Tricarbonylchromium complexes of - and metacyclophane were prepared and the interaction between the Cr(CO)3tripod and the cyclophane fragment was evaluated by both an experimental and a theoretical study. The tricarbonylchromium complex of metacyclophane could only be obtained in solution and was characterized by its1H NMR spectrum. The tricarbonylchromium complex of metacyclophane was isolated and an X-ray crystal structure was obtained, which reveals that no significant geometric changes occur upon coordination of the severely distorted aromatic ring. Computations on the tricarbonylchromium complexes of m-xylene, - and metacyclophane furthermore demonstrate that the corresponding complexation energy is remarkably unaffected by the degree of distortion of the aromatic ring. Theoretical analyses of the above model systems as well as complexes of planar and artificially deformed benzene with Cr(CO)3show that this is primarily the result of two counteracting effects: (i) a stabilization due to an increased back-donation from the metal center to the benzene and (ii) a destabilization due to the increasing strain in the aromatic ring. © 2008 Elsevier Ltd. All rights reserved.
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