Mitchell R. Malachowski

Novel mono- and binuclear Cu(II) complexes: synthesis, characterization and catecholase activity

Abstract Two new ligands, N , N -bis(3,5-dimethylpyrazol-1-ylmethyl)benzylamine (bpmba) and N , N , N ′, N ′- tetrakis(3,5-dimethylpyrazol-1-ylmethyl)-α,α′-di- amino- m -xylene (bpmdx) have been synthesized. Using these ligands, copper(II) complexes of the type [Cu(bpmba)(Cl) 2 ](Cl) 2 , [Cu 2 (bpmba) 2 (OCH 3 ) 2 ]- (BF 4 ) 2 and [Cu 2 (bpmdx)(X) 2 ]Y 2 where X = OCH 3 or Cl and Y = Cl or BF 4 have been prepared and characterized on the basis of elemental analysis, fast atom bombardment mass spectrometry, and UV—Vis spectroscopy. These show the ligands to coordinate as an N 3 and an N 6 donor set respectively. The ability of the complexes to catalyze the oxidation of catechol to quinone was studied by following the appearance of quinone spectrophotometrically. The binuclear complex [Cu 2 (bpmdx)(OCH 3 ) 2 ]- (BF 4 ) 2 reacts fastest with an oxidase activity of 0.467 μmol/mg min while the other three complexes have slower rates of oxidation.

Synthesis, characterization and catecholase activity of a series of novel mononuclear Cu(II) complexes derived from a tripodal ligand

Abstract A new tripodal ligand, N , N -bis(3,5-dimethylpyrazol -1-ylmethyl)-1-hydroxy-2-aminoethane (bpmhe), has been synthesized. Using this ligand, Cu(II) complexes of the type [Cu(bpmhe)X]Y where X = H 2 O, NO 3 , Br, Cl, or N 3 and Y = BF 4 , NO 3 , Br, or Cl have been prepared. This has resulted in the formation of mononuclear five-coordinate complexes as shown by UV-Vis spectroscopy and Fast Atom Bombardment Mass Spectrometry. The complexes were tested for their reactivity towards the oxidation of catechol to quinone by following the appearance of quinone spectrophotometrically. The complexes show differing rates of reaction depending on the nature of the exogenous fifth ligand with the azido complex showing the fastest rate of oxidation.

Effect of ligand donors on the catalytic properties of metal complexes. Copper(II) complexes as catalysts for the oxidation of 3,5-di-tert-butylcatechol

Abstract Copper(II) complexes 1–5 with the tetracentate ligand L 1 = N , N -bis(3,5-dimethylpyrazol-1-ylmethyl)-1-hydroxy-2-aminoethane (pzmhe) and 6–10 with the analogous N 3 O benzimidazole ligand L 2 = N , N -bis(2-benzimidazolylmethyl)-1-hydroxy-2-aminoethane (bbmhe) were prepared. The five-coordinate complexes [Cu(L)X]Y 1.2 (with 1, 6 : X = H 2 O, Y = BF 4 ; 2, 7 : X = NO 3 , Y = NO 3 ; 3, 8 : X = Br, Y = Br; 4, 9 : X = Cl, Y = Cl; 5, 10 : X = N 3 , Y = BF 4 ) were characterized by chemical analysis, absorption and EPR spectroscopies and cyclic voltammetry. The data show the complexes have square pyramidal geometry. All display chemically reversible one-electron redox behavior in acetonitrile. The E ° t values are more positive with L 1 than with L 2 by 144–234 mV. Oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone by these complexes was studied. The reaction rate depends on the nature of the heterocyclic donor, its basicity, steric effects, reduction potentials, and the type of exogenous donor present. Large rate variations were observed with the most effective catalysts those with pzmhe; the [Cu(pzmhe)N 3 ]BF 4 complex was most active with [Cu(bbmhe)Br]Br and [Cu(bbmhe)Cl]Cl complexes relatively inactive. Electrochemical data showed a non-linear relationship between their ability to oxidize catechols and their reduction potentials. The results point to the bulky ligand environment provided by the benzimidazoles as being responsible for the diminution of their rates of catalysis compared to the pyrazole complexes.

The preparation and catalytic properties of copper(II) complexes derived from a pyrazole containing ligand. X-ray crystal structure of [Cu(pzmhp)(BF4)](BF4)

