X-RAY STRUCTURAL AND NMR CHARACTERIZATION OF THE COPPER(I) DIMER [CU(DMPE)2]2(BF4)2, WHERE DMPE IS 1,2-BIS(DIMETHYLPHOSPHINO)ETHANE

The reaction of [Cu(CH3CN)4]BF4 with dmpe (where dmpe is 1,2-bis(dimethylphosphino)ethane) in methanol yields the air-stable, white solid [Cu(dmpe)2]2(BF4)2. This dimeric Cu(I) complex has been characterized by single-crystal X-ray crystallography, variable-temperature P-31 and Cu-63 NMR spectroscopy in solution, and solid-state CPMAS P-31 NMR spectroscopy. The complex crystallizes in the triclinic space group P1BAR with unit cell parameters a = 8.8390 (10) angstrom, b = 10.0080 (10) angstrom, c = 12.479 (2) angstrom, alpha = 99.300 (10)-degrees, beta = 95.640 (10)-degrees, gamma = 93.940 (10)-degrees, V = 1080.1 (2) angstrom 3, and Z = 2; R(w) = 4.20% for 5126 observed reflections [F > 6.0-sigma(F)]. The structure consists of a centrosymmetric [Cu(dmpe)2]2(2+) dimer and two disordered BF4- anions. The two copper atoms in the cation are bridged by two dmpe ligands to form a ten-membered Cu2P4C4 ring. Tetrahedral coordination around each copper atom is completed by a bidentate dmpe ligand. Cu-P bond lengths range from 2.263 (1) to 2.293 (1) angstrom. The P-Cu-P bond angle for the chelating dmpe ligand is 89.2 (1)-degrees, while the P-Cu-P angles linking different dmpe ligands range from 110.3 (1) to 116.9 (1)-degrees. The solution P-31 NMR spectrum at ambient temperature shows a well-resolved quartet centered at -14.6 ppm (relative to 85% H3PO4), while the Cu-63 NMR spectrum at room temperature consists of a quintet centered at 186.7 ppm (relative to [Cu(CH3CN)4]BF4 in CH3CN). The line spacings due to Cu-P coupling amount to 800 Hz in both spectra. Lowering the temperature causes line broadening; both the P-31 and the Cu-63 spectra start to collapse at -33-degrees-C due to quadrupolar relaxation of the copper atoms. The CPMAS P-31 solid-state spectrum shows a quartet centered at -22 ppm relative to solid ammonium phosphate; the asymmetry of the line spacings within this quartet is consistent with the distorted tetrahedral coordination observed in the crystal structure.