Peter Kamaras

SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF METAL COMPLEXES OF AN UNSYMMETRIC N3O TETRADENTATE SCHIFF BASE LIGAND

Abstract The nickel(II) and copper(II) complexes of the unsymmetrical N 3 O tetradentate Schiff base ligand, H 2 ambprsal, which is the 1:1:1 condensation product of 2-aminobenzaldehyde (amb), 1,3-diaminopropane (pr) and salicylaldehyde (sal), were prepared by the reaction of HsalprNH 2 (HsalprNH 2 is the 1:1 monocondensate of salicylaldehyde with 1,3-diaminopropane) with 2-aminobenzaldehyde, metal nitrate and triethylamine in methanol. Replacement of the nickel in Ni(ambprsal) with FeCl was accomplished by reaction of Ni(ambprsal) with dimethylglyoxime in benzene followed by reaction with iron(III) chloride. Structural investigation was carried out on the nickel(II) and copper(II) complexes. Both Ni(ambprsal) and Cu(ambprsal) are monomeric and approximately square planar. The six-membered ring containing the metal, the azomethine nitrogen atoms and the three carbins of the 1,3 diaminopropane bridge adopt the symmetrical boat conformation with the metal and the central carbon atoms occupying the bow and stern positions. The conformation of the ligand and the N 3 O donor set may both contribute to the high spin state of the iron atom in Fe(ambpral)Cl.

Synthesis and structural characterization of copper complexes of N4 tetradentate Schiff bases derived from N-alkylated 2-aminobenzaldehyde. Effects of cyclization, oxidation, and dinucleation

Abstract The structures of the copper complexes of 7,8,15,16,17,18-hexahydro-dibenzo[e,m][1,4,8,11]tetraazacyclotetradecine (Cu(2,2 mac)) 7,8,15,18-tetrahydro-dibenzo[e,m][1,4,8,11]tetraazacyclotetradecine-16,17-dionato (Cu(2,2 oxomac)) and Cu(NCH3 amben) and Cu(2,2 oxomac)Ni(hfa)2 are reported. The three copper complexes containing a 14-membered macrocycle are essentially square planar complexes and exhibit no short axial interactions. The analogous acyclic complex, Cu(NCH3 amben), exhibits an average tetrahedral distortion of 34.35° which appears to be due to steric repulsion between the two methyl groups. The dinuclear complex, which exhibits a planar exchange coupled oxamido core, was prepared by reaction of Cu(2,2 oxomac) with Ni(hfa)2. The analogous complex, Cu(2,2 oxomac)Cu(hfa)2, can be prepared by the same procedure or by reaction of Cu(2,2 mac) with Cu(hfa)2. The former method is a general synthetic route while the latter is specific for Cu(hfa)2 relying on its ability to catalyze the oxidization of the ethylene unit between the anilino nitrogen atoms to the oxamide (NCH2CH2N to NCOCON) under ambient conditions.

Mononuclear precursor of heterodinuclear models for unsymmetrical active sites of metalloproteins: Synthesis and structure of dichloro (2-bis(2-benzimidazolylmethyl) aminomethyl-6-[(2-benzimidazoliummethyl)(2-methoxyphenylmethyl)aminiummethyl]-4-methyl-phenoxo-O, N, N′, N″) FeIII bis-perchlorate bis-ethanol solvate

Abstract The reaction of the hydrochloride salt of the potentially dinucleating unsymmetrical ligand, 2-bis(2-benzimidazolylmethyl)aminomethyl-6-[(2-benzimidazolylmethyl)(2-methoxyphenylmethyl)aminomethyl]-4-methyl-phenol [N3(OH)N2—MeOB], with Fe(CIO 4 ) 3 · 6H 2 O in ethanol (and one equivalent of diphenylphosphate), followed by the addition of five equivalents of triethylamine, yielded a mononuclear complex [Fe III (Cl) 2 (N3(O)N2H 2 2+ —MeOB)](ClO 4 ) 2 ·2CH 3 CH 2 OH ( 1 ). The crystal structure of this complex shows a tridentate coordination of the bis(2-benzimidazolylmethyl)amino moiety in a facial manner. A distorted octahedral coordination around iron(III) is completed by one terminally coordinated phenolato moiety and two chloro ligands, one of which occupies an equatorial position. The monobenzimidazole branch at the 6-position of the ligand does not coordinate and is doubly protonated; the positive charge of the complex is compensated for by two perchlorate anions. The unusual behaviour of this ligand and the potential of complex 1 to serve as a molecular precursor for heterodinuclear Fe III M II unsymmetrical complexes is discussed.

