reaction pathway, a deuterium labeling experiment was executed (Scheme 5E).

The experiment utilized deuterated benzaldehyde and Me3SiCHN2 under optimized conditions. The results revealed a predominant formation of the (Z)-[D] 3a′ isomer, accounting for 65% of the product, alongside a less prevalent (E)-[D] 4a′ isomer at 13%. This outcome indicates the reaction pathway likely involves aryl migration rather than hydride migration13b or epoxide formation.33,13c

Preliminary density functional theory (DFT) computations, conducted at the RI-B3LYP/def2-svp D3BJ level34 with the CPCM solvent model for dichloromethane (using the ORCA 5.0 software),35 align with our experimental results (see the SI for details). Geometry optimization confirmed carbene 1′ as a distinct minimum on the potential energy surface. Although several potential ether and epoxy intermediates were identified, their formation was either energetically unfavorable or necessitated high activation energies, suggesting a negligible or nonexistent role in the mechanistic pathway.

Subsequently, our attention shifted to delineating the aryl migration pathway by examining the variations in potential energy associated with the modulation of pivotal carbon–carbon bond lengths; specifically, the bond between the migrating aryl carbon and the recipient CH carbon during the genesis of (Z)-isomer (3b) and (E)-isomer (4b). These investigations unveiled exothermic reaction pathways characterized by small activation barriers, thus substantiating the proposed mechanism that assigns a central role to the aryl group rearrangement.

Notably, our computational analysis indicated that the (Z)-isomer benefits from reduced steric hindrance between the trimethylsilyl segment and the large borane group, relative to its (E)-isomer counterpart, which likely affects the reaction’s stereoselectivity. Additionally, we estimated a marginal energetic preference for the (Z)-isomer, around 5 kJ/mol, corroborating the cis-product predominance observed in our experimental pursuits and offering a theoretical basis for the reaction’s observed stereoselectivity.

Integrating the information gathered thus far, we propose a mechanism for the synthesis of (Z)-silyl enol ethers from aromatic aldehydes, tentatively commencing with complex 1, as illustrated in Scheme 6. This mechanistic pathway suggests that the boron atom, situated in the secondary coordination sphere, plays a pivotal role in capturing and activating the aldehyde functional group. Following the addition of Me3SiCHN2, the evidence leans toward the emergence of a reactive cobalt–carbene rather than a cobalt-diazoalkane species, a conclusion supported by the consistent observation of vigorous gas evolution and the high-valent nature of the cobalt complex. This cobalt–carbene intermediate is theorized to facilitate the incorporation of the Me3SiCHN2 carbon into the aldehyde. The reaction sequence is then thought to continue with a Brook rearrangement and culminate in aryl migration, ultimately yielding the targeted (Z)-silyl enol ether product.

Scheme 6. Tentative Reaction Mechanism.

Scheme 6

Open in a new tab

Conclusion

Inspired by the inherent efficacy of natural catalytic systems, we have developed a cobalt-based catalyst specifically engineered for the stereoselective incorporation of a single carbon atom into aldehydes, facilitating the synthesis of (Z)-silyl enol ethers. Central to the catalyst’s design is a Lewis acidic boron center, strategically integrated within a triazine ligand, which plays a pivotal role in augmented bond activation. This advancement not only positions cobalt as a viable, cost-effective substitute for the traditionally favored noble metals but also adeptly addresses multiple prevailing challenges in the synthesis of silyl enol ethers. These challenges include obstacles like regioselectivity, the necessity for large quantities of additives, limited functional group tolerance, and the requirement for extreme reaction temperatures. Our methodology distinguishes itself by operating under comparatively milder conditions and demonstrating remarkable versatility, as evidenced by its ability to process a diverse array of aromatic aldehyde substrates, each possessing various functionalities. This achievement marks a substantial leap forward in the realm of controlled bond activations within synthetic chemistry. Future work will focus on similar systems, aiming to deepen our understanding, refine our methodology, and broaden the range of achievable chemical transformations.

Acknowledgments

We gratefully acknowledge the Max Planck Society for its generous financial support. The research presented herein was conducted under the auspices of the “Fuel Science Center” funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy–Exzellenzcluster 2186, The Fuel Science Center “ID: 90919832”. We thank Dr. Christophe Farès for his insightful discussions, particularly in the identification of 1″ via NMR spectroscopy. We are also deeply indebted to Prof. Dr. Walter Leitner for his consistent and enduring support. Open access funding is enabled and organized by Projekt DEAL.

Data Availability Statement

The data that support the findings of this study (e.g., general considerations, experimental methods, synthetic details, computed structures, copies of NMR spectra, and crystallographic data) are available in the Supporting Information of this article.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/jacs.3c10491.

  • General considerations, experimental methods, synthetic details, computed structures, copies of NMR spectra, and crystallographic data (PDF)

Author Contributions

# S.J., L.F., and V.C. contributed equally to this work.

Open access funded by Max Planck Society.

The authors declare no competing financial interest.

