Synthesis and Small Molecule Reactivity of trans-Dihydride Isomers of Ru(NHC)2(PPh3)2H2 (NHC = N‑Heterocyclic Carbene)

Addition of IMe4 (1,3,4,5-tetra­methyl­imidazol-2-ylidene) to Ru­(PPh3)3­HCl (in the presence of H2) or Ru­(PPh3)4­H2 gave the all-trans isomer of Ru­(IMe4)2­(PPh3)2­H2 (1a), whereas 1,3-diethyl-4,5-dimethylimidazol-2-ylidene (IEt2­Me2) reacted with Ru­(PPh3)4­H2 to form cis,cis,trans-Ru­(IEt2­Me2)2­(PPh3)2­H2 (2b). H/D exchange of 1a with C6D6 (elevated temperature) or D2 (room temperature) gave Ru­(IMe4)2­(PPh3)2­HD (1a-HD) and Ru­(IMe4)2­(PPh3)2­D2 (1a-D2). CO reacted with 1a to give a mixture of Ru­(IMe4)2­(PPh3)­(CO)­H2 (3) and Ru­(IMe4)2­(CO)3 (4); 2b reacted in a similar manner, although more slowly, allowing isolation of the monocarbonyl species Ru­(IEt2­Me2)2­(PPh3)­(CO)­H2 (5). Insertion of CO2 into one of the Ru–H bonds of 1a and 2b generated mixtures of major and minor isomers of the κ2-formate complexes Ru­(IMe4)2­(PPh3)­(OCHO)H (7/8) and Ru­(IEt2Me2)2(PPh3)­(OCHO)H (9/10). The hydridic nature of 1a and 2b was apparent by their reactivity toward MeI, which gave [Ru­(IMe4)2­(PPh3)2­H]I (11), Ru­(IEt2­Me2)2­(PPh3)­HI (12), [Ru­(IEt2­Me2)2­(PPh3)2­H]I (13), and Ru­(IEt2­Me2)­(PPh3)2­HI (14). Complexes 1a, 2b, 5, 9, 11, 13, and 14 were structurally characterized.