Calculations of One-Electron Redox Potentials of Oxoiron(IV) Porphyrin Complexes

Density functional theory calculations have been performed to calculate the one-electron redox potential for a series of oxoiron­(IV) porphyrin complexes of the form [(TMP)­Fe^IV(O)­(L)] (TMP = 5,10,15,20-tetramesitylporphyrinate). Different axial ligands were chosen (L = none, Im, ClO₄^–, CH₃CO₂^–, Cl^–, F^–, SCH₃^–) in order to compare the results with recent electrochemical experiments. The redox potentials were calculated with a Born–Haber cycle and the use of an internal reference, i.e. the absolute redox potential of ferrocene. Diverse methodologies were tested and show that the computed redox potentials depend strongly on the functional, the basis set, and the continuum models used to compute the solvation energies. Globally, BP86 gives better results for the geometries of the complexes than B3LYP and M06-L as well as more consistent values for the redox potentials. Although the results fit the experimental data for L = Im and L = ClO₄^–, the addition of the other anionic axial ligands to the oxoiron­(IV) porphyrin complex strongly lowers the redox potential, which is in disagreement with experimental observations. This important discrepancy is discussed

Formation of a Bridging Phosphinidene Thorium Complex

The synthesis and structural determination of the first thorium phosphinidene complex are reported. The reaction of 2 equiv of (C₅Me₅)₂Th­(CH₃)₂ with H₂P­(2,4,6-^<i>i</i>Pr₃C₆H₂) at 95 °C produces [(C₅Me₅)₂Th]₂(μ₂-P­[(2,6-<i>C</i>H₂CHCH₃)₂-4-^<i>i</i>PrC₆H₂] as well as 4 equiv of methane, 2 equiv from deprotonation of the phosphine and 2 equiv from C–H bond activation of one methyl group of each of the isopropyl groups at the 2- and 6-positions. Transition state calculations indicate that the steps in the mechanism are P–H, C–H, C–H, and then P–H bond activation to form the phosphinidene

Cleavage of Carbon Monoxide Promoted by a Dinuclear Tantalum Tetrahydride Complex

The reaction of one equivalent of carbon monoxide with the dinuclear tetrahydride complex ([NPN]­Ta)₂(μ-H)₄ (where NPN = PhP­(CH₂SiMe₂NPh)₂) results in the cleavage of the CO triple bond and formation of ([NPN]­Ta)­(μ-O)­(μ-H)­(Ta­[NPN′]) (where NPN′ = PhP­(CH₂SiMe₂NPh)­(CH₂SiMe₂NC₆H₄)) via extrusion of CH₄. The identity of the ditantalum complex was confirmed by single-crystal X-ray analysis, isotopic labeling studies, and GC-MS analysis of the methane released. DFT calculations were performed to provide information on the initial adduct formed and likely transition states for the process

Cleavage of Carbon Monoxide Promoted by a Dinuclear Tantalum Tetrahydride Complex

The reaction of one equivalent of carbon monoxide with the dinuclear tetrahydride complex ([NPN]­Ta)₂(μ-H)₄ (where NPN = PhP­(CH₂SiMe₂NPh)₂) results in the cleavage of the CO triple bond and formation of ([NPN]­Ta)­(μ-O)­(μ-H)­(Ta­[NPN′]) (where NPN′ = PhP­(CH₂SiMe₂NPh)­(CH₂SiMe₂NC₆H₄)) via extrusion of CH₄. The identity of the ditantalum complex was confirmed by single-crystal X-ray analysis, isotopic labeling studies, and GC-MS analysis of the methane released. DFT calculations were performed to provide information on the initial adduct formed and likely transition states for the process

Reduction of Carbon Dioxide Promoted by a Dinuclear Tantalum Tetrahydride Complex

The reaction of 1 equiv of carbon dioxide with the dinuclear tetrahydride complex ([NPN]­Ta)₂(μ-H)₄ [where NPN = PhP­(CH₂SiMe₂NPh)₂] results in the formation of ([NPN]­Ta)₂(μ-OCH₂O)­(μ-H)₂ via a combination of migratory insertion and reductive elimination. The identity of the ditantalum complex containing a methylene diolate fragment was confirmed by single-crystal X-ray analysis, NMR analysis, and isotopic labeling studies. Density functional theory calculations were performed to provide information on the structure of the initial adduct formed and likely transition states and intermediates for the process

Cleavage of Carbon Monoxide Promoted by a Dinuclear Tantalum Tetrahydride Complex

The reaction of one equivalent of carbon monoxide with the dinuclear tetrahydride complex ([NPN]­Ta)₂(μ-H)₄ (where NPN = PhP­(CH₂SiMe₂NPh)₂) results in the cleavage of the CO triple bond and formation of ([NPN]­Ta)­(μ-O)­(μ-H)­(Ta­[NPN′]) (where NPN′ = PhP­(CH₂SiMe₂NPh)­(CH₂SiMe₂NC₆H₄)) via extrusion of CH₄. The identity of the ditantalum complex was confirmed by single-crystal X-ray analysis, isotopic labeling studies, and GC-MS analysis of the methane released. DFT calculations were performed to provide information on the initial adduct formed and likely transition states for the process

Selectivity in the C–H Activation Reaction of CH₃OSO₂CH₃ with [1,2,4-(Me₃C)₃C₅H₂]₂CeH or [1,2,4-(Me₃C)₃C₅H₂][1,2-(Me₃C)₂-4-(Me₂CCH₂)C₅H₂]Ce: To Choose or Not To Choose

