Synthesis and Reactivity of Phosphinocarbyne Complexes

The successive treatment of [W­(CBr)­(CO)2(Tp*)] (Tp* = hydrotris­(3,5-dimethylpyrazol-1-yl)­borate) with nBuLi and ClPPh2 affords the phosphinocarbyne complex [W­(CPPh2)­(CO)2(Tp*)] (1), DFT interrogation of which suggests that reactions with electrophiles may involve both the phosphorus atom and/or the metal–carbon multiple bond. This is borne out in reactions of 1 with a variety of electrophilic reagents. With iodomethane or dimethylsulfide borane, electrophilic attack occurs exclusively at phosphorus to afford the compounds [W­(CPMePh2)­(CO)2(Tp*)]I ([2]­I) and [W­{CP­(BH3)­Ph2}­(CO)2(Tp*)] (3). The reaction of 1 with sulfur affords both the thiophosphorylcarbyne complex [W­{CP­(S)­Ph2}­(CO)2(Tp*)] (4) and the thioacyl complex [W­{η2-SCP­(S)­Ph2}­(CO)2(Tp*)] (5), though 4 fails to react with sulfur to provide 5. In a similar manner, the complexes 2 and 3 also fail to react with sulfur, indicating that increasing the valance of the phosphorus center of 1 deactivates the WC bond toward further attack. Addition of selenium to 1 occurs exclusively at phosphorus to afford [W­{CP­(Se)­Ph2}­(CO)2(Tp*)] (6) with no indication of selenoacyl formation. Reversible protonation of 1 with HBF4 in diethyl ether precipitates the phosphoniocarbyne salt [W­(CPHPh2)­(CO)2(Tp*)]­BF4, [8]­BF4, which, however, on dissolution in dichloromethane rearranges irreversibly to the thermodynamic (ΔGcacld = 22.4 kJmol–1) phosphinocarbene isomer [W­(η2CHPPh2)­(CO)2(Tp*)]­BF4, [9]­BF4.