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. 2025 Nov 11;10(46):56418–56430. doi: 10.1021/acsomega.5c08401

Synthesis and Characterization of a Pd(II)-Complex Bearing a Naphthalene-Based Macrocyclic Tetra N‑Heterocyclic Ligand

Mathias T Nielsen 1, Martin Nielsen 1,*
PMCID: PMC12658663  PMID: 41322538

Abstract

We report the synthesis of a novel macrocyclic salt containing four imidazolium units tethered by alternating ethylene and naphthalene units. The salt metalates Pd­(II), resulting in a macrocyclic tetra N-heterocyclic carbene (NHC) ligand. To investigate the fluxionality of this complex as a result of its macrocyclic nature, we synthesized a related Pd­(II) complex with two chelating NHCs for comparative analysis by 1H NMR spectroscopy.

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Introduction

Coordination complexes play a pivotal role in various fields of chemistry, such as catalysis, materials science, and pharmaceuticals. Significant efforts have been made to discover new ligands that can stabilize reactive metal centers and impart unique properties to coordination complexes by tuning stereoelectronic effects. Carbon-based ligands, such as N-heterocyclic carbenes (NHCs), have developed into contemporary ligands, finding diverse use in both coordination chemistry and homogeneous catalysis. − In this context, macrocyclic tetra-NHCs coordination complexes have witnessed significant advancements in recent years since Hahn’s metal-templated synthesis of a divalent platinum complex bearing a macrocyclic tetra-NHC ligand. For instance, several new structures have emerged, many demonstrating a coordination environment reminiscent to that of N-porphyrins. − However, the strongly electron-donating NHC ligands engender an electronic environment distinctive from the N-porphyrin congeners. , Several examples establish that NHC ligands aptly take part in stabilizing high-valent metal centers, enabling the formation of metal–ligand multiple bonds. Notable examples include Fe­(IV) oxo and Fe­(IV) imido complexes. Additionally, many of these high-valent adducts are reactive as evident from the isolation of dimerization products including an oxide bridged dimeric Fe­(III) complex, μ2-oxo-Fe­(III,IV) complex, dicobalt­(III) μ2-peroxo complex, and diiron­(III) disulfide-bridged complex. This reactivity may be altered via modifications to the linkers separating the imidazolylidene moieties. For example, incorporating chiral elements into the linker results in Fe-complexes that catalyze enantioselective aziridination reactions. , In contrast, by introducing too flexible linkers, the resulting complexes may instead demonstrate ligand-mediated reactions as the ligand fully envelops the metal ion. ,

We are interested in the coordination chemistry of complexes bearing a macrocyclic tetra-NHC ligand manifold with a potential outlook for applications of such complexes in catalysis. Because of how linker differences affect the reactivity of the resulting coordination complex, we sought to develop an alternating ethylene-naphthalene-based macrocycle and understand the resulting structure. Specifically, we wanted to understand whether this specific combination of alternating imidazole-2-ylidene spacers results in a complex fully “enveloping” the metal center. In this work, we present the synthesis of such a naphthalene-based macrocyclic tetra imidazolium salt, which metalates to form a Pd­(II) complex bearing a macrocyclic tetra-NHC ligand. The complex features a distinctive arrangement of the naphthalene-moieties potentially resembling a binding pocket. To understand whether the ligand of the resulting macrocyclic Pd­(II) complex demonstrates any fluxionality, and to assess the impact of such (lacking) fluxionality, we synthesized a related homoleptic Pd­(II) complex bearing two chelating NHCs to compare the 1H NMR spectra against one another and we find the macrocyclic complex demonstrates a significant robustness compared to the dichelate.

Results and Discussion

Synthesis and Solid-State Structure of the Proligand

Our desired pro-carbene ligand as the imidazolium-bromide salt, 1-Br 4 , was initially isolated from the reaction between 1,8-bis­(bromomethyl)­naphthalene and 1,2-bis imidazoleethane in a 1:1 ratio in N,N′-dimethylformamide (DMF), as detailed in Scheme , in low yields ranging from 3 to 10%. The connectivity of this salt was confirmed by single-crystal X-ray diffraction, and the molecular structure is shown in the lower part of Scheme . The composition of this salt was confirmed by high-resolution mass-spectroscopy ([M – 2Br]2+ = 396.0854, [M – 4Br]4+ = 158.0837), in addition to multidimensional, multinuclei nuclear magnetic resonance (NMR), confirming the C 2-symmetry of 1-Br 4 in solution, see Figures S1–S9 for all the relevant NMR data. We note that anion exchange affects the chemical shift values strongly in the 1H NMR spectrum, as seen in Figure , and is more pronounced for the imidazolium C2 proton (signal A), which shifts significantly upfield from 9.37 to 8.91 ppm, likely due to weaker hydrogen bonding to the PF6 anions in the latter case.

1. Synthesis of 1-Br 4 and the Solid-State Structure of Central the Macrocyclic Tetra Imidazolium Proligand as the Mixed Bromide-Hexafluorophosphate Salt, 1-(Br 2 , [PF 6 ] 2 ) .

1

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a Hydrogen atoms, co-crystallized solvent, and counterions are omitted for clarity. Thermal ellipsoids are shown at a 50% probability level. Atom color-coding: N blue and C gray.

1.

1

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1H NMR spectrum (in DMSO-d 6, selected range) of 1-Br 4 (top) and of 1-[PF 6 ] 4 (lower). The spectra featuring resonances and splitting patterns consistent with the solid-state structure presented in Scheme .

An alternative synthesis approach that circumvents impracticalities of the former, such as inconsistencies during workup, is shown in Scheme . While this approach is operationally simpler and more consistent, it suffers from a modest yield in the acetoxy functionalization, thus affording the desired pro-carbene ligand 1-[PF 6 ] 4 in approximately 10%, which is comparable to the initially presented synthesis. Other protection groups , were attempted, but failed to improve the final yield.

2. Convergent Synthesis of the Macrocyclic Tetraimidazolium Proligand 1-[PF 6 ] 4 .

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Synthesis and Characterization of Pd­(II)-Complex

With 1-Br 4 and 1-[PF 6 ] 4 in hand, we first attempted the desired Pd­(II) complex from the complexation of the free tetra-NHC macrocycle, leading to unidentified products. Instead, treating 1-Br 4 with Pd­(OAc)2 in the presence of excess NH4OAc allowed us to isolate the Pd­(II) dibromide salt [LPd]­[X] 2 , 2-Br 2 , in yields of up to 30% as an off-white powder. The molecular structure of 2-Br 2 is shown in the lower part of Scheme .

3. Synthesis and Solid-State Structure of Complex 2-Br 2 .

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a Hydrogen atoms, co-crystallized MeCN, and bromide counterions are omitted for clarity. Thermal ellipsoids are shown at a 50% probability level. Atom color-coding: N blue, C gray, and Pd sea green. Selected interatomic distances (Å) and angles (0): C1–Pd 2.029(3); C2–Pd 2.034(3); C3–Pd 2.056(2); C4–Pd; 2.050(3). C1–Pd–C3 174.62(11); C4–Pd–C2 169.03(11); C1–Pd–C4 84.39(10); C4–Pd–C3 97.04(10); C3–Pd–C2 85.08(10); C2–Pd–C1 92.56(10).

