Structure and bonding in the d4/d3 alkyne redox pairs [WX(CO)(MeCCMe)Tp′]z (X = F, Cl, Br and I; z = 0 and 1): halide stabilisation of electron deficient metal alkyne complexes

Bartlett, Ian M.; Carlton, Susannah; Connelly, Neil G.; Harding, David J.; Hayward, Owen D.; Orpen, A. Guy; Ray, Christopher D.; Rieger, Philip H.

doi:10.1039/a907912b

Cited by 18 publications

(8 citation statements)

References 5 publications

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“…The second line of this doublet overlaps with the g y signal, for which a smaller coupling constant A F = 60 G is estimated. These ESR data agree well with those reported for the d 3 tungsten derivative Tp*W(CO)(MeCCMe)F •+ , where the three hyperfine A F coupling constants (A 1 = 108 G, A 2 = 22 G, A 3 = 18 G) have been estimated . Hyperfine coupling with the phosphorus nuclei in 1 + was not observed.…”

Section: Resultssupporting

confidence: 90%

“…This is in accord with the computational findings, and consistent with a decrease of the Fe(d π )−Cl(p π ) electron repulsion (see below). A similar trend was also noted for the Cp*Fe(dppe) frameworks in the Fe(I/II) Cp*Fe(dppe) 0/+ and Fe(II/III) Cp*Fe(dppe)(C⋮C-1,4-C 6 H 4 NO 2 ) 0/+ pairs, for which the crystal structures of both members of each couple have been determined. 25e, Oxidatively induced M−Cl bond shortenings were also seen for Tp*W(CO)Cl(MeCCMe) 0/+ (0.09 Å), ReCl(CN t Bu) 3 (PCy 3 ) 2 0/+ (0.18 Å), and CpMoCl 2 (PMe 3 ) 2 0/+ (0.1 Å) …”

Section: Resultssupporting

confidence: 64%

“…However, this is not always true. For instance, several authors have clearly demonstrated that the order F - > Cl - > Br - > I - is characteristic of anion affinity for cationic, coordinatively unsaturated Rh(I), Pd(II), and W(II) moieties in media of low polarity.…”

Section: Resultsmentioning

confidence: 99%

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Theoretical, Thermodynamic, Spectroscopic, and Structural Studies of the Consequences of One-Electron Oxidation on the Fe−X Bonds in 17- and 18-Electron Cp*Fe(dppe)X Complexes (X = F, Cl, Br, I, H, CH₃)

et al. 2001

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The compounds Cp*Fe(dppe)X ([Fe]X) and the corresponding cation radicals [Fe*]X*+ are available for the series X = F, Cl, Br, I, H, CH3. This has allowed for a detailed investigation of the dependence of the nature of Fe-X bonding on the identity of X and the oxidation state (charge) of the complex. Cyclic voltammetry demonstrates that the electrode potentials for the [Fe]X0/+ couples decrease in the order I > Br > Cl > H > F > CH3. An "inverse halide order" is seen, in which the most electronegative X leads to the most easily oxidized complex. This suggests that F is the best donor among the halides. The halide trend is also reflected in NMR spectroscopic data. Mössbauer spectroscopy data also suggest that the F ligand is a strong donor (relative to H and CH3) in [Fe*]X*+. DFT calculations on CpFe(dpe)X ([Fe]X) model complexes nicely reproduce the trend in the electrode potentials for the [Fe*]X0/+ couples. Analysis of the theoretical data within the halogen series indicates that the energy of the [Fe]X HOMO does not correlate with the extent of its Fe(d(pi))-X(p(pi)) antibonding character, which varies in the order I > Br > Cl > F, but rather depends on the destabilizing electrostatic effect caused by X. This effect varies in the order F > Cl > Br > I. A thermochemical cycle that incorporates the [Fe*]X0/+ and [Fe*]0/+ electrode potentials was used to investigate the effect of the oxidation state of the complex on the homolytic bond dissociation energy (BDEhom), defined for the processes Fe-X --> Fe* + X* and Fe-X*+ --> Fe*+ + X*. For all X, it was found that a one-electron oxidation leads to a weakening of the Fe-X bond. This trend was reproduced by the DFT calculations. On the other hand, IR nu(Fe-X) spectroscopy data showed an increase in the stretching frequencies for X = H and Cl upon oxidation. X-ray crystallographic data showed a shortening of the Fe-Cl bond upon oxidation. The trends in IR and Fe-Cl bond distances were reproduced in the DFT calculations. The combined data therefore suggest that oxidation leads to weaker, but shorter, Fe-X bonds. A second thermochemical cycle was applied to investigate the effect of the one-electron oxidation on the heterolytic bond dissociation energies (BDEhet), defined for the processes Fe-X --> Fe+ + X- and Fe-X*+ --> Fe2+ + X-. In this case, the oxidation led to bond strengthening in all cases. The computed BDE values have been analyzed within Ziegler's transition state methodology and decomposed into two components, one electrostatic and one covalent, describing the interaction between the unrelaxed fragments. In all the computed BDEhom and BDEhet values of the [Fe]X models the electrostatic component is important. This helps to understand their respective variations upon oxidation.

