Synthesis and reactivity of the cationic methylene complex [Cp2Re=CH2]+

Reaction of Cp2ReCH2R (R = H, CH3) (Cp = eta(5)-C5H5) with [Ph3C]B(Ar')(4) (Ar' = 3,5-CF3)(2)C6H3) generates carbene complexes [Cp2Re=CH2]B(Ar')(4) (1) and [Cp2Re=CH(CH3)]B(Ar')(4)(3). Complex 1 is thermally robust and is only observed to decompose to [Cp2Re(C2H4)](+) and [Cp2Re(NCCD3)](+) upon prolonged thermolysis in acetonitrile-d(3) or upon addition of BF4- or PF6- salts. The formation of 1 is also observed upon reaction of [Cp2Re(CH3)H]B(Ar')(4) with CH2Cl2 at 0 degrees C to give [Cp2Re(CH2Cl)Cl]B(Ar')(4) (2) followed by treatment with Mg. The electrophilic nature of 1 is confirmed by adduct formation with PPh3, pyridine, and (CNBu)-Bu-t. Complex 1 reacts with halogens by 1,2-addition across the Re-C double bond to form halomethyl halide complexes [Cp2Re(CH2X)X]B(Ar')(4) (X = Cl, Br, I). Reaction of 1 with pyridine N-oxide gives the formaldehyde complex [Cp2Re(eta(2)-H2C=O)]B(Ar')(4) The formaldehyde ligand can be displaced in solution by reaction with PPh3, acetonitrile, or methylene chloride. Complex 1 reacts with sulfur-atom donor reagents to give the thioformaldehyde complex [Cp2Re(eta(2)-H2C=S)]B(Ar')(4). Reaction of 1 with N2CHSiMe3 generates the olefin complex [Cp2Re(eta(2)-H2C=CHSiMe3)]B(Ar')(4).