Shorter Argentophilic Interaction than Aurophilic Interaction in a Pair of Dimeric {(NHC)MCl}₂ (M = Ag, Au) Complexes Supported over a N/O-Functionalized N-Heterocyclic Carbene (NHC) Ligand

Abstract

Synthesis, structure, bonding, and photoluminescence studies of a pair of neutral dimeric silver and gold complexes of a N/O-functionalized N-heterocyclic carbene ligand exhibiting closed-shell d10...d10 argentophilic and aurophilic interactions, are reported. In particular, dimeric complexes of the type {[1-(benzyl)-3-(N-tert-butylacetamido)imidazol-2-ylidene]MCl}2 [M = Ag (2); Au (3)] displayed attractive metallophilic interaction in the form of a close ligand-unsupported metal...metal contact [3.1970(12) A in 2; 3.2042(2) A in 3] as observed from X-ray diffraction study and also was further verified by low temperature photoluminescence study at 77 K that showed the characteristic emission [527 nm for 2; 529 nm for 3] owing to the metal...metal interaction. The nature of the metallophilic interaction in these complexes was further probed using computational studies that estimated the metal...metal interaction energy to be 12.8 (2) and 8.6 kcal/mol (3). Notably, the argentophilic interaction was found to be stronger than the aurophilic interaction in this series of neutral dimeric complexes. The complexes 2 and 3 were synthesized sequentially, with the silver 2 complex prepared by the reaction of the 1-(benzyl)-3-(N-tert-butylacetamido)imidazolium chloride with Ag2O in 66% yield, while the gold 3 complex was obtained by the transmetallation reaction of the silver 2 complex with (SMe2)AuCl in 86% yield.

A Theoretical Insight into the Mechanism of the Silver‐Catalysed Transsiliranation Reaction

“…[26] Stationary points were characterised by the right number of negative eigenvalues of the exact Hessian matrix. Gibbs free energies (at 25°C) are discussed throughout the text.…”

Fischer-type gold(i) carbene complexes stabilized by aurophilic interactions

“…In addition, the corresponding AuAu Wiberg Bond Index (0.14 and 0.15 for 2 and 6, respectively) are also similar and comparable to the values found for related (NHC)AuCl dimers. 15 Interestingly, the Second Order Perturbation Theory (SOPT) of the NBO method indicates that the aurophilic interaction is characterized by the donation of electron density from a doubly occupied d atomic orbital of one Au(I) to an empty p atomic orbital of the adjacent metal (see Figure 4). The associated SOPT energy computed for 2 and 6 is quite remarkable (DE (2) = -9.4 and -9.3 kcal/mol, respectively), thus reflecting the importance of these aurophilic interactions in the global stabilization of the novel Fischer type Au(I)-carbene complexes described herein.…”

Another silver complex of 1,3-dibenzylimidazol-2-ylidene: Solution and solid-state structures

“…For instance, imidazole-and benzimidazole-based carbenes with short alkyl-chain substituents yield complexes of type B in the solid state [6,13], while those bearing long alkyl chains often result in complexes of type A 2 [14]. The exact geometry of this dimer A 2 can vary and a number of different structures has been reported, including the Ag 2 X 2 4-membered ring of 3 and 4 and a dimer formed by Ag-Ag interaction [8,15]. A study to determine the influence of the solvent showed that an increase in solvent polarity shifts the solution equilibrium from A to B for (IMes)AgCl (IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazole-2-ylidene) [8].…”