Synthesis and spectroscopic studies of organometallic Mn(I) complexes containing the novel mixed donor ligands 2-{MeSeCH(2−n)(SiMe3)n}C5H4N (n=0–2)

Treatment of MnBr(CO)5 with one equivalent of the bidentate ligand, 2-{RECH(2−n)(SiMe3)n}C5H4N (E=S, R=Me, Ph, n=0; E=Se, R=Me, n=0, 1, 2) affords the complexes [MnBr(CO)3L] as orange powders. The effect of stepwise substitution at the α-carbon of the ligand by a trimethylsilyl group was investigated using 77Se{1H}- and 55Mn-NMR, and IR spectroscopies. In the case of the pyridyl-selenoether-containing complexes, each additional Me3Si− group increases the σ-donating properties of the ligand, in turn reflected in increased Mn→CO backbonding. The solid-state structure of the parent [MnBr(CO)3{2-(PhSCH2)C5H4N}] showed the molecule to have distorted fac-octahedral geometry. All other compounds were assigned the same stereochemistry based on CO stretching frequency comparisons.