Arene transition metal complexes in reactions with nucleophilic reagents XIX. Transannular substituent effects in arene-chromium and iron complexes

Article abstract of DOI:10.1016/0022-328X(88)80398-X

As a result of coordination of chlorobenzene derivatives with the (η-C6H6)Cr⁺ fragment, the rate of methoxydechlorination was found to increase 14 fold.The effects of the transannular substituent on the rate of methoxydechlorination of (η-C6H5Cl)(η-C6H5X)Cr⁺A^- complexes (1) and on the dissociation constants of (η-C6H5CO2H)(η-C6H5X)Crⁿ acids n = 0 (2), 1+ (3) has been studied.A strong effect of X in the above reaction series has been found, which is defined by the linear correlation equations using the ?_p, ?⁰ and ?_R constants for complexes 1, 2 and 3 respectively.The arene-chromium and -iron complexes show a general tendency to increase the mesomeric contribution to the transannular substituent effect with an increase in the electron deficiency in the framework transmitting this effect.Comparison of the effects of X in complexes 1, 2 and 3 leads to the conclusion that there is an intermediate-like transition state in the methoxyde-chlorination of complexes 1, apparently proceeding with intermediate formation of metallorganic analogues of Meisenheimer complexes.