Supplementary Material

ja3c10491_si_001.pdf (8.9MB, pdf)

References

  1. a McEvoy J. P.; Brudvig G. W. Water-splitting chemistry of photosystem II. Chem. Rev. 2006, 106, 4455–4483. 10.1021/cr0204294. [DOI] [PubMed] [Google Scholar]; b Thorseth M. A.; Tornow C. E.; Tse E. C. M.; Gewirth A. A. Cu complexes that catalyze the oxygen reduction reaction. Coord. Chem. Rev. 2013, 257, 130–139. 10.1016/j.ccr.2012.03.033. [DOI] [Google Scholar]; c Broderick J. B.; Duffus B. R.; Duschene K. S.; Shepard E. M. Radical S-adenosylmethionine enzymes. Chem. Rev. 2014, 114, 4229–4317. 10.1021/cr4004709. [DOI] [PMC free article] [PubMed] [Google Scholar]; d Lubitz W.; Ogata H.; Rudiger O.; Reijerse E. Hydrogenases. Chem. Rev. 2014, 114, 4081–4148. 10.1021/cr4005814. [DOI] [PubMed] [Google Scholar]; e Liu J.; Chakraborty S.; Hosseinzadeh P.; Yu Y.; Tian S.; Petrik I.; Bhagi A.; Lu Y. Metalloproteins containing cytochrome, iron-sulfur, or copper redox centers. Chem. Rev. 2014, 114, 4366–4469. 10.1021/cr400479b. [DOI] [PMC free article] [PubMed] [Google Scholar]; f Solomon E. I.; Heppner D. E.; Johnston E. M.; Ginsbach J. W.; Cirera J.; Qayyum M.; Kieber-Emmons M. T.; Kjaergaard C. H.; Hadt R. G.; Tian L. Copper active sites in biology. Chem. Rev. 2014, 114, 3659–3853. 10.1021/cr400327t. [DOI] [PMC free article] [PubMed] [Google Scholar]; g Wang V. C.; Maji S.; Chen P. P.; Lee H. K.; Yu S. S.; Chan S. I. Alkane Oxidation: Methane Monooxygenases, Related Enzymes, and Their Biomimetics. Chem. Rev. 2017, 117, 8574–8621. 10.1021/acs.chemrev.6b00624. [DOI] [PubMed] [Google Scholar]; h Seefeldt L. C.; Hoffman B. M.; Peters J. W.; Raugei S.; Beratan D. N.; Antony E.; Dean D. R. Energy Transduction in Nitrogenase. Acc. Chem. Res. 2018, 51, 2179–2186. 10.1021/acs.accounts.8b00112. [DOI] [PMC free article] [PubMed] [Google Scholar]; i Dunham N. P.; Arnold F. H. Nature’s Machinery, Repurposed: Expanding the Repertoire of Iron-Dependent Oxygenases. ACS Catal. 2020, 10, 12239–12255. 10.1021/acscatal.0c03606. [DOI] [PMC free article] [PubMed] [Google Scholar]; j Van Stappen C.; Decamps L.; Cutsail G. E. 3rd; Bjornsson R.; Henthorn J. T.; Birrell J. A.; DeBeer S. The Spectroscopy of Nitrogenases. Chem. Rev. 2020, 120, 5005–5081. 10.1021/acs.chemrev.9b00650. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. For a selection of references related to the concept of metal–ligand cooperativity, refer to ref (3).
  3. a Vigalok A.; Milstein D. Advances in metal chemistry of quinonoid compounds: new types of interactions between metals and aromatics. Acc. Chem. Res. 2001, 34, 798–807. 10.1021/ar970316k. [DOI] [PubMed] [Google Scholar]; b Grützmacher H. Cooperating ligands in catalysis. Angew. Chem., Int. Ed. 2008, 47, 1814–1818. 10.1002/anie.200704654. [DOI] [PubMed] [Google Scholar]; c van der Vlugt J. I. Cooperative Catalysis with First-Row Late Transition Metals. Eur. J. Inorg. Chem. 2012, 2012, 363–375. 10.1002/ejic.201100752. [DOI] [Google Scholar]; d Ikariya T.; Shibasaki M.. Bifunctional Molecular Catalysis; Topics in Organometallic Chemistry; Springer: Berlin, 2011. [Google Scholar]; e Gunanathan C.; Milstein D. Metal-ligand cooperation by aromatization-dearomatization: a new paradigm in bond activation and ″green″ catalysis. Acc. Chem. Res. 2011, 44, 588–602. 10.1021/ar2000265. [DOI] [PubMed] [Google Scholar]; f Milstein D. Metal-ligand cooperation by aromatization-dearomatization as a tool in single bond activation. Philos. Trans. A Math. Phys. Eng. Sci. 2015, 373, 20140189. 10.1098/rsta.2014.0189. [DOI] [PubMed] [Google Scholar]; g Khusnutdinova J. R.; Milstein D. Metal-ligand cooperation. Angew. Chem., Int. Ed. 2015, 54, 12236–12273. 10.1002/anie.201503873. [DOI] [PubMed] [Google Scholar]; h Chatterjee B.; Chang W. C.; Werlé C. Molecularly Controlled Catalysis – Targeting Synergies Between Local and Non-local Environments. ChemCatChem. 2021, 13, 1659–1682. 10.1002/cctc.202001431. [DOI] [Google Scholar]; i Chatterjee B.; Chang W. C.; Jena S.; Werlé C. Implementation of Cooperative Designs in Polarized Transition Metal Systems-Significance for Bond Activation and Catalysis. ACS Catal. 2020, 10, 14024–14055. 10.1021/acscatal.0c03794. [DOI] [Google Scholar]; j Campos J. Bimetallic cooperation across the periodic table. Nat. Rev. Chem. 2020, 4, 696–702. 10.1038/s41570-020-00226-5. [DOI] [PubMed] [Google Scholar]; k Perez-Jimenez M.; Corona H.; de la Cruz-Martinez F.; Campos J. Donor-acceptor activation of Carbon Dioxide. Chem.—Eur. J. 2023, 29, e202301428 10.1002/chem.202301428. [DOI] [PubMed] [Google Scholar]
