Substitution and Cleavage in the Reactions of Some Benzyl(carbonyl)metal Complexes with Trifluoracetic Acid

Article abstract of DOI:10.1021/ja00527a031

Several benzyl(carbonyl)metal complexes, including benzyldicarbonylcyclopentadienyliron(II) (1), undergo substantial deuteration in the ortho and para positions prior to acydolysis of the carbon-metal bond in <2H1>trifluoracetic acid.Comparison of the rates of substitution with that for substitution in anisole shows that the metallomethyl substituents, e.g., CH2Fe(CO)2(C5H5), have large negative substituent constants indicative of very strong hyperconjugative electron donation in the transition states for substitution reactions.There is no evidence that electrophilic attack on the aromatic ring causes cleavage of the carbon-metal bond.The kinetics of the anaerobic acidolysis of 1 and of its 4-fluoro derivative in trifluoroacetic acid and in <2H1>trifluoroacetic acid in chlorinated solvents show that the acidolysis is first order with respect to acid and to substrate, is influenced by the nature of the cosolvent, and has a very high kinetic isotope effect, K_H/K_D = 15-25.It is suggested that these results are indicative of an attack on the metal prior to cleavage of the carbon-metal bond.