The Umbrella-Shaped Trimethylenemethane Ligand in Iron Carbonyl Chemistry: Comparison with Butadiene and Cyclobutadiene Analogues

Abstract

Reaction of Fe2(CO)9 with 3-chloro-2-(chloromethyl)propene is known to give the stable iron tricarbonyl complex [η4-(CH2)3C]Fe(CO)3, containing the umbrella-shaped trimethylenemethane ligand. The mononuclear complexes (CH2)3CFe(CO)n (n = 1–4) and the binuclear complexes [(CH2)3C]2Fe2(CO)n (n = 3–5) of this trimethylenemethane ligand have been studied here. The lowest energy [(CH2)3C]2Fe2(CO)5 structure has one bridging CO group and an Fe–Fe single bond but is disfavored with respect to dissociation into the mononuclear fragments [(CH2)3C]2Fe2(CO)3 + [(CH2)3C]2Fe2(CO)2. The lowest energy [(CH2)3C]2Fe2(CO)4 structure has two semibridging CO groups and an Fe═Fe double bond but is disfavored with respect to disproportionation into [(CH2)3C]2Fe2(CO)5 + [(CH2)3C]2Fe2(CO)3. In contrast to [(CH2)3C]2Fe2(CO)5 and [(CH2)3C]2Fe2(CO)4, the tricarbonyl [(CH2)3C]2Fe2(CO)3 appears to be a reasonable synthetic objective. The lowest energy structure has one terminal CO group, one semibridging CO group, one symmetrical bri...