C-H bond activation in the formation of an osmium(IV) metallacycle

The osmium methylimido complex [(eta(5)-C5H5)Os(NCH3)(CH2SiMe3)(2)][SO3CF3] , 1, reacts with PPh3 to give both the methyleneamido complex (eta(5)-C5H5) Os(NCH2)(CH2SiMe3)(2), 2, and the unique osmirtm(IV) hydride [(eta(5)-C5H5) Os(H)(PPh3){CCHSiMe3PPh2(C6H4)}][SO3CF3], 4 A single-crystal X-ray diffract ion study of 4 shows that this molecule has a distorted square pyramidal st ructure with the center of the cyclopentadienyl ring at the apex: This mole cule results from a series of reactions that includes two C-H activation st eps: alpha-hydrogen elimination and orthometalation.