Oxidative Verknuepfung von Phosphinomethanidliganden and Titanocen- und Bismutzentren: selektive C-C-, P-C- und P-P-Bindungsbildung

Article abstract of DOI:10.1016/0022-328X(93)86060-U

The reaction of Cp2TiCl2 with two equivalents of Lithium-phosphinomethanides is described.The reaction with LiCH2PMe2 leads to a C-C coupling product Cp2Ti, whereas with <(TMEDA)Li>2, the P-C coupling product Me3SiCH2PMe2=C(PMe2)(SiMe3), a P-ylide, is formed.An anlogous P-C coupling is observed with Li, whereby a novel titanocene heterocycle >, with an agostic Ti...H...C interaction, may be characterized as an intermediate.In contrast, with Li (without TMEDA) P-P coupling, yielding <(Me3Si)(H)C<*>PMe2>2, is observed exclusively.An analogous result is obtained with Li, leading to <(Me3Si)2C=PMe2>2, and, likewise, in the similar reaction of Cp2TiCl2 with Li, P-P coupling is observed leading to <(Me2P)(Me3Si)C=PMe2>2 and III(Me2P)2C(SiMe3)>>.With (TMEDA)Li, both P-P (34percent) and P-C (66percent) coupling are observed, yielding the P-ylides <(Ph2P)HC=PPh2>2 and Ph2PCH2PPh2=C(PPh2)2, respectively.The results are compared with the respective coupling reactions at bismuth centers: BiCl3 reacts with LiCH2PMe2 to give Bi(CH2PMe2)3; with <(TMEDA)Li>2 only 5percent of the P-C coupling product Me3SiCH2PMe2=C(PMe2)(SiMe3) are found, whereas 95percent of the P-P coupling product <(Me3Si)(H)C=PMe2>2 are obtained.Exclusive P-P coupling is also observed from BiCl3 and (TMEDA)Li and Li, respectively.The results clearly indicate that a metal-centered process, sensitive to steric and coordination effects, is active.Selective C-C, P-C and P-P coupling reactions are possible by selecting the appropriate combinations of reagents.The novel P-ylides are characterized by use of NMR spectroscopy; III<(Me2P)2C(SiMe3)>> and <(Me3Si)2C=PMe2>2 are further characterized by X-ray structure determinations.