Carbon−Hydrogen Bond Activation in Hydridotris(pyrazolyl)borate Complexes of Iridium

Methylene chloride solutions of the tris(1-pyrazolyl)borate (Tp) complexes TpIr(PPh 3 )(C 2 H 4 ) or TpIr(C 2 H 4 ) 2 react with excess PPh 3 via activation of a pyrazole C−H bond to form equilibrium mixtures of TpIr(PPh 3 )(C 2 H 4 ), ( N,C 5,N -Tp-H)Ir(PPh 3 ) 2 H ( 1 ), and free ethylene upon standing at room temperature. Complete conversion to 1 was accomplished by removing the displaced ethylene. The hydride complex 1 was purified by protonation at the unbound nitrogen of the pyrazole ring to afford cationic complex 2 as the BF 4 salt. Deprotonation of 2 affords complex 1 in good yield and purity. The structures of 1 and 2 have been elucidated using 1 H and 13 C NMR spectroscopy. The structures of TpIr(C 2 H 4 ) 2 and complex 2 (CH 3 CN solvate) been verified by X-ray crystallography. Reaction of isolated complex 1 with ethylene regenerates TpIr(PPh 3 )(C 2 H 4 ) in a reaction that is strongly inhibited by added PPh 3 .