Redox behaviour of imino-β-diketonato ligands and their rhodium(I) complexes

The redox behaviour of bidentate (BID) ligands containing either two O donor atoms (O,O’-BID ligand), a N and an O donor atom (N,O-BID ligand) or two N donor atoms (N,N’-BID ligand), and their rhodium complexes, are presented. The experimental reduction potential of the L,L’-BID ligands (L,L’ = N and O) and the experimental oxidation potential of [Rh(L,L’-BID)(CO)(PPh3)] complexes relate linearly. Though, complexes with an aromatic substituent group on the L,L’-BID ligand deviate slightly from the trend, due to the resonance effect through the extended π-system of the latter complexes. The experimental reduction potential of the L,L’-BID ligands relate linearly to the computational chemistry calculated energies of their lowest unoccupied molecular orbitals (LUMOs), whereas the experimental oxidation potential of the [Rh(L,L’-BID)(CO)(PPh3)] complexes related linearly to the computational chemistry calculated energies of their highest occupied molecular orbitals (HOMOs). In the latter relationship it is found that the data points cluster in four groups depending on both the donor atoms (N and O) and the substituent groups (amount of CF3 groups) on the coordinating L,L’-BID ligand

DFT studies of the redox behavior of oligo(aza)pyridines and experimental CVs of 4′-substituted terpyridines

The cyclic voltammograms of a series of substituted terpyridine ligands are presented, showing that reduction occur generally below −2 V versus the redox potential of ferrocene. Density functional theory (DFT) calculated energies and the theoretically calculated reduction potentials of a large series of substituted oligo(aza)pyridine ligands (terpyridine, bipyridine and phenanthroline) are determined and related to experimentally measured reduction potentials. A linear relationship is observed for the reduction potential of tpy ligands and the sum of the Hammett constant of the substituents on the ligands. It was found that the reduction potential of terpyridines relate linearly with various DFT calculated energies. It was further demonstrated that different oligo(aza)pyridines, namely phenanthrolines, bipyridines and the terpyridine ligands of this study, follow the same “reduction potentials – DFT energies” relationships

X-ray and electronic structure of tris(benzoylacetonato-κ2O,O')iron(III)

Solid state crystal data of d5 tris(benzoylacetonato-k2O,O0)iron(III), [Fe(ba)3], are presented. The mer isomer crystallized in the solid state. Density functional theory calculations show that both fac and mer isomers of [Fe(ba)3] can exist. Both fac and mer [Fe(ba)3] are high spin d5 complexes with the same ordering of the d-based molecular orbitals in order of increasing orbital energy, namely dxy < dyz z dxz < dz2 z dx2-y2.South African National Research Foundation (Grant No: 93442) and the Central Research Fund of the University of the Free State, Bloemfontein, South Africa.http://www.elsevier.com/ locate/molstruc2017-11-30hb2016Chemistr

Crystal and electronic structures of tris[4,4,4-Trifluoro-1-(2-X)-1,3-butanedionato]iron(III) isomers (X = thienyl or furyl) : an X-ray and computational study

Please read abstract in the article.Norwegian Supercomputing Program (NOTUR) (Grant No. NN4654K), the South African National Research Foundation and the Central Research Fund of the University of the Free State, Bloemfontein.http://www.elsevier.com/locate/molstruchb2014ai201

Synthesis and structure of novel triphenylarsine-substituted tungsten(0) Fischer carbene complexes

X-ray crystal structure determination, as well as IR and NMR spectroscopy of four novel triphenylarsinesubstituted tetracarbonyl tungsten(0) Fischer carbene complexes of general formula [(CO)4(AsPh3) WC(OEt)(Ar)], with Ar ¼ 2-thienyl (1), 2-furyl (2), 2-(N-methyl)pyrrolyl (3), 2,20 -bithienyl (4), revealed a cis-configuration for the substituted AsPh3 group relative to the carbene ligand for all four novel complexes. All X-ray structures showed that the WeC bond trans AsPh3 < WeC bond trans carbene < WeC bond trans CO. DFT calculations on all possible conformations of each complex due to the different possible positions of the ligands and carbene substituents to each other, correlated with the experimental results.The Norwegian Supercomputing Program (NOTUR) through a grant of computer time (Grant No. NN4654K) (JC), the South African National Research Foundation (JC, ML) and the Central Research Fund of the University of the Free State, Bloemfontein (JC) and the University of Pretoria (ML).http://www.elsevier.com/ locate/molstruc2017-02-28hb2016Chemistr

Electrochemistry of Triphenylarsine-substituted Tungsten(0) Fischer carbene complexes

A combined electrochemical and density functional theory study on four triphenylarsine-substituted tetracarbonyl tungsten(0) Fischer carbene complexes of general formula [(CO)4(AsPh3)WC(OEt)(Ar)], with Ar = 2-thienyl (1), 2-furyl (2), 2-(N-methyl)pyrrolyl (3), 2,20-bithienyl (4), revealed that electrochemical properties for these complexes follow the same trend as analogous pentacarbonyl and triphenylphosphine-substituted tetracarbonyl complexes in literature. The current results made it possible to establish a general trend for Fischer-type W-carbene complexes containing an aryl substituent, namely (largest metal oxidation and largest carbene carbon reduction potential) [(L) (CO)4WC(OEt)(2-thienyl)] > [(L)(CO)4WC(OEt)(2-furyl)] > [(L)(CO)4WC(OEt)(2-(N-methyl)pyrrolyl)] (L = CO, PPh3 or AsPh3).The Norwegian Supercomputing Program (NOTUR) through a grant of computer time (Grant No. NN4654K) (JC), the South African National Research Foundation (JC, ML), the Central Research Fund of the University of the Free State, Bloemfontein (JC) and the University of Pretoria (ML).http://www.elsevier.com/locate/electacta2016-12-31hb2016Chemistr

