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Syntheses, Reactivity, and π-Donating Ligand Metathesis Reaction of Five-Coordinate Sixteen-Electron Manganese(I) Complexes:  Crystal Structures of [Mn(CO)3(−TeC6H4-o-NH−)]-, [(Mn(CO)3)2(μ-SC6H4-o-S−S−C6H4-o-μ-S−)], [(CO)3Mn(μ-SC6H4-o-NH2−)]2, and [(CO)3Mn(μ-SC8N2H4-o-S−)]22-

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posted on 06.06.2001, 00:00 by Wen-Feng Liaw, Chien-Kuo Hsieh, Ging-Yi Lin, Gene-Hsiang Lee
The preparation of the varieties of five-coordinate sixteen-electron manganese(I) complexes [Mn(CO)3(−EC6H4-o-E‘−)]- (E = Te, Se, S, O; E‘ = NH, S, O) by (a) oxidative addition of 2-aminophenyl dichalcogenides to anionic manganese(0)-carbonyl, (b) π-donating ligand metathesis reaction of complex [Mn(CO)3(−TeC6H4-o-NH−)]-, and (c) reduction /deprotonation of the neutral dimetallic [(Mn(CO)3)2(μ-SC6H4-o-S−S−C6H4-o-μ-S−)]/[(CO)3Mn(μ-SC6H4-o-NH2−)]2 proved successful approaches in this direction. The IR νCO data of the coordinatively and electronically unsaturated [Mn(CO)3(−EC6H4-o-E‘−)]- (E = Te, Se, S, O; E‘ = NH, S, O) complexes suggest the relative order of π-donating ability of the series of bidentate ligands being [TeC6H4-o-NH]2- > [SeC6H4-o-NH]2- > [SC6H4-o-NH]2- > [SC6H4-o-S]2- > [SC6H4-o-O]2- > [OC6H4-o-O]2-. Proton NMR spectra of the [Mn(CO)3(−EC6H4-o-NH−)]- (E = Te, Se, S) derivatives show the low-field shift of the amide proton (1H NMR (C4D8O):  δ 9.66 (br) ppm (E = Te), 9.32 (br) ppm (E = Se), 8.98 (br) ppm (E = S)). The formation of the dimetallic [(CO)3Mn(μ-SC8N2H4-o-S−)]22- can be interpreted as coordinative association of two units of unstable mononuclear [(CO)3Mn(−SC8N2H4-o-S−)]- and reflects the π-donating ability of the bidentate ligand is responsible for the formation of pentacoordinate, sixteen-electron manganese(I) carbonyl complexes. The neutral bimetallic manganese(I)-bismercaptophenyl disulfide complex [(Mn(CO)3)2(μ-SC6H4-o-S−S−C6H4-o-μ-S−)] with internal S−S bond length of 2.222(1) Å and the five-coordinate sixteen-electron complex [Mn(CO)3(−SC6H4-o-S−)]- are chemically interconvertible. In a similar fashion, treatment of complex [Mn(CO)3(−SC6H4-o-NH−)]- with HBF4 yielded neutral dinuclear complex [(CO)3Mn(μ-SC6H4-o-NH2−)]2 and showed that the amine deprotonation is reversible. Investigations of π-donating ligand metathesis reactions of complex [Mn(CO)3(−TeC6H4-o-NH−)]- revealed that the stable intermediate, not the π-donating ability of bidentate ligands, is responsible for the final protonation/oxidation product. This argument is demonstrated by reaction of [Mn(CO)3(−TeC6H4-o-NH−)]- with 1,2-benzenedithiol, hydroxythiophenol, and catechol, respectively leading to the formation of [Mn(CO)3(−EC6H4-o-E‘−)]- (E = S, O; E‘ = S, O), although any π-donor containing the amido group is a more effective donor than any other π-donor lacking an amido group. Also, the reactions of [Mn(CO)3(−TeC6H4-o-NH−)]- with electrophiles occurring at the more electron-rich amide site support that the more electron-rich amide donor of the chelating 2-tellurolatophenylamido occupies an equatorial site as indicated by a shorter MnI−N bond length of the distorted trigonal bipyramidal [Mn(CO)3(−TeC6H4-o-NH−)]-.