TRANSFER OF OXYGEN AND SULFUR FROM ORGANIC-MOLECULES TO A ZR-IR BOND - EVIDENCE FOR AN UNUSUALLY RAPID ATOM ABSTRACTION REACTION

The early-late heterobimetallic complex Cp(2)Zr(mu-N-t-Bu)IrCp (1) ha s been found to undergo oxygen and sulfur abstraction reactions. Imido complex 1 reacts with Me(3)P=S, S-8, H2S, and thiiranes to form the b ridging sulfide complex 2 (Cp(2)Zr(mu-N-t-Bu)(mu-S)IrCp). The structu re of complex 2 was confirmed by an X-ray diffraction study. The addit ion of cis-2-butene sulfide to imido complex 1 gave only 2 and cis-2-b utene. Similarly, the addition of trans-2-butene sulfide resulted only in the formation of trans-2-butene. These results argue against mecha nisms for sulfur abstraction that involve ring-opened intermediates. I mido complex 1 was found to react with pyridine N-oxide, nitrous oxide , and styrene oxide to form the bridging oxo complex 4 (Cp(2)Zr(mu-N-t -Bu)(mu-O)IrCp), but it was unreactive toward cis-2-butene oxide or t riphenylphosphine oxide. A competition study revealed that cis-2-buten e sulfide, trans-2-butene sulfide, 2-methylpropene sulfide, propene su lfide, and ethylene sulfide reacted with complex 1 at very similar rat es. We believe that this weak selectivity is a result of inherently ve ry rapid-perhaps even diffusion-controlled-rates of reaction for the s ulfur atom abstraction. It may be that low activation barriers are an inherent property of cooperative two-metal atom transfer reactions.