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 [RuCl2(PP)(CO)](2) (3; PP = dcypb, 1,4-bis(dicyclohexylphosphino)butane) are established via (a) decarbonylation of mononuclear RuCl2(PP)(CO)(2) (4), (b) one-pot carbonylation-decarbonylation of RuCl(PP)(mu-Cl)(3)Ru(PP)(N-2) (1), and, most conveniently, (c) phosphine exchange of RuCl2(PPh3)(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)(mu-Cl)(2) (transoid, 3a; cisoid, 3b) and ionic { [Ru(PP)(CO)](2)(mu-Cl)(3)}Cl (3c) is present in benzene, chlorobenzene, or THF. In CH2Cl2 or CDCl3, only 3c is observed. This represents the first RU2X4L4 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 H-1, C-13, and P-31 NMR and IR spectroscopy, by microanalysis, and by X-ray crystallography (3a/3b, 3c, 4a/4b).