Reactivity of oxo-rhenium precursor trans-ReOCl3(OPPh3)(SMe2) with diaza heterocyclic congeners: Synthesis and spectroscopic characterization of mono and dinuclear compounds

The treatment of ReOCl₃(OPPh₃)(SMe₂) with an appropriate amount of 1,3]- and 1,4]-diaza heterocyclic ligands N  N (were N  N = pyrimidine (pym) and pyrazine (pyz)) in boiling acetonitrile under different reaction conditions yielded either the mononuclear ReOCl₃(OPPh₃)(pym) (1), ReOCl₃(OPPh₃)(pyz) (2) or dinuclear compounds ReOCl₃(OPPh₃)]₂(μ-pym) (3), ReOCl₃(OPPh₃)]₂(μ-pyz) (4). The new complexes were characterized in solution by means of NMR, IR, FIR, and UV–Vis spectroscopic methods. The molecular and crystal structures of 1, 3 and 4 were also determined by X-ray crystallography. All complexes adopt distorted octahedral geometries, with similar donor atoms arrangement, were axial positions are taken by terminal oxygen and triphenylphosphine oxide molecules. The equatorial planes are occupied by three chloride ligands and one nitrogen atom of the diaza ligand. The dinuclear complexes 3 and 4 comprise two equivalent six-coordinated monomeric units. Two halves of the dimer molecule are rotated about the Re–N  N–Re fragment: thus, an N-heterocyclic ring is stacked with two adjacent phenyl rings belonging to two triphenylphosphine oxide ligands. The preliminary results concerning the reactivity of the dimeric complexes point to their relative inertness in attempted further substitution towards synthesis of polynuclear complexes.