Simultaneous Observation of Doubly and Triply Chloride Bridged Isomers of an Electron-Rich Ruthenium Dimer:  Role of Dimer Geometry in Determining Reactivity

High-yield routes to the dimeric monocarbonyl complexes [RuCl 2 (PP)(CO)] 2 ( 3; PP = dcypb, 1,4-bis(dicyclohexylphosphino)butane) are established via (a) decarbonylation of mononuclear RuCl 2 (PP)(CO) 2 ( 4 ), (b) one-pot carbonylation−decarbonylation of RuCl(PP)(μ-Cl) 3 Ru(PP)(N 2 ) ( 1 ), and, most conveniently, (c) phosphine exchange of RuCl 2 (PPh 3 ) 3 with dcypb, followed by a carbonylation−decarbonylation sequence as in (b), all three steps being carried out in a one-pot procedure. One or three isomers of 3 can be observed by NMR analysis, depending on the solvent medium. A mixture of [RuCl(PP)(CO)] 2 (μ-Cl) 2 (transoid, 3a; cisoid, 3b ) and ionic {[Ru(PP)(CO)] 2 (μ-Cl) 3 }Cl ( 3c ) is present in benzene, chlorobenzene, or THF. In CH 2 Cl 2 or CDCl 3, only 3c is observed. This represents the first Ru 2 X 4 L 4 system (L = L, L‘) in which three of the possible edge-bridging and face-bridging isomers can be simultaneously observed and in which their ratio can be manipulated. Reactivity studies indicate that the face-sharing isomer 3c is considerably more stable than its edge-sharing isomers. Transformations of 3 are significantly accelerated by introduction of a donor solvent (methanol, THF). Product identities were established by 1 H, 13 C, and 31 P NMR and IR spectroscopy, by microanalysis, and by X-ray crystallography ( 3a / 3b, 3c, 4a / 4b ).