As shown in the lower part of Scheme , the connectivity of this salt as the desired Pd­(II) complex bearing a macrocyclic tetradentate NHC ligand was in addition to the solid-sate, corroborated by characteristic NMR spectra, see Figures S26–S30. Complex 2-Br 2 crystallizes within the monoclinic P21/c space group, showcasing a Pd­(II) center coordinated by four crystallographically distinct carbon atoms. The Pd–C bond lengths vary between 2.026(3), 2.037(3), 2.051(3), and 2.055(3) Å, respectively. Comparing structural parameters of the imidazolium/imidazole-2-ylidene moieties in the central fragments of 1-Br 2 [PF 6 ] 2 and in complex 2-Br 2 reveals changes in CNC angles as well as in the bond distances of CC and C­(carbene)–N, changes all consistent with the formation of an NHC complex. In the tetra imidazolium salt 1-Br 2 [PF 6 ] 2 , CNC angles are approximately 108°, contrasting with the slightly narrower angles, between 104.4(3)° and 105.6(3)° seen in complex 2-Br 2 . Additionally, the CC bond in complex 2-Br 2 contracts from around 1.350 Å (1-Br 2 [PF 6 ] 2 ) to between 1.343(5) and 1.347(5) Å. Additionally, C­(carbene)–N bond lengths expand from an average of 1.334 to 1.350 Å. These values are consistent with those observed in another complex that features a macrocyclic tetra NHC ligand. The coordination to Pd in complex 2 slightly deviates from the anticipated square planar geometry, as the Pd ion in complex 2 sits 0.141 Å above the plane defined by the four NHC groups, with each anchor tilted by approximately 4° from this plane. This subtle deviation may result from the macrocycle’s structural tension.

The 1H NMR spectrum of complex 2-[PF 6 ] 2 in CD3CN, at the top of Figure , features resonances consistent with the solid-state structure presented in Scheme . The {1H–1H} correlation spectroscopy [COSY] spectrum, shown in the lower part of Figure , delineates the coupling patterns within the respective spin systems and helps define the connectivity. The multiplets of the aromatic region, signals A through D, reflect the two different naphthalene-moieties, whereas the narrow doublets (3 J ∼ 2 Hz) D through G instead are owing to the C4 and C5 protons of the ylidene, respectively. We suggest that the non-first-order doublets’ resonances H, I, L, and M are attributed to two sets of diastereotopic benzylic methylene protons, and the characteristic ddd splitting pattern of the remaining four signals J, K, and L indicates that each diastereotopic proton in the ethylene linker experiences both geminal and vicinal couplings. Finally, the 13C NMR spectrum similarly demonstrates an analogous duplication of the signals, cf. Figure S32. Only a minor difference in chemical shifts, as seen in Figure S36, arises upon counterion exchange from 2-Br 2 to 2-[PF 6 ] 2.

2.

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1H NMR (top) spectrum and {1H–1H} COSY (lower) spectrum of 2-[PF 6 ] 2 (in CD3CN). The spectra feature resonances and splitting patterns consistent with the solid-state structure presented in Scheme .

Gratifyingly, using 1-[PF 6 ] 4 instead of 1-Br 4 , in combination with [Pd­(acn)4]­[PF6]2 and K2CO3 in MeCN, improved the isolated yield of 2-[PF 6 ] 2 to 45% yield, potentially due to better solubility of 1-[PF 6 ] 4 . Encouraged by this observation, we explored whether a transmetalation route from 1-Br 4 and 1-[PF 6 ] 4 via a “masked carbene” could produce complex 2-[PF 6 ] 2 in a greater yield. Initially, we found that treating 1-Br 4 with an excess of Ag2O in methanol allowed for the straightforward isolation of a white, light-sensitive powder. Subsequent transmetalation in the presence of a source of PF6 – led to improved yields of 2-[PF 6 ] 2 of up to 65%, when reacted with PdCl2 in an approximate ratio of 1:3 Ag­(I)/Pd­(II). Despite slight decomposition, the 1H- and 13C NMR spectra of the isolated material are consistent with a well-defined complex, see Figures S39–S41. Crystals suitable for X-ray diffraction, obtained from the reaction between 1-[PF 6 ] 4 and Ag2O, show two different Ag­(I)-complexes obtained from the same batch of crystals, see Figure S44. Figure S44a depicts a homoleptic trimeric hexasilver complex, whereas Figure S44b depicts a dimeric solvato adduct. In both instances, one Ag­(I) binds within the macrocycle by linearly bridging two trans-disposed imidazole-2-ylidenes, while the second Ag­(I) links the macrocycle to an adjacent one (or is coordinated by solvent) similar to that reported by Jenkins and co-workers. Although the limited quality of the data set precludes detailed analysis of bonding metrics, these tentative structures align with the observations from the 1H and 13C NMR spectra. − In coordinating solvents, such as MeCN, the silver intermediate likely exists in an equilibrium between the trimeric and dimeric state.

Variable-Temperature NMR Study

To determine the fluxional properties of 2-[PF 6 ] 2 in solution, we carried out a variable-temperature 1H NMR study presented in Figure . Specifically, we investigated whether the naphthalene moieties could flip between endo and exo orientations, potentially allowing for a “breathing” motion that would lead to a diendo situation and a cavity that exposes a would-be axial coordination site. To this end, we obtained 1H NMR spectra of complex 2-[PF 6 ] 2 over a temperature range from −30 to 70 °C. Interestingly, only subtle changes appear to take place as the solution of 2-[PF 6 ] 2 heats up. The overlapping aromatic signals began to split into three discernible signals and the second-most upfield-shifted benzylic proton experienced a slight downfield-shift. All ethylene signals largely remain unperturbed. This observation indicates no or very little dynamic motion of the naphthalene units, a stability likely resulting from the rigid molecular structure in solution, possibly supported by strong intramolecular interactions or a lack of flexible elements that might undergo conformational changes with temperature fluctuations, a consequence of the macrocyclic imparted strain. Based on these observations, we therefore suggest that the entity observed in solution is consistent with the solid-state structure shown in Scheme .

3.

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Variable-Temperature 1H NMR spectrum of 2-[PF 6 ] 2 (in CD3CN). The spectra feature resonances and splitting patterns consistent with the solid-state structure presented in Scheme .

Moreover, we tested the stability of complex 2-[PF 6 ] 2 by treating it to various reagents (PhICl2, Me3OBF4, MeOTf, and MeI), but, unfortunately, we observed complete decomposition in all cases.

Dichelate Analogue: Structural Comparison

We observed that the macrocyclic complex 2 exhibits a unique coordination geometry influenced significantly by its ligand structure. To further investigate the impact of ligand architecture, we synthesized a homoleptic Pd­(II) complex using bifurcated chelating ligands derived by essentially halving the macrocyclic ligand.

