Further evidence supporting an inner sphere mechanism in the NO reduction of the copper(II) complex Cu(dmp)2(2+) (dmp=2,9-dimethyl-1,10-phenanthroline).

Described are further studies directed towards elucidating the mechanism of the nitric oxide reduction of the copper(II) model system, Cu(dmp)2(2+) (I, dmp=2,9-dimethyl-1,10-phenanthroline). The reaction of I with NO in methanol results in the formation of Cu(dmp)2+ (II) and methyl nitrite (CH3ONO), with a second order rate constant kNO=38.1 M-1 s-1 (298K). The activation parameters for this reaction in buffered aqueous medium were measured to be DeltaH(double dagger)=41.6 kJ/mol and DeltaS(double dagger)=-82.7 kJ/mol deg. The addition of azide ion (N3-) as a competing nucleophile results in a marked acceleration in the rate of the copper(II) reduction. Analysis of the kinetics for the NO reduction of the bulkier Cu(dpp)(2)2+ (IV, dpp=2,9-diphenyl-1,10-phenanthroline) and the stronger oxidant, Cu(NO2-dmp)2(2+) (V, NO2-dmp=5-nitro-2,9-dimethyl-1,10-phenanthroline), gave the second order rate constants kNO=21.2 and 29.3 M-1 s-1, respectively. These results argue against an outer sphere electron transfer pathway and support a mechanism where the first step involves the formation of a copper-nitrosyl (Cu(II)-NO or Cu(I)-NO+) adduct. This would be followed by the nucleophilic attack on the bound NO and the labilization of RONO to form the nitrite products and the cuprous complex.

Effects of Sterics and Electronic Delocalization on the Photophysical, Structural, and Electrochemical Properties of 2,9-Disubstituted 1,10-Phenanthroline Copper(I) Complexes.

The syntheses, crystal structures, electronic absorption spectra, electrochemical properties, and photophysical properties of a series of copper(I) bis(phenanthroline) complexes are reported. The phenanthroline ligands that have been prepared and investigated are the following: dop (2,9-di-(2-methylphenyl)-1,10-phenanthroline), xop (2-(2-methylphenyl)-9-(2,6-dimethylphenyl)-1,10-phenanthroline), dpep (2,9-diphenylethynyl-1,10-phenanthroline), and dmesp (2,9-dimesityl-1,10-phenanthroline). The complex [Cu(dop)(2)](PF(6)).Et(2)O crystallizes in space group P&onemacr;with a = 11.854(3) Å, b = 14.705(3) Å, c = 15.866(4) Å, alpha = 107.81(2) degrees, beta = 106.72(2) degrees, gamma = 97.56(2) degrees, V = 2447.6(10) Å(3), and Z = 2. For 5739 unique data with F > 4.0sigma(F), R = 7.52%. The complex [Cu(xop)(2)](PF(6)).(3)/(2)CH(3)OH crystallizes in space group C2/c with a = 23.096(6) Å, b = 23.387(6) Å, c = 17.873(7) Å, beta = 100.08(3) degrees, V = 9505(5) Å(3), and Z = 8. For 5631 unique data with F > 4.0sigma(F), R = 6.02%. The complex [Cu(dpep)(2)](PF(6)) crystallizes in space group P&onemacr; with a = 13.327(7) Å, b = 14.114(7) Å, c = 15.175(5) Å, alpha = 87.23(4) degrees, beta = 66.48(3) degrees, gamma = 61.84(4) degrees, V = 2273(2) Å(3), and Z = 2. For 4851 unique data with F > 4.0sigma(F), R = 5.47%. The complex [Cu(dmesp)(dpep)](PF(6)) crystallizes in space group Pbca with a = 14.547(6) Å, b = 22.868(6) Å, c = 30.659(10) Å, V = 10199(6) Å(3), and Z = 8. For 2281 unique data with F > 4.0sigma(F), R = 9.43%. The electrochemical, spectral, and structural properties of [Cu(dop)(2)](+) and [Cu(xop)(2)](+) demonstrate that the copper coordination environment is more sterically encumbered and more rigid in these two complexes than the coordination environment in the comparison molecule [Cu(dpp)(2)](+) (dpp = 2,9-diphenyl-1,10-phenanthroline). A larger energy gap is predicted for [Cu(dop)(2)](+) and [Cu(xop)(2)](+) based on these data, and consequently, a blue-shifted emission is observed relative to [Cu(dpp)(2)](+). The room-temperature excited-state lifetimes in dichloromethane and methanol of the dop and xop complexes are shown to be shorter than the dpp complex, and these results are interpreted as due to a reduction in ligand pi-electron delocalization in the former two complexes. The complexes [Cu(dpep)(2)](+) and [Cu(dmesp)(dpep)](+) are shown to have increased ligand pi-electron delocalization relative to [Cu(dpp)(2)](+); however, neither complex displays room-temperature steady-state emission in dichloromethane.

