Facile ring opening of iron(III) and iron(II) complexes of meso-amino-octaethylporphyrin by dioxygen

Pyridine solutions of ClFe(III)(meso-NH(2)-OEP) undergo oxidative ring opening when exposed to dioxygen. The high-spin iron(III) complex, ClFe(III)(meso-NH(2)-OEP), has been isolated and characterized by X-ray crystallography. In the solid state, it has a five-coordinate structure typical for high-spin (S = 5/2) iron(III) complex. In chloroform-d solution, ClFe(III)(meso-NH(2)-OEP) displays an (1)H NMR spectrum characteristic of a high-spin, five-coordinate complex and is unreactive toward dioxygen. However, in pyridine-d(5) solution a temperature-dependent equilibrium exists between the high-spin (S = 5/2), six-coordinate complex, [(py)ClFe(III)(meso-NH(2)-OEP)], and the six-coordinate, low spin (S = 1/2 with the less common (d(xz)d(yz))(4)(d(xy))(1) ground state)) complex, [(py)(2)Fe(III)(meso-NH(2)-OEP)](+). Such pyridine solutions are air-sensitive, and the remarkable degradation has been monitored by (1)H NMR spectroscopy. These studies reveal a stepwise conversion of ClFe(III)(meso-NH(2)-OEP) into an open-chain tetrapyrrole complex in which the original amino group and the attached meso carbon atom have been converted into a nitrile group. Additional oxidation at an adjacent meso carbon occurs to produce a ligand that binds iron by three pyrrole nitrogen atoms and the oxygen atom introduced at a meso carbon. This open-chain tetrapyrrole complex itself is sensitive to attack by dioxygen and is converted into a tripyrrole complex that is stable to further oxidation and has been isolated. The process of oxidation of the Fe(III) complex, ClFe(III)(meso-NH(2)-OEP), is compared with that of the iron(II) complex, (py)(2)Fe(II)(meso-NH(2)-OEP); both converge to form identical products.     

New pincer-type diphosphinito (POCOP) complexes of NiII and NiIII

This communication reports the synthesis and characterization of the new, pincer-type, square-planar, 16-electron compounds {2,6-(OPPr(i)(2))(2)C(6)H(3)}Ni(II)Br, 1, and {(Pr(i)(2)POCH(2))(2)CH}Ni(II)Br, 2, and the square-pyramidal, 17-electron complex {(Pr(i)(2)POCH(2))(2)CH}Ni(III)Br(2), 3.     

Metal complexes of antibiotic drugs. Studies on dicluxacillin complexes of FeII, FeIII, CoII NiII and CuII

The synthesis and characterization of dicluxacillin (DC) complexes with di- and tri-valent metal ions are described. The nature of bonding of the chelated DC and its metal complexes structures have been elucidated on the basis of their spectroscopic (infrared, solid reflectance, magnetic spectra, mass and thermal analysis) properties. In all the complexes studied, the DC acts as a chelate monoanionic ligand with coordination involving the carboxylate O atom and the endocyclic N of the thiazole ring. The DC ligand forms mono-ligand complexes of the general formula [M(DC)(H2O)x(A)]. yH2O where DC is the uninegatively charged bidentate ligand and A = OAc in case of CuII and Cl in case of FeIII, FeII, CoII and NiII ions. IR, solid reflectance spectra and magnetic moment measurement are used to infer the structure and to illustrate the coordinating capacity of the ligand. From the thermal decomposition curves, the water molecules of crystallization are removed in a single stage while the decomposition of the ligand and coordinated water molecules occur in the second and subsequent stages. Different thermodynamic kinetic parameters namely activation energy (E*), enthalpy of activation (AH*), entropy of activation (AS*) and free energy change of activation (AG*) are calculated using Coats and Redfern equation.     