  4. a Cramer H. H.; Chatterjee B.; Weyhermuller T.; Werlé C.; Leitner W. Controlling the Product Platform of Carbon Dioxide Reduction: Adaptive Catalytic Hydrosilylation of CO2 Using a Molecular Cobalt(II) Triazine Complex. Angew. Chem., Int. Ed. 2020, 59, 15674–15681. 10.1002/anie.202004463. [DOI] [PMC free article] [PubMed] [Google Scholar]; b Cramer H. H.; Ye S.; Neese F.; Werlé C.; Leitner W. Cobalt-Catalyzed Hydrosilylation of Carbon Dioxide to the Formic Acid, Formaldehyde, and Methanol Level-How to Control the Catalytic Network?. JACS Au 2021, 1, 2058–2069. 10.1021/jacsau.1c00350. [DOI] [PMC free article] [PubMed] [Google Scholar]; c Chatterjee B.; Jena S.; Chugh V.; Weyhermüller T.; Werlé C. A Molecular Iron-Based System for Divergent Bond Activation: Controlling the Reactivity of Aldehydes. ACS Catal. 2021, 11, 7176–7185. 10.1021/acscatal.1c00733. [DOI] [Google Scholar]; d Chugh V.; Chatterjee B.; Chang W. C.; Cramer H. H.; Hindemith C.; Randel H.; Weyhermüller T.; Farès C.; Werlé C. An Adaptive Rhodium Catalyst to Control the Hydrogenation Network of Nitroarenes. Angew. Chem., Int. Ed. 2022, 61, e202205515 10.1002/anie.202205515. [DOI] [PMC free article] [PubMed] [Google Scholar]; e Cramer H. H.; Das S.; Wodrich M. D.; Corminboeuf C.; Werlé C.; Leitner W. Theory-guided development of homogeneous catalysts for the reduction of CO2 to formate, formaldehyde, and methanol derivatives. Chem. Sci. 2023, 14, 2799–2807. 10.1039/D2SC06793E. [DOI] [PMC free article] [PubMed] [Google Scholar]; f Chang W. C.; Randel H.; Weyhermüller T.; Auer A. A.; Farès C.; Werlé C. A Cooperative Rhodium/Secondary Phosphine Oxide [Rh/P(O)nBu2] Template for Catalytic Hydrodefluorination of Perfluoroarenes. Angew. Chem., Int. Ed. 2023, 62, e202219127 10.1002/anie.202303992. [DOI] [PubMed] [Google Scholar]
  5. a Nair V.; Vellalath S.; Babu B. P. Recent advances in carbon-carbon bond-forming reactions involving homoenolates generated by NHC catalysis. Chem. Soc. Rev. 2008, 37, 2691–2698. 10.1039/b719083m. [DOI] [PubMed] [Google Scholar]; b Ravelli D.; Protti S.; Fagnoni M. Carbon-Carbon Bond Forming Reactions via Photogenerated Intermediates. Chem. Rev. 2016, 116, 9850–9913. 10.1021/acs.chemrev.5b00662. [DOI] [PubMed] [Google Scholar]
  6. a Danishefsky S.; Kitahara T.; McKee R.; Schuda P. F. Reactions of silyl enol ethers and lactone enolates with dimethyl(methylene)ammonium iodide. The bis-.alpha.-methylenation of pre-vernolepin and pre-vernomenin. J. Am. Chem. Soc. 1976, 98, 6715–6717. 10.1021/ja00437a058. [DOI] [Google Scholar]; b Du Bois J.; Hong J.; Carreira E. M.; Day M. W. Nitrogen Transfer from a Nitridomanganese(V) Complex: Amination of Silyl Enol Ethers. J. Am. Chem. Soc. 1996, 118, 915–916. 10.1021/ja953659r. [DOI] [Google Scholar]; c Reetz M. T. Lewis Acid Induced α-Alkylation of Carbonyl Compounds. Angew. Chem., Int. Ed. 1982, 21, 96–108. 10.1002/anie.198200961. [DOI] [Google Scholar]; d Mukaiyama T. Titanium Tetrachloride in Organic Synthesis [New synthetic methods (21)]. Angew. Chem., Int. Ed. 1977, 16, 817–826. 10.1002/anie.197708171. [DOI] [Google Scholar]; e Du H.; Long J.; Shi Y. Catalytic asymmetric Simmons-Smith cyclopropanation of silyl enol ethers. Efficient synthesis of optically active cyclopropanol derivatives. Org. Lett. 2006, 8, 2827–2829. 10.1021/ol0609659. [DOI] [PubMed] [Google Scholar]; f Anada M.; Tanaka M.; Washio T.; Yamawaki M.; Abe T.; Hashimoto S. Catalytic enantioselective amination of silyl enol ethers using chiral dirhodium(II) carboxylates: asymmetric formal synthesis of (−)-metazocine. Org. Lett. 2007, 9, 4559–4562. 10.1021/ol702019b. [DOI] [PubMed] [Google Scholar]; g Belanger E.; Cantin K.; Messe O.; Tremblay M.; Paquin J. F. Enantioselective Pd-catalyzed allylation reaction of fluorinated silyl enol ethers. J. Am. Chem. Soc. 2007, 129, 1034–1035. 10.1021/ja067501q. [DOI] [PubMed] [Google Scholar]; h Poisson T.; Gembus V.; Dalla V.; Oudeyer S.; Levacher V. Organocatalyzed Enantioselective Protonation of Silyl Enol Ethers: Scope, Limitations, and Application to the Preparation of Enantioenriched Homoisoflavones. J. Org. Chem. 2010, 75, 7704–7716. 10.1021/jo101585t. [DOI] [PubMed] [Google Scholar]
  7. For a selection of references related to the synthesis of silyl enol ethers, please refer to ref (8).
