Antonio Belforte

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]

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), A, 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)A, 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.

Formation of alkylurethanes from carbon dioxide by regioselective O-alkylation of alkali-metal N,N-diethylcarbamates in the presence of complexing agents

Alkali-metal N,N-diethylcarbamates [M(O2CNEt2); M = Li, Na, or K] undergo N-alkylation with MeI, giving tertiary amine and carbon dioxide, in addition to MI; however, O-alkylation with formation of alkylurethane occurs preferentially in the presence of a polyfunctional complexing agent.

Synthesis and X-ray crystal structure of the first manganese(II) dialkylamido complex: {Mn3(µ-NEt2)6(µ-Cl)2[Li(THF)2]2}·(C7H16)(THF = tetrahydrofuran)

Reaction of MnCl2 with LiNEt2 in tetrahydrofuran(THF)/n-heptane afforded the pentanuclear title complex {Mn3(µ-NEt2)6(µ-Cl)2[Li(THF)]2}, whose molecular structure shows the presence of three tetrahedrally co-ordinated manganese atoms, joined by four bridging NEt2 groups [with Mn–N bond distances ranging from 2.089(4) to 2.203(4)A, the Mn ⋯ Mn distance being 2.917(1)A], and two Li(THF)2 moieties terminally bonded via diethylamido and chloride bridges.

Synthesis and reactivity of N,N-dialkylcarbamato complexes of manganese(II). Crystal and molecular structure of [Mn6(O2CNEt2)12], a hexamer with four five-co-ordinated manganese(II) atoms

The compounds [{Mn(O2CNR2)2}n](R = Me, Et, or Pri) have been prepared by treating [Mn(cp)2](cp =η5-C5H5) with CO2–NHR2 in organic solvents. These reactions may possibly involve the addition compound [Mn(cp)2]·NHR2. In the case of R = Et, the adduct has been isolated and characterized, and the space group, crystal data, and metal connectivity established. The structure of the N,N-diethylcarbamato complex has been solved by X-ray diffraction. Crystal data: monoclinic, space group C2/c, a= 18.546(3), b= 19.287(3), c= 24.877(3)A, β= 95.38(2)°, R= 0.078. It consists of hexameric units [Mn6(O2CNEt2)12], containing four five-co-ordinated Mn atoms, joined by bridging carbamato ligands. It was found to be unreactive towards nucleophiles, while by reaction with [{Ti(cp)2Cl}2] the new complex [Ti(cp)2(O2CNEt2)] has been obtained. Organic electrophiles react regioselectively at the oxygen or at the nitrogen atom of the carbamato ligand of the manganese complexes, and in the former case the CO2 fragment is retained in the reaction products.