Reactions of M{N(SiMe 3) 2} 2 (M=Mn, Fe or Co) with pyridine and 4,4′-bipyridyl: structural and magnetic studies

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The reactions of the aromatic nitrogen donor ligands pyridine (py) and 4,4′-bipyridyl (4,4′-bipy) with the transition metal silylamides M{N(SiMe 3) 2} 2 (M=Mn, Fe or Co) were investigated. Treatment of the metal amides with pyridine afforded the bispyridine complexes M{N(SiMe 3) 2}(py) 2 (M=Mn, 1a; Fe, 2a; Co, 3a). Distillation or sublimation of 2a or 3a afforded the monopyridine complexes M{N(SiMe 3) 2} 2(py) (M=Fe, 2b; Co, 3b). The addition of pyrazine (prz) to Mn{N(SiMe 3) 2} 2 also yielded the bispyrazine adduct Mn{N(SiMe 3) 2} 2(prz) 2, 1b. However, the reaction of 4,4′-bipyridyl with Fe{N(SiMe 3) 2} 2 or Co{N(SiMe 3) 2} 2 afforded the polymeric chain-like complexes {M{N(SiMe 3) 2} 2(4,4′-bipy)} ∞ (M=Fe, 4; Co, 5). With the exception of 2b, all complexes were characterized by X-ray crystallography. The complexes 1a, 1b, 2a and 3a displayed monomeric structures and metal geometries that are based on a tetrahedron with interligand angles that deviate markedly from idealized values. Complex 3b was found to have a distorted trigonal planar geometry. In contrast, complexes 4 and 5 displayed polymeric zig-zag chain structures which have four coordinate metal centers connected by 4,4′-bipyridyl ligands. Magnetic studies indicated that complexes 1– 3b have high-spin electron configurations and that the paramagnetic centers in 4 and 5 did not interact with each other through the 4,4′-bipyridyl ligands.