  8. a Hudrlik P. F.; Takacs J. M. Reactions of Ketones with Sodium Hydride or Potassium Hydride in Presence of Trimethylsilyl Chloride - Preparation of Trimethylsilyl Enol Ethers. J. Org. Chem. 1978, 43, 3861–3865. 10.1021/jo00414a016. [DOI] [Google Scholar]; b Suzuki H.; Koyama Y.; Moro-Oka Y.; Ikawa T. Novel peparation of silyl enol ethers from allyl alcohols. Tetrahedron Lett. 1979, 20, 1415–1418. 10.1016/S0040-4039(01)86165-7. [DOI] [Google Scholar]; c Miller R. D.; McKean D. R. The Facile Silylation of Aldehydes and Ketones using Trimethylsilyl Iodide: An Exceptionally Simple Procedure for the Generation of Thermodynamically Equilibrated Trimethylsilylenol Ethers. Synthesis 1979, 1979, 730–732. 10.1055/s-1979-28817. [DOI] [Google Scholar]; d Cazeau P.; Moulines F.; Laporte O.; Duboudin F. Methode simple pour la synthese rapide et stereoselective d’enoxysilanes d’aldehydes et de cetones. J. Organomet. Chem. 1980, 201, C9–C13. 10.1016/S0022-328X(00)87937-1. [DOI] [Google Scholar]; e Cazeau P.; Duboudin F.; Moulines F.; Babot O.; Dunogues J. A new practical synthesis of silyl enol ethers. Tetrahedron 1987, 43, 2075–2088. 10.1016/S0040-4020(01)86789-2. [DOI] [Google Scholar]; f Davis F. A.; Sankar Lal G.; Wei J. Stereo- and regioselective formation of silyl enol ethers via oxidation of vinyl anions. Tetrahedron Lett. 1988, 29, 4269–4272. 10.1016/S0040-4039(00)80471-2. [DOI] [Google Scholar]; g Chan T.-H. Formation and Addition Reactions of Enol Ethers. Comprehensive Organic Synthesis 1991, 595–628. 10.1016/B978-0-08-052349-1.00042-1. [DOI] [Google Scholar]; h Bonafoux D.; Bordeau M.; Biran C.; Dunoguès J. Stereoselective electrochemical synthesis of silyl enol ethers using a sacrificial magnesium anode. J. Organomet. Chem. 1995, 493, 27–32. 10.1016/0022-328X(94)05368-L. [DOI] [Google Scholar]; i Yamamoto Y.; Matui C. Preparation of silyl enol ethers by the reaction of ketones with silylamines and methyl iodide. Organometallics 1997, 16, 2204–2206. 10.1021/om960871a. [DOI] [Google Scholar]; j House H. O.; Czuba L. J.; Gall M.; Olmstead H. D. Chemistry of carbanions. XVIII. Preparation of trimethylsilyl enol ethers. J. Org. Chem. 1969, 34, 2324–2336. 10.1021/jo01260a018. [DOI] [Google Scholar]; k Haener R.; Laube T.; Seebach D. Regio- and diastereoselective preparation of aldols from.alpha.-branched ketone enolates generated from BHT ester enolates and organolithium reagents. In situ generation and trapping of ketenes from ester enolates. J. Am. Chem. Soc. 1985, 107, 5396–5403. 10.1021/ja00305a013. [DOI] [Google Scholar]; l Tsubouchi A.; Onishi K.; Takeda T. Stereoselective preparation of 1-siloxy-1-alkenylcopper species by 1,2-Csp2-to-O silyl migration of acylsilanes. J. Am. Chem. Soc. 2006, 128, 14268–14269. 10.1021/ja0658822. [DOI] [PubMed] [Google Scholar]; m Thiot C.; Wagner A.; Mioskowski C. Rh soaked in polyionic gel: an effective catalyst for dehydrogenative silylation of ketones. Org. Lett. 2006, 8, 5939–5942. 10.1021/ol0623670. [DOI] [PubMed] [Google Scholar]; n Herath A.; Montgomery J. Highly chemoselective and stereoselective synthesis of z-enol silanes. J. Am. Chem. Soc. 2008, 130, 8132–8133. 10.1021/ja802844v. [DOI] [PubMed] [Google Scholar]; o Tsubouchi A.; Enatsu S.; Kanno R.; Takeda T. Complete regio- and stereoselective construction of highly substituted silyl enol ethers by three-component coupling. Angew. Chem., Int. Ed. 2010, 49, 7089–7091. 10.1002/anie.201003152. [DOI] [PubMed] [Google Scholar]; p Konigs C. D.; Klare H. F.; Ohki Y.; Tatsumi K.; Oestreich M. Base-free dehydrogenative coupling of enolizable carbonyl compounds with silanes. Org. Lett. 2012, 14, 2842–2845. 10.1021/ol301089r. [DOI] [PubMed] [Google Scholar]; q Wang P. Y.; Duret G.; Marek I. Regio- and Stereoselective Synthesis of Fully Substituted Silyl Enol Ethers of Ketones and Aldehydes in Acyclic Systems. Angew. Chem., Int. Ed. 2019, 58, 14995–14999. 10.1002/anie.201909089. [DOI] [PubMed] [Google Scholar]
  9. a Stork G.; Hudrlik P. F. Isolation of Ketone Enolates as Trialkylsilyl Ethers. J. Am. Chem. Soc. 1968, 90, 4462–4464. 10.1021/ja01018a051. [DOI] [Google Scholar]; b Tanabe Y.; Misaki T.; Kurihara M.; Iida A.; Nishii Y. Silazanes/catalytic bases: mild, powerful and chemoselective agents for the preparation of enol silyl ethers from ketones and aldehydes. Chem. Commun. 2002, 1628–1629. 10.1039/b203783c. [DOI] [PubMed] [Google Scholar]; c Category 1, Organometallics, 1st ed.; Georg Thieme Verlag KG: Stuttgart, 2002; Vol. 4. [Google Scholar]; d Priebbenow D. L. Silicon-Derived Singlet Nucleophilic Carbene Reagents in Organic Synthesis. Adv. Synth. Catal. 2020, 362, 1927–1946. 10.1002/adsc.202000279. [DOI] [Google Scholar]
  10. a Anastas P. T.; Kirchhoff M. M.; Williamson T. C. Catalysis as a foundational pillar of green chemistry. Appl. Catal., A 2001, 221, 3–13. 10.1016/S0926-860X(01)00793-1. [DOI] [Google Scholar]; b Anastas P.; Eghbali N. Green chemistry: principles and practice. Chem. Soc. Rev. 2010, 39, 301–312. 10.1039/B918763B. [DOI] [PubMed] [Google Scholar]; c Zimmerman J. B.; Anastas P. T.; Erythropel H. C.; Leitner W. Designing for a green chemistry future. Science 2020, 367, 397–400. 10.1126/science.aay3060. [DOI] [PubMed] [Google Scholar]
