Oxidation of diphosphazane-bridged derivatives of diruthenium nonacarbonyl by silver(I) salts in protic solvents: synthesis, structural characterization and protonation of the adduct [Ru2{µ-η2-OC(O)}(CO)4{µ-(RO)2PN(Et)P(OR)2}2](R = Me or Pri) involving a novel mode of co-ordination of carbon dioxide
Abstract
Treatment of [Ru2(µ-CO)(CO)4{µ-(RO)2PN(Et)P(OR)2}2](R = Me or Pri) with AgSbF6 in methanol, ethanol or tetrahydrofuran–water resulted in the formation of the solvento species [Ru2(CO)5(R′OH){µ-(RO)2PN(Et)P(OR)2}2][SbF6]2 which is isolable for R′= H but which spontaneously deprotonates to the alkoxycarbonyl-bridged derivative [Ru2{µ-η2-OC(OR′)}(CO)4{µ-(RO)2PN(Et)P(OR)2}2]SbF6 for R′= Me or Et. The aqua species [Ru2(CO)5(H2O){µ-(RO)2PN(Et)P(OR)2}2][SbF6]2 was readily deprotonated in consecutive steps by appropriate bases to afford respectively the hydroxycarbonyl-bridged species [Ru2{µ-η2-OC(OH)}(CO)4{µ-(RO)2PN(Et)P(OR)2}2]SbF6 and the adduct [Ru2{µ-η2-OC(O)}(CO)4{µ-(RO)2PN(Et)P(OR)2}2] in which the carbon dioxide molecule adopts a novel bridging co-ordination mode; this deprotonation is reversible and treatment of the latter with HBF4·OEt2 leads to stepwise regeneration of the aqua species. The co-ordinated water molecule in [Ru2(CO)5(H2O){µ-(PriO)2PN(Et)P(OPri)2}2][SbF6]2 was readily displaced by acids HA derived from conjugate bases with potential co-ordinating properties such as thiolate ions R″S–(R″= H or Ph) or carboxylate ions R‴CO2–(R‴= H, Me, Ph or CF3), to produce monocationic pentacarbonyl species of the type [Ru2A(CO)5{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6; detection of an intermediate, presumably [Ru2(CO)5(HA){µ-(PriO)2PN(Et)P(OPri)2}2][SbF6]2, was possible for HA = HCO2H and MeCO2H. The sulfido derivatives [Ru2(SR″)(CO)5{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6(R″= H or Ph) rapidly decarbonylate in solution to afford the tetracarbonyl products [Ru2(µ-SR″)(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6 in which the sulfido group bridges the two ruthenium atoms. On the other hand the carboxylato derivatives [Ru2{OC(O)R‴}(CO)5{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6(R‴= H, Me, Ph or CF3) are stable to decarbonylation in solution at room or elevated temperatures but can be decarbonylated to the carboxylato-bridged products [Ru2{µ-η2-OC(R‴)O}(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6 by irradiation with ultraviolet light. The water molecule in [Ru2(CO)5(H2O){µ-(PriO)2PN(Et)P(OPri)2}2][SbF6]2 was also readily displaced by the conjugate bases of the above acids HA, but in contrast to that observed for the carboxylic acids R‴CO2H (R‴= H, Me or Ph), reaction of the aqua species with the corresponding carboxylate ions R‴CO2– led to direct formation of the carboxylato-bridged species [Ru2{µ-η2-OC(R‴)O}(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2]SbF6. Possible mechanisms for the formation of the various products are discussed as are the structures of [Ru2(CO)5(H2O){µ-(PriO)2PN(Et)P(OPri)2}2][SbF6]2·OCMe2, [Ru2{µ-η2-OC(OEt)}(CO)4{µ-(MeO)2PN(Et)P(OMe)2}2]SbF6, [Ru2{µ-η2-OC(Me)O}(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2]PF6 and [Ru2{µ-η2-OC(O)}(CO)4{µ-(PriO)2PN(Et)P(OPri)2}2], established X-ray crystallographically.
Please wait while we load your content...
