Hydride Donating Properties of - in the Presence of CO; Chemistry of Ruthenium Carbonyl Anions Relevant to the Catalysis of the Water Gas Shift Reaction

Article abstract of DOI:10.1021/ja00288a017

The chemistry of selected ruthenium carbonyl anions was studied with respect to the catalysis of the water gas shift reaction (WGSR: CO +H2O->CO2 + H2).Sodium and potassium salts of ^- in THF reacted with CO (1atm) to precipitate Ru3(CO)11 and probably metal hydride.In the presence of CO, ^- functioned as an apparent hydride donor to B(OCH3)3 and reacted with H2O to give H2.The effect of counterion (K⁺, Na⁺, Li⁺, N(CH3)4⁺, N(C2H5)4⁺) on the hydride donating reactions of ^- was studied.For catalysis of the WGSR, a catalytic cycle was proposed which involves ^- and Ru3(CO)12 and emphasizes the apparent hydridic nature of ^- in the presence of CO.An equilibrium between tetranuclear and trinuclear clusters under CO/H2 (1 atm) gas was shown to exist in aprotic media: K(soln) + 3CO(g) <*> K(soln) + 1/3Ru3(CO)12(s) + H2(g).Consistent with this equilibrium, in basic catalytic solutions derived from either H4Ru4(CO)12 or Ru3(CO)12 as catalyst precursors, activity decreased when H2 was allowed to accumulate in the system and the equilibrium shifted toward the formation of ^-.However, when H2 was continuously removed from the system by diffusion through a Pd thimble while CO remained behind, the equilibrium shifted toward ^- and the activity increased with increasing ^- concentration.The trinuclear combination ^--Ru3(CO)12 plays the dominant role in catalysis of the WGSR in this system, irrespective of whether the reaction is initiated by a tetranuclear or trinuclear ruthenium carbonyl.The effect of counterion (K⁺, Na⁺, Li⁺, N(CH3)4⁺, HN(C2H5)3⁺) and the effect of phosphine (DPPE=Ph2PCH2CH2PPh2; DPPM=Ph2PCH2PPh2) substitution on ^- were examined.Although the counterion had little effect on catalysis, the degree of phosphine substitution had a significant effect on catalytic activity.