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

Reaction of [Ir(mu-Cl)(ppy) 2] 2 (1) with 4 equivs of CNC6H4X (X = F 2a, Cl 2b, Br 2c, I 2d) in the presence of 2 equivs of AgOTf in dichloromethane at 20-25 degrees C furnished the bisisocyanide complexes [Ir(ppy)(2)(CNC6H4X)(2)](OTf) ([3a-d](OTf); 72-87%). Reaction of [3a-d](OTf) with an excess of gaseous ammonia at room temperature gave the bisdiaminocarbene species [Ir(ppy)(2){C(NH2)NHC6H4X}(2)](OTf) [5a-d](OTf) (73-83%); the two-step addition proceeds through an intermediate formation of appropriate monocarbene complexes [4a-d](OTf). Further reaction of [5a-d](OTf) with an excess of gaseous ammonia at 50 degrees C led to the cleavage of one diaminocarbene ligand to the cyanide ligand in [Ir(ppy)(2)(CN) {C(NH2)NHC6H4X}] (6a-d) and this transformation is accompanied with the elimination of a substituted aniline. Treatment of [5a-d](OTf) with N(CH2CH2OH)(3) at 50 degrees C resulted in the cleavage of the diaminocarbene ligand to the isocyanide and uncomplexed NH3; isocyanide remains bound to the iridium(III) center in [Ir(ppy)(2){C(NH2)NHC6H4X}(CNC6H4X)](OTf) (4a-d). All isolated compounds were characterized by elemental analyses (C, H, N), molar conductivity measurements, TG/DTA, HRESI+/--MS, FTIR, 1D (H-1, C-13{H-1}, F-19{H-1}) and 2D (H-1, H-1-COSY, H-1, C-13-HMQC/H-1, C-13-HSQC, H-1, C-13-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).