  11. a Shrestha R.; Dorn S. C.; Weix D. J. Nickel-catalyzed reductive conjugate addition to enones via allylnickel intermediates. J. Am. Chem. Soc. 2013, 135, 751–762. 10.1021/ja309176h. [DOI] [PMC free article] [PubMed] [Google Scholar]; b Lyons T. W.; Brookhart M. Cobalt-catalyzed hydrosilation/hydrogen-transfer cascade reaction: a new route to silyl enol ethers. Chem.—Eur. J. 2013, 19, 10124–10127. 10.1002/chem.201301502. [DOI] [PubMed] [Google Scholar]; c Guven S.; Kundu G.; Wessels A.; Ward J. S.; Rissanen K.; Schoenebeck F. Selective Synthesis of Z-Silyl Enol Ethers via Ni-Catalyzed Remote Functionalization of Ketones. J. Am. Chem. Soc. 2021, 143, 8375–8380. 10.1021/jacs.1c01797. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. a Johnson C. R.; Raheja R. K. Hydrosilylation of enones: platinum divinyltetramethyldisiloxane complex in the preparation of triisopropylsilyl and triphenylsilyl enol ethers. J. Org. Chem. 1994, 59, 2287–2288. 10.1021/jo00088a006. [DOI] [Google Scholar]; b Sumida Y.; Yorimitsu H.; Oshima K. Palladium-catalyzed preparation of silyl enolates from alpha, beta-unsaturated ketones or cyclopropyl ketones with hydrosilanes. J. Org. Chem. 2009, 74, 7986–7989. 10.1021/jo901513v. [DOI] [PubMed] [Google Scholar]
  13. a Zheng G. Z.; Chan T. H. Regiocontrolled Hydrosilation of Alpha, Beta-Unsaturated Carbonyl-Compounds Catalyzed by Hydridotetrakis(Triphenylphosphine)Rhodium(I). Organometallics 1995, 14, 70–79. 10.1021/om00001a015. [DOI] [Google Scholar]; b Dias E. L.; Brookhart M.; White P. S. Rhodium(I)-catalyzed homologation of aromatic aldehydes with trimethylsilyldiazomethane. J. Am. Chem. Soc. 2001, 123, 2442–2443. 10.1021/ja003608g. [DOI] [PubMed] [Google Scholar]; c Aggarwal V. K.; Sheldon C. G.; Macdonald G. J.; Martin W. P. A new method for the preparation of silyl enol ethers from carbonyl compounds and (trimethylsilyl)diazomethane in a regiospecific and highly stereoselective manner. J. Am. Chem. Soc. 2002, 124, 10300–10301. 10.1021/ja027061c. [DOI] [PubMed] [Google Scholar]
  14. For selected references delineating the strategy of integrating a Lewis acid moiety in proximity to transition metals to induce cooperative catalysis, consult ref (15).
  15. a Tseng K. N.; Kampf J. W.; Szymczak N. K. Modular Attachment of Appended Boron Lewis Acids to a Ruthenium Pincer Catalyst: Metal-Ligand Cooperativity Enables Selective Alkyne Hydrogenation. J. Am. Chem. Soc. 2016, 138, 10378–10381. 10.1021/jacs.6b03972. [DOI] [PubMed] [Google Scholar]; b Kiernicki J. J.; Zeller M.; Szymczak N. K. Hydrazine Capture and N-N Bond Cleavage at Iron Enabled by Flexible Appended Lewis Acids. J. Am. Chem. Soc. 2017, 139, 18194–18197. 10.1021/jacs.7b11465. [DOI] [PMC free article] [PubMed] [Google Scholar]; c Norwine E. E.; Kiernicki J. J.; Zeller M.; Szymczak N. K. Distinct Reactivity Modes of a Copper Hydride Enabled by an Intramolecular Lewis Acid. J. Am. Chem. Soc. 2022, 144, 15038–15046. 10.1021/jacs.2c02937. [DOI] [PMC free article] [PubMed] [Google Scholar]; d Drover M. W. A guide to secondary coordination sphere editing. Chem. Soc. Rev. 2022, 51, 1861–1880. 10.1039/D2CS00022A. [DOI] [PubMed] [Google Scholar]; e Clapson M. L.; Sharma H.; Zurakowski J. A.; Drover M. W. Cooperative Nitrile Coordination Using Nickel and a Boron-Containing Secondary Coordination Sphere. Chem.—Eur. J. 2023, 29, e202203763 10.1002/chem.202203763. [DOI] [PubMed] [Google Scholar]; f Demchuk M. J.; Zurakowski J. A.; Drover M. W. Iridium Diphosphine Complexes Featuring Pendant Lewis Acids: Efforts toward Selective Heteroarene Borylation. Eur. J. Inorg. Chem. 2023, 26, e202200731 10.1002/ejic.202200731. [DOI] [Google Scholar]; g Theulier C. A.; Garcia-Rodeja Y.; Miqueu K.; Bouhadir G.; Bourissou D. Lewis Acid-Assisted C(sp3)-C(sp3) Reductive Elimination at Gold. J. Am. Chem. Soc. 2023, 145, 10800–10808. 10.1021/jacs.3c01974. [DOI] [PubMed] [Google Scholar]
  16. a Burgos C. H.; Canales E.; Matos K.; Soderquist J. A. Asymmetric allyl- and crotylboration with the robust, versatile, and recyclable 10-TMS-9-borabicyclo[3.3.2]decanes. J. Am. Chem. Soc. 2005, 127, 8044–8049. 10.1021/ja043612i. [DOI] [PubMed] [Google Scholar]; b Peng F.; Hall D. G. Simple, stable, and versatile double-allylation reagents for the stereoselective preparation of skeletally diverse compounds. J. Am. Chem. Soc. 2007, 129, 3070–3071. 10.1021/ja068985t. [DOI] [PubMed] [Google Scholar]
  17. [Cp*Co(CH3CN)3](SbF6)2 (7) is itself derived from the commercially available Cp*Co(CO)I2.
