Group 11 Bis(alumanyl)metallates

Reactions of the coinage metal (CM) cyanides, CuCN, AgCN,
or K[Au(CN)2], with [{SiNDipp}AlK]2 ({SiNDipp} = {CH2SiMe2N(Dipp)}2; Dipp = 2,6-i-Pr2C6H3) result in KCN
metathesis and a series of “alumina-Gilman” reagents,
[({SiNDipp}Al)2CM]K (CM = Cu, Ag, or Au). The
latter species may be isolated in both charge-separated, [({SiNDipp}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 [({SiNDipp}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 [{SiNDipp}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, [{SiNDipp}Al(C6H6)•].