Carbon-hydrogen bond activation in hydridotris(pyrazolyl)borate complexes of iridium

Methylene chloride solutions of the tris(1-pyrazolyl)borate (Tp) complexes TpIr(PPh3)(C2H4) Or TpIr(C2H4)(2) react with excess PPh3 via activation of a pyrazole C-H bond to form equilibrium mixtures of TpIr(PPhs)(C2H4), (N,C- 5,N-Tp-H)Ir(PPh3)(2)H (1), and free ethylene upon standing at room temperat ure. Complete conversion to 1 was accomplished by removing the displaced et hylene. The hydride complex 1 was purified by protonation at the unbound ni trogen of the pyrazole ring to afford cationic complex 2 as the BF4 salt. D eprotonation of 2 affords complex 1 in good yield and purity. The structure s of 1 and 2 have been elucidated using H-1 and C-13 NMR spectroscopy. The structures of TpIr(C2H4)(2) and complex 2 (CH3CN solvate) been verified by X-ray crystallography. Reaction of isolated complex 1 with ethylene regener ates TpIr(PPh3)(C2H4) in a reaction that is strongly inhibited by added PPh 3.