Chloride labilization resulting from nucleophilic addition to cis-Ru(tpy)(CO)(2)Cl+PF6-: Synthesis and characterization of new CO2-bridged and formate complexes of ruthenium

Reaction of cis-Ru(tpy)(CO)(2)Cl+PF6- (1; tpy = 2,2':6',2 ''-terpyridyl) with aqueous Na2CO3 in acetonitrile yields the CO2-bridged complex cis,cis-(CH3CN)(CO)(tpy)Ru(CO2)Ru(tpy)(CO)(2)(2+)2PF(6)(-) (3). Reaction of 1 with aqueous NaOCHO yields the corresponding eta(1)-formato complex 4; reaction of 4 with aqueous Na2CO3 also provides 3. Reaction of 3 with CO results in displacement of acetonitrile and formation of 5, cis,cis-(CO)(2)(tpy)Ru(CO2)Ru(tpy)(CO)(2)(2+)2PF(6)(-). Reaction paths leading to 3 and 4 from 1 are thought to occur by base-assisted trans labilization of chloride resulting from conversion of a pi-acceptor ligand (CO) to a sigma-donor (COOH). Support for proposed steps in the reaction paths leading to 3 and 4 was provided by a trapping experiment in which 1 reacts with cis-Ru(bpy)(2)(CO)COOH+PF6- in the presence of aqueous Na2CO3 to give cis,cis-(CO)(bpy)(2)Ru(CO2)Ru(tpy)(CO)(2)(2+)2PF(6)(-) (7; bpy = 2,2'-bipyridyl), which has been structurally characterized. Parallels between these reactions and the halide labilizations which occur with ruthenium or rhenium polypyridyl complexes during photochemical or electrochemical reductions of CO2 are discussed.