The chemistry of copper(I) β-diketonate compounds. Part V. Syntheses and characterization of (β-diketonate)CuLn species where L = PBu3, PPh3, and PCy3; n = 1 and 2; crystal and molecular structures of (acac)Cu(PCy3), (tfac)Cu(PCy3), (hfac)Cu(PCy3), and (hfac)Cu(PCy3)2

Abstract

The compounds (β-diketonate)Cu(PR3)n, where β-diketonate = 1,1,1,5,5,5-hexafluoroacetylacetonate, hfac; 1,1,1-trifluoroacetylacetonate, tfac; and acetylacetonate, acac; R = n-butyl (n-Bu), phenyl (Ph), and cyclohexyl (Cy); n = 1 and 2, have been prepared. The monotriorganophosphine adducts were prepared in high yield by the reaction of the sodium salt of the corresponding β-diketonate with [ClCu(PR3)] with elimination of sodium chloride. The bis(triorganophosphine) adducts were prepared by the reaction of (β-diketonate)Cu(PR3) with one equivalent of triorganophosphine. These species were characterized by 1H, 13C, and 31P NMR spectroscopy, FTIR spectroscopy, mass spectroscopy, and by combustion elemental analysis. Four examples were structurally characterized by single crystal X-ray diffraction in the solid state. (acac)CuPCy3 crystallizes in the triclinic crystal system, space group [Formula: see text], where a = 13.502(6) Ǻ, b = 13.691(6) Ǻ, c = 5.781(6) Ǻ, α = 71.05(3)°, β = 67.50(3)°, γ = 64.81(3)°, Z = 4, and R = 5.42%. (tfac)CuPCy3 crystallizes in the monoclinic crystal system, space group P21/n, where a = 9.639(3) Ǻ, b = 22.717(7) Ǻ, c = 12.045(5) Ǻ, β = 111.67(3)°, Z = 4, and R = 7.22%. (hfac)CuPCy3 crystallizes in the monoclinic crystal system, space group P21/c, where a = 9.870(2) Ǻ, b = 17.314(4) Ǻ, c = 15.586(3) Ǻ, β = 99.74(2)°, Z = 4, and R = 5.29%. (hfac)Cu(PCy3)2 crystallizes in the monoclinic crystal system, space group P21/n, where a = 13.645(6) Ǻ, b = 19.252(13) Ǻ, c = 16.875(9) Ǻ, β = 102.02(4)°, Z = 4, and R = 7.20%. The compounds (β-diketonate)Cu(PCy3) are all monomeric in the solid state and possess approximately trigonal-planar copper coordination environments, although (tfac)Cu(PCy3) is significantly distorted from trigonal geometry. The Cu—O bond distances are significantly different in this species. The compound (hfac)Cu(PCy3)2 is monomeric in the solid state and possesses a distorted tetrahedral copper coordination environment. The distortion is believed to be due to the large steric demands of the PCy3 ligands that result in long Cu—P bond distances of 2.251(3) and 2.277(3) Ǻ, a large P—Cu—P angle of 141.3(1)°, long Cu—O distances of 2.213(5) and 2.251(5) Ǻ, and a small O—Cu—O angle of 80.8(2)° compared to the corresponding values for (hfac)Cu(PCy3). No trends in Cu—O bond distances between the compounds can be discerned, within the limits of error on the data, that would clearly enable a comparison of thermodynamic parameters such as bond length – bond strength relationships as a function of the β-diketonate substituents. However, the spectroscopic data revealed a number of trends as a function of the β-diketonate substituents, including an increase of ν(C=O and ν(C=C) in the order acac < tfac < hfac, analogous to the increase in their Lewis acidity. An increase in shielding of the 31P resonance of the triorganophosphine ligands was observed in the order hfac < tfac < acac, consistent with expected inductive effects based on the electronegativity of the β-diketonate substituents.