As outlined in Scheme , we leveraged transmetalation to affect a dichelating Pd­(II) complex [ Bn L 2 Pd]­[PF 6 ] 2 , 3-[PF 6 ] 2 , in high yields (88%) using an intermediary Ag­(I) complex of the diimidazolium hexafluorophosphate salt as the proligand. Allowing a saturated solution of 3 in MeCN to slowly evaporate at room temperature results in the formation of colorless crystals after a couple of days, which are suitable for single-crystal X-ray diffraction analysis.

4. Synthesis and Solid-State Structure of 3-[PF 6 ] 2 .

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a Hydrogen atoms, co-crystallized MeCN, and PF6-counterions are omitted for clarity. Thermal ellipsoids are shown at a 50% probability level. Atom color-coding: Pd sea green, N blue, and C gray. Selected interatomic distances (Å) and angles (0): C1–Pd 2.020(3), C2–Pd 2.058(3); C1–Pd–C11 180.00(18), C2–Pd–C21 180.0, C1–Pd–C2 84.96(12), C2–Pd–C11 95.04(12).

Complex 3 crystallizes within the monoclinic C2/c space group and demonstrates a square-planar Pd­(II) center coordinated by two symmetry-related chelating-NHC ligands featuring Pd–C bond lengths of 2.02 and 2.06 Å, respectively. The ylidene fragments reveal that 3 demonstrates bonding metrics similar to those of 2. Additionally, similar π-interactions to those identified in 2 were observed: these include interactions from a phenyl ring to an ylidene as well as an interaction between a phenyl ring of one chelating ligand to an ylidene of the other chelating ligand. However, these interactions are less evident in the 1H NMR spectrum of 3 compared to 2, as shown in Figure S51.

Finally, as presented in Figure , we obtained variable-temperature 1H NMR data of 3 over the same temperature gradient as that for 2-[PF 6 ] 2 . In contrast to the macrocyclic complex, the spectrum of 3 shows a downfield chemical shift and changes in multiplicities upon an increase in the temperature. Most noticeably, the benzylic proton resonance shifts between a nonfirst-order multiplet and a singlet, suggesting increased molecular flexibility or temperature-dependent conformational changes in solution. Hence, not surprisingly, although both complexes exhibit similar structural features in the solid state, these do not translate to similar behaviors in solution. Complex 2 maintains stable NMR spectral features over a wide temperature range, with minimal shifts in chemical shift or multiplicity, while complex 3 displays significant temperature sensitivity in these characteristics.

4.

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Variable-temperature 1H NMR spectrum of 3-[PF 6 ] 2 .

Conclusion

We have demonstrated the synthesis of a novel naphthalene-based macrocyclic tetra imidazolium proligand effected from an SN2 reaction between readily prepared precursors, 1,8-bis­(bromomethyl)­naphthalene and 1,2-bisimidazoleethane. We similarly present a longer, convergent synthesis of the same macrocyclic proligand in comparable yield. This proligand metalates into a monometallic complex bearing a macrocyclic tetra-NHC ligand, upon complexation with Pd­(II) to provide a macrocyclic complex that deviates from the expected square-planar coordination. A yield of up to 65% was isolated when transmetalating via an intermediary Ag­(I) adduct. From variable-temperature NMR studies, the solid-state structure appears to persist in solution and the structure is quite stable, limiting any applications toward, e.g., oxidative transformations. In contrast, a dichelate congener exhibits temperature-dependent flexibility in its geometrical properties.

Experimental Section

General Considerations and Instrumentation

All syntheses were performed in air, unless otherwise stated. Handling of air-sensitive reagents was conducted under inert gas conditions using standard Schlenk or glovebox techniques. When Schlenk manipulations were involved, all glassware was oven-dried for a minimum of 10 h or flame-dried using a blowtorch and cooled under a dynamic vacuum. Glassware employed in gloveboxes were similarly dried for a minimum of 10 h and cooled in an evacuated antechamber prior to use. Et2O, THF, MeCN, DMSO, and DMF were dried over activated aluminum oxide using an inert solvent purification system and further stored over 4 Å molecular sieves (Sigma).

1H, 13C, 19F, and 31P NMR spectra were recorded on a Bruker Ascend spectrometer with a Prodigy cryoprobe operating at 400 MHz for 1H NMR, 101 MHz for 13C, 377 MHz 19F NMR, and 162 MHz for 31P NMR. 1H and 13C chemical shifts are reported relative to SiMe4, using the residual solvent peak as internal reference. The specific deuterated solvent is stated for each compound. NMR spectra were analyzed using MestReNova software.

High-Resolution Mass Spectrometry and Elemental Analysis

HRMS measurements were taken on a Thermo Fisher Orbitrap Exploris 120, mounted with an H-ESI source. All spectra were recorded at 30 000 fwhm resolution. Elemental analyses were acquired by the Micro Analytical Laboratory at the Department of Chemistry, University of Copenhagen on a Thermo Fisher FlashEA 1112 analyzer. All handling was conducted under ambient conditions.

Infrared Spectroscopy (ATR-IR)

Solid-state attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy was performed employing a VERTEX 80 vacuum Fourier transform spectrometer from Bruker Optics GmbH equipped with a Germanium-coated KBr beam splitter, a LN2-cooled HgCdTe detector, and globar radiation source. The solid samples were brought in contact with a Germanium attenuated total reflection (ATR) crystal of a single-reflection ATR accessory from PIKE Technologies, Inc. Blocks of 300 coadded scans with a spectral resolution of 2 cm–1 were collected both with the sample and of the cleaned ATR crystal before and after sample measurements. Minor traces of residual water vapor absorption were subtracted and gentle corrections for baseline drifts were introduced before the final application of extended ATR corrections compensating for the wavelength-dependent penetration depth of the infrared probe beam into the sample.

Single-Crystal X-ray Structure Determination

A suitable crystal was harvested with a MiTeGen cryo loop and mounted on a goniometer attached to a SuperNova Dual Source CCD-diffractometer. Data were collected at the given temperature of K using Cu Kα (1-(Br 2 , [PF 6 ] 2 ), 2-Br 2 , and 3-[PF 6 ] 2 ) radiation under a stream of N2. Data integration ranging from 0.84 Å to 0.72 Å resolution was carried out using CrysAlis Pro software with reflection spot size optimization. Using Olex2, the structures were solved with the SHELXT structure solution program using Intrinsic Phasing and refined with the SHELXL refinement package using least squares minimization. The program PLATON was used to confirm an absence of missing symmetry elements. Non-hydrogen atoms were refined with anisotropic displacement parameters, and hydrogen atoms were added in idealized positions and refined by using a riding model.

Synthetic Methods

1,2-Bisimidazole Ethane

As in the literature. As an off-white powder of the title compound (4 g, 24% yield). 1 H NMR (400 MHz, DMSO-d 6): δ 7.36 (s, 1H), 6.99 (d, J = 1.3 Hz, 1H), 6.86 (d, J = 1.3 Hz, 1H), 4.32 (s, 2H). 13 C NMR (101 MHz, DMSO-d 6): δ 137.32, 128.49, 119.12, 46.63. Variations to this procedure include the use of 1,2-dibromo ethane, 1,2-bis­(triflato), and 1,2-bis­(tosylato) ethane instead of 1,2-DCE, resulting in an even lower yield.

