101 research outputs found
Computation Provides Chemical Insight into the Diverse Hydride NMR Chemical Shifts of [Ru(NHC)<sub>4</sub>(L)H]<sup>0/+</sup> Species (NHC = N-heterocyclic carbene; L = vacant, H<sub>2</sub>, N<sub>2</sub>, CO, MeCN, O<sub>2</sub>, P<sub>4</sub>, SO<sub>2</sub>, H<sup>-</sup>, F<sup>-</sup> and Cl<sup>-</sup>) and their [Ru(R<sub>2</sub>PCH<sub>2</sub>CH<sub>2</sub>PR<sub>2</sub>)<sub>2</sub>(L)H]<sup>+</sup> Congeners
Relativistic density functional theory calculations, both with and without the effects of spinâorbit coupling, have been employed to model hydride NMR chemical shifts for a series of [Ru(NHC)4(L)H]0/+ species (NHC = N-heterocyclic carbene; L = vacant, H2, N2, CO, MeCN, O2, P4, SO2, Hâ, Fâ and Clâ), as well as selected phosphine analogues [Ru(R2PCH2CH2PR2)2(L)H]+ (R = iPr, Cy; L = vacant, O2). Inclusion of spinâorbit coupling provides good agreement with the experimental data. For the NHC systems large variations in hydride chemical shift are shown to arise from the paramagnetic term, with high net shielding (L = vacant, Clâ, Fâ) being reinforced by the contribution from spinâorbit coupling. Natural chemical shift analysis highlights the major orbital contributions to the paramagnetic term and rationalizes trends via changes in the energies of the occupied Ru dÏ orbitals and the unoccupied Ï*RuâH orbital. In [Ru(NHC)4(η2-O2)H]+ a ÎŽ-interaction with the O2 ligand results in a low-lying LUMO of dÏ character. As a result this orbital can no longer contribute to the paramagnetic shielding, but instead provides additional deshielding via overlap with the remaining (occupied) dÏ orbital under the Lz angular momentum operator. These two effects account for the unusual hydride chemical shift of +4.8 ppm observed experimentally for this species. Calculations reproduce hydride chemical shift data observed for [Ru(iPr2PCH2CH2PiPr2)2(η2-O2)H]+ (ÎŽ = â6.2 ppm) and [Ru(R2PCH2CH2PR2)2H]+ (ca. â32 ppm, R = iPr, Cy). For the latter, the presence of a weak agostic interaction trans to the hydride ligand is significant, as in its absence (R = Me) calculations predict a chemical shift of â41 ppm, similar to the [Ru(NHC)4H]+ analogues. Depending on the strength of the agostic interaction a variation of up to 18 ppm in hydride chemical shift is possible and this factor (that is not necessarily readily detected experimentally) can aid in the interpretation of hydride chemical shift data for nominally unsaturated hydride-containing species. The synthesis and crystallographic characterization of the BArF4â salts of [Ru(IMe4)4(L)H]+ (IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene; L = P4, SO2; ArF = 3,5-(CF3)2C6H3) and [Ru(IMe4)4(Cl)H] are also reported
Structural variation, dynamics, and catalytic application of palladium(II) complexes of di-N-heterocyclic carbene-amine ligands
A series of palladium(II) complexes incorporating di-NHC-amine ligands has been prepared and their structural, dynamic and catalytic behaviour investigated. The complexes [trans-(k(2)-(CN)-C-tBu(Bn)CN(Bn)C-tBu)PdCl2] (12) and [trans-(kappa(2)-(CN)-C-Mes(H)C-Mes)PdCl2] (13) do not exhibit interaction between the amine nitrogen and palladium atom respectively. NMR spectroscopy between - 40 and 25 degrees C shows that the di-NHC-amine ligand is flexible expressing C-s symmetry and for 13 rotation of the mesityl groups is prevented. In the related C-1 complex [(kappa(3)-(CN)-C-tBu(H)C-tBu)PdCl][CI] (14) coordination of NHC moieties and amine nitrogen atom is observed between -40 and 25 degrees C. Reaction between 12 - 14 and two equivalents of AgBF4 in acetonitrile gives the analogous complexes [trans-(kappa(2)-(CN)-C-tBu(Bn)C-tBu)PdCl2] (12) and [trans-(kappa(CN)-C-2Mes(H)C-Mes)PdCl2] (13) do not exhibit interaction between the amine nitrogen and palladium atom respectively. NMR spectroscopy between -40 ans 25 degrees C shows the di-NHC-amine ligand is flexible expressing C-s symmetry and for 13 rotation of the mesityl groups is prevented. In the related C-1 complex [kappa(3)-(CN)-C-tBu(H)C-tBu)PdCI][CI] (14) coordination of NHC moieties and amine nitrogen atom is observed between -40 and 25 degrees C.Reaction between 12-14 and two equivalents of AgBF4 in acetonitrile gives the analogous complexes [trans-(kappa(2)-(CN)-C-tBu(H)(CPd)-Pd-tBu(MeCN)(2)][BF4](2) (15), [trans-(kappa(CN)-C-2Mes(H)C-Mes)Pd(MeCN)(2)[BF4](2 (16)) and [(kappa(3)-(CN)-C-tBu(H)C-tBu)Pd(MeCN)][BF4](2) (17) indicating that ligand structure determines amine coordination. The single crystal X-ray structures of 12, 17 and two ligand imidazolium salt precursors C-tBu(H)N(Bn)C(H) (tBu)][CI](2) (2) and [C-tBu(H) N(H)C(H)(tBu)][BPh4](2) (4) have been determined. Complexes 12-14 and 15-17 have been shown to be active precatalysts for Heck and hydroamination reactions respectively
