Facile oxidation-based synthesis of sterically encumbered four-coordinate bis(2,9-di-tert-butyl-1,10-phenanthroline)copper(I) and related three-coordinate copper(I) complexes

A new oxidation-based synthetic route was developed for synthesis of Cu(I) complexes with weakly coordinating ligands, leading to the synthesis of the elusive [Cu(dtbp)(2)](+) (dtbp, 2,9-di-tert-butyl-1,10-phenanthroline) complex that may be useful as a sensor or as a dye for dye- sensitized solar cells. An acetone solution of either 1 or 2 equiv of dtbp was added to excess Cu(0) and 1 equiv of AgY ( Y is O3SCF3-, BF4-, SbF6-, or B(C6F5)(4)(-)) in a nitrogen-filled glove box. Following filtration and evaporation under vacuum, crystallization from CH2Cl2 and hexanes results in X-ray quality crystals of Cu(dtbp)(O3SCF3) (1), Cu(dtbp)(BF4) (2), [Cu(dtbp)(acetone)][SbF6] (3), [Cu(dtbp)(2)][ B(C6F5)(4)]center dot CH2Cl2 (4 center dot CH2Cl2), [Cu(dtbp)(2)][BF4]center dot CH2Cl2 (5 center dot CH2Cl2), and [Cu(dtbp)(2)][SbF6]center dot CH2Cl2 (6 center dot CH2Cl2). Complexes 1-6 were characterized by X-ray crystallography and NMR. The Cu atom in complexes 1-3 exhibited distorted trigonal coordination geometries, reflecting the steric effect of the bulky tert-butyl substituents. The structures of the pseudotetrahedral complexes 4, 4 center dot CH2Cl2, 5 center dot CH2Cl2, and 6 center dot CH2Cl2 revealed the longest average Cu-N distances (2.11 angstrom, 2.11 angstrom, 2.10 angstrom, and 2.11 angstrom, respectively) in this class of compounds-longer by more than three standard deviations from the average.