The synthesis of the new multidentate ligand N,N′-bis(3,5-dimethylpyrazol-l-ylmethyl)-1,3-diamino-2-hydroxypropane (pzmhp) is described along with the preparation of a series of copper(II) complexes derived from this ligand. These complexes have the form [Cu(pzmhp)X]X where X = BF4 or ClO4 and [Cu(pzmhp)X2] where X = Cl or Br. The complexes have been characterized on the basis of elemental analysis, IR spectroscopy, magnetic susceptibility, solution conductivity, and fast atom bombardment mass spectrometry. These methods show the ligand to coordinate to copper(II) in a mononuclear fashion with the ligand acting as an N4 donor set with an uncomplexed alcohol oxygen. The single-crystal X-ray structure of [Cu(pzmhp)(BF4)](BF4) (1) shows it to be triclinic with space group P1, with cell dimensions . The asymmetric unit comprises twice the formula unit. Each copper ion is in a distorted square planar environment of four nitrogens from the ligand ; additionally, two fluorine atoms are in (Semi-)coordinate axial positions , completing the distorted elongated octahedron around copper(II). Cyclic voltammetry shows that each complex is reduced reversibly in a one-electron process; reduction potentials range from a high of 0.00 V for [Cu(pzmhp)(BF4)](BF4) (1) to −0.205 V for [Cu(pzmhp)(Cl)2] versus Ag/AgCl. The ability of the complexes to catalyze the oxidation of 3,5-di-tert-butylcatechol to 3,5-di-tert-butylquinone was studied showing all of the complexes to be catalytically active. The complexes with weakly corrdinating counterions, ([Cu(pzmhp)(BF4)](BF4) (1) and [Cu(pzmhp)(ClO4)][ClO4) (2)), have activities of 0.031 and 0.028 mmol substrate per mg catalyst per min respectively, while the complexes with stronger coordinating anions ([Cu(pzmhp)(Br)2] (3) and [Cu2(pzmhp)(Cl)2]∗dH2O (4)), have lower catalytic capabilities with activities of 0.015 and 0.007 mmol substrate per mg catalyst per min respectively.

A chiral, heterometallic metal-organic framework derived from a tris(chelate) coordination complex

A novel tris(chelate) metalloligand has been used to synthesize a chiral, heterometallic metal-organic framework that is robust to solvent removal and shows selective uptake of nitroaromatic compounds.

Comparative study of the catalytic oxidation of catechols by copper(II) complexes of tripodal ligands

Copper(II) complexes of the ligands tris(2-pyridylmethyl)amine (tpyma), tris(2-pyridylethyl)amine (tpyea), tris(3,5-dimethylpyrazol-1-ylmethyl)amine (tpzma) and tris(3,5-dimethylpyrazol-1-ylethyl)-amine (tpzea) were prepared. The complexes, [Cu(ligand)Cl]Cl or [Cu(ligand)(H2O)][BF4]2, were characterized by a combination of absorption and EPR spectroscopies and chemical analysis. The ability of the complexes to oxidize 3,5-di-tert-butylcatechol to 3,5-di-tert-butyl-o-benzoquinone has been studied and the results show that the rate of reaction is dependent on the nature of the heterocyclic donor, its basicity, steric considerations, the chelate ring size and the type of exogenous donor present. Large variations in the rate were observed with the most effective catalysts being those with pyridine donors which formed six-membered chelate rings; the complex [Cu(tpyea)(H2O)][BF4]2 was the most active while [Cu(tpzea)(H2O)][BF4]2 and [Cu(tpzea)Cl]Cl were inactive. Electrochemical data for the series of compounds show that there is a non-linear relationship between their ability to oxidize catechols and their reduction potentials. The most effective catalysts were those complexes which exhibited reduction potentials close to 0.00 V, while those that deviated from that potential by 200–300 mV in either direction were largely inactive. Within the range of complexes which were active, a steric match between the substrate and the complex also largely defined their reactivity. Comparisons to the biological system tyrosinase are drawn.

The design and synthesis of novel dinucleating macrocycles derived from cyclam

Abstract The preparation of two new polypyrazole ligands based on the cyclam macrocycle is described. The molecules each contain four pyrazole and four aliphatic nitrogen donor atoms and are capable of simultaneously binding to two metal ions in an unsymmetrical dinucleating fashion.

The Synthesis of Tetrapyranozole Substitued Phenols

The synthesis of two new potentially dinucleating tetrapyrazole substituted phenols is described. The compounds 2,6-bis[(bis(pyrazol- 1-ylmethyl)amino)methyl] phenol (1) and 2,6-bis[(bis(3,5-dimethylpyrazol-1-ylmethyl)amino)methyl]phenol (2) were prepared via the pyrazolylmethylation of amines

The preparation of Cu(II) complexes derived from a novel pyrazole containing dinucleating ligand

Abstract The synthesis of the new heptadentate dinucleating ligand 2,6-bis[(bis(3,5-dimethylpyrazol-1-ylmethyl)amino) methyl]phenol (bpamp) ( 3 ) is described. The preparation of Cu(II) complexes of the form [Cu 2 (bpamp)X](BF 4 ) 2 where X=Cl ( 8 ) or N 3 ( 9 ) derived from this ligand is detailed. These complexes have been characterized on the basis of elemental analysis, IR spectroscopy, fast atom bombardment mass spectrometry and UV-Vis spectroscopy. The results indicate that ligand 3 coordinates to Cu(II) in a dinuclear fashion with the ligand acting as an N 6 O donor set. These results are consistent with 8 and 9 existing as five-coordinate Cu(II) complexes each bound to three nitrogen atoms, an endogenous phenolate oxygen and an exogenous bridge. The spectroscopic data indicate that for 9 the azide bridges the coppers in a μ-1,1 fashion.