Detection of Pd(III) and Pd(IV) intermediates during the aerobic oxidative C-C bond formation from a Pd(II) dimethyl complex

The dimethyl Pd ^II complex ( ^MeN4)Pd ^IIMe ₂ ( ^MeN4 = N,N′-dimethyl-2,11-diaza[3, 3](2,6)pyridinophane) is readily oxidized by dioxygen in the presence of protic solvents to selectively eliminate ethane. UV-vis, EPR, ESI-MS, and NMR studies reveal the formation of several Pd ^III and Pd ^IV intermediates during the aerobically induced C-C bond formation reaction, including the key intermediate [(κ ³- ^MeN4)Pd ^IVMe ₃] ⁺, which leads to ethane elimination. The latter complex was also synthesized independently and structurally characterized to reveal a distorted octahedral geometry that is proposed to promote facile reductive elimination. Overall, this study represents a rare example of aerobic oxidation of an organometallic Pd ^II precursor that leads to a well-defined Pd ^IV species, which undergoes selective C-C bond formation under ambient conditions.