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.