1,8-Bis­(hydroxymethyl) Naphthalene

Adapted from literature. 1,8-Naphthalic anhydride (100 g, 0.505 mol, 1.0 equiv) was added to a flame-dried 2 L three-neck round-bottom flask fitted with a stir bar and a thermometer under a stream of N2. The flask was evacuated and backfilled with N2 gas before being submerged into an ice bath and adding 1.2 L of dry THF. The suspension was stirred until the thermometer reached about 5 °C before LiAlH4 (25 g, 95 w/w %, 626 mmol, 1.25 equiv) was portion wise added, with caution, at a rate that did not cause the reaction mixture to exceed a temperature of 35 °C. [Safety warning: the authors strongly urge the use of LiAlH4 (LAH) as pellets as we found the exothermic nature of the reaction much more manageable at this scale]. The heterogeneous mixture was stirred under an atmosphere of N2 for at least 48 h, standing in the ice bath slowly coming to room temperature. The water bath was replenished with new ice, and the mixture was dropwise added with caution to ice-chilled water until bubbling subsided, causing the precipitation of aluminum hydroxides. The suspension was transferred to a 1 L glass beaker (1/3 of the volume at a time), and ice cold 6 M HCl was added until all the formed aluminum hydroxides were dissolved as evident from the two phases, and the beaker’s content was transferred to a separatory funnel. It is important that during neutralization, the temperature of the THF solution does not become too hot as 1H,3H-benzo­[de]­isochromene otherwise forms. The aqueous fractions were combined and further extracted with portions of 100 mL of THF until the extraction volume no longer assumed any (slightly) yellow color. The combined organic fractions were then washed with brine (3 × 100 mL), dried over MgSO4, solvent removed in vacuo, and the solid was recrystallized from EtOAc, yielding a white powder of the title compound (80.7 g, 85% yield). 1 H NMR (400 MHz, DMSO-d 6): δ 7.86 (dd, J = 8.1, 1.4 Hz, 1H), 7.63 (dd, J = 7.0, 1.4 Hz, 1H), 7.46 (dd, J = 8.1, 7.0 Hz, 1H), 5.28 (t, J = 5.4 Hz, 1H), 5.09 (d, J = 5.4 Hz, 2H). 13 C NMR (101 MHz, DMSO-d 6): δ 138.51, 135.07, 130.04, 129.01, 128.09, 124.90, 63.66.

1,8-Bis­(bromomethyl)­naphthalene

Commercially available from Sigma. To a 250 mL flame-dried Schlenk-flask equipped with a stir bar was added 1,8-bis­(hydroxymethyl)­naphthalene (30 g, 160 mmol, 1.0 equiv) that was subjected to vacuum for 45 min before being backfilled with N2 and dried glyme (or dioxane, 160 mL, 1 M). The suspension was submerged into an ice bath before PBr3 (19 mL, 200 mmol, 1.25 equiv) slowly was added under vigorous stirring. The ice bath was removed, and the mixture was stirred for at least 2 h. The mixture was poured into ice water (400 mL), stirred for 20 min, and the precipitate was collected on a glass-frit (M-coarseness), which was washed with MeOH until the filtrate was colorless, and the powder was dried on the frit in air, yielding a light-sensitive white powder of the title compound (46.9 g, 94% yield). Upon extended exposure to light, the powder was recrystallized from minimum amounts of benzene. 1 H NMR (400 MHz, CDCl3): δ 7.78 (dd, J = 8.1, 1.4 Hz, 1H), 7.52 (dd, J = 7.1, 1.4 Hz, 1H), 7.35 (t, J = 8.1, 7.1 Hz, 1H), 5.20 (s, 2H). 13 C NMR (101 MHz, CDCl3): δ 136.25, 133.55, 133.19, 132.07, 129.16, 125.85, 37.34. Spectral data are consistent with Sigma’s product.

1-Br 4

To a 500 mL flame-dried Schlenk-flask equipped with a stir bar were added 1,2-bisimidazoleethane (10.4 g, 63.7 mmol, 1.0 equiv) and 1,8-bis­(bromomethyl)­naphthalene (20 g, 63.7 mmol, 1.0 equiv), and the powders were subjected to vacuum for at least 30 min before being backfilled with N2. The solids were dissolved in 320 mL of SPS-quality DMF, and the solution was then heated to 100 °C under a slight vacuum for 48 h. The reaction mixture was reduced to 1/3 of the original volume of DMF in vacuo, cooled to rt, 2 times the volume of acetone was added, and the precipitate was collected on an M-coarseness glass-frit. The precipitate was recrystallized in small amounts of MeOH (no more than 2 mL at a time), yielding a white powder of the target compound in about 3–10% yield. The powder is hygroscopic. 1H NMR (400 MHz, DMSO-d 6): δ 9.34 (s, 2H), 8.06 (d, J = 8.0 Hz, 2H), 7.97 (t, J = 1.7 Hz, 2H), 7.76 (t, J = 1.7 Hz, 2H), 7.54 (t, J = 8.0, 7.2 Hz, 2H), 6.99 (d, J = 7.2 Hz, 2H), 6.44 (s, 4H), 4.89 (s, 4H). 13C NMR (101 MHz, DMSO-d 6): δ 137.16, 135.21, 130.87, 130.38, 128.71, 126.59, 125.71, 123.88, 123.40, 53.53, 48.80. HRMS m/z calcd [C40H40N8 Br2–2Br]2+ [M – 2Br]2+, 396.0856; found, 396.0854. [M – 4Br]4+, 158.0839; found, 158.0837. Crystals suitable for a single crystal.

X-ray diffraction was performed from slow solvent evaporation from a concentrated methanolic solution; however, these all contain a lot of poorly defined cocrystallized water. Instead, 20 mg of this material was dissolved in about 10 mL of water at rt, and a solution of 7.8 mg KPF6 in 2 mL of water was added using a glass Pasteur pipet. Immediately, a white precipitate formed, and the pipet was used to perform multiple pull–push motions to mix the suspension. The solid was recovered, washed with more water, dissolved in about 4 mL of MeCN, dried over Na2SO4, filtered, and the volume was split between four 5 mL vials that were placed inside a 24 mL scintillation vial halfway filled with Et2O. The vials were capped with a lid, placed inside a refrigerator, and crystals suitable for SCXRD were obtained over the span of several days.

