Coordinatively unsaturated hydridoruthenium(II) complexes of N-heterocyclic carbenes

The saturated imidazolin-2-ylidene compounds RNC3H4NR, with R = mesityl (SIMes), 2,6-diisopropylphenyl, were synthesized by use of diamines that were prepared by the hydrogenation of the corresponding diimines catalyzed by RuHCl(R-binap)(RR-dach)/(KOBu)-Bu-t in toluene. The ligands IMes (MesNC(3)H(2)NMes) and SIMes react with RuHCl(PPh3)(3) to give RuH(SIMes-H)(PPh3)(2) (1) and RuH(IMes-H)(PPh3)(2) (2), respectively, where there is cyclo-metalation of a C-H bond of an ortho Ar-CH3 group. The reaction of RuHCl(PPh3)(3) with (IBu)-Bu-t ((BuNC3H2NBu)-Bu-t-Bu-t) produces (IBu)-Bu-t-HCl and a red solution that, upon reaction with H-2, produces the dihydride Ru(H)(2)(ItBu)(PPh3)(2) as a mixture of the two isomers 3a (trans PPh3 ligands) and 3b (cis PPh3). These isomers have an agostic C-H bond from a methyl group. There is an interesting windshield wiper exchange of coordinated tert-butyl groups occurring in isomer 3a, as monitored in solution by VT NMR with a free energy of activation of 11.8 kcal/mol. The reaction of 2 with CO at 20 degreesC produces (OC-34)-RuH(CO)(PPh3)(2)(IMes-H) (4), while at 68 degreesC it forms the Ru(O) complex Ru(CO)(3)(PPh3)(IMes) (5). The reaction of 2 with phenol results in the formation of RuH(eta(5)-C6H5O.HOPh)(IMes)(PPh3) (6). The structures of complexes 1, 3a, 5, and 6 have been characterized by single-crystal X-ray diffraction.