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Section: Resultssupporting

confidence: 90%

Section: Resultssupporting

confidence: 64%

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Theoretical, Thermodynamic, Spectroscopic, and Structural Studies of the Consequences of One-Electron Oxidation on the Fe−X Bonds in 17- and 18-Electron Cp*Fe(dppe)X Complexes (X = F, Cl, Br, I, H, CH₃)

et al. 2001

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“…Intramolecular oxidation of W II by the terminal carbeniumc entre could lead to ab iradical or triplet state which is NMR silent. [15,[34][35][36] The existence of at ungsten-based S = 1/2 system was confirmed by an EPR experiment. The Xb and spectrum in solution (see Supporting Information, Figure S1) displayed ani sotropic hyperfine coupling A I = 26 10 À4 cm À1 to 127 I( I = 5/2, 100 %) centreda t< g > = 2.003, while signs for an additional organic radicalw ere missing.…”

Section: Cyclization Mechanismmentioning

confidence: 78%

Facile Synthesis of a Stable Side‐on Phosphinyne Complex by Redox Driven Intramolecular Cyclisation

Lange

Schröder

Oberem

et al. 2020

Chemistry A European J

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Alkyne complexes with vicinal substitution by a Lewis acid and a Lewis base at the coordinated alkyne are prospective frustrated Lewis pairs exhibiting a particular mutual distance and, hence, a specific activation potential. In this contribution, investigations on the generation of a WII alkyne complex bearing a phosphine as Lewis base and a carbenium group as Lewis acid are presented. Independently on potential substrates added, an intramolecular cyclisation product was always isolated. A subsequent deprotonation step led to an unprecedented side‐on λ5‐phosphinyne complex, which is interpreted as highly zwitterionic according to visible absorption spectroscopy supported by TD‐DFT. Low‐temperature 31P NMR and EPR spectroscopic measurements combined with time‐dependent IR‐spectroscopic monitoring provided insights in the mechanism of the cyclisation reaction. Decomposition of the multicomponent IR spectra by multivariate curve resolution and a kinetic hard‐modelling approach allowed the derivation of kinetic parameters. Assignment of the individual IR spectra to potential intermediates was provided by DFT calculations.

