OXIDATION OF DIPHOSPHAZANE-BRIDGED DERIVATIVES OF DIRUTHENIUM NONACARBONYL BY SILVER(I) SALTS IN PROTIC SOLVENTS - SYNTHESIS, STRUCTURAL CHARACTERIZATION AND PROTONATION OF THE ADDUCT [RU2(MU-ETA-2-OC(O))(CO)4-(MU-(RO)2PN(ET)P(OR)2)2] (R=ME OR PR-I) INVOLVING A NOVEL MODE OF COORDINATION OF CARBON-DIOXIDE

Treatment of [Ru2(mu-CO)(CO),{mu-(RO)2PN(Et)P(OR)2)2] (R = Me or Pr(i)) with AgSbF6 in methanol, ethanol or tetrahydrofuran-water resulted in the formation of the solvento species [Ru2(CO)5(R'OH){mu-(RO)2PN(Et)P(OR)2}2] [SbF6]2 which is isolable for R' = H but which spontaneously deprotonatesto the alkoxycarbonyl-bridged derivative [Ru2{mu-eta2-OC(OR')}(CO)4{mu-(RO)2PN(Et)P(OR)2}2]SbF6 for R' = Me or Et. The aqua species [Ru2(CO)5(H2O){mu-(RO)2PN(Et)P(OR)2}2] [SbF6], was readily deprotonated in consecutive steps by appropriate bases to afford respectively the hydroxycarbonyl-bridged species [Ru2{mu-eta2-OC(OH)}(CO)4{p-(RO)2PN(Et)P(OR)2}2]SbF6 and the adduct [Ru2{mu-eta2-OC(O)}(CO)4{mu-(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){mu-(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{mu-(PriO)2PN(Et)P(OPri)2)2]SbF6, detection of an intermediate, presumably [RU2(CO)5-(HA){mu-(PriO)2PN(Et)P(OPri)2}2] [SbF6]2, was possible for HA = HCO2H and MeCO2H. The sulfido derivatives [RU2(SR'')(CO)5{mu-(PriO)2PN(Et)P(OPri)2}2]SbF6 (R'' = H or Ph) rapidly decarbonylate in solution to afford the tetracarbonyl products [RU2(mu-SR'')(CO)4{mu-(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{mu-(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{mu-eta2-OC(R''')O}(CO)4{mu-(PriO)2PN(Et)P(OPri)2}2]SbF6 by irradiation with ultraviolet light. The water molecule in [Ru2(CO)5(H2O){mu-(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{mu-eta2-OC(R''')O}(CO)4(mu-(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){mu-(PriO)2PN(Et)P(OPri)2}2][SbF6]2.OCMe2, [RU2{mu-eta2-OC(OEt)}(CO)4{mu-(MeO)2PN(Et)P(OMe)2}2]SbF6, [Ru2{mu-eta2-OC(Me)O}(CO)4{mu-(PriO)2PN(Et)P(OPri)2}2]PF6 and [RU2{mu-eta2-OC(O)}(CO)4{mu-(PriO)2-PN(Et)P(OPri)2}2], established X-ray crystallographically.