  18. Although the molecular structure of 1 showcases acetonitrile binding to both the metal center and boron, an interesting observation arises from the 11B NMR of 1. It not only reveals the chemical shift of acetonitrile bound to boron (11B: δ 58.17 ppm) but also presents a typical chemical shift suggestive of free boron unattached to any solvent molecule (11B: δ 88.08 ppm). This finding indicates the potential coexistence of complex 1 in solution, both with and without acetonitrile bound at the boron site.
  19. The determination of the relative stereochemistry of the products was made by analyzing the differing J coupling constants (Janti > Jsyn) obtained from 1H NMR measurements, see; Vollhardt K. P. C.; Schore N. E.. Organic chemistry: structure and function; Macmillan, 2003. [Google Scholar]
  20. In our most recent exploratory efforts aimed at expanding the substrate scope, we have delved into the reactivity of alkyl aldehydes. These initial experiments have unveiled a pronounced selectivity in the formation of product 5, which is a noteworthy discovery. This selectivity echoes the reactivity patterns commonly associated with alkyl substrates in similar chemical processes. The preliminary data gleaned from these studies shed light on the nuanced steric and electronic influences that govern selectivity, thus contributing to a more granular understanding of the reaction mechanisms. The insights derived from these findings not only bolster the theoretical framework within which these types of reactions are understood but also pave the way for tailored catalyst design in future work.
  21. Notably, neither ligand A nor 9-HBBN showed reactivity when deployed independently as catalysts.
  22. a Kramer G. W.; Brown H. C. Organoboranes.17. Reaction of Organometallics with Dialkylborane Derivatives - Synthesis of Mixed Organoboranes Not Available Via Hydroboration. J. Organomet. Chem. 1974, 73, 1–15. 10.1016/S0022-328X(00)80375-7. [DOI] [Google Scholar]; b Neumuller B.; Gahlmann F. Diorganogallium Fluorides - the Crystal-Structure of the Mixed-Crystal [B(CH2Ph)3]0,92[Ga(CH2Ph)3]0,08.NCMe. Z. Anorg. Allg. Chem. 1992, 612, 123–129. 10.1002/zaac.19926120121. [DOI] [Google Scholar]; c Burkhardt E.; Pichlmair S.. New borane-amine complexes and their application in Suzuki-type cross-coupling reactions. WO2009133045 (A1), November 5, 2009.; d Povie G.; Villa G.; Ford L.; Pozzi D.; Schiesser C. H.; Renaud P. Role of catechol in the radical reduction of B-alkylcatecholboranes in presence of methanol. Chem. Commun. 2010, 46, 803–805. 10.1039/B917004A. [DOI] [PubMed] [Google Scholar]; e Povie G.; Marzorati M.; Bigler P.; Renaud P. Role of equilibrium associations on the hydrogen atom transfer from the triethylborane-methanol complex. J. Org. Chem. 2013, 78, 1553–1558. 10.1021/jo302576c. [DOI] [PubMed] [Google Scholar]; f Yang D. T.; Mellerup S. K.; Wang X.; Lu J. S.; Wang S. N. Reversible 1,1-Hydroboration: Boryl Insertion into a C-N Bond and Competitive Elimination of HBR2 or R-H. Angew. Chem., Int. Ed. 2015, 54, 5498–5501. 10.1002/anie.201500487. [DOI] [PubMed] [Google Scholar]; g Körte L. A.; Blomeyer S.; Peters J.-H.; Mix A.; Neumann B.; Stammler H.-G.; Mitzel N. W. Dynamic Exchange in Intramolecular Lewis Pairs with Multiple Lewis-Acidic Functions. Organometallics 2017, 36, 742–749. 10.1021/acs.organomet.6b00935. [DOI] [Google Scholar]
  23. Notably, the addition of Me3SiCHN2 (1 equiv) to the reaction mixture containing 1 and MeOH (4 equiv) did not result in a significant shift in the boron chemical spectrum, suggesting that Me3SiCHN2 does not displace the oxygen-bound methanol from boron. A similar lack of new signal, suggesting diazo binding at boron, was found in the 11B NMR of a freshly prepared CD2Cl2 solution of 1, conducted in the presence of Me3SiCHN2 (6 equiv).
  24. These findings yield essential insights into the dynamic behavior of the reaction and lend credence to the idea that the carbonyl might be activated at boron before interacting with Me3SiCHN2. This understanding provides tangible substance to the observed improvement in catalytic efficiency, particularly in the presence of boron.
  25. a Bellow J. A.; Stoian S. A.; van Tol J.; Ozarowski A.; Lord R. L.; Groysman S. Synthesis and Characterization of a Stable High-Valent Cobalt Carbene Complex. J. Am. Chem. Soc. 2016, 138, 5531–5534. 10.1021/jacs.6b02747. [DOI] [PubMed] [Google Scholar]; b Planas O.; Roldan-Gomez S.; Martin-Diaconescu V.; Parella T.; Luis J. M.; Company A.; Ribas X. Carboxylate-Assisted Formation of Aryl-Co(III) Masked-Carbenes in Cobalt-Catalyzed C-H Functionalization with Diazo Esters. J. Am. Chem. Soc. 2017, 139, 14649–14655. 10.1021/jacs.7b07880. [DOI] [PubMed] [Google Scholar]; c Grass A.; Bellow J. A.; Morrison G.; Zur Loye H. C.; Lord R. L.; Groysman S. One electron reduction transforms high-valent low-spin cobalt alkylidene into high-spin cobalt(ii) carbene radical. Chem. Commun. 