The structures and reactivity of NHC-supported copper(i) triphenylgermyls.

Deprotonation of triphenyl germane with NHC-supported copper alkoxides afforded four novel (NHC)CuGePh(3) complexes. Of these, (IPr)CuGePh(3) (IPr = :C{N(2,6-iPr(2)C(6)H(3))CH}(2)) was selected for further investigation. Analysis by EDA-NOCV indicates it to be a germyl nucleophile and its σ-bond metathesis reaction with a range of p-block halides confirmed it to be a convenient source of [Ph(3)Ge](-). The Cu-Ge bond of (IPr)CuGePh(3) underwent π-bond insertions with tBuNCS, CS(2), and PhNCO to furnish a series of germyl substituted carboxylate derivatives, (IPr)CuXC(Y)GePh(3) (X = S, NPh; Y = S, NtBu, O), which were structurally characterised. (IPr)CuGePh(3) inserted phenyl acetylene, providing both the Markovnikov and anti-Markovnikov products. The (NHC)CuGePh(3) compounds were validated as catalytic intermediates; addition of 10 mol% of NHC-copper(i) alkoxide to a mixture of triphenyl germane and a tin(iv) alkoxide resulted in a tin/germanium cross coupling with concomitant formation of alcohol. Moreover, a catalytic hydrogermylation of Michael acceptors was developed with Ph(3)GeH adding to 7 activated alkenes in good conversions and yields in the presence of 10 mol% of NHC-copper(i) alkoxide. In all cases, this reaction provided the β-germylated substrate implicating nucleophilicity at germanium.