Cleavage of acyclic diaminocarbene ligands at an iridium(iii) center. Recognition of a new reactivity mode for carbene ligands.

Reaction of [Ir(μ-Cl)(ppy)] (1) with 4 equivs of CNCHX (X = F 2a, Cl 2b, Br 2c, I 2d) in the presence of 2 equivs of AgOTf in dichloromethane at 20-25 °C furnished the bisisocyanide complexes Ir(ppy)(CNCHX) (3a-d; 72-87%). Reaction of 3a-d with an excess of gaseous ammonia at room temperature gave the bisdiaminocarbene species Ir(ppy){C(NH)NHCHX} 5a-d (73-83%); the two-step addition proceeds through an intermediate formation of appropriate monocarbene complexes 4a-d. Further reaction of 5a-d with an excess of gaseous ammonia at 50 °C led to the cleavage of one diaminocarbene ligand to the cyanide ligand in [Ir(ppy)(CN){C(NH)NHCHX}] (6a-d) and this transformation is accompanied with the elimination of a substituted aniline. Treatment of 5a-d with N(CHCHOH) at 50 °C resulted in the cleavage of the diaminocarbene ligand to the isocyanide and uncomplexed NH; isocyanide remains bound to the iridium(iii) center in Ir(ppy){C(NH)NHCHX}(CNCHX) (4a-d). All isolated compounds were characterized by elemental analyses (C, H, N), molar conductivity measurements, TG/DTA, HRESI-MS, FTIR, 1D (H, C{H}, F{H}) and 2D (H,H-COSY, H,C-HMQC/H,C-HSQC, H,C-HMBC) NMR, and also by X-ray diffraction (for the bisisocyanide 3, the diaminocarbene/isocyanide 4, the bisdiaminocarbene 5, and the diaminocarbene/cyanide 6 type complexes).