N-Heterocyclic Carbene Analogues of Nucleophilic Phosphinidene Transition Metal Complexes

Abstract

Chloride abstraction from the complexes [(η6-p-cymene){(IDipp)P}MCl] (2 a, M=Ru; 2 b, M=Os) and [(η5-C5Me5){(IDipp)P}IrCl] (3 b, IDipp=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBArF) in the presence of trimethylphosphine (PMe3), 1,3,4,5-tetramethylimidazolin-2-ylidene (MeIMe) or carbon monoxide (CO) afforded the complexes [(η6-p-cymene){(IDipp)P}M(PMe3)]BArF] (4 a, M=Ru; 4 b, M=Os), [(η6-p-cymene){(IDipp)P}Os(MeIMe)]BArF] (5) and [(η5-C5Me5){(IDipp)P}IrL][BArF] (6, L=PMe3; 7, L=MeIMe; 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 31P 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 PMe3 complex, and its formation can be rationalized by PMe3 dissociation and formation of a putative 16-electron intermediate [(η5-C5Me5)Ir{P(IDipp)}I][BArF], which undergoes C−H activation at one of the Dipp isopropyl groups and addition along the iridium-phosphorus bond to afford an unusual η3-benzyl coordination mode.