A magnetostructural study of linear NiII MnIII NiII, NiII CrIII NiII and triangular Ni(II)3 species containing (pyridine-2-aldoximato)nickel(II) unit as a building block

Three trinuclear complexes, NiII MnIII NiII, NiII CrIII NiII and Ni(II)3 based on (pyridine-2-aldoximato)nickel(II) units are described. Two of them, and , contain metal-centers in linear arrangement, as is revealed by X-ray diffraction. Complex is a homonuclear complex in which the three nickel(II) centers are disposed in a triangular fashion. The compounds were characterized by various physical methods including cyclic voltammetric and variable-temperature (2-290 K) susceptibility measurements. Complexes and display antiferromagnetic exchange coupling of the neighbouring metal centers, while weak ferromagnetic spin exchange between the adjacent Ni II and Cr III ions in is observed. The experimental magnetic data were simulated by using appropriate models.     

Excellent chiralselectivity in sulfur-bridged CoIIIMCoIII (M = NiII and PdII) trinuclear complexes containing 1,2-cyclohexanediamine

The reaction of [Ni(aet)2] with [CoCl2(R,R-chxn)2]+ (aet = 2-aminoethanethiolate, R,R-chxn = 1R,2R-cyclohexanediamine) in water gave a CoIIINiIICoIII trinuclear complex, DeltaRRDeltaRR-[Ni(Co(aet)(2-)(R,R-chxn))2]4+ ([1a]4+), in which two cis(S)-[Co(aet)2(R,R-chxn)]+ units are linked by a central NiII ion through sulfur bridges. The two CoIII units in [1a]4+ uniformly adopt the Delta configuration, which is induced by the chirality of the terminal R,R-chxn ligands. The central NiII ion in [1a]4+ was replaced by a PdII ion to produce an analogous CoIIIPdIICoIII trinuclear complex, DeltaRRDeltaRR-[Pd(Co(aet)2(R,R-chxn))2]4+ ([2a]4+), with retention of the Delta configuration. When racemic R,R/S,S-chxn was employed instead of R,R-chxn, not only the chirality about two CoIII centers but also the chirality about two chxn ligands was unified in the S-bridged trinuclear structure, leading to the selective formation of a pair of enantiomers, DeltaRRDeltaRR/LambdaSSLambdaSS-[M(Co(aet)2(chxn))2]4+ (M = NiII ([1b]4+) and PdII ([2b]4+)). The stereochemical and spectroscopic features of these complexes are discussed on the basis of the electronic absorption, CD, and NMR spectroscopies, along with the crystal structures of [1a]4+ and [2a]4+.     

Metal template synthesis of chromium(III) complexes

Chromium(III) complexes of Schiff bases resulting from the condensation of one mole of diacetyl with two moles of ethylene-diamine or 1,3 diaminopropane has been isolated by metal template reaction. The isolated complexes have been assigned cis configurations.     

Ethanol oxidation by imidorhenium(V) complexes: formation of amidorhenium(III) complexes

