ansa-chromocene complexes. 1. Synthesis and characterization of Cr(II) carbonyl and tert-butyl isocyanide complexes

ansa-Calcocene compounds are effective reagents for the synthesis of ansa-c hromocene complexes from CrCl2 in the presence of a trapping ligand such as carbon monoxide or an isonitrile. A variety of ansa-chromocene carbonyl an d tert-butyl isocyanide complexes have been prepared in this manner in high yields. The X-ray crystal structure of one of these complexes, [trans-1,2- (3,4-(CH3O)(2)C6H3)(2)C2H2{eta(5)-C5H4}(2)]CrCO, is described. Electrochemi cal studies on these complexes show that the isonitrile derivatives are mor e easily oxidized than the carbonyl derivatives. Preliminary examination of the reactivity of these complexes indicates that the nature of the substit ution along the ethanediyl ansa-bridge influences the relative stabilities of the carbonyl complexes to oxidation in air, the ease with which the carb onyl ligands undergo substitution with tert-butyl isocyanide, and the relat ive sensitivities of the tert-butyl isocyanide adducts to photodecompositio n. The ansa-bridge substitution also appears to influence the ability of th e complexes to undergo structural changes, such as ring slippage, as reveal ed in their cyclic voltammograms.