A one-pot reduction route to bimetallic manganese 1,8-naphthyridine complexes.

Reaction of the dinucleating ligand 2,7-bis(6-methyl-2-pyridyl)-1,8-naphthyridine ( Me L) with the Mn I and Mn II precursors MnBr(CO) 5 and MnCl 2 resulted in the formation of the monometallic complexes [MnBr(CO) 3 ( Me L)] (1) and [MnCl 2 ( Me L)] (3). In both cases, formation of bimetallic manganese complexes could be achieved by reduction with KC 8 , yielding the carbonyl-bridged complex [Mn 2 (CO) 6 ( Me L)] (2) and the helicate complex [Mn 2 ( Me L) 2 ] (4), respectively. EPR results demonstrate that 4 represents a novel, weakly antiferromagnetically coupled homovalent dimer ( J = -0.85 cm -1 ). The two formally Mn 0 ions are both high spin ( S = 3/2) and exhibit a zero-field splitting of ≈1 cm -1 , suggesting reduction of the complex is substantially ligand centered, and may be better described as a Mn II complex coupled to two open shell singlet ligands [MnII2( Me L 2- ) 2 ]. X-ray crystallography, UV-Vis spectroscopy and DFT analysis support this finding.