The reaction of Re(NC6H4R)Cl3(PPh3)2 (R = H, 4-Cl, 4-OMe) with 1,2-bis(diphenylphosphino)ethane (dppe) is investigated in refluxing ethanol. The reaction produces two major products, Re(NC6H4R)Cl(dppe)(2)2+ (R = H, 1-H; R = Cl, 1-Cl; R = OMe, 1-OMe) and the rhenium(III) species Re(NHC6H4R)Cl(dppe)2+ (R = H, 2-H; R = Cl, 2-Cl). Complexes 1-H (orthorhombic, Pcab, a = 22.3075(10) A, b = 23.1271(10) A, c = 23.3584(10) A, Z = 8), 1-Cl (triclinic, P1, a = 11.9403(6) A, b = 14.6673(8) A, c = 17.2664(9) A, alpha = 92.019(1) degrees, beta = 97.379(1) degrees, gamma = 90.134(1) degrees, Z = 2), and 1-OMe (triclinic, P1, a = 11.340(3) A, b = 13.134(4) A, c = 13.3796(25) A, alpha = 102.370(20) degrees, beta = 107.688(17) degrees, gamma = 114.408(20) degrees, Z = 1) are crystallographically characterized and show an average Re-N bond length (1.71 A) typical of imidorhenium(V) complexes. There is a small systematic decrease in the Re-N bond length on going from Cl to H to OMe. Complex 2-Cl (monoclinic, Cc, a = 24.2381(11) A, b = 13.4504(6) A, c = 17.466(8) A, beta = 97.06900(0) degrees, Z = 4) is also crystallographically characterized and shows a Re-N bond length (1.98 A) suggestive of amidorhenium(III). The rhenium(III) complexes exhibit unusual proton NMR spectra where all of the resonances are found at expected locations except those for the amido protons, which are at 37.8 ppm for 2-Cl and 37.3 ppm for 1-H. The phosphorus resonances are also unremarkable, but the 13C spectrum of 2-Cl shows a significantly shifted resonance at 177.3 ppm, which is assigned to the ipso carbon of the phenylamido ligand. The extraordinary shifts of the amido hydrogen and ipso carbon are attributed to second-order magnetism that is strongly focused along the axially compressed amido axis. The reducing equivalents for the formation of the Re(III) product are provided by oxidation of the ethanol solvent, which produces acetal and acetaldehyde in amounts as much as 30 equiv based on the quantity of rhenium starting material. Equal amounts of hydrogen gas are produced, suggesting that the catalyzed reaction is the dehydrogenation of ethanol to produce acetaldehyde and hydrogen gas. Metal hydrides are detected in the reaction solution, suggesting a mechanism involving beta-elimination of ethanol at the metal center. Formation of the amidorhenium(III) product possibly arises from migration of a metal hydride in the imidorhenium(V) complex.     

Metal complexes of tetrapyrazinoporphyrazines — effective catalysts of the oxidation of mercaptans

The catalytic activity of the tetrapyrazinoporphyrazine complexes of cobalt and iron have been studied in the oxidation of aliphatic mercaptans by molecular oxygen. n-Butyl mercaptan was used as the model compound. The metallotetrapyrazinoporphyrazines tested exhibited a considerably higher catalytic activity than cobalt phthalocyanine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1257–1259, September, 1984.     

Metal complexes of N-tosylamidoporphyrin: cis-acetato-N-tosylimido-meso-tetraphenylporphyrinatothallium(III) and trans-acetato-N-tosylimido-meso-tetraphenylporphyrinatogallium(III)

The crystal structures of acetato-N-tosylimido-meso-tetraphenylporphyrinatothallium(III), Tl(N-NTs-tpp)(OAc) (1), and acetato-N-tosylimido-meso-tetraphenylporphyrinatogallium(III), Ga(N-NTs-tpp)(OAc) (2), were determined. The coordination sphere around the Tl3+ ion is a distorted square-based pyramid in which the apical site is occupied by a chelating bidentate OAc- group, whereas for the Ga3+ ion, it is a distorted trigonal bipyramid with O(3), N(3), and N(5) lying in the equatorial plane. The porphyrin ring in the two complexes is distorted to a large extent. For the Tl3+ complex, the pyrrole ring bonded to the NTs ligand lies in a plane with a dihedral angle of 50.8 degrees with respect to the 3N plane, which contains the three pyrrole nitrogens bonded to Tl3+, but for the Ga3+ complex, this angle is found to be only 24.5 degrees. In the former complex, Tl3+ and N(5) are located on the same side at 1.18 and 1.29 A from its 3N plane, but in the latter one, Ga3+ and N(5) are located on different sides at -0.15 and 1.31 A from its 3N plane. The free energy of activation at the coalescence temperature Tc for the intermolecular acetate exchange process in 1 in CD2Cl2 solvent is found to be delta G++171 = 36.0 kJ/mol through 1H NMR temperature-dependent measurements. In the slow-exchange region, the methyl and carbonyl (CO) carbons of the OAc- group in 1 are separately located at delta 18.5 [3J(Tl-13C) = 220 Hz] and 176.3 [2J(Tl-13C) = 205 Hz] at -110 degrees C.     

