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-CdropC-SiMe3 (2) and the benzyne complex [Cp2Zr(eta(2)-C6H4)] (1) resulted preferentially in the formation of the zirconaindene metallacycle with the metal alpha-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 sigma-P-Zr interaction occurs in the alpha-phosphino zirconaindene metallacycle. Addition of HCl (.) Et2O on the cyclic alpha-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-CdropC-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-CdropC-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(eta(2)-Ph2P-Cequivalent toC-SiMe3)] (14). (C) 2004 Elsevier B.V. All rights reserved.