Variable pathways for oxygen atom insertion into metal-carbon bonds: the case of Cp*W(O)2(CH2SiMe3).

CpW(O)(2)(CH(2)SiMe(3)) (1) (Cp = η(5)-pentamethylcyclopentadienyl) reacts with oxygen atom donors (e.g., H(2)O(2), PhIO, IO(4)(-)) in THF/water to produce TMSCH(2)OH (TMS = trimethylsilyl). For the reaction of 1 with IO(4)(-), the proposed pathway for alcohol formation involves coordination of IO(4)(-) to 1 followed by concerted migration of the -CH(2)TMS ligand to the coordinated oxygen of IO(4)(-) with concomitant dissociation of IO(3)(-) to produce CpW(O)(2)(OCH(2)SiMe(3)) (3), which undergoes protonolysis to yield free alcohol. In contrast to the reaction with IO(4)(-), the reaction of 1 with H(2)O(2) results in the formation of the η(2)-peroxo complex CpW(O)(η(2)-O(2))(CH(2)SiMe(3)) (2). In the presence of acid (HCl) or base (NaOH), complex 2 produces TMSCH(2)OH. The conversion of 2 to TMSCH(2)OH catalyzed by Brønsted acid is proposed to occur through protonation of the η(2)-peroxo ligand, which facilitates the transfer of the -CH(2)TMS ligand to a coordinated oxygen of the η(2)-hydroperoxo ligand. In contrast, the hydroxide promoted conversion of 2 to TMSCH(2)OH is proposed to involve hydroxide coordination, followed by proton transfer from the hydroxide ligand to the peroxide ligand to yield a κ(1)-hydroperoxide intermediate. The migration of the -CH(2)TMS ligand to the coordinated oxygen of the κ(1)-hydroperoxo produces an alkoxide complex, which undergoes protonolysis to yield free alcohol.