Transfer of oxygen and sulfur from organic molecules to a Zr-Ir bond. Evidence for an unusually rapid atom abstraction reaction

Article abstract of DOI:10.1021/ja00145a015

The early-late heterobimetallic complex Cp₂Zr(μ-N-t-Bu)IrCp* (1) has been found to undergo oxygen and sulfur abstraction reactions. Imido complex 1 reacts with Me₃P=S, S₈, H₂S, and thiiranes to form the bridging sulfido complex 2 (Cp₂Zr(μ-N-t-Bu)(μ-S)IrCp*). The structure of complex 2 was confirmed by an X-ray diffraction study. The addition of cis-2-butene sulfide to imido complex 1 gave only 2 and cis-2-butene. Similarly, the addition of trans-2-butene sulfide resulted only in the formation of trans-2-butene. These results argue against mechanisms for sulfur abstraction that involve ring-opened intermediates. Imido complex 1 was found to react with pyridine N-oxide, nitrous oxide, and styrene oxide to form the bridging oxo complex 4 (Cp₂Zr(μ-N-t-Bu)(μ-O)IrCp*), but it was unreactive toward cis-2-butene oxide or triphenylphosphine oxide. A competition study revealed that cis-2-butene sulfide, trans-2-butene sulfide, 2-methylpropene sulfide, propene sulfide, and ethylene sulfide reacted with complex 1 at very similar rates. We believe that this weak selectivity is a result of inherently very rapid - perhaps even diffusion-controlled - rates of reaction for the sulfur atom abstraction. It may be that low activation barriers are an inherent property of cooperative two-metal atom transfer reactions.