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

Abstract

Addition of IMe 4 (1,3,4,5-tetramethylimidazol-2-ylidene) to Ru(PPh 3 ) 3 HCl (in the presence of H 2 ) or Ru(PPh 3 ) 4 H 2 gave the all-trans isomer of Ru(IMe 4 ) 2 (PPh 3 ) 2 H 2 ( 1a ), whereas 1,3-diethyl-4,5-dimethylimidazol-2-ylidene (IEt 2 Me 2 ) reacted with Ru(PPh 3 ) 4 H 2 to form cis, cis, trans -Ru(IEt 2 Me 2 ) 2 (PPh 3 ) 2 H 2 ( 2b ). H/D exchange of 1a with C 6 D 6 (elevated temperature) or D 2 (room temperature) gave Ru(IMe 4 ) 2 (PPh 3 ) 2 HD ( 1a-HD ) and Ru(IMe 4 ) 2 (PPh 3 ) 2 D 2 ( 1a-D 2 ). CO reacted with 1a to give a mixture of Ru(IMe 4 ) 2 (PPh 3 )(CO)H 2 ( 3 ) and Ru(IMe 4 ) 2 (CO) 3 ( 4 ); 2b reacted in a similar manner, although more slowly, allowing isolation of the monocarbonyl species Ru(IEt 2 Me 2 ) 2 (PPh 3 )(CO)H 2 ( 5 ). Insertion of CO 2 into one of the Ru–H bonds of 1a and 2b generated mixtures of major and minor isomers of the κ 2 -formate complexes Ru(IMe 4 ) 2 (PPh 3 )(OCHO)H ( 7 / 8 ) and Ru(IEt 2 Me 2 ) 2 (PPh 3 )(OCHO)H ( 9 / 10 ). The hydridic nature of 1a and 2b was apparent by their reactivity toward MeI, which gave [Ru(IMe 4 ) 2 (PPh 3 ) 2 H]I ( 11 ), Ru(IEt 2 Me 2 ) 2 (PPh 3 )HI ( 12 ), [Ru(IEt 2 Me 2 ) 2 (PPh 3 ) 2 H]I ( 13 ), and Ru(IEt 2 Me 2 )(PPh 3 ) 2 HI ( 14 ). Complexes 1a, 2b, 5, 9, 11, 13, and 14 were structurally characterized.