High-Spin Manganese(II) Complexes of an Amido/Bis(Phosphine) PNP Ligand

Syntheses of several Mn complexes supported by a monoanionic amido/bis(phosphino) PNP ligand (PNP = [2-P(CHMe2)2-4-MeC6H3]2N) from anhydrous MnCl2 are reported. Treatment of (PNP)Li (2) with MnCl2 in tetrahydrofuran (THF) led to isolation of either (PNP)Mn(μ-Cl)2Li(THF)2 (5) or (PNP)MnCl (6), depending on the workup. Reaction of 6 with 2 equiv of MeLi resulted in isolation of (PNP)Mn(μ-Me)2Li(THF)2 (7) that is structurally similar to 5. Reduction of 6 in the presence of pyridine produced material analytically consistent with (PNP)Mn(py)3 (8), whereas reduction in the presence of 2,2′-bipyridine gave fully characterized (PNP)Mn(bipy) (9). Compounds 5 and 7 display magnetic moments indicative of high-spin Mn(II) (S = 5/2). The magnetic moment of 9 (S = 2) was interpreted as an antiferromagnetic combination of a high-spin Mn(II) center and a singly reduced bipyridine ligand. Addition of a single CO ligand to 9 generated diamagnetic, low-spin (PNP)Mn(bipy)(CO) (10). Solid-state structures of 5, 7, 9, and 10 were determined by X-ray diffraction methods and used in conjunction with density functional theory studies to analyze the electronic nature of the (PNP)Mn complexes under study.