2020, 56, 8416–8419. 10.1039/D0CC03028G. [DOI] [PubMed] [Google Scholar]; d Epping R. F. J.; Vesseur D.; Zhou M.; de Bruin B. Carbene Radicals in Transition-Metal-Catalyzed Reactions. ACS Catal. 2023, 13, 5428–5448. 10.1021/acscatal.3c00591. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. a Dartiguenave M.; Menu M. J.; Deydier E.; Dartiguenave Y.; Siebald H. Crystal and molecular structures of transition metal complexes with N- and C-bonded diazoalkane ligands. Coord. Chem. Rev. 1998, 178, 623–663. 10.1016/S0010-8545(98)00117-9. [DOI] [Google Scholar]; b Ingleson M. J.; Pink M.; Fan H.; Caulton K. G. Redox chemistry of the triplet complex (PNP)Co(I). J. Am. Chem. Soc. 2008, 130, 4262–4276. 10.1021/ja074378+. [DOI] [PubMed] [Google Scholar]; c Bonyhady S. J.; Goldberg J. M.; Wedgwood N.; Dugan T. R.; Eklund A. G.; Brennessel W. W.; Holland P. L. Cobalt(II) Complex of a Diazoalkane Radical Anion. Inorg. Chem. 2015, 54, 5148–5150. 10.1021/acs.inorgchem.5b00673. [DOI] [PubMed] [Google Scholar]; d Bonyhady S. J.; DeRosha D. E.; Vela J.; Vinyard D. J.; Cowley R. E.; Mercado B. Q.; Brennessel W. W.; Holland P. L. Iron and Cobalt Diazoalkane Complexes Supported by beta-Diketiminate Ligands: A Synthetic, Spectroscopic, and Computational Investigation. Inorg. Chem. 2018, 57, 5959–5972. 10.1021/acs.inorgchem.8b00468. [DOI] [PubMed] [Google Scholar]; e Aghazada S.; Fehn D.; Heinemann F. W.; Munz D.; Meyer K. Cobalt Diazo-Compounds: From Nitrilimide to Isocyanoamide via a Diazomethanediide Fleeting Intermediate. Angew. Chem., Int. Ed. 2021, 60, 11138–11142. 10.1002/anie.202016539. [DOI] [PMC free article] [PubMed] [Google Scholar]; f Yruegas S.; Semproni S. P.; Chirik P. J. (PNP)Cobalt-Catalyzed Olefination of Diazoalkanes. Organometallics 2022, 41, 3138–3144. 10.1021/acs.organomet.1c00688. [DOI] [Google Scholar]
  27. Five distinct mixtures were generated by adjusting the ratio of complex 1 to Me3SiCHN2, ranging from 1:1 to 1:10. Each addition of Me3SiCHN2 was immediately followed by NMR spectroscopy to record instantaneous changes.
  28. The ability of the metal to rapidly activate the diazo molecule and convert it into subsequent products also transcends the significance of the reagent addition sequence on the selectivity of the intended reaction. The gradual addition of diazoalkane to a mixture containing complex 1 and 4-methyl benzaldehyde, rather than the reverse order, markedly affects both yield and selectivity. When 4-methyl benzaldehyde was introduced to a solution containing complex 1 and diazoalkane, a mere 33% conversion and a Z/E ratio of 27/6 were observed, in stark contrast to the 99% conversion and Z/E ratio of 87/13 achieved when diazoalkane was introduced to the mixture.
  29. When one recognized the potential for this species to form in situ under catalytically relevant conditions, its capability as a catalyst was evaluated using optimized reaction conditions (Scheme 5C3). When complex 1″ served as a catalyst, silyl enol ethers were produced with selectivity (Z/E = 85/15) and a yield of 3b (85%), analogous to the results observed with complex 1.
  30. a Notably, the formation of 1″ was not observed when compound 1 was combined with the aldehyde substrate before the introduction of any Me3SiCHN2. In such scenarios, complex 1 remained unaltered in the solution after the reaction. This fact mirrors the observation that only one equivalent of Me3SiCHN2 is required to synthesize (Z)-silyl enol ether from the aldehyde. It also elucidates why the gradual addition of diazoalkane to a mixture containing compound 1 and the aldehyde, rather than vice versa, markedly influences the reaction. Consequently, the in situ formation of 1″ in the reaction mixture seems plausible but appears to be limited when the aldehyde is present in the solution.; b Seidel G.; Furstner A. Suzuki reactions of extended scope: the ’9-MeO-9-BBN variant’ as a complementary format for cross-coupling. Chem. Commun. 2012, 48, 2055–2070. 10.1039/c2cc17070a. [DOI] [PubMed] [Google Scholar]
  31. Nitrogen release is profoundly observed within seconds of trimethylsilyldiazomethane addition to the complex, even at low temperatures (i.e., −80 °C).