Structure and magnetism of electronically distorted iron(III) Schiff-base complexes

The reaction of [Fe(salen)Cl][H2salen =N,N′-bis(salicylidene)ethane-1,2-diamine] with an excess of L [imidazole (Him), 1-,2- or 4-methylimidazole (1-,2- or 4-mim)] in acetone resulted in the isolation of heterobisadducts, [Fe(salen)L(Cl)](L = Him, 1- or 2-mim) and a homobisadduct, [Fe(salen)L2]Cl (L = 4-mim). The structures of [Fe(salen)(1-mim)Cl] and [Fe(salen)(4-mim)2]Cl were determined by single-crystal X-ray diffraction: [Fe(salen)(1-mim)Cl], monoclinic, space group p21/c, Z= 4, a= 9.8510(10), b= 15.9830(10), c= 12.8350(10)A, β= 107.610(10)°; [Fe(salen)(4-mim)2]Cl, orthorhombic, space group Fdd2, Z= 8, a= 21.7650(10), b= 12.5040(10), c= 18.508(2)A. The structures were refined by full-matrix least-squares methods on F2 to R= 0.0537 and 0.0338 for 2609 and 1207 reflections, respectively. A significant difference between the two structures is that the dihedral angle between the two phenyl rings of the salen ligand is 17.5° for [Fe(salen)(1-mim)Cl] and 4.4° for [Fe(salen)(4-mim)2]Cl. All of the complexes were characterized by variable-temperature magnetic susceptibility and Mossbauer spectroscopy. The heterobisadducts, which have a N3O2Cl donor set, exhibit an admixed electronic ground state whereas the homobisadduct is high spin. Another N3O2Cl donor set molecule has been found to exhibit a temperature-dependent spin equilibrium, 2T ⇌6A, as evidenced by variable-temperature magnetic susceptibility, ESR and Mossbauer spectroscopies.

Synthesis and characterization of iron (III) complexes of N4 schiff base macrocycles

Abstract Iron(III) complexes of the diprotic N4 Schiff base macrocycles, 7,8,15,16,17,18-hexahydro-dibenzo[e,m] [1,4,8,11]tetraazacyclotetradecine (H2(2,2mac)) and 8,9,16,17,18,19-hexahydro-7H-dibenzo[e,n][1,4,8,12]tetraazacyclopentaadecine(H2(3,2mac)), were prepared by the metathesis reaction of anhydrous iron (III) bromide with the disodium or magnesium complexes of the dianionic ligands in THF under an inert atmosphere. The complexes exhibit the intermediate spin state as evidenced by magnetic susceptibility and Mossbauer spectroscopy. Fe(3,2 mac)Br is structurally characterized as a distorted square pyramid with the four nitrogen atoms in the basal positions and the bromide occupying the axial site. The average iron to nitrogen bond distance is 1.921 A.

Ligand oxidation in N4 tetradentate Schiff base complexes catalyzed by copper(II) hexafluoroacetylacetonate dihydrate: reaction details and structures

The ethylene unit connecting the two anilino nitrogen atoms of the copper or nickel complexes of 7,8,15,16,17,18-hexahydro-dibenzo[e,m][1,4,8,11]tetraazacyclotetradecine [H2(2,2 mac)] and 8,9,16,17,18,19-hexahydro-7H-dibenzo[e,n][1,4,8,12]tetraazacyclopentaadecine [H2(3,2 mac)], i.e. M(2,2 mac) and M(3,2 mac), are oxidized in chloroform at room temperature under atmospheric conditions in the presence of Cu(hfa)2·(H2O)2 to the oxamide (N–CH2–CH2–N– to N–CO–CO–N–). If Cu(hfa)2·(H2O)2 is present in stoichiometric amounts the isolated product of the reaction is the dinuclear complex, M(3,2 oxomac)Cu(hfa)2. The dinuclear complex can also be prepared by direct reaction of M(3,2 oxomac) (prepared by another method) with Cu(hfa)2·(H2O)2. The dinucleation reaction of M(3,2 oxomac) with M(hfa)2 is quite general but the ligand oxidation of M(3,2 mac) is specific for Cu(hfa)2·(H2O)2. Reaction of Cu(3,2 mac) with Hhfa or H2(3,2 mac) with Cu(hfa)2·(H2O)2 results not in oxidation of the macrocycle but in protonation to give Cu{H2(3,2 mac)}(hfa)2. The oxidation of Cu(3,2 mac) in an 18O2 atmosphere does not result in a significant incorporation of 18O. However, nearly quantitative incorporation of 18O is achieved when the reaction is carried out under air in the presence of H218O. The structures of Cu(3,2 mac), Cu(3,2 oxomac), Cu(3,2 oxomac) Cu(hfa)2 and Cu{H2(3,2 mac)}(hfa)2 are reported.