Eduardo J. S. Vichi

Photolytic preparation of (benzylideneacetone)-carbonylphosphineiron(0) complexes: the molecular structures of Fe(CO)2(PEt3)(bda) and Fe(CO)2(PPhMe2)(bda)(bda=benzylideneacetone)

Abstract The (benzylideneacetone) carbonylphosphine iron(0) complexes, Fe(CO)2L(bda), Fe(CO)L′2(bda) and Fe(CO)(dpe)(bda)(L = PEt3, PPhMe2, Me; L′ = PPhMe2, PPh2Me; dpe = [Ph2P(CH2)]2) have been prepared by irradiating the corresponding tetracarbonylmonophosphine iron(0), tricarbonyldiphosphine iron(0) or tricabonyl-1,2-bis (diphenylphosphine)ethane iron(0) complexes in benzene in the presence of benzylideneacetone. The X-ray crystal structures of the complexes with L = PEt3 (A) and PPhMe2 (B) have been determined, and show that the Fe atom adopts a distorted octahedral coordinated geometry in which three of the sites are occupied by the bda ligand. The bond parameters in the bda ligand suggest that this coordinated group is intermediate between its ground and first excited states. The complex Fe(CO)2(PEt3(bda) crystallises in the monoclinic space group P2l/c with a 10.203(3), b 12.964(4), c 16.960(6) A, β 120.00(2)°, and Z = 4. The structure was solved by a combination of Patterson and Fourier diffence techniques and refined by blocked full matrix least squares to R = 0.035 for 3351 unique observed diffratometer data. The complex Fe(CO)2(PPhMe2)(bda) also crystallises in space group P2l/c, with a 8.134(3), b 21.394(8), c 11.658(5) A, β 108.18(2)° and Z = 4. The structure was solved and refined as above to R = 0.036 for 3498 diffractometer data. The IR and 1H NMR data for all the complexes studied agree with the observed structures.

Carbon dioxide hydrogenation over iron containing catalysts

Abstract Iron silicalite samples with a different degree of crystallinity have been synthesized and characterized. Reduced samples were then tested as catalysts for carbon dioxide hydrogenation. It is observed that whenever the zeolitic phase is present, reduction of the iron species is strongly encumbered. As a consequence, over such catalysts the reverse water-gas shift reaction occurs specifically while formation of hydrocarbons does not occur. This is attributed to the lack of formation of surface carbidic species which appear to be responsible for the hydrocarbon formation.

PREPARATION, CHARACTERIZATION AND ELECTROCHEMICAL STUDIES OF 1,1'-BIS( DIPHENYLPHOSPHINO)FERROCENE (DPPF) DERIVATIVES. CRYSTAL STRUCTURE OF DPPFCO(NO) 2 SBF6

Abstract The neutral dppfFe(NO)2 (1), the novel cationic [dppfCo(NO)2][SbF6] (2), as well as the dppfFe(CO)3 (3) dppf = 1,1′-bis-(diphenylphosphino)ferrocene) complexes were prepared and characterized. The interaction between the two metallic centers through the dppf ligand was studied in the solid state by 57Fe Mossbauer spectroscopy and in solution by cyclic voltammetry. The Mossbauer parameters are compared with those of other dppfMLn, complexes. Electrochemical studies performed on these complexes show the great influence of the MLn moiety on the redox processes of the dppf iron center. The crystal structure of complex 2 was determined (C34H28CoF6FeN2O2P2Sb). The compound crystallizes in the triclinic, space group P 1 , a = 10.441(2), b = 10.755(2), c = 17.320(5) A , α = 104.10(2), β = 0.504(10), γ = 111.504(10)°, U = 1744.7(7) A 3 , Z = 2, R = 0.0765, wR2 = 0.1878 . In this complex, the cobalt atom is coordinated to two nitrosyl ligands and to phosphorus atoms of the dppf ligand, providing a distorted tetrahedral geometry.

Electron paramagnetic resonance study of chromosilicalite

An electron paramagnetic resonance (EPR) study of crystalline chromosilicalite has been presented with the purpose of characterization of the distribution of Cr3+sites in the solid. In addition, a deconvolution process is described whereby the EPR parameters can be analysed.

Kinetics and mechanisms of dissociation of tris(2,2′-bipyridine)iron(II) complex in aqueous salts solutions

Abstract The pseudo first order rate of acid hydrolysis of the complex cation Fe(bipy) 3 2+ , has been determined in aqueous solutions of varying concentrations of LiCl, NaCl, KCl, Nh 4 Cl, NaBr, KBr, NH 4 Br, MgCl 2 , CaCl 2 , SrCl 2 , BaCl 2 , and MgBr 2 at 20.0, 25.0, and 30.0 °C in the presence of 0.012 mol kg −1 HCl, to avoid reformation of the complex. The rate rises with the salt concentration, reaching a maximum at ca. 0.5 to 1 mol kg −1 in chloride and ca. 0.3 mol kg −1 for bromide. Afterwards a linear decrease occurs with different slopes, which depends on the cation and anion involved. These trends are ascribed to the removal of water molecules from the bulk solvent by incorporation in the hydration shells of the cations of the salts and to ion-pair formation.

