Synthesis and reactivity of manganese(II) dialkylamido complexes. Crystal and molecular structure of [Mn3(µ-NEt2)6-(µ-Cl)2{Li(thf)2}2]·C7H16(thf = tetrahydrofuran) and [Mn2(µ-NPri2)2(NPri2)2

Abstract

By reaction of MnCl2 with LiNR2(R = Me, Et or Pri) the corresponding dialkylamido complexes were prepared. The compounds [Mn3(µ-NEt2)6(µ-Cl)2{Li(thf)2}2]1(thf = tetrahydrofuran), [Mn2(µ-NPri2)2-(NPri2)2]2 and [Mn2(NMe2)4(LiCl)]3 were isolated, and the molecular and crystal structures of 1 and 2 determined by single-crystal X-ray diffraction methods. Crystal data: 1, monoclinic, space group C2/c, a= 18.81(1), b= 20.45(2), c= 18.15(2), Å, β= 113.31(8)°, R= 0.063; 2, monoclinic, space group P2/1c, a= 9.361(2), b= 9.724(2), c= 16.883(2)Å, β= 100.91(1)°, R= 0.046. The pentanuclear compound 1 consists of a trinuclear Mn3(NEt2)6Cl2 core, built up by edge-sharing of the three co-ordination tetrahedra, which are connected by four bridging diethylamido ligands, and terminally bonded to the Li(thf)2 moieties via chloride and amido bridges. The homoleptic compound 2 contains two three-co-ordinated manganese atoms, joined by two bridging dialkylamido groups, with an overall planar arrangement of the Mn2N4 skeleton. Both 1 and 2 react with CO2 to give the expected dialkylcarbamato complexes. The reactions of 1–3 with CO result in reductive carbonylation to [Mn(CO)5]–. The compounds also catalyse the selective carbonylation of secondary amines to dialkylformamides, a 87% yield of Et2NC(O)H being obtained from NHEt2 and CO at atmospheric pressure, in 24 h, in the presence of 1, at room temperature.