The coordination chemistry of selenophosphite ligands. Synthesis and characterization of heterometallic tetranuclear clusters [M{CpFe(CO)2P(Se)(OR)2}3](PF6) (M = Cu, Ag; R = nPr, iPr) and [Cu(μ-X) {CpFe(CO)2P(Se)(OiPr)2}]2 (X = Cl, Br)

Abstract

A neutral selenium donor ligand, [CpFe(CO)₂P(Se)(OR)₂] is used for the construction of Cu^I and Ag^I complexes with a well-defined coordination environment. Four clusters [M{CpFe(CO)₂P(Se)(OR)₂}₃](PF₆), (where M = Cu, R = ⁿPr, 1; R = ⁱPr, 2 and M = Ag, R = ⁿPr, 3; R = ⁱPr, 4) are isolated from the reaction of [M(CH₃CN)₄(PF₆)] (where M = Cu or Ag) and [CpFe(CO)₂P(Se)(OR)₂] in a molar ratio of 1 : 3 in acetonitrile at 0 °C. The reaction of [CpFe(CO)₂P(Se)(OⁱPr)₂] with cuprous halides in acetone produce two mixed-metal, Cu^I₂Fe^II₂clusters, [Cu(μ-X) {CpFe(CO)₂P(Se)(OⁱPr)₂}]₂ (X = Cl, 5; Br, 6). All six clusters have been fully characterized spectroscopically (¹H, ¹³C, ³¹P, and ⁷⁷Se NMR, IR), and by elemental analyses. X-Ray crystal structures of 1 and 3 consist of discrete cationic clusters in which three iron–selenophosphito fragments are linked to the central copper or silver atom viaselenium atoms. Both clusters 1 and 3 crystallize in the noncentrosymmetric, hexagonal space groupP2c. The coordination geometry around the copper or silver atom is perfect trigonal-planar with Cu–Se and Ag–Se distances, 2.3505(7) and 2.5581(7) Å, respectively. X-Ray crystallography also reveals that each copper center in neutral heterometallic clusters 5 and 6 is trigonally coordinated to two halide ions and a selenium atom from the selenophosphito–iron moiety. The structures can also be delineated as a dimeric unit which is generated by an inversion center and has a Cu₂X₂ parallelogram core. The dihedral angle between the Cu₂X₂ plane and the plane composed of Cp ring is found to be 24.62 and 84.58° for compound 5 and 6, respectively. Hence the faces of two opposite Cp rings are oriented almost perpendicular to the Cu₂X₂ plane in 6, but are close to be parallel in 5. This is the first report of the coordination chemistry of the anionic selenophosphito moiety [(RO)₂PSe]⁻, the conjugated base of a secondary phosphine selenide, which acts as a bridging ligand with P-coordination on iron and Se-coordination to copper or silver.