Add time:08/19/2019 Source:sciencedirect.com
The regioselectivity of the coupling reactions of the internal acetylenic derivative Ph2P–CC–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–CC–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–CC–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–CC–SiMe3)] (14).
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