Reactivity of Low-Valent Iridium, Rhodium, and Platinum Complexes with Di- and Tetrasubstituted Hydrazines

Three complexes, IrCl(PEt₃)₃, Rh(NNN)Cl (NNN = 2,6-(CyNCH)₂C₅H₃N), and (NN)PtMe₂ [NN = 1,10-phenanthroline (phen) or 2,2′-bipyridine (bpy)], have been investigated for N−N oxidative addition reactivity with di- and tetrasubstituted hydrazines. The reaction of IrCl(PEt₃)₃with 1,2-diphenylhydrazine (PhNHNHPh) forms the cyclometalated azobenzene complex (Et₃P)₂Cl(H)Ir(C₆H₄NNPh) (1) and the 2:1 complex [(Et₃P)₂Cl(H)Ir]₂(μ-C₆H₄NNC₆H₄) (2). The Rh(NNN)Cl pincer complex catalyzes the disproportionation of PhNHNHPh to azobenzene and aniline with no change in the Rh complex. The reaction of (bpy)PtMe₂ with the hydrazine AcNHNHC(O)CH₂CH₂CHCH₂ (3) yields the platinum metallacycle (bpy)Pt(η²-AcN-NC(O)(CH₂)₂CHCH₂ (4). Although IrCl(PEt₃)₃, Rh(NNN)Cl, and (NN)PtMe₂ all undergo facile oxidative addition of other X−Y bonds, such reactivity is not observed for hydrazines; in the Ir and Pt systems there is a clear preference for cleavage of the stronger N−H bond over the N−N bond. The tetrasubstituted hydrazines tetraphenylhydrazine, 1,2-diphenyl-1,2-dimethylhydrazine, bisuccinimide, biphthalimide, and N-dimethylamino phthalimide do not react with IrCl(PEt₃)₃, Rh(NNN)Cl, and (NN)PtMe₂. This lack of reactivity appears to be due to kinetic rather than thermochemical factors.