Catalytic P ? H Activation by Ti and Zr Catalysts

Catalytic dehydrocoupling of phosphines was investigated using the anionic zirconocene trihydride salts [Cp* 2 Zr(μ-H) 3 Li] 3 (la) or [Cp* 2 Zr(μ-H) 3 K(thf) 4 ] (1b), and the metallocycles [CpTi(NPtBu 3 )(CH 2 ) 4 ] (6) and [Cp*M-(NPtBu 3 )(CH 2 ) 4 ] (M=Ti 20, Zr 21) as catalyst precursors. Dehydrocoupling of primary phosphines RPH 2 (R=Ph, C 6 H 2 Me 3 , Cy, C 10 H 7 ) gave both dehydrocoupled dimers RP(H)P(H)R or cyclic oligophosphines (RP) n (n=4, 5) while reaction of tBu 3 C 6 H 2 PH 2 gave the phosphaindoline tBu 2 (Me 2 CCH 2 )C 6 H 2 PH (9). Stoichiometric reactions of these catalyst precursors with primary phosphines afforded [Cp* 2 Zr((PR) 2 )H][K(thf) 4 ] (R=Ph 2, Cy 3, C 6 H 2 Me 3 4), [Cp* 2 Zr((PPh) 3 )H] [K(thf) 4 ] (5), [CpTi(NPtBu 3 )(PPh) 3 ] (7) and [CpTi(NPtBu 3 )(μ-PHPh)]2 (8), while reaction of 6 with (C 6 H 2 tBu 3 )PH 2 in the presence of PMe 3 afforded [CpTi(NPtBu 3 )(PMe 3 )(P(C 6 H 2 tBu 3 )] (10). The secondary phosphines Ph 2 PH and (PhHPCH 2 ) 2 CH 2 also undergo dehydrocoupling affording (Ph 2 P) 2 and (PhPCH 2 ) 2 CH 2 . The bisphosphines (CH 2 PH 2 ) 2 and C 6 H 4 (PH 2 ) 2 are dehydrocoupled to give (PCH 2 CH 2 PH) 2 (12) and (C 6 H 4 P(PH)) 2 (13) while prolonged reaction of 13 gave (C 6 H 4 P 2 ) 8 (14). The analogous bisphosphine Me 2 C 6 H 4 (PH) 2 (17) was prepared and dehydrocoupling catalysis afforded (Me 2 C 6 H 2 P(PH)) 2 (18) and subsequently [(Me 2 C 6 H 2 P 2 ) 2 (μ-Me 2 C 6 H 2 P 2 )] 2 (19). Stoichiometric reactions with these bisphosphines gave [Cp* 2 Zr(H)(PH) 2 C 6 -H 4 ][Li(thf) 4 ] (22), [CpTi(NPtBu 3 )(PH) 2 -C 6 H 4 ] 2 (23) and [Cp*Ti(NPtBu 3 )(PH) 2 -C 6 H 4 ] (24). Mechanistic implications are discussed.