Dithioether complexes of manganese carbonyl halides: synthesis, 55Mn NMR spectroscopic, X-ray crystallographic and electrochemical studies

Abstract

Reaction of [Mn(CO)5X] (X = Cl, Br or I) with RS(CH2)nSR (R = Me or Ph, n = 2; R = Me, n = 3) or C6H4(SMe)2-o yielded the neutral manganese(I) complexes [MnX(CO)3{RS(CH2)nSR}] or [MnX(CO)3{C6H4(SMe)2-o}] as yellow or orange solids. These compounds have been characterised using IR, 1H and 13C-{1H} NMR spectroscopy, FAB mass spectrometry and microanalyses. X-Ray crystallographic analyses on two examples confirmed a fac-tricarbonyl arrangement, with the dithioether ligand chelating. The complex [MnCl(CO)3(MeSCH2CH2SMe)] adopts the DL arrangement, while [MnBr(CO)3(PhSCH2CH2SPh)] is in the meso-2 form in the solid state. Manganese-55 NMR spectroscopic studies show that δ(55Mn) lies in the range +67 to –567 for these compounds, and shifts to low frequency according to the series X = Cl → Br → I. For the compounds involving PhSCH2CH2SPh or MeSCH2CH2CH2SMe pyramidal inversion is rapid on the NMR timescale at 300 K, giving a single broad 55Mn NMR peak. The 55Mn NMR spectra of the compounds involving MeSCH2CH2SMe and C6H4(SMe)2-o show three distinct resonances indicative of the three NMR distinguishable invertomers, meso-1, meso-2 and DL, the population of the meso-1 form decreasing with increasing halogen size. Reaction of [MnBr(CO)5] with 1 molar equivalent of MeSCH2SMe yielded the heterobridged dinuclear complex [Mn2(CO)6(µ-Br)2(µ-MeSCH2SMe)]. The crystal structure revealed a pseudo-A-frame complex in which the two manganese(I) octahedra edge-share via two bromides with the dithioether bridging the Mn2Br2 core, giving Mn· · ·Mn 3.71 Å.