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.