General procedure for anion exchange of imidazolium-bromide salts. In air. 1-Br 4 (1.0 equiv) or Bn LH 2 -Br 2 (1.0 equiv) was dissolved in deionized water (10 mM), before a Na/K-salt (1.02 equiv. per imidazolium moiety) of the desired counterion, e.g., NaPF6 or KPF6, was added to the solution, and the mixture was heated to 80 °C overnight under stirring. The suspension was cooled to room temperature, and the solid was collected on a glass-frit (M-coarseness), which was washed with H2O, MeOH, and finally Et2O before the powder was left to dry in the air on the frit for at least 2 h. The resulting white powder was redissolved in MeCN, passed through the filter, and MeCN was removed in vacuo, leaving behind the desired compound as a white solid in nearly quantitative yield (95 to >99%). To test for residual bromide, to an aliquot of the MeCN solution was added AgPF6. Upon formation of a precipitate, the solid was dissolved in MeCN and an excess of KPF6, and the mixture was refluxed for 2–4 h. Any solids were discarded from filtration, the MeCN removed in vacuo, and the solid was with H2O, MeOH, and Et2O as described above.

1-[PF6]4

1H NMR (400 MHz, DMSO-d 6): δ 8.92 (s, 2H), 8.10 (d, J = 8.1 Hz, 2H), 7.94 (t, J = 1.8 Hz, 2H), 7.76 (s, 2H), 7.56 (t, J = 8.1, 7.3 Hz, 2H), 6.97 (d, J = 7.3 Hz, 2H), 5.96 (s, 4H), 4.82 (s, 4H). 13 C NMR (101 MHz, DMSO): δ 137.24, 135.27, 130.79, 130.32, 128.96, 127.26, 125.83, 124.01, 123.44, 52.65, 48.82. HRMS m/z calcd [C40H40N8P2F12]2+ [M – 2PF6]2+, 461.1324; found, 461.1324. [M – 4PF6]4+, 158.0836; found, 158.0838.

(8-(Hydroxymethyl)­naphthalen-1-yl)­methyl Acetate, NaphL­(OH, OAc)

1,8-Bis­(hydroxymethyl) naphthalene (25 g, 0.13 mol, 1.0 equiv) was added to a flame-dried 2 L three-neck round-bottom flask fitted with a stir bar under a stream of N2. Under stirring, the flask was evacuated and kept under a dynamic vacuum for 30 min before it was backfilled with N2. The flask was then subjected to three times of vacuum followed by N2 backfill, before 750 mL of dry THF was added to the diol. NaH (5.43 g, 0.136 mol, 1.05 equiv, 60 w/w %) was portion wise added to the solution under an overpressure of N2 gas, and the mixture was left to stir until bubbling had subsided, which could take several hours. The flask was then fitted with a flame-dried addition funnel, and once it cooled to the touch, acetic anhydride (12.46 mL, 0.132 mol, 1.02 equiv) was added, which was dropwise introduced to the mixture, at a rate of about 1–2 drops per second. The stirring was increased at about the halfway point of addition as the formed NaOAc results in a thick slurry. The mixture was continuously stirred overnight at room temperature after the anhydride had been added. The next day, about 300 mL of brine was added to the solution, which was stirred for a couple of minutes and the biphasic mixture was transferred to a separatory funnel. Addition of up to 100 mL of EtOAc is helpful in the event of emulsification. The (slightly) yellow organic layer was washed with another two portions of 100 mL of brine, then dried over Na2SO4, and THF was removed in vacuo, resulting in a sticky off-white residue. This residue was then suspended in about 150 mL of Et2O and stirred for about 10 min to form a fine suspension, and the filtrate was collected by filtration using a glass-fiber filter (M-coarseness). After the filter cake was washed twice more with about 25 mL of Et2O, the ether fractions were combined dried over Na2SO4, and solvent was removed in vacuo, affording a yellow/orange oil. The white filter cake consists of unreacted starting material and may be recovered. The mono ester was separated by flash chromatography eluting in Et2O/pentane (1:1) (R F = ∼0.45) to obtain the title compound as a light-yellow oil in yields ranging from 25 to 45%. Addition of acetic anhydride at low temperatures or substitution with acetyl chloride increases diester formation.

1 H NMR (400 MHz, DMSO-d 6): δ 7.98 (d J = 8.1, Hz, 2H), 7.93 (d, J = 8.1 Hz, 1H), 7.63 (td, J = 7.0, Hz, 3H), 7.50 (td, J = 8.1, 7.0 Hz, 3H), 5.73 (s, 2H), 5.41 (t, J = 5.4 Hz, 1H), 4.91 (d, J = 5.4 Hz, 2H), 2.05 (s, 3H). 13 C NMR (101 MHz, DMSO-d 6): δ 170.08 (CO), 137.54, 135.11, 131.77, 130.60, 130.52, 130.32, 129.49, 129.26, 125.28, 124.94, 66.75 (CH2OAc), 63.58 (CH2OH), 20.87 (CH3). HRMS m/z calcd [C11H9O]− [M – H–CH2CO2CH3]−, 157.0659; found, 157.0658.

1,1′-(Ethane-1,2-diyl)­bis­(3-((8-(acetoxymethyl)­naphthalen-1-yl)­methyl)-1H-imidazole-3-ium) Chloride, [L­(H, OAc)]2[Cl–]2

In air. NaphL­(OH, OAc) (5 g, 21.7 mmol, 1.0 equiv) was suspended in DCM (75 mL) and pyridine (2.63 mL, 32.6 mmol, 1.5 equiv) added before the flask was submerged into an ice bath and stirred for 10 min. SOCl2 (1.74 mL, 23.9 mmol, 1.05 equiv) was dropwise added to the solution using an addition funnel, at a rate that did not cause the reaction mixture to exceed the boiling point of DCM. Afterward, the mixture was kept under continued stirring in the ice bath, slowly coming to room temperature overnight. The next morning, 30 mL of saturated aqueous ammonium chloride was added to the mixture, and the biphasic mixture was transferred to a separatory funnel. The organic phase was washed three times more with 10 mL of sat. NH4Cl, twice with 10 mL of H2O, and twice with 5 mL of brine, which left a bright yellow organic phase. The organic phase was dried over Na2SO4 and the solvent was removed in vacuo, leaving behind an oily yellow residue, which was used without any further purification: NaphL­(Cl, OAc) (6.5 g, 26.1 mmol, 1.0 equiv) and 1,2-diimidazole ethane (1.94 g, 12.0 mmol, 0.96 equiv) were added to a 250 mL round-bottom flask and suspended in 100 mL of MeCN. The flask was fitted with a Vigreux glass condenser before the mixture was heated to a gentle simmering and stirred overnight. Some white powder had formed the next day. The mixture was allowed to fully cool to room temperature before Et2O was added until a precipitate no longer formed. The white precipitate was collected on a glass-fiber filter (M-coarseness), and the filter cake was suspended in Et2O and washed until the filtrate was colorless, and the filter cake was allowed to dry on the frit for several hours, resulting in the desired product in about 85% yield (6.71 g, 10.2 mmol).

