Synthesis, structure and electrochemistry of Fischer alkoxy- and aminocarbene complexes of tungsten : the use of DFT to predict and understand oxidation and reduction potentials

Reactions of Fischer alkoxycarbene complexes [W(CO)5{C(OEt)Ar}], Ar = thienyl (1) or furyl (2), with ethylene diamine lead to the formation of two different reaction products: an aminolysis product (5 or 6) where the ethoxy substituent of the carbene ligand is replaced by the ethylene diamine moiety, as well as a chelated product where aminolysis and substitution of one carbonyl ligand had taken place, yielding 7 or 8. Aminolysis of 1 and 2 with cyclohexyl amine (CHA) produced the aminocarbene complexes 3 (Ar = thienyl) and 4 (Ar = furyl). Complexes 1-8 are electrochemically investigated by means of cyclic voltammetry. The relative shifts in the oxidation and reduction potentials are discussed and related to density functional theory (DFT) calculated energies. DFT calculations further show that the oxidation center is located on the metal and the carbonyl groups, while the reduction center is localized on the carbene moiety and is strongly influenced by the electronic properties of its substituents. Crystal structures of 1-4, 6 and 8 are reported.Norwegian Supercomputing Program (NOTUR) through a grant of computer time (Grant No. NN4654K) (J.C.), the South African National Research Foundation (J.C.) and the Central Research Fund of the University of the Free State, Bloemfontein (J.C.), and the University of Pretoria (M.L. and P.H.v.R.).http://pubs.acs.org/journal/orgnd7hb201

Consequences of electron-density manipulations on the X-ray photoelectron spectroscopic properties of ferrocenyl-β-diketonato complexes of manganese(III). structure of [Mn(FcCOCHCOCH3)3]

Reaction of [Mn3(OAc)6O·3H2O](+) (1) with ferrocenyl β-diketones of the type FcCOCH2COR with R = CF3 (2a) and CH3 (2b), Ph = C6H5 (2c), and Fc = Fe(II)(η(5)-C5H4)(η(5)-C5H5) (2d) yielded a series of ferrocene-functionalized β-diketonato manganese(III) complexes 3a-3d, respectively, of general formula [Mn(FcCOCHCOR)3]. The mixed-ligand β-diketonato complex [Mn(FcCOCHCOFc)2(FcCOCHCOCH3)] (4) was obtained by reacting mixtures of diketones 2b and 2d with 1. A single-crystal X-ray structure determination of 3b (Z = 2, triclinic, space group P1̅) highlighted a weak axial elongating Jahn-Teller effect and a high degree of bond conjugation. An X-ray photoelectron spectroscopic study, by virtue of linear relationships between group electronegativities of ligand R groups, χR, or ∑χR, and binding energies of both the Fe 2p3/2 and Mn 2p3/2 photoelectron lines, confirmed communication between molecular fragments of 2a-2d as well as 3a-3d. This unprecedented observation allows prediction of binding energies from known β-diketonato side group χR values.J.C.S. acknowledges the NRF (Grant 2054243) and the UFS for financial support. Financial support from Syngaschem BV, The Netherlands, and the UFS is also gratefully acknowledged (B.E.B., E.E., and J.C.S.).http://pubs.rsc.org/en/journals/journalissues/ic2017-03-31hb2016Chemistr

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

Tetrabenzoporphyrin and -mono-, - Cis -di- and tetrabenzotriazaporphyrin derivatives: Electrochemical and spectroscopic implications of meso CH Group replacement with nitrogen

