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.