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“…Insight into the structure and bonding of metal alkyne complexes has also been gained by systematic study of their redox properties. In particular, the ramifications of changes in both formal d-electron count and the number of electrons donated by the alkyne ligands across a series of complexes have been elegantly probed. − These studies demonstrate that alkyne ligands are extremely flexible in the bonding modes that they can adopt within the coordination sphere of metals: a property that may enhance their reactivity . As well as providing insight into the electronic structure of metal alkyne complexes, one-electron-transfer reactions may also initiate some interesting intramolecular ligand couplings.…”

Section: Introductionmentioning

confidence: 99%

One-Electron Reduction of Molybdenum η²(4e)-Alkyne Complexes as a Pathway to the η²(3e) Vinyl Ligand

et al. 2007

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Reaction of the molybdenum alkyne complex [Mo(P{OMe}3)2(η2{4e}-PhC2Ph)(η5-C5H5)][BF4] with K[Fe(CO)2(η5-C5H5)] results in the formation of the η2(3e)-vinyl complex and [Fe(CO)2(η5-C5H5)]2. A study of the reaction by EPR spectroscopy implies that the reaction proceeds via [Mo(P{OMe}3)2(η2{4e}-PhC2Ph)(η5-C5H5)], which is then thought to undergo a hydrogen-abstraction reaction to give the observed product. The same radical was observed in the reaction of [Mo(P{OMe}3)2(η2{4e}-PhC2Ph)(η5-C5H5)][BF4] with LiBEt3H, implying the presence of an alternative mechanistic pathway to the direct addition of hydride to the molybdenum alkyne complex.

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Structure and bonding in the d4/d3 alkyne redox pairs [WX(CO)(MeCCMe)Tp′]z (X = F, Cl, Br and I; z = 0 and 1): halide stabilisation of electron deficient metal alkyne complexes

Cited by 18 publications

References 5 publications

Theoretical, Thermodynamic, Spectroscopic, and Structural Studies of the Consequences of One-Electron Oxidation on the Fe−X Bonds in 17- and 18-Electron Cp*Fe(dppe)X Complexes (X = F, Cl, Br, I, H, CH₃)

Theoretical, Thermodynamic, Spectroscopic, and Structural Studies of the Consequences of One-Electron Oxidation on the Fe−X Bonds in 17- and 18-Electron Cp*Fe(dppe)X Complexes (X = F, Cl, Br, I, H, CH₃)

Facile Synthesis of a Stable Side‐on Phosphinyne Complex by Redox Driven Intramolecular Cyclisation

One-Electron Reduction of Molybdenum η²(4e)-Alkyne Complexes as a Pathway to the η²(3e) Vinyl Ligand

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Structure and bonding in the d4/d3 alkyne redox pairs [WX(CO)(MeCCMe)Tp′]z (X = F, Cl, Br and I; z = 0 and 1): halide stabilisation of electron deficient metal alkyne complexes

Cited by 18 publications

References 5 publications

Theoretical, Thermodynamic, Spectroscopic, and Structural Studies of the Consequences of One-Electron Oxidation on the Fe−X Bonds in 17- and 18-Electron Cp*Fe(dppe)X Complexes (X = F, Cl, Br, I, H, CH3)

Theoretical, Thermodynamic, Spectroscopic, and Structural Studies of the Consequences of One-Electron Oxidation on the Fe−X Bonds in 17- and 18-Electron Cp*Fe(dppe)X Complexes (X = F, Cl, Br, I, H, CH3)

Facile Synthesis of a Stable Side‐on Phosphinyne Complex by Redox Driven Intramolecular Cyclisation

One-Electron Reduction of Molybdenum η2(4e)-Alkyne Complexes as a Pathway to the η2(3e) Vinyl Ligand

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Product

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Theoretical, Thermodynamic, Spectroscopic, and Structural Studies of the Consequences of One-Electron Oxidation on the Fe−X Bonds in 17- and 18-Electron Cp*Fe(dppe)X Complexes (X = F, Cl, Br, I, H, CH₃)

Theoretical, Thermodynamic, Spectroscopic, and Structural Studies of the Consequences of One-Electron Oxidation on the Fe−X Bonds in 17- and 18-Electron Cp*Fe(dppe)X Complexes (X = F, Cl, Br, I, H, CH₃)

One-Electron Reduction of Molybdenum η²(4e)-Alkyne Complexes as a Pathway to the η²(3e) Vinyl Ligand