The experimental reaction of [1,2,4-(Me₃C)₃C₅H₂]₂CeH, Cp′₂CeH, and CH₃OSO₂CH₃ begins by α-C–H activation of the SCH₃ group, forming Cp′₂CeCH₂SO₂(OCH₃), which evolves into Cp′₂CeOCH₃ with elimination of CH₂ (and presumably SO₂). Prolonged heating of this mixture (days at 60 °C) forms Cp′₂CeOSO₂CH₃ and CH₃OCH₃. The metallacycle [1,2,4-(Me₃C)₃C₅H₂]­[1,2-(Me₃C)₂-4-(Me₂CCH₂)­C₅H₂]­Ce, when presented with the choice of C–H bonds in CH₃S and CH₃O groups, deprotonates both with comparable rates, ultimately forming Cp′₂CeOCH₃ and Cp′₂CeOSO₂CH₃ at 20 °C. The experimental studies are illuminated by DFT calculations on the experimental systems, which show that the hydride selects the more acidic CH₃S bond, whereas the metallacycle reacts with C–H bonds of both the CH₃S and CH₃O groups of CH₃OSO₂CH₃. In the metallacycle reaction, the initially formed regioisomers, Cp′₂CeCH₂SO₂(OCH₃) and Cp′₂CeCH₂OSO₂CH₃, rearrange to the observed products, Cp′₂CeOCH₃ and Cp′₂CeOSO₂CH₃, respectively. Furthermore, C–H activation at the SCH₃ group forms two isomers of Cp′₂CeCH₂SO₂(OCH₃) in the reaction of CH₃OSO₂CH₃ with the metallacycle and only one in the reaction with the hydride. The lack of selectivity in the reactions of the metallacycle relative to the hydride is due to the metallacycle’s greater thermodynamic advantage and lower energy barriers, which are linked to the higher bond energy of Ce–H relative to Ce–C in the metallacycle

Carbon Monoxide Activation via O-Bound CO Using Decamethylscandocinium–Hydridoborate Ion Pairs

Ion pairs [Cp*₂Sc]⁺[HB­(<i>p-</i>C₆F₄R)₃]⁻ (R = F, <b>1-F</b>; R = H, <b>1-H</b>) were prepared and shown to be unreactive toward D₂ and α-olefins, leading to the conclusion that no back-transfer of hydride from boron to scandium occurs. Nevertheless, reaction with CO is observed to yield two products, both ion pairs of the [Cp*₂Sc]⁺ cation with formylborate (<b>2-R</b>) and borataepoxide (<b>3-R</b>) counteranions. DFT calculations show that these products arise from the carbonyl adduct of the [Cp*₂Sc]⁺ in which the CO is bonded to scandium through the oxygen atom, not the carbon atom. The formylborate <b>2-R</b> is formed in a two-step process initiated by an abstraction of the hydride by the carbon end of an O-bound CO, which forms an η²-formyl intermediate that adds, in a second step, the borane at the carbon. The borataepoxide <b>3-R</b> is suggested to result from an isomerization of <b>2-R</b>. This unprecedented reaction represents a new way to activate CO via a reaction channel emanating from the ephemeral isocarbonyl isomer of the CO adduct

Formation of a Uranium Trithiocarbonate Complex via the Nucleophilic Addition of a Sulfide-Bridged Uranium Complex to CS₂

The uranium­(IV)/uranium­(IV) μ-sulfide complex [{((^AdArO)₃N)­U}₂(μ-S)] reacts with CS₂ to form the trithiocarbonate-bridged complex [{((^AdArO)₃N)­U}₂(μ-κ²:κ²-CS₃)]. The trithiocarbonate complex can alternatively be formed in low yields from low-valent [((^AdArO)₃N)­U­(DME)] through the reductive cleavage of CS₂

Are Solvent and Dispersion Effects Crucial in Olefin Polymerization DFT Calculations? Some Insights from Propylene Coordination and Insertion Reactions with Group 3 and 4 Metallocenes

The primary insertion (or 1,2-insertion) of propylene into (C₅Me₅)₂YCH₂CH₂CH­(Me)₂, as well as the primary and secondary (or 2,1) insertions of propylene into the activated <i>ansa</i>-zirconocene complex [{Ph­(H)­C-(3,6-<i>t</i>Bu₂Flu)­(3-<i>t</i>Bu-5-Me-C₅H₂)}­ZrMe]⁺ were calculated with several DFT methods to find the most adequate methodology for the computation of metallocene-catalyzed olefin polymerization reactions. For the yttrium system, both solvent corrections and dispersion corrections are needed to determine energies of coordination and activation barriers in agreement with experimental data. Dispersion corrections were included directly via the use of specific functionals like B97D and M06 or were added as empirical corrections (GD3BJ) to the B3PW91 calculations. For the zirconocene system, the best method is a combination of B3PW91 with solvent corrections incorporated with the SMD continuum model. The dispersion corrections, included via both GD3BJ and M06, tend to overestimate the stabilization of the adducts because of the high steric bulk of the zirconocene system. The addition of dispersion corrections shifts the energy profiles toward lower values but does not affect the relative activation barriers. Implementation of entropy corrections counterbalances almost perfectly the dispersion corrections. The same observations arise from the study of the C–H activations of propylene induced by the zirconocene complex