1 H NMR (400 MHz, DMSO-d 6): δ 9.32 (broad singlet, 1H), 8.06 (d, J = 8.0 Hz, 1H), 8.03 (d, J = 8.0 Hz, 1H), 7.90 (t, J = 1.8 Hz, 1H), 7.81 (t, J = 1.8 Hz, 1H), 7.72 (dd, J = 7.2, 1.4 Hz, 1H), 7.58 (t, J = 7.6 Hz, 1H), 7.50 (t, J = 7.6 Hz, 1H), 7.07 (d, J = 7.2 Hz, 1H), 6.10 (s, 2H), 5.50 (s, 2H), 4.80 (s, 2H), 2.09 (s, 3H). 13 C NMR (101 MHz, DMSO-d 6): δ 170.08, 137.54, 135.23, 131.71, 131.05, 130.89, 130.85, 129.81, 129.71, 128.46, 125.71, 125.44, 123.36, 123.29, 66.52 (CH2OAc), 52.17, 48.57, 20.95 (CH3). HRMS m/z calcd [C36H36O4N4Cl–Cl]+ [M – Cl]+, 623.2412; found, 623.2410. [M – 2Cl]2+, 294.1363; found, 294.1360.

1,1′-(Ethane-1,2-diyl)­bis­(3-((8-(hydroxymethyl)­naphthalen-1-yl)­methyl)-1H-imidazole-3-ium) Hexafluorophosphate, [L­(H, OH)]2[PF6]2

The di­(acetato, imidazolium chloride) salt [L­(H, OAc)]2[Cl–]2 (1.0 g, 1.52 mmol, 1.0 equiv) was dissolved in 50 mL of deionized water in a 100 mL round-bottom flask, and the solution was sparged with N2-gas for about 20 min. Concurrently, KOH (255.2 mg, 4.55 mmol, 3.0 equiv) was dissolved in about 5 mL of water in a small vial and was similarly sparged with N2. After 20 min, the KOH solution was transferred to the round-bottom flask in one go, the solution sparged for 5 min, and the solution was stirred overnight at room temperature. The solution was acidified with a 1 M HCl solution until pH 4–5 and KPF6 (586 mg, 3.18 mmol, 2.1 equiv) was dissolved in minimum amounts of water and added to the slightly acidic solution, which causes a white precipitate to form. After stirring for another 10 min, the solid was recovered on a glass-fiber frit (M-coarseness) and the filter cake was washed extensively with H2O and left to dry for 30 min. The cake was redissolved in MeCN, passed through the frit, dried over MgSO4, and solvent removed in vacuo, resulting in a white powder of the desired product in an okay yield of around 60% (723 mg). Other sources of PF6 work fine for this step, such as NaPF6 and NH4PF6.

1 H NMR (400 MHz, DMSO-d 6): δ 8.93 (d, J = 2.0 Hz, 1H), 8.03 (d, J = 8.1 Hz, 1H), 8.00 (dd, J = 8.2, 1.4 Hz, 1H), 7.77 (t, J = 1.7 Hz, 1H), 7.69 (s, 1H), 7.65 (d, J = 7.1 Hz, 1H), 7.55 (t, J = 7.6 Hz, 1H), 7.50 (t, J = 7.7 Hz, 1H), 7.09 (d, J = 7.1 Hz, 1H), 6.22 (s, 2H), 5.73 (t, J = 5.4 Hz, 1H), 4.80 (d, J = 5.4 Hz, 2H), 4.66 (s, 2H). 13 C NMR (101 MHz, DMSO-d 6): δ 136.99, 136.78, 135.40, 130.94, 130.65, 130.06, 129.96, 128.71, 125.79, 125.19, 123.25, 123.19, 64.53, 52.36, 48.67. HRMS m/z calcd [C32H32O2N4PF6–PF6]+ [M – PF6]+, 649.2162; found, 649.2156. [M – 2PF6]2+, 252.1257; found, 252.1255.

1,1′-(Ethane-1,2-diyl)­bis­(3-((8-(chloromethyl)­naphthalen-1-yl)­methyl)-1H-imidazole-3-ium) Hexafluorophosphate, [L­(H, Cl)]2[PF6]2

4 mL of SOCl2 was added to a 10 mL round-bottom flask, which subsequently was chilled over an ice bath. Once the di­(hydroxymethyl, imidazolium chloride) salt [L­(H, OH)]2[PF6]2 (1 g, 1.26 mmol, 1.0 equiv) portion wise had been added to the chilled SOCl2, the ice bath was removed, and the suspension was allowed to stir for 3 h. The SOCl2 suspension was quickly added to a 500 mL beaker containing 300 mL of ice-chilled water and a stir bar, and the mixture was stirred for 5 min. Most of the water was decanted off, the precipitate was collected on a glass-fiber frit (M-coarseness), and the precipitate was with small amounts of MeOH followed by 3 × 50 mL of H2O. The sticky residue was left to dry until it became a manageable powder (anywhere from 30–90 min) before it was dissolved in MeCN, dried over MgSO4, and the solvent was removed in vacuo, yielding the desired di­(chloromethyl, imidazolium hexafluorophosphate)-salt in acceptable yields of about 85% (890 mg, 1.07 mmol). The powder was used without further purification.

1 H NMR (400 MHz, DMSO-d 6): δ 9.06 (s, 1H), 8.09 (d, J = 8.0 Hz, 1H), 8.05 (d, J = 8.1 Hz, 1H), 7.86 (d, J = 2.2 Hz, 1H), 7.82 (d, J = 7.0 Hz, 1H), 7.77 (s, 1H), 7.60 (t, J = 7.6 Hz, 1H), 7.51 (t, J = 7.7 Hz, 1H), 7.06 (d, J = 7.2 Hz, 1H), 6.21 (s, 2H), 5.21 (s, 2H), 4.70 (s, 2H), 3.42–3.34 (m, 7H), 2.52 (s, 1H). 13 C NMR (101 MHz, DMSO-d 6): δ 117.87, 115.95, 113.67, 113.06, 112.22, 111.74, 109.80, 109.40, 109.34, 106.48, 106.07, 103.94, 103.87, 32.85, 29.18, 29.08. HRMS m/z calcd [C32H30N4Cl2PF6–PF6]+ [M – PF6]+, 685.1484; found, 685.1479. [M – 2PF6]2+, 270.0918; found, 270.0917.

1-[PF 6 ] 4 from the partial annulation approach. A 500 mL round-bottom flask equipped with a stir bar was charged with [L­(H, Cl)]2[PF6]2 (2.08 g, 2.5 mmol, 1.0 equiv), 1,2-diimidazole ethane (404.8 mg, 2.5 mmol, 1.0 equiv), and 170 mL of MeCN. The flask was fitted with a Vigreux glass condenser, and the mixture was brought to a gentle reflux for 30 h. After 30 h, the flask was moved out of the oil bath and KPF6 (964.6 mg, 5.24 mmol, 2.1 equiv) was added to the hot suspension, before the flask was resubmerged into the oil bath, which continued to stir at a gentle reflux for an additional 4 h. To ensure all chloride had been exchanged, a small aliquot was added to a 5 mL vial containing AgPF6. Upon the formation of AgCl precipitate, the reaction was heated for another 2 h. This step was repeated until no more AgCl precipitates. The suspension was then cooled to room temperature and filtered through Celite, and the solvent was removed in vacuo, yielding a brown residue. This (brown) residue was suspended in about 5 mL of cold (0 °C) acetone, and the suspension was transferred to a glass-fiber filter (M-coarseness). It is sometimes necessary to scrape the oil for several minutes until a powder forms. The white powder was sequentially washed with 2–4 mL of cold acetone until the filtrate was colorless. Finally, the white powder was washed with H2O (3 × 20 mL) and MeOH (3 × 20 mL), and the powder was left to dry on the filter, yielding the desired macrocycle of the tetra (imidazolium hexafluorophosphate) salt as a white powder in 60% yield (1.82 g). 1H and 13C NMR spectra as well as HR-MS data are consistent with those listed above.

