Chloride Labilization Resulting from Nucleophilic Addition to <i>cis</i>-Ru(tpy)(CO)<sub>2</sub>Cl<sup>+</sup>PF<sub>6</sub><sup>-</sup>:  Synthesis and Characterization of New CO<sub>2</sub>-Bridged and Formate Complexes of Ruthenium

Reaction of <i>cis</i>-Ru(tpy)(CO)<sub>2</sub>Cl<sup>+</sup>PF<sub>6</sub><sup>-</sup> (<b>1</b>; tpy = 2,2‘:6‘,2‘‘-terpyridyl) with aqueous Na<sub>2</sub>CO<sub>3</sub> in acetonitrile yields the CO<sub>2</sub>-bridged complex <i>cis</i>,<i>cis</i>-(CH<sub>3</sub>CN)(CO)(tpy)Ru(CO<sub>2</sub>)Ru(tpy)(CO)<sub>2</sub><sup>2+</sup>2PF<sub>6</sub><sup>-</sup> (<b>3</b>). Reaction of <b>1</b> with aqueous NaOCHO yields the corresponding η<sup>1</sup>-formato complex <b>4</b>; reaction of <b>4</b> with aqueous Na<sub>2</sub>CO<sub>3</sub> also provides <b>3</b>. Reaction of <b>3</b> with CO results in displacement of acetonitrile and formation of <b>5</b>, <i>cis</i>,<i>cis</i>-(CO)<sub>2</sub>(tpy)Ru(CO<sub>2</sub>)Ru(tpy)(CO)<sub>2</sub><sup>2+</sup>2PF<sub>6</sub><sup>-</sup>. Reaction paths leading to <b>3</b> and <b>4</b> from <b>1</b> 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 <b>3</b> and <b>4 </b>was provided by a trapping experiment in which <b>1</b> reacts with <i>cis-</i>Ru(bpy)<sub>2</sub>(CO)COOH<sup>+</sup>PF<sub>6</sub><sup>-</sup> in the presence of aqueous Na<sub>2</sub>CO<sub>3</sub> to give <i>cis</i>,<i>cis</i>-(CO)(bpy)<sub>2</sub>Ru(CO<sub>2</sub>)Ru(tpy)(CO)<sub>2</sub><sup>2+</sup>2PF<sub>6</sub><sup>-</sup> (<b>7</b>; 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 CO<sub>2</sub> are discussed.