X-ray structure and reactivity of bis(2,2'-bipyridine)carbonylhydridoruthenium hexafluorophosphate hemi(acetone), a possible intermediate in the water-gas shift reaction catalyzed by ruthenium polypyridyl complexes

Abstract

The structure of (Ru(C/sub 10/H/sub 8/N/sub 2/)/sub 2/(CO)H)PF/sub 6/ x 1/2 C/sub 3/H/sub 6/O is reported. The compound crystallizes in the monoclinic C2/c space group with unit cell parameters a = 26.680 (4) A, b = 7.005 (3) A, c = 25.936 (2) A, and ..beta.. = 93.96 (2)/sup 0/ (V = 4836.04 A/sup 3/, Z = 8). The cationic species has a cis geometry for CO and H. The ruthenium-hydride and ruthenium-carbon distances are 1.68 (4) and 1.804 (6) A, respectively. The average ruthenium-nitrogen distance is 2.109 A. In acidic solution the title compound acts as a hydride donor to produce dihydrogen gas in a pseudo-first-order reaction; the second-order rate constant for this reaction is 0.105 -/+ 0.01 dm/sup 3/ mol/sup -1/ s/sup -1/ at 303 K with an activation energy 56 -/+ 2 kJ mol/sup -1/. A value of -100 -/+ 8 J mol/sup -1/ deg/sup -1/ has been obtained for the entropy of activation. The consequences of these results for the possible reaction mechanism of the homogeneous water-gas shift reaction catalyzed by (Ru(bpy)/sub 2/(CO)Cl)/sup +/ are discussed. 15 references, 4 figures, 6 tables.