COPPER CHEMISTRY OF PYRIDYLALKYLBENZAMIDE LIGANDS: MODELING THE CUZ CENTER OF N2OR AND COORDINATION POLYMER CHEMISTRY

Abstract

In nature, the reduction of N2O to N2 is the terminal step of the denitrification process, which is catalyzed by nitrous oxide reductase (N2OR). The catalytic CuZ center was found to be a novel μ4-sulfide bridged tetranuclear copper cluster. Much effort has been done to model the CuZ site to help us understand the structure and function relationship. Questions still remain about the catalytic mechanism, including the synthesis of accurate model complexes. In order to pursue the goal of modeling CuZ of N2OR, we have explored the copper chemistry of two new pyridylalkylamide ligands containing phenol groups appended to the amide, 2-hydroxyl-N-(2-pyridylmethyl) benzamide (HLPhOH) and 2-hydroxyl-N-(2-pyridylethyl) benzamide (HLPhOH′). Two copper(I) and three copper(II) complexes with HLPhOH and HLPhOH′ were synthesized and characterized by X-ray crystallography. Both [Cu(HLPhOH)2(CH3CN)]BF4 (1) and [Cu(HLPhOH′)2]BF4 (2) are mononuclear copper(I) complexes. [Cu(HLPhOH)2Cl2] (3) is a monocopper(II) complex with octahedral geometry. [Cu4(LPhO)4] (4) is a tetracopper(II) complex with a cubane-like Cu4O4 core structure. [Cu2(LPhO′)2(CH3OH)2] (5) is a binuclear copper(II) complex with a distorted square pyramidal geometry. A naked [Cu16S10]4- cluster was obtained by the reaction of [Cu4(LPhO)4] with (nBu4N)SH, which can partially model the structure of the CuZ center. Three copper(II) complexes with substituted pyridyl(bis-phenol)amide ligands: 6,6'-(2-methyl-2(pyridine-2-yl)propane-1,3diyl)bis(azanediyl)bis(methylene)bis-(2,4-dibromophenol) (H2LBr2-amine), 6,6'-(2-methyl-2(pyridine-2-yl)propane-1,3diyl)bis(azanediyl)bis(methylene)bis-

(2-methoxyphenol) (H2LMeO-amine), and 2,2'-(2-methyl-2(pyridine-2-yl)propane-1,3diyl)bis(azanediyl)bis(methylene)bis-(4-nitrophenol) (H2LNO2-amine) were synthesized and characterized by spectroscopic studies. [Cu(LBr2-amine)] (6) and [Cu(LNO2-amine)] (7) are mononuclear copper(II) complexes with square pyramidal geometry. [Cu(LMeO-amine)Na(CH3OH)2] (8) is a heterometallic binuclear complex. The CV features of complexes: [Cu(LtBu-amine)(CH3OH)], [Cu3(Lamine)2(CH3CN)2](ClO4)2, [Cu(LBr2-amine)] (6) and [Cu(LNO2-amine)] (7) are interpreted by Hammett analysis. Pyrazine-containing ligands N-(pyridine-2-yl)methyl)pyrazine-2-carboxamide (HLPz) and N-(pyridine-2-yl)ethyl)pyrazine-2-carboxamide (HLPz') led us to the synthesis and characterization of a series of 1D coordination polymers. [Cu(HLPz)Cl]n (9) is a 1D coordination polymer with Cu2Cl2 core bridged by two HLPz ligands. [Cu(LPz)(Py)2]+ (10) is a mononuclear copper complex with a square pyramidal geometry. [Cu2(LPz)2( 4,4′-bipy)(OTf)2] (11) is a binuclear copper complex bridged by a twisted 4,4′-bipy ligand. Both [Cu(LPz)(N3)]n (12) and [Cu (LPz′)(N3)]n (13) are 1D coordination polymers bridged by end-on and end-to-end bridging azides, respectively. When thioether-containing ligands 2-(methylsulfanyl)-N-[2-(pyridine-2-yl)methyl]acetamide (2-HLN2S) and 2-(methylsulfanyl)-N-[2-(pyridine-2-yl)ethyl]acetamide (2-HLN2S') are used in the synthesis of the copper complexes. [Cu(2-LN2S)(CH3OH)]n(OTf) (14) and [Cu(2-LN2S')(OTf)]n (15) are 1D coordination polymers connected by the carbonyl oxygen from the corresponding ligand. Cu(2-HLN2S')(CH3OH)Cl] (16) is a mononuclear copper complex with a distorted square pyramidal geometry.