Models for the Molybdenum(VI/V) Centers of the Molybdenum Hydroxylases and Related Enzymes. Geometry, Electronic Structure, and EPR g-Tensor Predictions from ab Initio and Semiempirical Molecular Orbital Studies

Peng, Gang; Nichols, Jeff; McCullough, E. A.; Spence, J. T.

doi:10.1021/ic00091a029

Cited by 41 publications

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“…The spectra were simulated with the general spin Hamiltonian in Equation (1) with two equivalent nuclei: [31] Geometries were fully optimized as minima at the b3-lyp level [32] by using the Turbomole TZVP basis [30c,f] (small-core pseudopotential [30c,e] on Rh or Ir). EPR parameters [33] were calculated with the ADF [34] program system by using the bp86 [35] functional with the ZORA/TZP basis set supplied with the program (all electron, core double zeta, valence triple zeta polarized basis set on all atoms), using the coordinates from the structures optimized in Turbomole as input. Orbital and spin density plots were generated with Molden.…”

Section: Methodsmentioning

confidence: 99%

Intervalent Bis(μ‐aziridinato)M^IIM^I Complexes (M=Rh, Ir): Delocalized Metallo‐Radicals or Delocalized Aminyl Radicals?

Tejel

Ciriano

Passarelli

et al. 2008

Chemistry A European J

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Reactions of the methoxo complexes [{M(mu-OMe)(cod)}(2)] (cod=1,5-cyclooctadiene, M=Rh, Ir) with 2,2-dimethylaziridine (Haz) give the mixed-bridged complexes [{M(2)(mu-az)(mu-OMe)(cod)(2)}] [(M=Rh, 1; M=Ir, 2). These compounds are isolated intermediates in the stereospecific synthesis of the amido-bridged complexes [{M(mu-az)(cod)}(2)] (M=Rh, 3; M=Ir, 4). The electrochemical behavior of 3 and 4 in CH(2)Cl(2) and CH(3)CN is greatly influenced by the solvent. On a preparative scale, the chemical oxidation of 3 and 4 with [FeCp(2)](+) gives the paramagnetic cationic species [{M(mu-az)(cod)}(2)](+) (M=Rh, [3](+); M=Ir, [4](+)). The Rh complex [3](+) is stable in dichloromethane, whereas the Ir complex [4](+) transforms slowly, but quantitatively, into a 1:1 mixture of the allyl compound [(eta(3),eta(2)-C(8)H(11))Ir(mu-az)(2)Ir(cod)] ([5](+)) and the hydride compound [(cod)(H)Ir(mu-az)(2)Ir(cod)] ([6](+)). Addition of small amounts of acetonitrile to dichloromethane solutions of [3](+) and [4](+) triggers a fast disproportionation reaction in both cases to produce equimolecular amounts of the starting materials 3 and 4 and metal--metal bonded M(II)--M(II) species. These new compounds are isolated by oxidation of 3 and 4 with [FeCp(2)](+) in acetonitrile as the mixed-ligand complexes [(MeCN)(3)M(mu-az)(2)M(NCMe)(cod)](PF(6))(2) (M=Rh, [8](2+); M=Ir, [9](2+)). The electronic structures of [3](+) and [4](+) have been elucidated through EPR measurements and DFT calculations showing that their unpaired electron is primarily delocalized over the two metal centers, with minor spin densities at the two bridging amido nitrogen groups. The HOMO of 3 and 4 and the SOMO of [3](+) and [4](+) are essentially M--M d-d sigma*-antibonding orbitals, explaining the formation of a net bonding interaction between the metals upon oxidation of 3 and 4. Mechanisms for the observed allylic H-atom abstraction reactions from the paramagnetic (radical) complexes are proposed.

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Section: Methodsmentioning

confidence: 99%

Intervalent Bis(μ‐aziridinato)M^IIM^I Complexes (M=Rh, Ir): Delocalized Metallo‐Radicals or Delocalized Aminyl Radicals?

Tejel

Ciriano

Passarelli

et al. 2008

Chemistry A European J

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“…[ 33 ] Orbitals and spin densities were visualised with the Molden program. [34] The EPR parameters [35] of [3]C and [4]C were calculated with the ADF [36] program system using the BP86 [31] functional with the ZORA/TZP basis sets supplied with the program (all electron, core double-z, valence triple-z polarised basis set on all atoms), using the coordinates from the structures optimised in Turbomole (BP86, SV(P)) as input.…”

Section: Syntheses Of the Complexesmentioning

confidence: 99%

Ligand‐Centred Reactivity of Bis(picolyl)amine Iridium: Sequential Deprotonation, Oxidation and Oxygenation of a “Non‐Innocent” Ligand

