| This work investigated the Lewis acid assisted acylations of anionic transition metal complexes by N-acylimidazoles. The most important of these were N-formylimidazole, 1. Transition metal formyl complexes have been proposed as reactive intermediates in Fischer-Tropsch type reactions. In addition to 1; N-acetyl-, 11, N-pivaloyl-, 13, and N-benzoylimidazole, 15, were examined. The transition metal complexes studied were; (eta)('5)-C(,5)H(,5)W(CO)(,3)('-), (eta)('5)-C(,5)H(,5)W(CO)(,2)PPh(,3)('-), and Na(,2)M(CO)(,4) (M = Fe,Ru,Os).; Initial studies were conducted on Na(,2)Fe(CO)(,4), 3, since most of the resultant acyl complexes had previously been synthesized and characterized. The formylation of 3 by 1 was found to be dependent upon the type of solvent, the type of Lewis acid, and the concentration of Lewis acid. Optimal yields were obtained in hexamethylphosphoramide, using two equivalents of (MeO)(,3)B per equivalent of 1. These reaction conditions enabled the synthesis of the unreported anionic formyl complexes, NaRu(CO)(,4)CHO and NaOs(CO)(,4)CHO, from Na(,2)Ru(CO)(,4) and Na(,2)Os(CO)(,4), respectively. Attempts at formylating 3 with dimethylformamide and ethyl formate were unsuccessful. Reaction products were characterized by ('1)H NMR, ('13)C NMR, and/or infrared spectroscopy.; Acylations of 3 by 1 and 11 occurred only in the presence of a Lewis acid. When a Lewis acid was not present, 1 decarbonylated and 11 underwent a Claisen-type condensation. In the case of substrates 13 and 15, where there were no (alpha)-hydrogens, the acylation reactions proceeded both in the presence and absence of a Lewis acid. Kinetic measurements indicated that the reaction of 3 with 13, in the absence of a Lewis acid, was second order. This reaction was dramatically accelerated by a Lewis acid.; Other bases caused decarbonylation and condensation reactions of 1 and 11. Most significant of these were sodium imidazolate, 6, a by-product in the acylation reactions. Spectral data indicated that 6 was the only imidazole species strongly interactive with (MeO)(,3)B.; The results were interpreted in terms of the Lewis acid complexing with and preventing the by-product 6 from interfering in the formylation reaction. The Lewis acid was also theorized as aiding the leaving ability of the imidazolate anion in the acylation reactions. |
