Dynamic behaviour of octahedral complexes of manganese(I). X-Ray crystal structure of fac-[Mn(η1-1,8-naphthyridine)-η2-1,8-naphthyridine)(CO)3]ClO4 · CH2Cl2

The addition of 1,8-naphthyridine (naph) to a solution of [Mn(OClO3)(naph)(CO)3] at room temperature affords the octahedral complex [Mn (η1-naph)(η2-naph)(CO)3]ClO4 (1). This complex can also be obtained when naph is added to a solution of [Mn(OClO3) (CO)5]. When naph is reacted with [Mn(OClO3)(CO)5] at − 80°C and with 1 : 1 molar ratio, [Mn(η1-naph)(CO)5]ClO4 (3) is obtained. This complex changes into (1) at temperatures above 0°C. The crystal structure of [Mn(η1-naph)(η2-naph) (CO)3]ClO4 (monoclinic, space group P21/a, a = 16.006(3) A, b = 12.024(2) A, c = 13.004(2) A, β = 109.85 (2)°, Z = 4) shows that the manganese atom displays a slightly distorted octahedral coordination being linked to three facial carbonyl ligands, to two nitrogen atoms of a bidentate 1,8-naphthyridine (η2-naph) and to another nitrogen atom of a monodentate 1,8-naphthyridine (η1-naph). A detailed variable temperature 1H NMR study shows this structure persist in solution at low temperature. At higher temperature the complex is fluxional and there is a rapid exchange of the coordination modes of the two naph ligands: the bidentate becomes monodentate and the monodentate bidentate. The mechanism is intramolecular, the rate-limiting step being the opening of the four-membered ring formed by the metal and the η2-naph.