A Dinuclear Gold(I) Bis(Carbene) Complex Based on a Ditopic Cyclic (Aryl)(Amino)Carbene Framework

Abstract

A dinuclear gold(I) bis(carbene) complex based on a 1,5dihydropyrazolo[3,4-f]indazoline-3,7-diylidene ligand framework is reported. The bridging bis(carbene) ligand is the first example of a ditopic cyclic (aryl)(amino)carbene (CArAC). The ligand precursor 2,6-diethyl-1,5-diphenyl-1,5-dihydropyrazolo[3,4-f]indazole-2,6-diium (2H 2 ) is readily available from the literature-known starting material 1,5-diphenyl-1,5-dihydropyrazolo[3,4-f]indazole (1) and two equivalents of the Meerwein salt [Et 3 O][BF 4 ]. The NHC gold(I) hydroxide complex [IPrAuOH] proved to be a valuable precursor for the synthesis of the dinuclear gold complex [(IPr) 2 Au 2The compounds under study were fully characterized by various methods, also including X-1320 ray crystallographic studies on single crystals of 2H 2 and 3. The ligand was developed in order to explore a possibly enhanced mediation of electronic metal-to-metal communication via the π-system. Density functional theory calculations revealed, however, that the electronic communication in the parent system, or in other ring-substituted derivatives, is only small and predominantly mediated by the σ-bond framework. The calculations also predict that the introduction of an additional donor functionality to the central arene ring of the ditopic bis(carbene), which is able to act as bridging entity and forms an additional metal-ligand bond, increases the communication between the two central metal atoms. The amount of electronic communication in the bis(carbene) complexes under study appears to be a direct function of the number of metal-ligand contacts. envisaged that the communication between the d π (p π ) orbitals of the metals and the π-system of the ditopic bis(NHC) (π L ) is mediated by M=C π-bonding. Detailed investigations by several groups have revealed, however, that the intermetallic communication in these systems is only weak. [6] Scheme 1. Selected Janus bis(NHC) complexes known from the literature. [5] Journal of Inorganic and General Chemistry Zeitschrift für anorganische und allgemeine Chemie www.zaac.wiley-vch.de ARTICLE One "drawback" of NHC-based ditopic bis(carbenes) is, among others, [7] owed to the fact that NHCs are predominant σ-donor ligands and that the strength of the M=C π-(back) bonding is commonly weak. Compared to NHCs, cyclic (alkyl) (amino)carbenes (CAAC) developed in 2005 by the group of Bertrand [8] are both more nucleophilic and more electrophilic than NHCs, i.e. the M=C π-interaction is much stronger in CAAC metal complexes. [9] In the context of Janus/ditopic [3b] bis(carbenes) showing a possibly enhanced mediation of the intermetallic communication by the π-system, the aromatic analogues, i.e. cyclic (aryl)(amino)carbenes (CArACs), seemed to be particularly attractive. Although the isolation of free, meaning stable or persistent versions of CArACs remained elusive until now, [10] indirect routes to a few mononuclear transition metal complexes have been reported in recent years (Scheme 2). [11] Ditopic variants have, as far as we are aware, no...

Insights into the past and future of Janus-di-N-heterocyclic carbenes

“…Related to these type of Janus di-NHCs, in 2016 the group of Breher's described a benzo-fused di-pyrazolylidene and its coordination to gold (60, in Scheme 19). 47 The authors performed detailed experimental and computational studies (on Rh-based model complexes 61) in order to determine the ability of the ligand to mediate electronic metal-to-metal communication, and concluded that this coupling is a direct function of the number of metal-ligand contacts, in line with the findings published by Albrecht and co-workers for the Janus-bisimidazolylidene 44. 42 Although the benzo-bis-NHCs ligand in 60 and 61 do not establish the coordination to the two metals strictly in a 'directionally-opposed' manner, we consider it a close relative of the Janus-di-NHC family.…”

Can Tetrylone Act in a Similar Fashion to Tetrylene in Ni(CO)2 Complexes? A Theoretical Study based on a Comparison using DFT Calculations

“…The chemistry of the heavier homologues of N‐heterocyclic carbenes (NHCs) such as silylenes, germylenes, stannylenes and plumbylenes called tetrylenes, has been less intensively explored than that of NHCs . N‐heterocyclic carbenes show bonding similar to that of electron‐rich trialkylphosphanes with strong σ‐donors with negligible π‐accepting ability . More recent studies have shown that NHCs have a significant π‐accepting ability, which, however, is much weaker that its strong σ‐donor ability.…”

Cyclic (Alkyl)- and (Aryl)-(amino)carbene Coinage Metal Complexes and Their Applications

“…Gold complexes can be prepared by deprotonation of the corresponding aldiminium salts with LiN­(SiMe 3 ) 2 at −78 °C in the presence of (Me 2 S)­AuCl as shown for 50a , whereas the copper analogue is obtained by treatment of the salt precursor with CuOAc . Alternatively, a transmetalation route can be used as exemplified by the preparation of 51 , ,− or even by reaction with the Nolan NHC gold­(I) hydroxide [IPrAuOH} , as described by Breher et al for the dinuclear complex 52 (Scheme ). Note that complexes based on ditopic NHCs, analogous to 52 have been discussed as building blocks for electronically coupled systems. , …”

“…Gold complexes can be prepared by deprotonation of the corresponding aldiminium salts with LiN(SiMe 3 ) 2 at −78 °C in the presence of (Me 2 S)AuCl as shown for 50a, 12 whereas the copper analogue is obtained by treatment of the salt precursor with CuOAc. 106 Alternatively, a transmetalation route can be used as exemplified by the preparation of 51, 13,107−109 or even by reaction with the Nolan NHC gold(I) hydroxide [IPrAuOH} 32,110 as described by Breher et al 111 for the dinuclear complex 52 (Scheme 16). Note that complexes based on ditopic NHCs, analogous to 52 have been discussed as building blocks for electronically coupled systems.…”