Tejel

Rı́o

Ciriano

et al. 2009

Chemistry A European J

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Treatment of [Ir(bpa)(cod)](+) complex [1](+) with a strong base (e.g., tBuO(-)) led to unexpected double deprotonation to form the anionic [Ir(bpa-2H)(cod)](-) species [3](-), via the mono-deprotonated neutral amido complex [Ir(bpa-H)(cod)] as an isolable intermediate. A certain degree of aromaticity of the obtained metal-chelate ring may explain the favourable double deprotonation. The rhodium analogue [4](-) was prepared in situ. The new species [M(bpa-2H)(cod)](-) (M = Rh, Ir) are best described as two-electron reduced analogues of the cationic imine complexes [M(I)(cod)(Py-CH(2)-N=CH-Py)](+). One-electron oxidation of [3](-) and [4](-) produced the ligand radical complexes [3](*) and [4](*). Oxygenation of [3](-) with O(2) gave the neutral carboxamido complex [Ir(cod)(py-CH(2)-N-CO-py)] via the ligand radical complex [3](*) as a detectable intermediate.

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“…There have been a number of computational attempts to determine the relationship between experimental EPR parameters and electronic structure for a variety of transition metal complexes. Previous studies on molybdenyl complexes have tended to use bonding coefficients from separate calculations in approximate LCAO expressions for g values. ,,, Only recently have attempts been made to calculate EPR parameters of transition metal complexes by direct evaluation of the relevant matrix elements over complete molecular wave functions. − This has been made possible by the development of reasonably reliable and efficient density functional methods for electronic structure calculations of transition metal complexes …”

Section: Introductionmentioning

confidence: 99%

Density Functional Calculations ofgValues and Molybdenum Hyperfine Coupling Constants for a Series of Molybdenum(V) Oxyhalide Anions

and

Westmoreland

1997

Inorg. Chem.

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The electronic structures of the ions [MoOCl4]-, [MoOF5]2-, [MoOCl4(H2O)]-, and [MoOBr4(H2O)]- have been calculated by spin-polarized density functional calculations. The results confirm and extend previous calculations on these ions. In addition, the output eigenfunctions and eigenvalues have been used to calculate g values and molybdenum hyperfine coupling constants. The results reproduce the trends in the experimental parameters well but tend to overestimate the magnitudes of both the g values and the hyperfine coupling constants. It is shown from the calculated EPR parameters that the contributions of low-energy charge transfer states and the covalencies of the ground and excited states are the major contributors to deviations of g values from the spin-only value. Ligand-based spin−orbit coupling becomes important with increasing atomic number for the halides but never dominates. The molybdenum hyperfine couplings are dominated by Fermi contact terms which, in turn, originate primarily from spin polarization of the core 4s electrons. A comparison of [MoOCl4]- with [MoOCl4(H2O)]- indicates that the changes in EPR parameters observed on adding a sixth ligand to the coordination sphere arise from electronic structural changes due to geometrical distortions and not to specific electronic contributions from the added ligand.

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Models for the Molybdenum(VI/V) Centers of the Molybdenum Hydroxylases and Related Enzymes. Geometry, Electronic Structure, and EPR g-Tensor Predictions from ab Initio and Semiempirical Molecular Orbital Studies

Cited by 41 publications

References 0 publications

Intervalent Bis(μ‐aziridinato)M^IIM^I Complexes (M=Rh, Ir): Delocalized Metallo‐Radicals or Delocalized Aminyl Radicals?

Intervalent Bis(μ‐aziridinato)M^IIM^I Complexes (M=Rh, Ir): Delocalized Metallo‐Radicals or Delocalized Aminyl Radicals?

Ligand‐Centred Reactivity of Bis(picolyl)amine Iridium: Sequential Deprotonation, Oxidation and Oxygenation of a “Non‐Innocent” Ligand

Density Functional Calculations ofgValues and Molybdenum Hyperfine Coupling Constants for a Series of Molybdenum(V) Oxyhalide Anions

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Models for the Molybdenum(VI/V) Centers of the Molybdenum Hydroxylases and Related Enzymes. Geometry, Electronic Structure, and EPR g-Tensor Predictions from ab Initio and Semiempirical Molecular Orbital Studies

Cited by 41 publications

References 0 publications

Intervalent Bis(μ‐aziridinato)MIIMI Complexes (M=Rh, Ir): Delocalized Metallo‐Radicals or Delocalized Aminyl Radicals?

Intervalent Bis(μ‐aziridinato)MIIMI Complexes (M=Rh, Ir): Delocalized Metallo‐Radicals or Delocalized Aminyl Radicals?

Ligand‐Centred Reactivity of Bis(picolyl)amine Iridium: Sequential Deprotonation, Oxidation and Oxygenation of a “Non‐Innocent” Ligand

Density Functional Calculations ofgValues and Molybdenum Hyperfine Coupling Constants for a Series of Molybdenum(V) Oxyhalide Anions

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Intervalent Bis(μ‐aziridinato)M^IIM^I Complexes (M=Rh, Ir): Delocalized Metallo‐Radicals or Delocalized Aminyl Radicals?

Intervalent Bis(μ‐aziridinato)M^IIM^I Complexes (M=Rh, Ir): Delocalized Metallo‐Radicals or Delocalized Aminyl Radicals?