Complex 2-[PF 6 ] 2 , [LPd]­[PF6]2

From deprotonation-metalation. Inside an argon-filled glovebox, a 20 mL scintillation vial equipped with a stir bar was charged with 1-[PF 6 ] 4 (100 mg, 82.5 μmol, 1.0 equiv), PdCl2 (15.06 mg, 84.9 μmol, 1.03 equiv), AgPF6 (43 mg, 170 μmol), K2CO3 (114 mg, 0.825 mmol, 10.0 equiv), and the powders were suspended in MeCN (12 mL). The vial was placed on top of a heat plate and stirred for around 18 h at 75 °C. The day after, a small aliquot was taken for 1H NMR, in DMSO-d 6, to confirm full consumption of the starting material. Once established, the vial was cooled to room temperature and brought outside the glovebox, where the solution was passed through a pad of Celite fitted inside a glass Pasteur pipet. The pad was washed with addition portions of MeCN (2 × 4 mL), before the combined MeCN fraction was concentrated to ∼1 mL, placed inside a 5 mL glass vial, which was placed inside a 20 mL scintillation vial containing Et2O, and left for overnight Et2O-vapor diffusion at room temperature. If a black material was obtained, the solid was dissolved in minimum amounts of acetone and the solution was passed through a pad of activated charcoal; the solvent then removed in vacuo. The resulting white powder was collected on a glass-fiber filter and washed with 2 × 4 mL of THF, H2O, and MeOH before the powder was redissolved in MeCN and dried over MgSO4. The desiccant was filtered off and MeCN was removed in vacuo, leaving a white crystalline material of the Pd-complex in moderate yield (38.0 mg, 45%). Crystals suitable for single-crystal X-ray diffraction were obtained from the slow solvent evaporation of the complex in a MeCN solution at room temperature.

1 H NMR (400 MHz, CD3CN): δ 8.00 (dd, J = 8.0, 1.6 Hz, 2H), 7.88 (dd, J = 8.0, 1.6 Hz, 2H), 7.68 (dt, J = 7.0, 1.3 Hz, 2H), 7.65–7.53 (overlapping multiplets, 8H), 7.29 (d, J = 2.0 Hz, 2H), 6.99 (d, J = 2.1 Hz, 2H), 6.80 (d, J = 2.1 Hz, 2H), 6.06 (d, J = 15.5 Hz, 2H), 5.61 (d, J = 15.5 Hz, 2H), 5.13 (ddd, J = 15.0, 7.3, 4.7 Hz, 2H), 4.89 (ddd, J = 15.0, 7.3, 4.7 Hz, 2H), 4.55–4.33 (overlapping multiplets, 6H), 3.92 (d, J = 15.9 Hz, 2H). 13 C NMR (101 MHz, CD3CN): δ 168.03, 167.93, 137.33, 134.67, 134.31, 133.46, 132.69, 132.48, 131.88, 129.97, 127.88, 126.44, 125.66, 124.55, 123.88, 122.08, 118.30, 54.91, 54.18, 49.74, 48.47. 19F NMR (377 MHz, CD3CN): δ −72.95 (d, J = 711.2 Hz). 31 P NMR (162 MHz, CD3CN): δ −144.62 (hep, J = 711.2 Hz). HRMS m/z calcd [C40H36N8Pd–2PF6]2+ [M – 2PF6]2+, 367.1043; found, 367.1049. Elemental analysis Calcd (%) for C40H36N8PdP2F12: C, 46.87; H, 3.54; N, 10.93. Found: C, 47.05; H, 3.57; N, 10.98.

2-[PF 6 ] 2

From transmetalation, directly using the filtrate from the reaction with Ag2O. Inside an argon-filled glovebox, a 20 mL scintillation vial equipped with a stir bar was charged with 1-[PF 6 ] 4 (100 mg, 82.5 μmol, 1.0 equiv), Ag2O (202 mg, 0.825 mmol, 10 equiv, 95% wt), and the powders were suspended in MeCN (12 mL). The vial was capped with a lid and placed on top of a heat plate and stirred for around 18 h at 50 °C. The day after, a small aliquot was taken for 1H NMR, in DMSO-d 6, to confirm full consumption of the starting material. Otherwise, the mixture was allowed to stir for another 4 h. The vial was then removed from the stir plate to allow most of the solid material to settle at the bottom. If the solution turns brown, the liquid is carefully passed through several columns of activated charcoal placed inside a glass Pasteur pipet until a clear filtrate is obtained. The combined MeCN volumes were reduced to about 15 mL in a single vial in vacuo before PdCl2 (15.06 mg, 84.9 μmol, 1.03 equiv), and a new stir bar was added to the solution. The suspension was stirred overnight at 75 °C, producing a lot of precipitate. The next morning, the vial was brought outside of the glovebox; the solution was passed through a pad of Celite, concentrated to about 2 mL of solvent, which was distributed between four 5 mL vials. These vials were placed inside 24 mL scintillation vials half filled with THF and left for overnight vapor diffusion. Most of the liquid was decanted off, the solids combined in one vial, and then washed with 2 × 2 mL each of THF, H2O, and MeOH before the powder was redissolved in MeCN and dried over MgSO4. The desiccant was filtered off, and MeCN was removed in vacuo, leaving a white crystalline material of the Pd-complex in greater yield (54.8 mg, 65%).

To prepare the column of activated charcoal inside the glovebox: A 23 cm Pasteur pipet was fitted with a Whatman filter, and a slurry of activated charcoal in MeCN was transferred onto this filter; the charcoal was compressed on top of the filter by using a pipet bulb to push out the solvent. The “column” of charcoal was gradually built until the desired height of 3–4 cm of packed material was reached.