Computation Provides Chemical Insight into the Diverse Hydride NMR Chemical Shifts of [Ru(NHC)<sub>4</sub>(L)H]<sup>0/+</sup> Species (NHC = N-heterocyclic carbene; L = vacant, H<sub>2</sub>, N<sub>2</sub>, CO, MeCN, O<sub>2</sub>, P<sub>4</sub>, SO<sub>2</sub>, H<sup>-</sup>, F<sup>-</sup> and Cl<sup>-</sup>) and their [Ru(R<sub>2</sub>PCH<sub>2</sub>CH<sub>2</sub>PR<sub>2</sub>)<sub>2</sub>(L)H]<sup>+</sup> Congeners
International audienceRelativistic density functional theory calculations, both with and without the effects of spinâorbit coupling, have been employed to model hydride NMR chemical shifts for a series of [Ru(NHC)4(L)H]0/+ species (NHC = N-heterocyclic carbene; L = vacant, H2, N2, CO, MeCN, O2, P4, SO2, Hâ, Fâ and Clâ), as well as selected phosphine analogues [Ru(R2PCH2CH2PR2)2(L)H]+ (R = iPr, Cy; L = vacant, O2). Inclusion of spinâorbit coupling provides good agreement with the experimental data. For the NHC systems large variations in hydride chemical shift are shown to arise from the paramagnetic term, with high net shielding (L = vacant, Clâ, Fâ) being reinforced by the contribution from spinâorbit coupling. Natural chemical shift analysis highlights the major orbital contributions to the paramagnetic term and rationalizes trends via changes in the energies of the occupied Ru dÏ orbitals and the unoccupied Ï*RuâH orbital. In [Ru(NHC)4(η2-O2)H]+ a ÎŽ-interaction with the O2 ligand results in a low-lying LUMO of dÏ character. As a result this orbital can no longer contribute to the paramagnetic shielding, but instead provides additional deshielding via overlap with the remaining (occupied) dÏ orbital under the Lz angular momentum operator. These two effects account for the unusual hydride chemical shift of +4.8 ppm observed experimentally for this species. Calculations reproduce hydride chemical shift data observed for [Ru(iPr2PCH2CH2PiPr2)2(η2-O2)H]+ (ÎŽ = â6.2 ppm) and [Ru(R2PCH2CH2PR2)2H]+ (ca. â32 ppm, R = iPr, Cy). For the latter, the presence of a weak agostic interaction trans to the hydride ligand is significant, as in its absence (R = Me) calculations predict a chemical shift of â41 ppm, similar to the [Ru(NHC)4H]+ analogues. Depending on the strength of the agostic interaction a variation of up to 18 ppm in hydride chemical shift is possible and this factor (that is not necessarily readily detected experimentally) can aid in the interpretation of hydride chemical shift data for nominally unsaturated hydride-containing species. The synthesis and crystallographic characterization of the BArF4â salts of [Ru(IMe4)4(L)H]+ (IMe4 = 1,3,4,5-tetramethylimidazol-2-ylidene; L = P4, SO2; ArF = 3,5-(CF3)2C6H3) and [Ru(IMe4)4(Cl)H] are also reported
Probing Intermetallic Coupling in Dinuclear N-Heterocyclic Carbene Ruthenium(II) Complexes
Improved Sonogashira CâC Coupling Through Clay Supported Palladium Complexes with Tridentate Pincer Bis-carbene Ligands.
Triazolediylidenes: A Versatile Class of Ligands for the Preparation of Discrete Molecules of Homo- and Hetero-Binuclear Complexes for Improved Catalytic Applications
Ring-expanded N-heterocyclic carbene complexes of ruthenium
The six-membered N-heterocyclic carbene 1,3-bis(2,4,6-trimethylphenyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene (6-Mes) reacts with Ru(PPh3)3(CO)HF to afford Ru(6-Mes)(PPh3)(CO)HF (1), which is converted to the five-coordinate CâH activated carbene complex Ru(6-Mes)âČ(PPh3)(CO)H (2) upon treatment with Et3SiH. The hydride chloride precursor Ru(PPh3)3(CO)HCl affords a mixture of products with 6-Mes, but reacts cleanly with 1,3-bis(isopropyl)-3,4,5,6-tetrahydropyrimidin-2-ylidene (6-iPr) to give the six-coordinate activated complex Ru(6-iPr)âČ(PPh3)2(CO)H (3a), in which the hydride is trans to the methylene arm of the activated NHC. This complex isomerizes in solution with ÎH and ÎS values of 98.2 ± 4.6 kJ molâ1 and 15.5 ± 14.5 J molâ1 Kâ1. The major product from the isomerization, 3b, in which the hydride ligand is trans to carbene, can be made directly by reaction of 6-iPr with Ru(PPh3)3(CO)H2
Comparison of simulation models for Perovskite solar cells
In this work, a comparison of two models for the simulation of the electrical behavior of perovskite solar cells is presented. The two models considered are the well-known one diode model and an analytical model recently presented by Sun et al. These models are detailed in section 3. A perovskite solar cell was fabricated and
characterized in order to compare real measurement results with simulation results obtained by using both models.
The fabrication and characterization processes are also summarized in the experimental section.Peer ReviewedPostprint (published version
An N-Heterocyclic Carbene/Iridium Hydride Complex from the Oxidative Addition of a Ferrocenyl-Bisimidazolium Salt: Implications for Synthesis
An N-Heterocyclic Carbene/Iridium Hydride Complex from the Oxidative Addition of a Ferrocenyl-Bisimidazolium Salt: Implications for Synthesis
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