Variable Pathways for Oxygen Atom Insertion into Metal-Carbon Bonds: The Case of Cp*W(O)2(CH2SiMe3)

Cp*W(O)(2)(CH2SiMe3) (1) (Cp* = eta(5)-pentamethylcyclopentadienyl) reacts with oxygen atom donors (e.g., H2O2, PhIO, IO4-) in THF/water to produce TMSCH2OH (TMS = trimethylsilyl). For the reaction of 1 with IO4-, the proposed pathway for alcohol formation involves coordination of IO4- to 1 followed by concerted migration of the -CH2TMS ligand to the coordinated oxygen of IO4- with concomitant dissociation of IO3- to produce Cp*W(O)(2)(OCH2SiMe3) (3), which undergoes protonolysis to yield free alcohol. In contrast to the reaction with IO4-, the reaction of 1 with H2O2 results in the formation of the eta(2)-peroxo complex Cp*W(O)(eta(2)-O-2)(CH2SiMe3) (2). In the presence of acid (HCl) or base (NaOH), complex 2 produces TMSCH2OH. The conversion of 2 to TMSCH2OH catalyzed by Bronsted acid is proposed to occur through protonation of the eta(2)-peroxo ligand, which facilitates the transfer of the -CH2TMS ligand to a coordinated oxygen of the eta(2)-hydroperoxo ligand. In contrast, the hydroxide promoted conversion of 2 to TMSCH2OH is proposed to involve hydroxide coordination, followed by proton transfer from the hydroxide ligand to the peroxide ligand to yield a kappa(1)-hydroperoxide intermediate. The migration of the -CH2TMS ligand to the coordinated oxygen of the kappa(1)-hydroperoxo produces an alkoxide complex, which undergoes protonolysis to yield free alcohol.