Preparation and single-crystal characterization of manganese(II) complexes of dichalcogenoimidodiphosphinato ligands. Monomeric versus dimeric Mn[(OPPh2)(XPPh2)N]2 (X=S, O)

Manganese(II) compounds of the type Mn[(XPR2)(YPR′2)N]2 (X, Y=O, S; R, R′=Me, Ph), were prepared by metathesis reactions between MnCl2·4H2O and the alkaline salt of the corresponding ligand. IR data are consistent with the coordination of the phosphorus ligand in a deprotonated form. The ESR spectra exhibit resolved hyperfine structure only for the Mn[(OPMe2)(SPPh2)N]2 derivative. The crystal and molecular structures of Mn[(OPPh2)(YPPh2)N]2 (Y=O, S) were determined by X-ray diffractometry. The crystal of the tetraphenylthioimidodiphosphinato derivative contains monomeric, spiro-bicyclic Mn[(OPPh2)(SPPh2)N]2 units, with a distorted tetrahedral MnO2S2 core, as a result of monometallic biconnective phosphorus ligands. By contrast, in the crystal of the tetraphenylimidodiphosphinato analogue distinct [Mn{(OPPh2)2N}2]2 dimers are present, in which the MnO5 core has a trigonal bipyramidal geometry. The coordination pattern of the four imidodiphosphinato ligands differs. Two of them act as monometallic biconnective (chelating) units, leading to six-membered MnO2P2N rings. The other two ligands act as bimetallic triconnective units, which results in a fused tricyclic Mn2O4P4N2 system. The central four-membered Mn2O2 ring is slightly bent [Mn(1)O(5)O(8)/Mn(2)O(5)O(8) dihedral angle 23.9°]. The overall conformation of the [Mn{(OPPh2)2N}2]2 dimer might be described as cis, i.e. with six-membered MnO2P2N rings formed by ligands of the same type placed on the same side of the four-membered Mn2O2 ring.