Chloride Labilization Resulting from Nucleophilic Addition to cis-Ru(tpy)(CO)2Cl+PF6-:  Synthesis and Characterization of New CO2-Bridged and Formate Complexes of Ruthenium

Reaction of cis-Ru(tpy)(CO)2Cl+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)22+2PF6- (3). Reaction of 1 with aqueous NaOCHO yields the corresponding η1-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)22+2PF6-. 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 π-acceptor ligand (CO) to a σ-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)2Ru(CO2)Ru(tpy)(CO)22+2PF6- (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.