Ligand displacement and oxidation reactions of methyl(oxo)rhenium(V) complexes

Compounds that contain the anion [MeReO(edt)(SPh)](-) (3-) were synthesized with the countercations 2-picolinium (PicH+3-) and 2,6-lutidinium (LutH+3-), where edt is 1,2-ethanedithiolate. Both PicH+3- and MeReO(edt)(tetramethylthiourea) (4) were crystallographically characterized. The rhenium atom in each of these compounds exists in a five-coordinate distorted square pyramid. In the solid state, PicH+3- contains an anion with a short (d(SH) = 232 pm) and nearly linear hydrogen-bonded (N-H.S) interaction to the cation. Ligand substitution reactions were studied in chloroform. Displacement of PhSH by PPh(3) follows second-order kinetics, d[MeReO(edt)(PPh(3))]/dt = k[PicH+3-][PPh3], whereas with pyridines an unusual form was found, d[MeReO(edt)(Py)]/dt = k[PyH+3-][Py](2), in which the conversion of PicH+3- to PyH+3- has been incorporated. Further, added Py accelerates the formation of [MeReO(edt)(PPh3)], v = k.[PicH+3-].[PPh3].[Py]. Compound 4, on the other hand, reacts with both PPh(3) and pyridines, L, at a rate given by d[MeReO(edt)(L)]/dt = k.[4].[L]. When PicH+3- reacts with pyridine N-oxides, a three-stage reaction was observed, consistent with ligand replacement of SPh(-) by PyO, N-O bond cleavage of the PyO assisted by another PyO, and eventual decomposition of MeRe(O)(edt)(OPy) to MeReO(3). Each of first two steps showed a large substituent effect; Hammett analysis gave rho(1) = -5.3 and rho(2) = -4.3.     

Ligand-enabled oxidation of gold(i) complexes with o-quinones

Chelating P^P and hemilabile P^N ligands were found to trigger the oxidation of Au(i) complexes by o-benzoquinones. The ensuing Au(iii) catecholate complexes have been characterized by NMR spectroscopy, single crystal X-ray diffraction and X-ray absorption spectroscopy. They adopt tetracoordinate square-planar structures. Reactivity studies substantiate the reversibility of the transformation. In particular, the addition of competing ligands such as chloride and alkenes gives back Au(i) complexes with concomitant release of the o-quinone. DFT calculations provide insight about the structure and relative stability of the Au(i) o-quinone and Au(iii) catecholate forms, and shed light on the 2-electron transfer from gold to the o-quinone.

Chelating P^P and hemilabile P^N ligands were found to trigger the oxidation of Au(i) complexes by o-benzoquinones.     

Metal oxidation promoted C-H activation in manganese complexes of N-confused porphyrin

The N-confused porphyrin complex Mn(II)(NCHPP)Br exhibits a nonplanar porphyrin ring with an inner core C-H on the inverted pyrrole ring. The aerobic metal oxidation promotes the dissociation of an inner-core proton on the inverted pyrrole ring and changes the N-confused porphyrin conformation to a planar porphyrin ring to form Mn(III)(NCPP)Br. The conjugate systems and metal oxidation states are confirmed by crystal structures as well as spectroscopic data. The reverse reaction can be achieved by treating the Mn(III)(NCPP)Br with p-toluenesulfonhydrazide.     

Allylation and oxidation reactions promoted by cobalt(II) complexes

Two examples of radical reactions involving cobalt complexes are described. The first one concerns the reactions of allylcobaloximes with 2-bromo 2-phenylacetonitriles leading to the corresponding monoallyl derivatives. It is shown that both the rate and regioselectivity of the reactions are affected by the nature of the substituents on the phenyl group: electron-withdrawing groups give higher rates and highly regiospecific reactions. The second type of radical reaction which finds useful synthetic applications is the oxidation of phenols by 02 catalyzed by Schiff base cobalt complexes. By choosing carefully the catalyst and the solvent, these oxidations can be highly selective, quinones being the major oxidation products in most cases.     