Nonperipherally hexyl-substituted metal-free tetrabenzoporphyrin (2H-TBP, 1a) tetrabenzomonoazaporphyrin (2H-TBMAP, 2a), tetrabenzo-cis-diazaporphyrin (2H-TBDAP, 3a), tetrabenzotriazaporphyrin (2H-TBTAP, 4a), and phthalocyanine (2H-Pc, 5a), as well as their copper complexes (1b-5b), were synthesized. As the number of meso nitrogen atoms increases from zero to four, Îmax of the Q-band absorption peak becomes red-shifted by almost 100 nm, and extinction coefficients increased at least threefold. Simultaneously the blue-shifted Soret (UV) band substantially decreased in intensity. These changes were related to the relative electron-density of each macrocycle expressed as the group electronegativity sum of all meso N and CH atom groups, âχR. X-ray photoelectron spectroscopy differentiated between the three different types of macrocyclic nitrogen atoms (the Ninner, (NH)inner, and Nmeso) in the metal-free complexes. Binding energies of the Nmeso and Ninner,Cu atoms in copper chelates could not be resolved. Copper insertion lowered especially the cathodic redox potentials, while all four observed redox processes occurred at larger potentials as the number of meso nitrogens increased. Computational chemical methods using density functional theory confirmed 1b to exhibit a Cu(II) reduction prior to ring-based reductions, while for 2b, Cu(II) reduction is the first reductive step only if the nonperipheral substituents are hydrogen. When they are methyl groups, it is the second reduction process; when they are ethyl, propyl, or hexyl, it becomes the third reductive process. Spectro-electrochemical measurements showed redox processes were associated with a substantial change in intensity of at least two main absorbances (the Q and Soret bands) in the UV spectra of these compounds

Properties of manganese(III) ferrocenyl-β-diketonato complexes revealed by charge transfer and multiplet splitting in the Mn 2p and Fe 2p X-ray photoelectron envelopes

A series of ferrocenyl-functionalized β-diketonato manganese(III) complexes, [Mn(FcCOCHCOR)3] with R = CF3, CH3, Ph (phenyl) and Fc (ferrocenyl) was subjected to a systematic XPS study of the Mn 2p3/2 and Fe 2p3/2 core-level photoelectron lines and their satellite structures. A charge-transfer process from the β-diketonato ligand to the Mn(III) metal center is responsible for the prominent shake-up satellite peaks of the Mn 2p photoelectron lines and the shake-down satellite peaks of the Fe 2p photoelectron lines. Multiplet splitting simulations of the photoelectron lines of the Mn(III) center of [Mn(FcCOCHCOR)3] resemble the calculated Mn 2p3/2 envelope of Mn3+ ions well, indicating the Mn(III) centers are in the high spin state. XPS spectra of complexes with unsymmetrical β-diketonato ligands (i.e., R not Fc) were described with two sets of multiplet splitting peaks representing fac and the more stable mer isomers respectively. Stronger electron-donating ligands stabilize fac more than mer isomers. The sum of group electronegativities, σχR, of the β-diketonato pendant side groups influences the binding energies of the multiplet splitting and charge transfer peaks in both Mn and Fe 2p3/2 photoelectron lines, the ratio of satellite to main peak intensities, and the degree of covalence of the Mn-O bond

Can electrochemical measurements be used to predict X-ray photoelectron spectroscopic data?: the case of Ferrocenyl-β-Diketonato complexes of Manganese(III)

In order to better understand intramolecular communication between molecular fragments, a series of ferrocene-functionalized β-diketonato manganese(III) complexes, [Mn(FcCOCHCOR)3] with R = CF3, 1, CH3, 2, Ph = C6H5, 3, and Fc = FeII(η5-C5H4)(η5-C5H5), 4, the mixed ligand β-diketonato complex [Mn(FcCOCHCOFc)2(FcCOCHCOCH3)], 5, as well as the acac complex [Mn(CH3COCHCOCH3)3], 6, were subjected to an electrochemical and X-ray photoelectron spectroscopy (XPS) study. The ferrocenyl (FeII) and MnIII redox potentials, E°′, and photoelectron lines were sufficiently resolved in each complex to demonstrate a linear correlation between E°′ and group electronegativities of ligand R groups, R, or ςR, as well as with binding energies of both the Fe 2p3/2 and Mn 2p3/2 photoelectron lines. These relationships are consistent with effective communication between molecular fragments of 1-5. From these relationships, prediction of Mn and Fe core electron binding energies in [Mn(R1COCHCOR2)3] complexes from known manganese and/or ferrocenyl redox potentials are, therefore, now possible. Ligand infrared carbonyl stretching frequencies were successfully related to binding energy as a measure of the energy required for inner-sphere reorganization. In particular it became possible to explain why, upon electrochemical oxidation or photoionization, the ferrocenyl FeII inner-shell of 1-5 needs more energy in complexes with ligands bearing electron-withdrawing (CF3) groups than in ligands bearing electron-donating groups such as ferrocenyl. The XPS determined entity Iratio (the ratio between the intensities of the satellite and main metal 2p3/2 photoelectron lines) is an indication not only of the amount of charge transferred, but also of the degree of inner-sphere reorganization. Just as for binding energy, the quantity Iratio was also found to be related to the energy requirements for the inner-sphere reorganization depicted by the vibrational frequency, vco