Fischer mono- and biscarbene complexes of tungsten with mono- and dimeric heteroaromatic substituents

An electrochemical study of a series of mono- and biscarbene complexes of tungsten pentacarbonyl with mono- and dimeric heteroarene substituents are reported and compared in CH3CN and DCM. Results revealed that the order of oxidation (reduction) depends largely on the aryl substituent attached to the carbene carbon (2-thienyl, 2-furyl or 2-(N-methylpyrrolyl)). The order of oxidation (reduction) for monocarbene complexes containing a monomeric heteroarene substituent ((1)–(3)), a dimeric heteroarene substituent ((4)–(6)) or biscarbene complexes connected with a heteroarene substituent ((7)–(9)) is the same, namely 2-thienyl > 2-furyl > 2-(N-methylpyrrolyl). Carbene complexes containing a larger conjugated heteroarene substituent attached to the carbene carbon reduce more easily than the monomeric analogues. Tungsten biscarbene complexes exhibit two separate oxidation potentials for the two metal centres or one large oxidation peak, consistent with the simultaneous oxidation of the two W metal centres.Norwegian Supercomputing Program (NOTUR) through a grant of computer time (Grant No. NN4654K), the South African National Research Foundation, the Central Research Fund of the University of the Free State, Bloemfontein and the University of Pretoria.http://www.elsevier.com/locate/jelechem2016-02-28hb201

Molybdenum(0) Fischer ethoxycarbene complexes : synthesis, x-ray crystal structures and DFT study

The synthesis and structural investigations are presented of molybdenum(0) Fischer carbene complexes with general formula [L(CO)4MoC(OEt)(Ar)] with L = CO, PPh3, AsPh3 and Ar = 2-thienyl, 2-furyl, 2-(N-methyl)pyrrolyl, 2,2’-bithienyl. The X-ray crystal structures, along with NMR and IR spectroscopy, revealed a cis-orientation of the carbene and pnictogen ligands (PPh3 or AsPh3) for all the substituted complexes. A density functional theory study of all possible conformers indicated, in agreement with experimental results, that the cis-isomers (PPh3 or AsPh3 cis relative to the carbene ligand) are more stable than the corresponding trans-isomers, and that most stable conformers have the aryl group syn to the ethoxy group for Ar = 2-thienyl, 2-(N-methyl)pyrrolyl, 2,2’-bithienyl and anti to the ethoxygroup for Ar = 2-furyl.The Norwegian Supercomputing Program (NOTUR) through a grant of computer time (Grant No. NN4654K) (JC), the South African National Research Foundation (JC, ML) and the Central Research Fund of the University of the Free State, Bloemfontein (JC) and the University of Pretoria (ML).http://www.elsevier.com/locate/poly2018-01-31hb2017Chemistr

Electrochemical behaviour and structure of novel phosphine- and phosphite-substituted tungsten(0) Fischer carbene complexes

tThe electrochemical behaviour of a series of sixteen novel Fischer ethoxy- and aminocarbenecomplexes of the type [(CO)4(PPh3)W = C(X)R] with R = 2-thienyl or 2-furyl and X = OEt or NHCy,(1-4), [(CO)3(dppe)W = C(X)R] with R = 2-thienyl or 2-furyl and X = OEt or NHCy, (5-8) (dppe = 1,2-bis(diphenylphosphino)ethane) and [(CO)4P(OPh)3W = C(X)R] with R = 2-thienyl or 2-furyl and X = OEtor NHCy, (9-12) is investigated by means of cyclic voltammetry. The complexes all exhibit a two-electronoxidation process that is W-based and a one-electron reduction that is mainly localized on the carbeneligand. Complexes 1-4 and 9-12 are considerably more difficult to oxidize than 5-8 due to the better -acceptor ability of the (CO)4(PR 3) (R = Ph or OPh) ligand combination than that of (CO)3(dppe). Den-sity functional theory calculations on the neutral, reduced and oxidized complexes confirmed the role ofthe frontier orbitals in the oxidation and reduction processes and enabled formulation of mathematicalrelationships that can be used to predict experimental measured potentials. X-ray crystal structures of2cis, 3 and 5 are discussed.http://www.elsevier.com/locate/electactahb201

UV-Vis Spectroscopy, Electrochemical and DFT Study of Tris(β-diketonato)iron(III) Complexes with Application in DSSC: Role of Aromatic Thienyl Groups

A series of tris(β-diketonato)iron(III) complexes, with the β-diketonato ligand bearing different substituent groups, have been synthesized and characterized by Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis) and mass spectroscopic methods. The maximum band UV-Vis absorption wavelengths of the tris(β-diketonato)iron(III) complexes were in the range of 270–380 nm. The complexes have very good solubility in various solvents such as chloroform, dichloromethane, ethyl acetate, tetrahydrofurane, dimethylsulphoxide and dimethylformamide. After the syntheses and characterization processes, spectroscopic and electrochemical properties of these tris(β-diketonato)iron(III) complexes were investigated. A density functional theory (DFT) study related to the spectroscopic and electrochemical properties of the tris(β-diketonato)iron(III) complexes was used to investigate the possible application of these complexes as dye sensitizers or redox mediators in dye-sensitized solar cells