Electrochemical Synthesis and Structure of Sn[Co(CO)₄]₄ and Its Use as a Stable Precursor of [Co(CO)₄]^- for the Catalysis of Hydrolysis of Propylene Carbonate

The complex Sn[Co(CO)₄]₄ (I) has been prepared in high yield by the controlled potential electrolysis of Co₂(CO)₈ in the presence of a tin anode. The major advantage afforded by this electrochemical synthesis is to produce I quickly and cleanly. Results of an X-ray diffraction study on I are reported. We have established that I and Co₂(CO)₈ are very active catalysts for the hydrolysis of cyclic organic carbonates. The 100% selectivity in monoglycol is in marked contrast to other catalytic systems that require an excess of water to inhibit production of polyglycols. Studies, under various CO pressures, of the catalytic activities of Co₂(CO)₈ and I during the hydrolysis of propylene carbonate have led us to suggest that (i) [Co(CO)₄]^- is the active moiety, (ii) I can eliminate Co₂(CO)₈, and (iii) I is more stable than Co₂(CO)₈ at low CO pressures. Isotopic analysis of the remaining substrate and products after the hydrolysis of propylene carbonate by H₂¹⁸O show that (iv) the attack of water occurs at the carbonyl site of the carbonate and (v) it is likely that hydration is activated by [Co(CO)₄]^-.