Group 11 Bis(alumanyl)metallates

Abstract

Reactions of the coinage metal (CM) cyanides, CuCN, AgCN, or K[Au(CN)₂], with [{SiN^Dipp}AlK]₂ ({SiN^Dipp} = {CH₂SiMe₂N(Dipp)}₂; Dipp = 2,6-i-Pr₂C₆H₃) result in KCN metathesis and a series of “alumina-Gilman” reagents, [({SiN^Dipp}Al)₂CM]K (CM = Cu, Ag, or Au). The latter species may be isolated in both charge-separated, [({SiN^Dipp}Al)₂CM]⁻[K(THF)₆]⁺, or contact ion pair forms when crystallized in the presence or absence of THF. Computational analysis apportions a high degree of covalency to the CM–Al metal bonding and attribution of an aluminum oxidation state that is best represented as Al(II). This latter inference is supported by the experimental observation of THF activation, deduced to result from the competitive single electron reduction of the group 11 center during the synthesis of the bis(alumanyl)metalates. UV photolysis of [({SiN^Dipp}Al)₂Ag]K provided a product of 2-fold Al(II) radical addition to benzene. This species is also synthesized by a modification of the reaction that gave rise to the initially identified cuprate metathesis product. The intermediacy of [{SiN^Dipp}Al^•] radicals, which are proposed to add to benzene in a stepwise manner, is supported by the observation of in situ recorded EPR spectra, the simulated parameters of which have been assigned to the singly aluminated benzene product, [{SiN^Dipp}Al(C₆H₆)^•].