Formation of Cyclometallated N‐Heterocyclic Carbene (NHC) Complexes from L n RuCl 2 (L = Cyclooctadiene, PPh 3 , DMSO) Precursors

Both [Ru(cod)Cl 2 ] n and [Ru(PPh 3 ) 3 Cl 2 ] react with the N‐ i Pr substituted N‐heterocyclic carbene I i Pr 2 Me 2 [1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene] at elevated temperature to give the cyclometallated triscarbene product [Ru(I i Pr 2 Me 2 )′(I i Pr 2 Me 2 ) 2 Cl] ( 1 ), which also contains an agostically bound NHC ligand. Although [Ru(cod)Cl 2 ] n fails to react with the bulkier tert ‐butyl carbene I t Bu 2 [1,3‐di‐ tert ‐butylimidazol‐2‐ylidene], [Ru(PPh 3 ) 3 Cl 2 ] affords the cyclometallated monocarbene complex [Ru(I t Bu 2 )′(PPh 3 ) 2 Cl] ( 2 ). Cyclometallation of the N ‐ethyl derivative IEt 2 Me 2 [1,3‐diethyl‐4,5‐dimethylimidazol‐2‐ylidene] takes place upon heating with [Ru(DMSO) 4 Cl 2 ] to give the tris‐DMSO product, [Ru(IEt 2 Me 2 )′(DMSO) 3 Cl] ( 3 ), which undergoes substitution of the S‐bound DMSO ligands in the presence of CO and PPh 3 to yield [Ru(IEt 2 Me 2 )′(CO) 3 Cl] ( 4 ) and [Ru(IEt 2 Me 2 )′(PPh 3 ) 2 Cl] ( 6 ). In contrast, IEt 2 Me 2 reacts with [Ru(PPh 3 ) 3 Cl 2 ] to give [Ru(IEt 2 Me 2 ) 4 Cl 2 ] ( 7 ). The molecular structures of compounds 1 – 4 , 6 and 7 have been determined.