Reductive disproportionation of carbon dioxide by dianionic carbonylmetalates of the transition metals

Carbon dioxide reacts readily with M2(M'(CO)5) (M = Li, Na, K, M' = W; M = K, M' = Cr, Mo, W) to give the corresponding group 6 hexacarbonyls (M(CO)6) and alkali metal carbonates. The reaction of Li2(W(CO)5) with excess 13CO2 at -78 C gives (W(CO)5(13CO)), confirming that the reaction involves reductive disproportionation of CO2 to CO and CO3(2-). The group 8 carbonylmetalates Na2(M(CO)4) (M = Fe, Ru, Os) react with CO2 to give (M(CO)5) and carbonate, and Na2(V(eta-C5H5)(CO)3) reacts with CO2 to give (V(eta-C5H5)(CO)4) and carbonate, indicating that reductive disproportionation is a general reaction of dianionic carbonylmetalates with CO2. Careful addition of one equivalent of CO2 to a solution of Li2(W(CO)5) at -78 C leads to an intermediate 1:1 adduct with an IR spectrum consistent with formulation as Li2(W(CO)5(eta 1-CO2)). The principal 13C absorption at 223.4 delta of a sample of Li2(W(CO)5(eta 1-13CO2)) prepared at -78 C exhibits Jw-c = 92 Hz, consistent with the central C being directly bonded to W and superscript 2 hybridized. Oxide scrambling from coordinated CO2 to coordinated CO at higher temperatures results in complex signals between 205 and 201 sigma assigned to the carbonyl ligands.