Gold(I) Alkynyls Supported by Mono- and Bidentate NHC Ligands: Luminescence and Isolation of Unprecedented Ionic Complexes

Reactions of NHC center dot HX (NHC = 1-benzyl-3-methylbenzimidazol-2-ylidene, X = Br-, PF6-). and (AuC equivalent to CR)(n) (R = Ph, C3H6OH) in the presence of Cs2CO3 initially afford compounds of the general formula [(NHC)(2)Au](2)[(RC2)(2)Au]X, which can be isolated by crystallization. With increased reaction time, only the expected mononuclear complexes of the type [NHCAuC equivalent to CR] are produced. The crystal structure of [(NHC)(2)Au](2)[(PhC2)(2)Au]-PF6 reveals an unprecedented triple-decker array upheld by a remarkably short (2.9375(7) angstrom. unsupported Au center dot center dot center dot Au center dot center dot center dot Au contact. The mononuclear complex [NHCAuC equivalent to CPh] was found to crystallize as three distinct polymorphs and a pseudopolymorph, which depending on the intermolecular Au center dot center dot center dot Au distances emit blue, green,or yellow light. Two synthetic approaches were employed for the preparation of a series of dinuclear NHC-ligated Au(I) alkynyl complexes of the general formula {NHC-(CH2)(n)-NHC(AuC equivalent to CR)2]; Where NHC = N-benzylbenzimidazol-2-ylidene, R = Ph, C3H6OH, C6H10OH, and n = 1-3. In solution, the complexes with aliphatic substituents on the alkynyl fragment are nonemissive, whereas their phenyl-bearing congeners demonstrate characteristic metal-perturbed (3)[IL(C equivalent to CPh)] emission, In the solid state, a clear correlation between intermolecular aurophilic interactions and luminescence was established, including their role in the luminescent thermochromism of the phenylalkynyl complexes. The relationship between the Au center dot center dot center dot Au distance and emission energy was found to be inverse: i.e., the shorter the aurophilic contact, the higher the emission energy. We tentatively attribute this behavior to a smaller extent of excited-state distortion for a structure with a shorter Au center dot center dot center dot Au separation.