Heterobimetallic activation of dioxygen: characterization and reactivity of novel Cu(I)-Ge(II) complexes

Reaction of the known germylene GeN(SiMe3)2]2 and a new heterocyclic variant Ge(NMes)2(CH)2] with L(Me2)Cu]2 (L(Me2) = the beta-diketiminate derived from 2-(2,6-dimethylphenyl)amino-4-(2,6-dimethylphenyl)imino-2-pentene) yielded novel Cu(I)-Ge(II) complexes L(Me2)Cu-Ge(NMes)2(CH)2] (1a) and L(Me2)Cu-GeN(SiMe3)2]2 (1b), which were characterized by spectroscopy and X-ray crystallography. The lability of the Cu(I)-Ge(II) bond in 1a and b was probed by studies of their reactivity with benzil, PPh3, and a N-heterocyclic carbene (NHC). Notably, both complexes are cleaved rapidly by PPh3 and the NHC to yield stable Cu(I) adducts (characterized by X-ray diffraction) and the free germylene. In addition, the complexes are highly reactive with O2 and exhibit chemistry which depends on the bound germylene. Thus, oxygenation of 1a results in scission and formation of thermally unstable L(Me2)CuO2, which subsequently decays to (L(Me2)Cu)2(mu-O)2], while 1b yields L(Me2)Cu(mu-O)2GeN(SiMe3)2]2, a novel heterobimetallic intermediate having a Cu(III)(mu-O)2Ge(IV)]3+ core. The isolation of the latter species by direct oxygenation of a Cu(I)-Ge(II) precursor represents a new route to heterobimetallic oxidants comprising copper.