Binding of isocyanides to five-coordinate, durene-capped hemes

Abstract

Solution data at 20 °C are presented for the binding of t-butylisocyanide and tosylmethylisocyanide (TMIC) to the five-coordinate hemes Fe(porp)(Cy2Im), where Cy2Im = 1,5-dicyclohexylimidazole and porp = the dianion of some durene-capped porphyrins with variable length linking methylene straps on either side of the durene moiety (4/4, 5/5, or 7/7 methylenes). The tBuNC and TMIC ligands are used to probe the steric nature of the distal binding site under the cap, in particular the respective "central" and "peripheral" effects as defined by Traylor etal. The binding constants range from 1.1 × 109 M−1 for the 7/7—TMIC system to immeasurably small for the 4/4—tBuNC system, this range spanning data reported in the literature for related anthracene- and adamantane-capped systems.