N-Heterocyclic Carbene Analogues of Nucleophilic Phosphinidene Transition Metal Complexes.

Chloride abstraction from the complexes [(η -p-cymene){(IDipp)P}MCl] (2 a, M=Ru; 2 b, M=Os) and [(η -C Me ){(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 ) in the presence of trimethylphosphine (PMe ), 1,3,4,5-tetramethylimidazolin-2-ylidene ( IMe) or carbon monoxide (CO) afforded the complexes [(η -p-cymene){(IDipp)P}M(PMe )]BAr ] (4 a, M=Ru; 4 b, M=Os), [(η -p-cymene){(IDipp)P}Os( IMe)]BAr ] (5) and [(η -C Me ){(IDipp)P}IrL][BAr ] (6, L=PMe ; 7, L= 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 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 complex, and its formation can be rationalized by PMe dissociation and formation of a putative 16-electron intermediate [(η -C Me )Ir{P(IDipp)}I][BAr ], which undergoes C-H activation at one of the Dipp isopropyl groups and addition along the iridium-phosphorus bond to afford an unusual η -benzyl coordination mode.