Facile Oxidation-Based Synthesis of Sterically Encumbered Four-Coordinate Bis(2,9-di-<i>tert</i>-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]•CH2Cl2 (4•CH2Cl2), [Cu(dtbp)2][BF4]•CH2Cl2 (5•CH2Cl2), and [Cu(dtbp)2][SbF6]•CH2Cl2 (6•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•CH2Cl2, 5•CH2Cl2, and 6•CH2Cl2 revealed the longest average Cu−N distances (2.11 Å, 2.11 Å, 2.10 Å, and 2.11 Å, respectively) in this class of compoundslonger by more than three standard deviations from the average.