Bi- and Trinuclear Complexes of Group 4 Metal and Palladium Bridged by OPPh₂Groups: Synthesis and High Catalytic Activities in Double Hydrophosphinylation of 1-Octyne

Abstract

The early−late heterobinuclear complexes Cp 2 M(μ-OPPh 2 ) 2 PdMe 2 (M = Ti ( 1 ), Zr ( 2 ), and Hf ( 3 )) were synthesized by the reaction of PdMe 2 (tmeda) (tmeda = Me 2 NCH 2 CH 2 NMe 2 ) with respective metallocene diphosphinite ligands Cp 2 M(OPPh 2 ) 2 prepared from Cp 2 MCl 2 (M = Ti, Zr, and Hf) and LiOPPh 2 . The complexes 1 − 3 catalyzed the addition (hydrophosphinylation) of HP(O)Ph 2 to 1-octyne to give mainly not the single-addition product n -Hex-CH═CHP(O)Ph 2 ( 4a ) or n -Hex-C{P(O)Ph 2 }═CH 2 ( 4b ) but the double-addition product n -Hex-CH{P(O)Ph 2 }CH 2 P(O)Ph 2 ( 5 ) at 40 °C in low yields. The yield of 5 was, however, substantially improved to >95% for 2 and 3 when tertiary phosphine PR 3 such as PMePh 2 was added to the catalytic system. The stoichiometric reaction of the complexes 1 − 3 with the phosphorus substrate HP(O)Ph 2 and PMePh 2 afforded in situ the trinuclear complexes H(PMePh 2 )Pd(μ-OPPh 2 ) 3 M(μ-OPPh 2 ) 3 PdH(PMePh 2 ), which were found to exhibit the high catalytic activities similar to those of their parent complexes 1 − 3 in the presence of PR 3 and were thus proposed to be a practical catalyst. On the basis of the above findings, simple mixtures of mononuclear Cp 2 MCl 2 and PdMe 2 (tmeda) complexes together with PMePh 2 could be used successfully as precatalysts for the double hydrophosphinylation of 1-octyne with HP(O)Ph 2 to give satisfactory results comparable to those attained with the preorganized binuclear complexes 2 and 3 with PMePh 2 added.