Intramolecular Conformational Control in Ferrocenes Bearing Podand Dipeptide Chains

Abstract

Ferrocenes bearing podand dipeptide chains were demonstrated to induce intramolecular conformational regulation through hydrogen bondings. The single-crystal X-ray structure determination of the ferrocene bearing the podand dipeptide chains -Gly-l-Pro-OEt confirmed the formation of two intramolecular interchain hydrogen bondings between CO (Gly) and NH (another Gly) of each podand dipeptide chain (N(1)···O(102), 2.910 Å; N(101)···O(2), 2.898 Å; N(201)···O(302), 2.85 Å; N(301)···O(202), 2.87 Å) to give a 10-membered hydrogen-bonded ring. The ferrocene bearing the podand dipeptide chains -l-Pro-Gly-OEt is also considered to form two rigid intramolecular interchain hydrogen bondings between CO (bridging) and NH (another Gly) to give a 14-membered hydrogen-bonded ring. Such an ordered conformation was supported by the induced circular dichroism. On the other hand, the ferrocene bearing one dipeptide chain -Gly-l-Pro-OEt is packed in a helically ordered arrangement with one turn of 15.65 Å pitch height through a network of intermolecular hydrogen bonds, within which the distance between the closest ferrocene units is 7.95 Å (Fe−Fe).