Synthesis and Reactivity of the Hydrido- and Alkylrhenium Methylidene Complexes Cp(PMe3)2(R)ReCH2 (R = H, CH3)

Protonolysis of the dimethylrhenium(III) compound Cp*(PMe3)2Re(CH3)2 (3) led to formation of the highly reactive hydridorhenium methylidene compound [Cp*(PMe3)2Re(CH2)(H)][OTf] (4), which was characterized spectroscopically at low temperature. Although 4 decomposed above −30 °C, reactivity studies performed at low temperature indicated it was in equilibrium with the coordinatively unsaturated methylrhenium complex [Cp*(PMe3)2Re(CH3)][OTf] (2). Methylidene complex 4 was found to react with PMe3 to afford [Cp*(PMe3)3Re(CH3)][OTf] (6) and with chloride anion to give Cp*(PMe3)2Re(Me)Cl (7). When BArf anion was added to 4, the thermally stable methylrhenium methylidene complex [Cp*(PMe3)2Re(CH2)(CH3)][BArf] (8) was isolated upon warming to room temperature. The mechanisms of formation of both 4 and 8 are discussed in detail, including DFT calculations. The novel carbonyl ligated complex Cp*(CO)2Re(CH3)OTf (12) was prepared, isolated, and found to not undergo migration reactions to form methylidene complexes.