Chemistry of the metal carbonyls. Part LXIX. Synthesis and reactions of complexes of manganese containing the substituted and unsubstituted 2,5-dioxacyclopentylidene ligand

Abstract

Addition of 2-chloroethyl chloroformate to [Mn(CO)₅]^– affords [Mn{C(O)·O·CH₂·CH₂Cl}(CO)₅], which can also be obtained by treating [Mn(CO)₆]⁺ with 2-chloroethanol. Reaction of this acyl complex with AgPF₆ or AgBF₄ results in an intramolecular cyclisation reaction to give the 2,5-dioxacyclopentylidene complex [Mn[graphic omitted]-(CO)₅]⁺. This cationic complex reacts with halide anions (X = Cl, Br, I) in methanol to give the neutral carbene species [MnX[graphic omitted](CO)₄], but in acetone or acetonitrile as solvent, a competitive ring-opening reaction becomes important. Reaction of the cyclic alcohol, trans-2-chlorocyclopentanol, with [Mn(CO)₆]⁺ affords the acyl complex [Mn{C(O)·O[graphic omitted](H)Cl}(CO)5], which cyclises with AgBF₄ to give the carbene complex [Mn[graphic omitted](CO)5]⁺. Treatment of the latter with halide anions affords neutral complexes without any competitive ring-opening. These neutral, halogeno-carbene(carbonyl)manganese complexes react with phosphines, phosphites, and arsines to give stereospecifically the fac-substituted isomers; there is no evidence for displacement of the carbene ligand. An unusual deuterium exchange reaction of the substituted halogeno-complexes is discussed.