Abstract: | Redox‐unstable cuprous hydridotriphenylborate was isolated as an N‐heterocyclic carbene adduct (IPr)Cu(HBPh3)] (IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene) with good thermal stability. Although this compound displays a contact ion‐pair structure, CuIH‐like catalytic activity was envisaged in carbonyl hydrosilylation. Sufficient moisture stability allowed the catalysis in aqueous/organic media. Mechanistic study further showed that a phenyl group on the borate anion is abstracted by (IPr)Cu]+ to give the cationic organocopper complex (IPr)2Cu2(μ‐Ph)]BPh4]. |