Cooperative Bimetallic Effects on New Iridium(III) Pyrazolate Complexes: Hydrogen−Hydrogen, Carbon−Hydrogen, and Carbon−Chlorine Bond Activations

Abstract

The reaction of fac-[IrH2(NCCH3)3(PiPr3)]BF4 (1) with potassium pyrazolate gave the binuclear 34-electron complex [Ir2(μ-H)(μ-Pz)2H3(NCCH3)(PiPr3)2] (2). The structure of 2 was determined by X-ray diffraction. An electrostatic potential calculation located three terminal hydride ligands and one hydride bridging both iridium centers. The feasibility of this arrangement was studied by EHMO calculations. The spectroscopic data for 2 show that the complex is rigid in solution on the NMR time scale. In solution, the acetonitrile ligand of 2 dissociates. The activation parameters for this dissociation process in toluene-d8 are ΔH⧧ = 20.9 ± 0.6 kcal mol-1 and ΔS⧧ = 2.5 ± 1.3 e.u. Reaction of 2 with various Lewis bases (L) gives the substitution products [Ir2(μ-H)(μ-Pz)2H3(L)(PiPr3)2] (L = C2H4 (3), CO (4), HPz (5)). The reaction of complex 5 with C2H4 yields the ethyl derivative [Ir2(μ-H)(μ-Pz)2(C2H5)H2(HPz)(PiPr3)2] (6); this reaction is reversible. Complexes 2 and 3 react with CHCl3 to give CH2Cl2 and the comp...