Add time:07/31/2019         Source:sciencedirect.com

Rate constants have been measured for the α-metallation of some arylmethanes, of 5H-dibenzo[a,d]cycloheptene and its dihydro derivative, free and complexed with tricarbonylchromium, by potassium hydride in tetrahydrofuran in the presence of 18-crown-6 ether. The stable solutions of the complexed anions have been studied by 13C NMR spectroscopy. With the free ligands the kinetic acidity depends upon the structure to a great extent, but in the corresponding complexes the rates of metallation do not vary appreciably. On the basis of the 13C chemical shift data a close similarity is suggested between the electronic structures of the arylmethyl and dibenzotropenyl anions which would account for their very similar metallation rates.

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