Synthesis and study of the fluxional behavior of octahedral manganese(I) complexes with a monodentate 1,8-naphthyridine ligand. X-ray crystal structure of fac-[Mn(η¹-1,8-naph)(η²-phen)(CO)₃]ClO₄·½CH₂Cl₂ (naph = 1,8-naphthyridine, phen = o-phenanthroline)

The addition of 1,8-naphthyridine (naph) to a solution of [Mn(OClO₃)(chel)(CO)₃] (chel = o-phenanthroline (phen), 2,2′-bipyridyl (bpy)) affords the octahedral complexes [Mn(η-naph)(η-chel)(CO)₃]ClO₄. The crystal structure of [Mn(η¹-naph)(η²-phen)-(CO)₃]ClO₄·½CH₂Cl₂ (monoclinic, space group P2₁/a, a = 19.019 (4) Å, b = 16.120 (3) Å, c = 8.368 (2) Å, β = 90.68 (2)°, Z = 4) shows that in the complex ion the manganese atom displays a slightly distorted octahedral coordination, being linked to three carbonyl ligands in a fac position, to two nitrogen atoms of a bidentate o-phenanthroline ligand (η-phen), and to another nitrogen atom of a monodentate 1,8-naphthyridine ligand (η-naph). A detailed variable-temperature ^lH NMR study shows that this structure persists in solution at low temperature for both complexes. At higher temperature these complexes are fluxional species in which there is a rapid exchange of the site of manganese coordination between the two nitrogen atoms of the monodentate 1,8-naphthyridine. For this process an approximate activation energy of 63 kJ/mol has been obtained for both complexes. The mechanism for the 1,3-shift is, apparently, intramolecular and is such that the manganese-naphthyridine interaction is probably never lost during the process.