Investigation in the coupling of zirconocene complexes and trimethylsilyl(diphenylphosphino)acetylene. P–C bond cleavage chemistry from protonolysis reactions

The regioselectivity of the coupling reactions of the internal acetylenic derivative Ph2P–CC–SiMe3 (2) and the benzyne complex [Cp2Zr(η2-C6H4)] (1) resulted preferentially in the formation of the zirconaindene metallacycle with the metal α-carbanions stabilized by the trimethylsilyl group. We have been able to structurally characterize the two regiosomers. The unusual acute Zr–C–P angle and the short Zr–P distance revealed that a significant Lewis-base/Lewis-acid σ-P–Zr interaction occurs in the α-phosphino zirconaindene metallacycle. Addition of HCl · Et2O on the cyclic α-silyl zirconindene complex led to competition reactions between (i) the nucleophilic attack of the lone pair of the phosphino group followed by P–C cleavage to form Ph2PH and Ph–CC–SiMe3 (7) and (ii) protonolysis of the Zr–CSi bond to give the Z-vinyl silyl phosphino product Ph2PC(Ph)C(H)SiMe3 (8). When the lone electron pair of the phosphino group is engaged intramolecularly with the metal center to achieve the stable 18-electron configuration protonolysis reaction on the Zr–C bonds to give the Z-vinyl silyl phosphino product Ph2PC(H)C(Ph)SiMe3 (9) is the unique process observed. Protonolysis reaction on the complexes prepared in situ from the addition of 2 and zirconocene like reagents “[Cp2Zr]” gave Ph2PH, H–CC–SiMe3, and Ph2PC(H)C(H)SiMe3 (18) which resulted from the competitive P–C and Zr–C bond cleavage processes of the transient alkyne complex Cp2Zr(η2-Ph2P–CC–SiMe3)] (14).