Synthesis, characterization, and bromine substitution by 4,4'-di(5-nonyl)-2,2'-bipyridine in Cu(II)(4,4'-di(5-nonyl)-2,2'-bipyridine)Br(2).

The crystal structure of a novel compound Cu(II)(dNbpy)Br(2) (dNbpy = 4,4'-di(5-nonyl)-2,2'-bipyridine), which is used in the reverse atom transfer radical polymerization, is reported. Cu(II)(dNbpy)Br(2) crystallizes in the triclinic P1 space group with a = 12.5283(11) A, b = 15.0256(14) A, c = 17.7900(16) A, alpha = 90.350(2) degrees, beta = 99.360(2) degrees, gamma = 107.937(2) degrees, and Z = 2. The Cu(II) center in the complex has a distorted square planar geometry and is coordinated by two nitrogen atoms of a single dNbpy ligand (Cu-N = 2.011(7) and 2.022(7) A) and two bromine atoms (Cu-Br = 2.3621(14) and 2.3567(13) A). The similarity of the absorption spectra in the solid state and in solution suggested that the geometry of the complex remained unchanged upon dissolution. In the presence of dNbpy, Cu(II)(dNbpy)Br(2) undergoes Br substitution to form ionic Cu(II)(dNbpy)(2)BrBr. DeltaH degrees and DeltaS degrees values for this equilibrium were negative and dependent on the polarity of the medium. It was found that, under the typical polymerization conditions (T > or =90 degrees C and the total copper concentration in the range 1.0 x 10(-2)-1.0 x 10(-1) M), Cu(II)Br(2) and 2 equiv of dNbpy will predominantly form the neutral Cu(II)(dNbpy)Br(2) complex. In a polar medium under the same conditions, Cu(II)(dNbpy)(2)BrBr is preferred.