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

Deprotonation of triphenyl germane with NHC-supported copper alkoxides afforded four novel (NHC)CuGePh3 complexes. Of these, (IPr)CuGePh3 (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 sigma-bond metathesis reaction with a range of p-block halides confirmed it to be a convenient source of [Ph3Ge](-). The Cu-Ge bond of (IPr)CuGePh3 underwent pi-bond insertions with tBuNCS, CS2, and PhNCO to furnish a series of germyl substituted carboxylate derivatives, (IPr)CuXC(Y)GePh3 (X = S, NPh; Y = S, NtBu, O), which were structurally characterised. (IPr)CuGePh3 inserted phenyl acetylene, providing both the Markovnikov and anti-Markovnikov products. The (NHC)CuGePh3 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 Ph3GeH 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 beta-germylated substrate implicating nucleophilicity at germanium.