Kinetics and mechanisms of dissociation of metal chelates. II. The acid-catalyzed dissociation of tris(pyridine-2-acetaldehyde-N-Methylimine)iron(II)☆☆☆

Abstract The kinetics of the acid-catalyzed dissociation of tris(pyridine-2-acetaldehyde-N-Methylimine)iron(II) were investigated photometrically in 2 M HClLiCl mixtures, ranging from 2 × 10 −5 to 2 M in HCl. The rate of dissociation was shown to be first order in complex. Experimental rate data are in agreement with a mechanism previously suggested for related iron-diimine complexes with unsymmetric ligands. The mechanism consists of two simultaneous reaction paths differing by the sequence in which the bonds between the metal atom and the two different moieties of the ligand are broken. Values for the rate constants and activation parameters of the rate-determininig step were estimated and compared with the values reported for related iron-diimine complexes. The influence of the methyl group, present in the chromophore, on the bonding ability of the ligand is discussed on the basis of these values.

Synthesis and electrochemical characterization of bimetallic ruthenium complexes with the bridging eta2( s,s )-1,3-butadiyne-1,4-diyl ligand

The bis(ruthenium)alkyne complex [cis-{RuCl (bpy)2(m-CoC-)}]2 (1) was obtained by treatment of 1 equiv of either 1,4-bis(trimethylsilyl)-1,3-butadiyne or bis(trimetylsilyl)acetylene with 2 equiv of cis-[RuCl2(bpy)2].2H2O, NaF and NaBF4 salts in methanol/CH2Cl2 mixture (10/1) in 52% and 35% yields, respectively. 1H, 13C{H} NMR and principally electrochemical analyses confirmed that the same product was obtained from the two reactions. Cyclic voltammetric analyses of (1) from 0 to 1.20 V displays two one-electron quasi-reversible oxidation peaks attributed to the Ru(II)/Ru(III) couple. The redox processes are separated by 520 mV, indicating a significant electronic communication between the two metallic centers.

(Sorbic acid)Fe(CO)2L complexes with L=CO, P(OPh)3, PPh3, and PEt3. Photolytic preparation, spectral properties, and bonding

Abstract The (sorbic acid)Fe(CO) 2 L complexes, with L = CO, P(OPh) 3 , PPh 3 and PEt 3 , have been prepared by irradiating the corresponding Fe(CO) 4 L compounds in benzene in the presence of sorbic acid. The Mossbauer spectra are compatible with the structure of a tetragonal pyramid with the iron(0) atom located in the center of the base. The values of the isomer shift, δ, seem to indicate that d π -L π ★ back bonding is predominant for L = CO, significant for L = P(OPh) 3 , and negligible for L = PPh 3 and PEt 3 . The order of decrease of the frequencies ν(CO) of the coordinated sorbic acid parallels the order of increase of the σ-donor ability of L.

Effects of the ligands on the electrochemical oxidation of (benzylydeneacetone)Fe(CO)2L, with L = CO, phosphines and phosphites

Abstract Half-peak oxidation potentials, E p/2 ox were obtained for two congeneric series of (BDA)Fe(CO) 2 L (BDA=(C 6 H 5 )CHCHC(O)CH 3 , benzylideneacetone) complexes, one with L=CO, phosphites and the other with L=phosphites. Correlations of the E p/2 ox data with ligand parameters such as Giering electronic parameter, χ d , for the phosphorus ligands, and Mossbauer isomer shifts, − δ , and quadrupole splittings, Δ E q , for the iron atom are presented. These correlations helped to describe and quantify the electronic effects of the phosphorous ligands on the Lewis acid iron(0) center. Transmission of these effects to the BDA ligand throughout the metal center was also examined. The results support the idea that d π L π* back bonding is predominant for L=CO, significant for L=phosphites, and small for L=phosphines.

INTRAZEOLITE METAL CARBONYL KINETICS : 12CO SUBSTITUTION IN MO(12CO)6-NA56Y BY PME3 AND 13CO

The first kinetic study is reported for archetypical substitution reactions of PMe3 and 13CO with the well defined intrazeolite system, Mo(12CO)6-Na56Y, for which excellent isosbestic points and first order behaviour are obtained, the activation parameters indicate a highly ordered ‘supramolecular’ transition state consisting of activated Mo(12CO)6 and PMe3 or 13CO all anchored to the Na+ ions in the α-cage of the host lattice.