Dinuclear Alkynyl Gold(I) Complexes Containing Bridging N‑Heterocyclic Dicarbene Ligands: New Synthetic Routes and Luminescence

A series of dinuclear alkynyl gold­(I) complexes of the type [(AuCCR′)2{μ-(Im-R)2(CH2)n}] (R′ = tBu, SiMe3, Ph, C6H4X-4 (X = OMe, CF3, or NO2), 3-pyridyl (Pyl), 2,2′-bipyridin-5-yl (Bpyl); Im-R = N-methylimidazol-N-yl-2-ylidene (Im-Me), N-butylimidazol-N-yl-2-ylidene (Im-Bu), N-benzylimidazol-N-yl-2-ylidene (Im-Bz); n = 1, 3, 5) have been synthesized by (1) deprotonation of arylacetylenes with K2CO3 in the presence of [(AuCl)2{μ-(Im-R)2(CH2)n}], (2) the “acac method”, i.e., the reaction of [(AuCl)2{μ-(Im-R)2(CH2)n}] with Tl­(acac) and, subsequently, with HCCR′, and (3) the reaction of [Au­(CCR′)]n with [(AgBr)2{μ-(Im-R)2(CH2)n}]. In addition, mononuclear complexes [(AuCCR′)­(Im-R2)], where Im-R2= N,N′-dimethylimidazol-2-ylidene and R′ = SiMe3 or Im-R2 = N,N′-dibenzylimidazol-2-ylidene and R′ = tBu, have been prepared by method 2 or 3, respectively. A dinuclear complex containing two AuCl units connected by an acyclic dicarbene ligand results from the attack of N,N′-diethylpropylenediamine to the isocyanide ligand of [AuCl­(CNtBu)]. The photophysical properties of the new gold­(I) chloro and alkynyl bis­(carbene) complexes have been studied. Most of the dinuclear alkynyl complexes prepared are emissive at room temperature in the solid state or in solution. Complexes derived from aryl- or heteroarylalkynes give structured emissions that have been assigned to gold-perturbed intraligand 3[π→π*]­(CCAr) excited states.