Synthesis of hexanuclear molybdenum clusters containing phosphine oxideligands

Abstract

We report the direct preparation of two new octahedral hexanuclear molybdenum cluster complexes containing phosphine oxide ligands, namely, [Mo₆(μ₃-Cl)₈{OP(n-Pr)₃}₂Cl₄] and [Mo₆(μ₃-Cl)₈(OPEt₃)₂Cl₄], from Mo₆Cl₁₂ and the corresponding phosphine oxide ligands. Both of these complexes were characterized by NMR and IR spectroscopies, cyclic voltammetry and elemental analysis. Further, a single-crystal X-ray structure determination of [Mo₆(μ₃-Cl)₈{OP(n-Pr)₃}₂Cl₄] was obtained: [Mo₆(μ₃-Cl)₈{OP(n-Pr)₃}₂Cl₄] crystallizes in the monoclinic space group, P2₁/n with a = 10.0685(16) Å, b = 15.617(2) Å, c = 15.693(3) Å, β = 91.799(5)°, and R1 = 0.0288. A trans arrangement of the phosphine oxide ligands was observed, where both ligands are bonded to the molybdenum cluster through the oxygen atoms. We also investigated the reaction of [Mo₆(μ₃-Cl)₈{P(n-Pr)₃}₂Cl₄] with a variety of oxidizing agents and found that the coordinated tri(n-propyl)phosphine ligands are cleanly oxidized by H₂O₂ to the corresponding phosphine oxides, yielding [Mo₆(μ₃-Cl)₈{OP(n-Pr)₃}₂Cl₄].