Synthesis, Characterization And Characterization Of Copper (Ⅱ) Complexes Containing Benzimidazole Dendritic Ligands

Superoxide dismutase, hemocyanin and urease as metalloenzymes involved in series of biochemical reactions including electron transfer, oxygen transport and activation and hydrolysis of amide. Because protein molecules have large molecular weight and complicate structure. It is difficult to investigate their chemical mechanism. So small molecule model compounds are useful to mimic the central active structure and function of such metalloenzymes.Bis（2-benzimidazolylmethyl）, tris（2-benzimidazolylmethyl）amine, 2,6-bis[bis（2- benzimidazolylmethyl）aminomethyl]-4-methylphenol were used as ligands. Fifteen copper（II） and nickel（II） complexes containing the above ligand were synthesized and structurally characterized by FT-IR, UV-vis and X-ray crystallography. These complexes could be used to model the active site structures of superoxide dismutase, hemocyanin and urease.Four mononuclear Cu（II） complexes [Cu（dibim）（pic）]ClO₄ （1）, [Cu（ntb）（pic）] -ClO₄·CH₃OH·2H₂O （2）, [Cu（ntb）（2,6-pda）]·CH₃OH·3H₂O （3） [Cu（ntb）（2,5-pda）]·6H3OH·H₂O （4） were synthesized, where dibim is bis（2-benzimidazolylmethyl）amine, ntb is tris（2-benzimidazolylmethyl）amine, pic is anion of picolinic acid,2,6-pda is dianion of pyridine-2,6-dicarboxylic acid and 2,5-pda is dianion of pyridine-2,5-dicarboxylic acid. All of the four copper（II） complexes are mononuclear. The geometry of complex 1 is square pyramidal. Complex 2 and 4 both have distorted trigonal bipyramidal configuation. The geometry of complex 3 is distorted octahedron. Because of the strong chelating effect of pyridine-2,6-dicarboxylate anion, two benzimidazolyl groups in ntb ligand are coordinated with copper（II） atom and the other is not coordinated. One-dimensional, two-dimensional, three-dimensional stacking structures are formed, since there are lots of uncoordinated NH groups, pyridine N atoms and carboxlyate oxygen atoms.Five mononuclear nickel complexes [Ni（dibim）（2,5-pda）（CH₃OH）]·4CH₃OH （5）, [Ni（dibim）（2,6-pda）] （6）, [Ni（dibim）（pic）（H₂O）]ClO₄·CH₃OH （7）, [Ni（ntb）（2,6-pda）]·CH₃OH （8） and [Ni（ntb）（3,5-pdc）]·CH₃OH （9） were synthesized and characterized. In all the above nickel complexes, each nickel（II） atom is six-coordinated with distorted octahedron geometry. The similar supermolecular structures as copper complexes are also formed Two dinuclear Nickel complexes [Ni2（bbap）（Hnic）（nic）]（ClO₄）2·6CH₃OH （10） and [Ni2（bbap）（O2C-C6H4-p-NO2）（O2COC2H5）]ClO₄ （11） were synthesized and characterized, where Hbbap is 2,6-bis[bis（2-benzimidazolylmethyl）aminomethyl]-4-methylphenol. Two Ni（II） ions are bridged by the phenolate O atom of bbap-, two carboxlyate O atoms of two nicotinate anions.One is normal nicotinate and the other is nicotinate with the pyridine connected with a proton which transferred from the dinucleating Hbbap ligand. [Ni2L（O2C-C6H4-p-NO2）（O2CO C2H5）]ClO₄ （12） was prepared by reaction of Ni（ClO₄）2·6H₂O, Hbbap, sodium 4-nitrobenzoate in alkaline ethanol solution. The structure shows that the two nickel（II） ions are bridged by one phenoxy unit of bbap-, one carboxylate of 4-nitrobenzoate and one monoethyl carbonate. The monoethyl carbonate originates from the interaction of the dinuclear species with atomospheric carbon dioxide in ethanol solution.Three dinuclear copper（II） complexes [Cu2（bbap）（O2C-C₆H₄-p-OCH₃）]（ClO₄）2·6CH₃OH （12）, [Cu2（Hbbap）（pia）2]（ClO₄）4·3CH₃OH·H₂O （13） and [Cu2（Hbbap）（O2C-C6H4-p-NO2）2（ClO₄）] -ClO₄·4CH₃CN （14）.were obtained, where pia is picolinamide. In complex 12, the copper（II） atoms are double bridged by a phenolato-O atom of bbap- and a carboxylate group of p-methoxybenzoate anion. Both copper（II） atoms have square pyramidal geometry. In complex 13 and 14, the dinuclating ligand Hbbap is not deprotonated. Both complexes are six-coordinated and have octahedral geometry. In complex 13, each of the two picolinamides coordinates to one copper（II） atom in a bidentate chelating N, O mode. In complex 14, both p-nitrobenzoate carboxylate group coordinates with the two Cu（II） ions with monodentate mode.