BIMETALLIC ANIONIC FORMYL COMPLEXES - SYNTHESIS AND PROPERTIES
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Three bimetallic anionic formyl complexes, Li+[Mn2(CO)9(CHO)]~ (2), Li+[ReMn(CO)9(CHO)] (3), and Li+[m-Re2(CO)9(CHO)] (4), are prepared by the reaction of Li(C2H5)3BH with the corresponding neutral metal carbonyl dimers MM'(CO)10. Whereas 2 has a half-life of ca. 8 min at room temperature, 4 is stable for days and is easily isolated as a THF solvate. When 2-4 are treated with electrophiles such as benzaldehyde, Fe(CO)s, and n-octyl iodide, hydride transfer occurs to give benzyl alcohol (after protonation), Li [Fe(CO)4(CHO)], and octane, respectively. Heterobimetallic formyl 3 is a weaker hydride donor than 2 and 4. Reaction of 4 with CH3I gives CH4 (ca. 50%). However, complex reactions occur when 2 and 4 are treated with CH3SG3F and strong acids, contrary to our original report of CH4 and H2 evolution,. Formyl 2 is stabilized by added (C2H5)3B and decomposes disproportionately to Mn2(CO)10 (0.5 equiv), Li+[Mn(CO)5] (1.0 equiv), and H2 (0.5 equiv). An initial Mn-Mn bond cleavage step is proposed. The only characterizable product from the thermolysis of 4 is Re2(CO)10, but photolysis gives Li+[Re2(CO)9(H)]. When K+[Re2(CO)9(CHO)] is treated with 1 equiv of K(sec-C4H9)3BH, reduction to formaldehyde (21%) and K2[Re2(CO)9] (92%) occurs. 1983, American Chemical Society. All rights reserved.