Structures of the Copper(I) and Copper(II) Complexes of 2,9-Diphenyl-1,10-phenanthroline: Implications for Excited-State Structural Distortion.

The syntheses, crystal structures, and electronic absorption spectra of the copper(I) and copper(II) complexes of 2,9-diphenyl-1,10-phenanthroline (dpp) are reported. The complex [Cu(dpp)(2)](PF(6)) (1) crystallizes in space group P2(1)/c with a = 11.081(4) Å, b = 25.491(8) Å, c = 14.263(5) Å, beta = 92.84(3) degrees, Z = 4, and V = 4024(2) Å(3). For 4813 unique data with F > 4.0sigma(F), R = 5.41% and R(w) = 6.43%. The coordination geometry about the copper(I) center in [Cu(dpp)(2)](+) is best described as distorted tetrahedral with approximate C(2) symmetry. The structure of [Cu(dpp)(2)](+) is largely determined by interligand pi-stacking interactions that occur between the phenyl groups of one ligand and the phenanthroline moiety of the other ligand. Solution-state absorption and (1)H NMR spectra indicate that the [Cu(dpp)(2)](+) complex is fluxional in solution, rocking between two enantiomeric structures of C(2) molecular symmetry through an intermediate of C(s)() symmetry. The complex [Cu(dpp)(2)](ClO(4))(2) (2) crystallizes in space group P&onemacr; with a = 7.809(3) Å, b = 13.027(6) Å, c = 20.344(10) Å, alpha = 87.68(4) degrees, beta = 89.16(4) degrees, gamma = 79.26(4) degrees, Z = 2, and V = 2032(1) Å(3). For 4943 unique data with F > 4.0sigma(F), R = 5.22% and R(w) = 5.37%. The coordination geometry about the copper(II) center in [Cu(dpp)(2)](2+) is best described as flattened tetrahedral with approximate D(2) symmetry. There are no interligand pi-stacking interactions in the structure of [Cu(dpp)(2)](2+). The four-coordinate geometry in [Cu(dpp)(2)](2+) persists in solution on the basis of solution-state and solid-state absorption spectroscopy. Structural distortion in the metal-to-ligand charge-transfer excited state of [Cu(dpp)(2)](+) is discussed on the basis of the structures of 1 and 2.

A Photoluminescent Copper(I) Complex with an Exceptionally High CuII /CuI Redox Potential: [Cu(bfp)2 ]+ (bfp=2,9-bis(trifluoromethyl)-1,10-phenanthroline).

Unprecedented stabilization of the copper(I) oxidation state is demonstrated for the complex cation [Cu(bfp)2 ]+ (1) due to the steric and electronic effects of the CF3 groups (E1/2 (CuII /CuI )=+1.55 V vs. SCE). The redox existence range of the copper(I) species is remarkably high at 2.77 V. It is emissive in solution at room temperature and shows great potential as a photocatalyst; in the excited state it is a very potent photooxidant.