  32. a Dzik W. I.; Zhang X. P.; de Bruin B. Redox noninnocence of carbene ligands: carbene radicals in (catalytic) C-C bond formation. Inorg. Chem. 2011, 50, 9896–9903. 10.1021/ic200043a. [DOI] [PubMed] [Google Scholar]; b Lu H.; Dzik W. I.; Xu X.; Wojtas L.; de Bruin B.; Zhang X. P. Experimental evidence for cobalt(III)-carbene radicals: key intermediates in cobalt(II)-based metalloradical cyclopropanation. J. Am. Chem. Soc. 2011, 133, 8518–8521. 10.1021/ja203434c. [DOI] [PubMed] [Google Scholar]; c Zhou M.; Wolzak L. A.; Li Z.; de Zwart F. J.; Mathew S.; de Bruin B. Catalytic Synthesis of 1 H-2-Benzoxocins: Cobalt (III)-Carbene Radical Approach to 8-Membered Heterocyclic Enol Ethers. J. Am. Chem. Soc. 2021, 143, 20501–20512. 10.1021/jacs.1c10927. [DOI] [PMC free article] [PubMed] [Google Scholar]; d Epping R. F. J.; Hoeksma M. M.; Bobylev E. O.; Mathew S.; de Bruin B. Cobalt(II)-tetraphenylporphyrin-catalysed carbene transfer from acceptor-acceptor iodonium ylides via N-enolate-carbene radicals. Nat. Chem. 2022, 14, 550–557. 10.1038/s41557-022-00905-4. [DOI] [PubMed] [Google Scholar]
  33. This inference is further corroborated by the substrate scope, wherein substrates having electron-donating functionality (2p–w) demonstrate higher selectivity towards (Z)-enol ether as compared to those bearing an electron-withdrawing group (2ae–ai).
  34. a Becke A. D. Density-functional exchange-energy approximation with correct asymptotic behavior. Phys. Rev. A 1988, 38, 3098–3100. 10.1103/PhysRevA.38.3098. [DOI] [PubMed] [Google Scholar]; b Lee C.; Yang W.; Parr R. G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 1988, 37, 785–789. 10.1103/PhysRevB.37.785. [DOI] [PubMed] [Google Scholar]; c Andrae D.; Häußermann U.; Dolg M.; Stoll H.; Preuß H. Energy-adjustedab initio pseudopotentials for the second and third row transition elements. Theoretica chimica acta 1990, 77, 123–141. 10.1007/BF01114537. [DOI] [Google Scholar]; d Becke A. D. Density-functional thermochemistry. I. The effect of the exchange-only gradient correction. J. Chem. Phys. 1992, 96, 2155–2160. 10.1063/1.462066. [DOI] [Google Scholar]; e Weigend F.; Ahlrichs R. Balanced basis sets of split valence, triple zeta valence and quadruple zeta valence quality for H to Rn: Design and assessment of accuracy. Phys. Chem. Chem. Phys. 2005, 7, 3297–3305. 10.1039/b508541a. [DOI] [PubMed] [Google Scholar]; f Weigend F. Accurate Coulomb-fitting basis sets for H to Rn. Phys. Chem. Chem. Phys. 2006, 8, 1057–1065. 10.1039/b515623h. [DOI] [PubMed] [Google Scholar]; g Weigend F. Hartree–Fock exchange fitting basis sets for H to Rn. J. Comput. Chem. 2008, 29, 167–175. 10.1002/jcc.20702. [DOI] [PubMed] [Google Scholar]; h Bykov D.; Petrenko T.; Izsák R.; Kossmann S.; Becker U.; Valeev E.; Neese F. Efficient implementation of the analytic second derivatives of Hartree-Fock and hybrid DFT energies: a detailed analysis of different approximations. Mol. Phys. 2015, 113, 1961–1977. 10.1080/00268976.2015.1025114. [DOI] [Google Scholar]; i Caldeweyher E.; Bannwarth C.; Grimme S. Extension of the D3 dispersion coefficient model. J. Chem. Phys. 2017, 147, 034112. 10.1063/1.4993215. [DOI] [PubMed] [Google Scholar]; j Caldeweyher E.; Ehlert S.; Hansen A.; Neugebauer H.; Spicher S.; Bannwarth C.; Grimme S. A generally applicable atomic-charge dependent London dispersion correction. J. Chem. Phys. 2019, 150, 154122. 10.1063/1.5090222. [DOI] [PubMed] [Google Scholar]; k Garcia-Rates M.; Neese F. Efficient implementation of the analytical second derivatives of hartree-fock and hybrid DFT energies within the framework of the conductor-like polarizable continuum model. J. Comput. Chem. 2019, 40, 1816–1828. 10.1002/jcc.25833. [DOI] [PubMed] [Google Scholar]; l Garcia-Rates M.; Neese F. Effect of the Solute Cavity on the Solvation Energy and its Derivatives within the Framework of the Gaussian Charge Scheme. J. Comput. Chem. 2020, 41, 922–939. 10.1002/jcc.26139. [DOI] [PubMed] [Google Scholar]; m Neese F. The SHARK integral generation and digestion system. J. Comput. Chem. 2023, 44, 381–396. 10.1002/jcc.26942. [DOI] [PubMed] [Google Scholar]
  35. a Neese F. The ORCA program system. Wiley Interdiscip. Rev. Comput. Mol. Sci. 2012, 2, 73–78. 10.1002/wcms.81. [DOI] [Google Scholar]; b Neese F.; Wennmohs F.; Becker U.; Riplinger C. The ORCA quantum chemistry program package. J. Chem. Phys. 2020, 152, 224108. 10.1063/5.0004608. [DOI] [PubMed] [Google Scholar]; c Neese F. Software update: The ORCA program system-Version 5.0. Wiley Interdiscip. Rev. Comput. Mol. Sci. 2022, 12, e1606 10.1002/wcms.1606. [DOI] [Google Scholar]

Associated Data

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

Supplementary Materials

ja3c10491_si_001.pdf (8.9MB, pdf)

Data Availability Statement

The data that support the findings of this study (e.g., general considerations, experimental methods, synthetic details, computed structures, copies of NMR spectra, and crystallographic data) are available in the Supporting Information of this article.

Articles from Journal of the American Chemical Society are provided here courtesy of American Chemical Society

RESOURCES