Properties of Manganese(III) Ferrocenyl-β-Diketonato Complexes Revealed by Charge Transfer and Multiplet Splitting in the Mn 2p and Fe 2p X-Ray Photoelectron Envelopes

A series of ferrocenyl-functionalized β-diketonato manganese(III) complexes, [Mn(FcCOCHCOR)3] with R = CF3, CH3, Ph (phenyl) and Fc (ferrocenyl) was subjected to a systematic XPS study of the Mn 2p3/2 and Fe 2p3/2 core-level photoelectron lines and their satellite structures. A charge-transfer process from the β-diketonato ligand to the Mn(III) metal center is responsible for the prominent shake-up satellite peaks of the Mn 2p photoelectron lines and the shake-down satellite peaks of the Fe 2p photoelectron lines. Multiplet splitting simulations of the photoelectron lines of the Mn(III) center of [Mn(FcCOCHCOR)3] resemble the calculated Mn 2p3/2 envelope of Mn3+ ions well, indicating the Mn(III) centers are in the high spin state. XPS spectra of complexes with unsymmetrical β-diketonato ligands (i.e., R not Fc) were described with two sets of multiplet splitting peaks representing fac and the more stable mer isomers respectively. Stronger electron-donating ligands stabilize fac more than mer isomers. The sum of group electronegativities, ΣχR, of the β-diketonato pendant side groups influences the binding energies of the multiplet splitting and charge transfer peaks in both Mn and Fe 2p3/2 photoelectron lines, the ratio of satellite to main peak intensities, and the degree of covalence of the Mn–O bond

Electrochemical Evidence of Intramolecular Electronic Communication in Zr and Hf Phthalocyanines Bearing Ferrocene-Containing β‑Diketonato Axial Ligands: Structure of [PcHf(FcCOCHCOC₆H₅)₂]

The series of zirconium­(IV) and hafnium­(IV) phthalocyanine complexes [PcM­(FcCOCHCOR)₂] (Pc = phthalocyaninato; M = Zr; R = CF₃ (<b>1</b>), CH₃ (<b>2</b>), C₆H₅ (<b>3</b>), Fc ((C₅H₅)­Fe­(C₅H₄), <b>4</b>), as well as M = Hf ; R = CF₃ (<b>5</b>), CH₃ (<b>6</b>), C₆H₅ (<b>7</b>), and Fc (<b>8</b>)) were synthesized. A single-crystal X-ray diffraction analysis of the structure of [PcHf­(FcCOCHCOC₆H₅)₂], <b>7</b> (<i>Z</i> = 2, space group <i>P</i>1̅), showed the two axial β-diketonato ligands were orientated in such a way that the ferrocenyl groups were positioned diagonally opposite each other. From the structural determination of <b>7</b> it was clear that these complexes have a distorted <i>D</i>_4<i>h</i> symmetry at the coordination site of the metal centers, which explains a splitting of the UV–vis Q band into Q_<i>x</i> and Q_<i>y</i> components with 3 ≤ Δλ_max,Q ≤ 10 nm. Cyclic and square wave voltammetric studies in CH₂Cl₂/[N­(ⁿBu)₄]­[B­(C₆F₅)₄] allowed observation of at least three phthalocyaninato macrocycle-based redox couples as well as all (i.e., two or four) well-resolved ferrocenyl couples in <b>1</b>–<b>8</b>. For M = Zr and R = Fc, formal reduction potentials of the four ferrocenyl groups were found to be <i>E</i>°′ = 296, 386, 538, and 687 mV versus free ferrocene. Spectroelectrochemical evidence, UV–vis Q-band maximum wavelengths, and HOMO–LUMO energy gaps as expressed by Δ<i>E</i>°′_I–III = Δ<i>E</i>°′_wave I – Δ<i>E</i>°′_wave III were mutually consistent, indicating that the first phthalocyaninato ring-based oxidation occurs before ferrocenyl oxidations take place. The potential for each redox process was found to be dependent on the sum of β-diketonato R-group group electronegativities, Σχ_R. Mathematical relationships for the dependency of <i>E</i>°′ on Σχ_R for all four observed ring-based redox processes as well as for the ferrocenyl-based redox processes were determined. This allowed prediction of potentials for redox processes that fall outside the workable potential window of the solvent. No significant differences were found between the corresponding redox potentials of zirconium and hafnium analogues bearing the same axial ligands

