N‐Heterocyclic Carbene Analogues of Nucleophilic Phosphinidene Transition Metal Complexes

Chloride abstraction from the complexes [(η(6)‐p‐cymene){(IDipp)P}MCl] (2 a, M=Ru; 2 b, M=Os) and [(η(5)‐C(5)Me(5)){(IDipp)P}IrCl] (3 b, IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) with sodium tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate (NaBAr(F)) in the presence of trimethylphosphine (PMe(3)), 1,3,4,5‐tetramethylimidazolin‐2‐ylidene ((Me)IMe) or carbon monoxide (CO) afforded the complexes [(η(6)‐p‐cymene){(IDipp)P}M(PMe(3))]BAr(F)] (4 a, M=Ru; 4 b, M=Os), [(η(6)‐p‐cymene){(IDipp)P}Os((Me)IMe)]BAr(F)] (5) and [(η(5)‐C(5)Me(5)){(IDipp)P}IrL][BAr(F)] (6, L=PMe(3); 7, L=(Me)IMe; 8, L=CO). These cationic N‐heterocyclic carbene‐phosphinidene complexes feature very similar structural and spectroscopic properties as prototypic nucleophilic arylphosphinidene complexes such as low‐field (31)P NMR resonances and short metal‐phosphorus double bonds. Density functional theory (DFT) calculations reveal that the metal‐phosphorus bond can be described in terms of an interaction between a triplet [(IDipp)P](+) cation and a triplet metal complex fragment ligand with highly covalent σ‐ and π‐contributions. Crystals of the C−H activated complex 9 were isolated from solutions containing the PMe(3) complex, and its formation can be rationalized by PMe(3) dissociation and formation of a putative 16‐electron intermediate [(η(5)‐C(5)Me(5))Ir{P(IDipp)}I][BAr(F)], which undergoes C−H activation at one of the Dipp isopropyl groups and addition along the iridium‐phosphorus bond to afford an unusual η(3)‐benzyl coordination mode.