Reactions of Mn(I) Centers with Ligands Derived from 2-(Methylthio)aniline

Although thioethers are considered soft donors, examples of coordination to Mn(I) centers have been documented (J. Chem. Soc. Dalton Trans., 1998, 2225-2231). Improved sulfur chelation is possible by strategic positioning of thioether moieties in acyclic multidentate or macrocyclic ligand frames. To explore the potential S-coordination between low valent manganese and N,N,S-ligand donor sets, the Schiff base ligands: 2-pyridyl-N-(2’ methylthiophenyl)methyleneimine (pmtpm) and 2-quinoline-N-(2’-methylthiophenyl)methyleneimine (qmtpm) have been prepared. Reactions of pmtpm and qmtpm with Mn(CO)₅Br afforded the neutral species [Mn(pmtpm)(CO)₃Br] (1) and [Mn(qmtpm)(CO)₃Br] (2), respectively. X-ray crystallographic analyses reveal the absence of S-coordination in 1 and 2. The use of a different starting salt, [Mn(CO)₃(MeCN)₃]ClO₄ containing labile MeCN groups yielded products lacking metal-thioether bonds when reacted with either pmtpm or qmtpm. Spectroscopic and structural characterization of the resulting carbonyls will be discussed. Strategies for improved ligand design to achieve thioether chelation are ongoing.