Properties of manganese(III) ferrocenyl-β-diketonato complexes revealed by charge transfer and multiplet splitting in the Mn 2p and Fe 2p X-ray photoelectron envelopes

\u3cp\u3eA series of ferrocenyl-functionalized β-diketonato manganese(III) complexes, [Mn(FcCOCHCOR)3] with R = CF3, CH3, Ph (phenyl) and Fc (ferrocenyl) was subjected to a systematic XPS study of the Mn 2p\u3csub\u3e3/2\u3c/sub\u3e and Fe 2p\u3csub\u3e3/2\u3c/sub\u3e core-level photoelectron lines and their satellite structures. A charge-transfer process from the β-diketonato ligand to the Mn(III) metal center is responsible for the prominent shake-up satellite peaks of the Mn 2p photoelectron lines and the shake-down satellite peaks of the Fe 2p photoelectron lines. Multiplet splitting simulations of the photoelectron lines of the Mn(III) center of [Mn(FcCOCHCOR)3] resemble the calculated Mn 2p\u3csub\u3e3/2\u3c/sub\u3e envelope of Mn3+ ions well, indicating the Mn(III) centers are in the high spin state. XPS spectra of complexes with unsymmetrical β-diketonato ligands (i.e., R not Fc) were described with two sets of multiplet splitting peaks representing fac and the more stable mer isomers respectively. Stronger electron-donating ligands stabilize fac more than mer isomers. The sum of group electronegativities, σχR, of the β-diketonato pendant side groups influences the binding energies of the multiplet splitting and charge transfer peaks in both Mn and Fe 2p\u3csub\u3e3/2\u3c/sub\u3e photoelectron lines, the ratio of satellite to main peak intensities, and the degree of covalence of the Mn-O bond.\u3c/p\u3

Synthesis, spectroscopy and electrochemistry in relation to DFT computed energies of ferrocene- and ruthenocene-containing β-diketonato iridium(III) heteroleptic complexes. Structure of [(2-pyridylphenyl)2Ir(RCCOCHCOCH3]

A series of new ferrocene- and ruthenocene-containing iridium(III) heteroleptic complexes of the type [(ppy)2Ir(RCOCHCOR′)], with ppy = 2-pyridylphenyl, R = Fc = FeII(η5-C5H4)(η5-C5H5) and R′ = CH3 (1) or Fc (2), as well as R = Rc = RuII(η5-C5H4)(η5-C5H5) and R′ = CH3 (3), Rc (4) or Fc (5) was synthesized via the reaction of appropriate metallocene-containing β-diketonato ligands with [(ppy)2(μ-Cl)Ir]2. The single crystal structure of 3 (monoclinic, P21/n, Z = 4) is described. Complexes 1–5 absorb light strongly in the region 280−480 nm the metallocenyl β-diketonato substituents quench phosphorescence in 1–5. Cyclic and square wave voltammetric studies in CH2Cl2/[N(nBu)4][B(C6F5)4] allowed observation of a reversible IrIII/IV redox couple as well as well-resolved ferrocenyl (Fc) and ruthenocenyl (Rc) one-electron transfer steps in 1−5. The sequence of redox events is in the order Fc oxidation, then IrIII oxidation and finally ruthenocene oxidation, all in one-electron transfer steps. Generation of IrIV quenched phosphorescence in 6, [(ppy)2Ir(H3CCOCHCOCH3)]. This study made it possible to predict the IrIII/IV formal reduction potential from Gordy scale group electronegativities, χR and/or ΣχR′ of β-diketonato pendent side groups as well as from DFT-calculated energies of the highest occupied molecular orbital of the species involved in the IrIII/IV oxidation at a 98 % accuracy level