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

Abstract

Deprotonation of triphenyl germane with NHC-supported copper alkoxides afforded four novel (NHC)CuGePh₃ complexes. Of these, (IPr)CuGePh₃ (IPr = :C{N(2,6-iPr₂C₆H₃)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 [Ph₃Ge]⁻. The Cu–Ge bond of (IPr)CuGePh₃ underwent π-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 β-germylated substrate implicating nucleophilicity at germanium.