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 Cp2M(μ-OPPh2)2PdMe2 (M = Ti (1), Zr (2), and Hf (3)) were synthesized by the reaction of PdMe2(tmeda) (tmeda = Me2NCH2CH2NMe2) with respective metallocene diphosphinite ligands Cp2M(OPPh2)2 prepared from Cp2MCl2 (M = Ti, Zr, and Hf) and LiOPPh2. The complexes 1−3 catalyzed the addition (hydrophosphinylation) of HP(O)Ph2 to 1-octyne to give mainly not the single-addition product n-Hex-CH═CHP(O)Ph2 (4a) or n-Hex-C{P(O)Ph2}═CH2 (4b) but the double-addition product n-Hex-CH{P(O)Ph2}CH2P(O)Ph2 (5) at 40 °C in low yields. The yield of 5 was, however, substantially improved to >95% for 2 and 3 when tertiary phosphine PR3 such as PMePh2 was added to the catalytic system. The stoichiometric reaction of the complexes 1−3 with the phosphorus substrate HP(O)Ph2 and PMePh2 afforded in situ the trinuclear complexes H(PMePh2)Pd(μ-OPPh2)3M(μ-OPPh2)3PdH(PMePh2), which were found to exhibit the high catalytic activities similar to those of their parent complexes 1−3 in the presence of PR3 and were thus proposed to be a practical catalyst. On the basis of the above findings, simple mixtures of mononuclear Cp2MCl2 and PdMe2(tmeda) complexes together with PMePh2 could be used successfully as precatalysts for the double hydrophosphinylation of 1-octyne with HP(O)Ph2 to give satisfactory results comparable to those attained with the preorganized binuclear complexes 2 and 3 with PMePh2 added.