Intramolecular conformational control in ferrocenes bearing podand dipeptide chains

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 Angstrom; N(101). . .O(2), 2.898 Angstrom; N(201). . .O(302), 2.85 Angstrom; N(301)Angstrom . . .O(202), 2.87 Angstrom) 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 Angstrom pitch height through a network of intermolecular hydrogen bonds, within which the distance between the closest ferrocene units is 7.95 Angstrom (Fe-Fe).