Cu(I) and Ag(I) complexes of two sterically demanding Xylyl-Substituted phosphine Ligands: Synthesis, Characterization, and structural examination

Abstract

Two sterically demanding tertiary phosphines, PiPr2Xyl and PtBu2Xyl, (Xyl = 2,6-dimethylphenyl), the latter reported here for the first time, have been used to synthesize a series of dinuclear complexes of the general formula [M(μ-X)PR2Xyl]2, (R = iPr, tBu; M = Cu: X = Cl, Br, I, OTf; M = Ag: X = OTf, NTf2). All compounds have been characterized by multinuclear NMR spectroscopy in solution and, with the exception of AgNTf2(PtBu2Xyl), by X-ray diffraction analyses. The doubly halido-bridged compounds [Cu(μ-X)PR2Xyl]2 (R = iPr, tBu; X = Cl, Br, I) display Ci, C2-like, or C1 molecular symmetry, depending on the anion and the R group, and enclose planar or disphenoidal [CuX]2 cores with short, bonding Cu—Cu distances in case of X = I. On the other hand, centrosymmetric 8-membered rings with twist-chair conformations are found in the solid state structures of [M(μ-OTf)PR2Xyl]2 (R = iPr, tBu; M = Cu, Ag) and [Ag(μ-NTf2)PiPr2Xyl]2, with the anions in a κ2-μ2 coordination mode. Additionally, the cationic complex [Cu(PR2Xyl)2]+ has been obtained as a triflate or BArF salt (BArF- = B{3,5-(CF3)2C6H3}4-), and shows C2-like symmetry in the solid state, with PCuP angles of ca. 168-169° and synclinal dispositions of the Xyl groups with respect to the P∙∙∙P axis. Comparative discussion of relevant NMR data of Cu(I), Ag(I), and Au(I) adducts of the title phosphines is also provided.