Mixed-ligand rhenium(V) oxo monomers with triphenylphosphine oxide and lopsided and symmetrical heterocyclic ligands. Putative intermediates in rhenium(V) oxo synthetic chemistry

Abstract

Normally, ReOCl3 (Me2S) (OPPh3) (1) serves as a useful source of ReO3+ or ReOClx(3−x)+ for the synthesis of Re complexes by ligand exchange. Complexes of the type ReOCl3(OPPh3)(L) (L = 1,5,6-trimethylbenzimidazole (Me3Bzm) (2); 3,5-lutidine (3,5-lut) (3); pyridine (py) (4)) were prepared from 1 and one equivalent of L. Formation of these mixed-ligand complexes is unsual because the normally labile OPPh3 in 1 was retained. Addition of non-coordinating triethylamine (NEt3) gave [HNEt3][ReOCl4(OPPh3] (5). The anion in 5 has been populated to be an intermediate in some synthetic schemes. ReOCl3(OPPh3)(Me3Bzm) (2) was characterized by X-ray crystallography. Crystallographic data are: C28H27Cl3N2O2PRe, P21/c, a = 18.503(3), b = 9.780(2), c = 15.735(4) A, β = 97.56(2)°, Dcalc = 1.76 g cm−3, Z = 4, R = 0.041, Rw = 0.066 for 3193 independent reflections. In 2, the pseudo-octahedral Re has the OPPh3 ligand trans to the oxo ligand, and one of the OPPh3 phenyl rings lies nearly over the five-membered ring of Me3Bzm. Reaction of ReOCl3(OPPh3)(Me3Bzm) (2) with one equivalent of 3,5-lut or py resulted in the precipitation of mixed-ligand species best formulated as Re2O3Cl4(Me3Bzm)2(3,5-lut)2 (6) and Re2O3Cl4(Me3Bzm)2(py)2 (7), respectively.