Bn LH 2 –Br 2

As in literature, in air. A round-bottom flask (25 mL) was charged with 1,2-bisimidazole ethane (500 mg, 3.1 mmol, 1.0 equiv), which was dissolved in MeCN (15 mL, 100 mM) before a slight excess of benzyl bromide (1.11 g (0.770 mL), 2.10 equiv) was added to the solution. The flask was fitted with a reflux condenser, and the mixture was brought to gentle reflux for 12 h. The solution was cooled to rt, enough acetone was added until precipitation started, and the mixture was stirred for 5 min, and the precipitate was collected on an M-coarseness glass-frit (20 mL). The mixture was washed with acetone (3 × 10 mL), Et2O (3 × 10 mL), and was left to dry over the frit for 2 h, yielding an off-white powder of the bromide salt in nearly quantitative yield (1.52 g, 98% yield). 1 H NMR (400 MHz, DMSO-d 6): δ 9.24 (s, 1H), 7.82 (d, J = 1.8 Hz, 1H), 7.68 (t, J = 1.8 Hz, 1H), 7.44–7.33 (m, 5H), 5.42 (s, 2H), 4.72 (s, 2H). 13 C NMR (101 MHz, DMSO): δ 136.74, 134.47, 128.99, 128.80, 128.26, 122.95, 122.86, 52.09, 48.47.

Bn LH 2 -[PF 6 ] 2

Following the procedure outlined under anion exchange, a white powder was isolated in a 98% yield.

1 H NMR (400 MHz, DMSO-d 6): δ 9.12 (t, J = 1.8 Hz, 2H), 7.81 (t, J = 1.8 Hz, 2H), 7.64 (t, J = 1.8 Hz, 2H), 7.47–7.39 (overlapping multiplet, 6H), 7.35 (dd, J = 7.6, 1.9 Hz, 4H), 5.39 (s, 2H), 4.68 (s, 4H). 13 C NMR (101 MHz, DMSO): δ 136.77, 134.50, 129.08, 128.90, 128.26, 123.08, 122.92, 52.17, 48.56.

Elemental analysis Calcd (%) for C22H24N4F 12 P 2 : C, 41.65; H, 3.81; N, 8.83. Found: C, 41.66; H, 3.80; N, 8.80.

[BnLAg]2[PF6]2

A 50 mL round-bottom flask was wrapped in foil and Bn LH 2 -[PF 6 ] 2 (200 mg, 0.32 mmol, 1.0 equiv), Ag2O (183 mg (95 w/w %), 0.79 mmol, 2.5 equiv), and 20 mL of MeCN added. The mixture was heated overnight at 50 °C. The warm mixture was filtered through Celite, and the Celite was washed with an additional 10 mL of MeCN. The combined filtrate was dried over MgSO4, filtered, and MeCN was removed in vacuo excluding light, yielding a white powder in good yield (165.2 mg, 88% yield).

1 H NMR (400 MHz, DMSO-d 6): δ 7.49 (d, J = 1.8 Hz, 1H), 7.42 (d, J = 1.8 Hz, 1H), 7.25 (dd, J = 5.0, 1.9 Hz, 3H), 6.97 (dd, J = 6.6, 2.8 Hz, 2H), 5.13 (s, 2H), 4.64 (s, 2H).

13 C NMR (101 MHz, DMSO): δ 179.92 (d, J = 211.0 Hz [1 J(13C–109Ag)]), 179.91 (d, J = 181.7 Hz [1 J(13C–107Ag)]), 179.01, 136.96, 128.69, 127.90, 126.76, 122.94, 122.54, 54.10, 50.84.

We were unable to obtain a satisfactory elemental analysis as the powder quickly decomposes upon light exposure.

3-[PF 6 ] 2 , [ Bn L 2 Pd]­[PF 6 ] 2 , from transmetalation of [BnLAg]2[PF6]2. A 20 mL scintillation vial equipped with a stir bar was charged with PdCl2(MeCN)2 (37.6 mg, 0.145 mmol, 1.02 equiv) and dissolved in MeCN (10 mL). To the now yellow solution was added [BnLAg]2[PF6]2 (169 mg, 0.142 mmol, 1.0 equiv), and the mixture was heated to 70 °C overnight. The now colorless solution was cooled to rt, filtered through Celite, concentrated to ∼1 mL, placed inside a 5 mL glass vial, which was placed inside a 20 mL scintillation vial containing Et2O, and left for overnight Et2O-vapor diffusion at rt. The resulting white powder was collected on a glass-fiber filter, washed with 2 × 5 mL of MeCN/Et2O (1:6), and redissolved in MeCN, and the solvent was removed in vacuo, leaving a white crystalline material of the Pd-complex in good yield (140 mg, 91%). Crystals suitable for single-crystal X-ray diffraction were obtained from slow evaporation of MeCN.

1 H NMR (400 MHz, CD3CN): δ 7.32–7.25 (overlapping multiplet, 3H), 7.05 (d, J = 2.0 Hz, 1H), 6.91 (d, J = 2.0 Hz, 1H), 6.72–6.65 (multiplet, 2H), 4.95–4.78 (multiplet, 1H), 4.74 (s, 2H), 4.55–4.40 (multiplet, 1H).

13 C NMR (101 MHz, CD3CN): δ 167.82 (C 2–Pd), 136.93, 130.01, 128.92, 126.62, 124.73, 124.33, 54.63, 48.69.

19 F NMR (377 MHz, CD3CN): δ −72.95 (d, J = 706.7 Hz).

31 P NMR (162 MHz, CD3CN): δ −144.62 (hep, J = 706.7 Hz).

Elemental analysis Calcd (%) for C44H44F12N8P 2 Pd: C, 48.88; H, 4.10; N, 10.36. Found: C, 48.33; H, 4.10; N, 10.38.

HRMS m/z calcd [C44H44N8Pd – 2PF6]2+, 395.1356; found, 395.1362.

Supplementary Material

ao5c08401_si_001.cif (753.6KB, cif)
ao5c08401_si_002.cif (841.3KB, cif)
ao5c08401_si_003.cif (1.1MB, cif)
ao5c08401_si_004.cif (675.4KB, cif)
ao5c08401_si_005.cif (6.8MB, cif)
ao5c08401_si_006.pdf (3.2MB, pdf)

Acknowledgments

The authors thank Independent Research Fund Denmark (8102-00004B and 1127-00172B) and VILLUM FONDEN (53069) for generous funding. The authors also acknowledge The NMR CenterDTU and the Villum Foundation for access to the 600 MHz spectrometer. The authors finally would like to thank Kasper Enemark-Rasmussen for his help with NMR data collection, Mariusz Kubus for his help with obtaining XRD, and René W. Larsen for his help with obtaining IR-data.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.5c08401.

  • CIF files pertaining to 1-(Br 2 , [PF 6 ] 2 ) (CIF)

  • CIF files pertaining to 2-Br 2 (CIF)

  • CIF files pertaining to 3-[PF 6 ] 2 (CIF)

  • wit_exp_288_auto.cif (CIF)

  • exp_300-241120-MC-072-5a_auto.cif (CIF)

  • Characteristic spectra of the compounds described in this manuscript in addition to relevant data on crystallographically characterized structures (PDF)

The authors declare no competing financial interest.

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Associated Data

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Supplementary Materials

ao5c08401_si_001.cif (753.6KB, cif)
ao5c08401_si_002.cif (841.3KB, cif)
ao5c08401_si_003.cif (1.1MB, cif)
ao5c08401_si_004.cif (675.4KB, cif)
ao5c08401_si_005.cif (6.8MB, cif)
ao5c08401_si_006.pdf (3.2MB, pdf)

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