Novel modified chiral NiII complexes with the Schiff bases of (E)-and (Z)-2-aminobut-2-enoic acids: Synthesis and study

Ni^II complexes with the Schiff bases of (E)-and (Z)-2-aminobut-2-enoic acids were obtained with (S)-N-(2-benzoylphenyl)-1-(2-chlorobenzyl)pyrrolidine-2-carboxamide and (S)-N-(2-benzoylphenyl)-1-(3,4-dimethylbenzyl)pyrrolidine-2-carboxamide as new chiral auxiliaries. Asymmetric addition of nucleophiles to the C=C bond of these complexes was studied. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 428–435, March, 2006.     

Syntheses and oxidation of methyloxorhenium(V) complexes with tridentate ligands

Four new methyloxorhenium(V) compounds were synthesized with these tridentate chelating ligands: 2-mercaptoethyl sulfide (abbreviated HSSSH), 2-mercaptoethyl ether (HSOSH), thioldiglycolic acid (HOSOH), and 2-(salicylideneamino)benzoic acid (HONOH). Their reactions with MeReO(3) under suitable conditions led to these products: MeReO(SSS), 1, MeReO(SOS), 2, MeReO(OSO)(PAr(3)), 3, and MeReO(ONO)(PPh(3)), 4. These compounds were characterized spectroscopically and crystallographically. Compounds 1 and 2 have a five-coordinate distorted square pyramidal geometry about rhenium, whereas 3 and 4 are six-coordinate compounds with distorted octahedral structures. The kinetics of oxidation of 2 and 3 in chloroform with pyridine N-oxides follow different patterns. The oxidation of 2 shows first-order dependences on the concentrations of 2 and the ring-substituted pyridine N-oxide. The Hammett analysis of the rate constants gives a remarkably large and negative reaction constant, rho = -4.6. The rate of oxidation of 3 does not depend on the concentration or the identity of the pyridine N-oxide, but it is directly proportional to the concentration of water, both an accidental and then a deliberate cosolvent. The mechanistic differences have been interpreted as reflecting the different steric demands of five- and six-coordinate rhenium compounds.     

Metal complexes of 2-acetylpyridine N(4)-dihexyl- and N(4)-dicyclohexylthiosemicarbazones

Summary 2-Acetylpyridine N(4)-dihexyl- and N(4)-dicyclohexylthiosemicarbazone, HAc4DHex and HAc4DCHex, respectively, and Fe^III, Co^II, Co^III, Ni^II, Cu^II and Zn^II complexes have been prepared and characterized by molar conductivities, magnetic susceptibilities and spectroscopic techniques. For many of the complexes, loss of the N(2)H hydrogen occurs, and the ligands coordinate to the metal centres as NNS monoanionic, tridentate ligands, e.g., [M(NNS)X] (M = Co^II, Ni^II, Cu^II, NNS = Ac4DHex or Ac4DCHex and X = Cl or Br), [Fe(NNS)₂]ClO₄, [Co(NNS)₂]BF₄, [Cu(NNS)NO₃] and [Zn(NNS)OAc]. Zn^II ion is also chelated by neutral ligands in [Zn(HNNS)X₂] (X = Cl, Br). In addition, [Ni(Ac4DHex)-(HAc4DHex)]X (X = BF₄, ClO₄) and [Ni(HAc4DCHex)₂]-(BF₄)₂ are reported where the neutral thiosemicarbazone is coordinated via the pyridyl nitrogen, azomethine nitrogen and thione sulfur. Crystal structure determinations of HAc4DCHex and [Cu(Ac4DHex)Br] show the former to contain the bifurcated hydrogen bonded form and the latter to be planar with no significant interaction between neighbouring centres.