Manganese(I) selenoether chemistry: synthesis, multinuclear NMR studies and the structures of [MnCl(CO)(3)(MeSeCH2CH2SeMe)], [MnCl(CO)(3)(MeSeCH2CH2CH2SeMe)] and [MnBr(CO)(3){C6H4(SeMe)(2)-o}]

Reaction of [Mn(CO)(5)X] (X = Cl, Br or I) with RSe(CH2)(n)SeR (R = Me or P h, n = 2; R = Me, n = 3) or C6H4(SeMe)(2)-o in refluxing CHCl3 yielded the neutral manganese(II) complexes [MnX(CO)(3) (RSe(CH2)(n)SeR}] or [MnX(CO)(3 )C6H4(SeMe)(2)-o}] as yellow or orange solids. Infrared spectroscopic studi es confirmed the fac-tricarbonyl arrangement. Proton,C-13-{H-1}, Se-77-{H-1 } and Mn-55 NMR spectroscopy has been used to probe the solution behaviour, and show that only those compounds involving PhSeCH2CH2SePh are undergoing rapid pyramidal inversion on the NMR timescale, with the individual NMR di stinguishable invertomers observed for the other complexes (meso-1, meso-2 and DL) in varying ratios. X-Ray crystallographic analyses on three example s confirmed a fac-tricarbonyl arrangement, with the diselenoether ligand ch elating: [MnCl(CO)(3)(MeSeCH2CH2SeMe)] and [MnCl(CO)(3)(MeSeCH2CH2CH2SeMe)] adopt the DL arrangement, while [MnBr(CO)(3){C6H4(SeMe)(2)-o}] is in the m eso-2 form in the solid state. These are the first structure determinations on selenoether complexes of manganese(I) carbonyl halides. Most importantl y Mn-55 NMR spectroscopic studies show that delta(Mn-55) is to low frequenc y of those of the corresponding thioether compounds, lying in the range del ta - 175 to -702, the lowest frequencies occurring for the iodo derivatives . The CO stretching frequencies and 55Mn NMR shifts show that, for a given X, the manganese(I) centre in [MnX(CO)(3)(diselenoether)] is more shielded than in [MnX(CO)(3)(dithioether)], possibly indicating increased a donation in the former.