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-D
2
). 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.