Catalytic P--H activation by Ti and Zr catalysts

Catalytic dehydrocoupling of phosphines was investigated using the anionic zirconocene trihydride salts Cp*2Zr(mu-H)3Li]3 (1 a) or Cp*2Zr(mu-H)3K(thf)4] (1 b), and the metallocycles CpTi(NPtBu3)(CH2)4] (6) and Cp*M(NPtBu3)(CH2)4] (M=Ti 20, Zr 21) as catalyst precursors. Dehydrocoupling of primary phosphines RPH2 (R=Ph, C6H2Me3, Cy, C10H7) gave both dehydrocoupled dimers RP(H)P(H)R or cyclic oligophosphines (RP)n (n=4, 5) while reaction of tBu3C6H2PH2 gave the phosphaindoline tBu2(Me2CCH2)C6H2PH 9. Stoichiometric reactions of these catalyst precursors with primary phosphines afforded Cp*2Zr((PR)2)H]K(thf)4] (R=Ph 2, Cy 3, C6H2Me3 4), Cp*2Zr((PPh)3)H]K(thf)4] (5), CpTi(NPtBu3)(PPh)3] (7) and CpTi(NPtBu3)(mu-PHPh)]2 (8), while reaction of 6 with (C6H2tBu3)PH2 in the presence of PMe3 afforded CpTi(NPtBu3)(PMe3)(P(C6H2tBu3)] (10). The secondary phosphines Ph2PH and (PhHPCH2)2CH2 also undergo dehydrocoupling affording (Ph2P)2 and (PhPCH2)2CH2. The bisphosphines (CH2PH2)2 and C6H4(PH2)2 are dehydrocoupled to give (PCH2CH2PH)2)(12) and (C6H4P(PH))2 (13) while prolonged reaction of 13 gave (C6H4P2)(8) (14). The analogous bisphosphine Me2C6H4(PH)2 (17) was prepared and dehydrocoupling catalysis afforded (Me2C6H2P(PH))2 (18) and subsequently (Me2C6H2P2)2(mu-Me2C6H2P2)]2 (19). Stoichiometric reactions with these bisphosphines gave Cp*2Zr(H)(PH)2C6-H4]Li(thf)4] (22), CpTi(NPtBu3)(PH)2C6H4]2 (23) and Cp*Ti(NPtBu3)(PH)2C6H4] (24). Mechanistic implications are discussed.