N-Heterocyclic Carbene Stabilized trans-Dihydrido Aqua and Ethanol Complexes of Ruthenium:  Precursors to Complexes with Ru−Heteroatom Bonds

Attempts to isolate the bis-N-heterocyclic carbene complex Ru(AsPh3)(IMes)2(CO)H2 (IMes = bis(1,3-(2,4,6-trimethylphenyl)imidazol-2-ylidene)) by crystallization with either ethanol or hexane yields instead the ethanol and water complexes Ru(IMes)2(CO)(EtOH)H2 (1) and Ru(IMes)2(CO)(H2O)H2 (2), respectively. Both multinuclear NMR spectroscopy and X-ray crystallography demonstrate that these two compounds are isostructural with a trans arrangement of the hydride ligands. Thermolysis of 1 results in decarbonylation of the bound ethanol ligand to yield Ru(IMes)2(CO)2H2 (3). Substitution of the coordinated solvent ligands in 1 or 2 occurs readily with p-ethoxyphenol to give Ru(IMes)2(CO)(HOC6H4-p-OEt)H2 (4), while treatment of 2 with 1-propanethiol affords the thiol complex Ru(IMes)2(CO)(HSCH2CH2CH3)H2 (8). Reaction of 8 with CO gives the thiolate hydride species Ru(IMes)2(CO)2(SCH2CH2CH3)H (9), whereas addition of CO to either 1 or 2 affords Ru(IMes)2(CO)3 (5). The hydroxy hydride complex Ru(IMes)2(CO)2(OH)H (6) has been isolated as an intermediate on the pathway from 2 to 5. Addition of CO2 or p-HO2CC5H4N to solutions of 2 yields the bicarbonate complex Ru(IMes)2(CO)(κ2-O2COH)H (10) and the isonicotinate species Ru(IMes)2(CO)(κ2-O2CC5H4N)H (11), respectively. Addition of CO to 10 affords Ru(IMes)2(CO)2(η1-O2COH)H (7). Treatment of complex 2 with excess acetonitrile yields the N-imidoylimidato complex Ru(IMes)2(CO)(NHC(CH3)NC(CH3)O)H (12), which arises from the formal addition of two molecules of acetonitrile in head-to-tail fashion across the RuO−H bond. Compounds 1, 2, 6, 7, 8, 9, 11, and 12 have been structurally characterized by single-crystal X-ray diffraction.