Advances in Molecular Quantum Chemistry Contained in the Q-Chem 4 Program Package

A summary of the technical advances that are incorporated in the fourth major release of the Q-Chem quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation theories, methods for electronically excited and open-shell species, tools for treating extended environments, algorithms for walking on potential surfaces, analysis tools, energy and electron transfer modelling, parallel computing capabilities, and graphical user interfaces. In addition, a selection of example case studies that illustrate these capabilities is given. These include extensive benchmarks of the comparative accuracy of modern density functionals for bonded and non-bonded interactions, tests of attenuated second order Møller–Plesset (MP2) methods for intermolecular interactions, a variety of parallel performance benchmarks, and tests of the accuracy of implicit solvation models. Some specific chemical examples include calculations on the strongly correlated Cr2 dimer, exploring zeolite-catalysed ethane dehydrogenation, energy decomposition analysis of a charged ter-molecular complex arising from glycerol photoionisation, and natural transition orbitals for a Frenkel exciton state in a nine-unit model of a self-assembling nanotube

Elusive Phosphine Copper(I) Boryl Complexes: Synthesis, Structures, and Reactivity

We report the first isolation of phosphine copper boryl complexesspecies pivotal to numerous copper-catalyzed borylation reactions. The reaction of diboron(4) derivatives with copper <i>tert</i>-butoxide complexes of phosphine ligands allows the isolation of the dimeric μ-boryl-bridged Cu­(I) complexes [(<i>i</i>Pr₃P)­Cu–Bdmab]₂ (<b>4</b>) and [(C₆H₄(Ph₂P)₂)­Cu–Bpin]₂ (<b>6</b>) with Cu···Cu distances of 2.24–2.27 Å (dmab = (NMe)₂C₆H₄, pin = (OCMe₂)₂)). A slightly more sterically demanding boryl ligand furnishes the unprecedented multinuclear copper boryl complex [(<i>i</i>Pr₃P)₂Cu₈(B­(<i>i</i>PrEn))₃(O<i>t</i>Bu)₃] (<b>5</b>), a potential intermediate of the decomposition of an initial Cu­(I) boryl complex (<i>i</i>PrEn = (N<i>i</i>Pr)₂C₂H₄). All complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy, and elemental analysis. DFT computations support the nature of these unique complexes and give insight into their electronic structures

A stable enol from a 6-substituted benzanthrone and its unexpected behaviour under acidic conditions

Treatment of benzanthrone (1) with biphenyl-2-yl lithium leads to the surprisingly stable enol 4, which is converted by dehydrogenation into the benzanthrone derivative 7. Under acidic conditions 4 isomerises to the spiro compound 11 and the bicyclo[4.3.1]decane derivative 12. Furthermore, the formation of 7 and the hydrogenated compound 13 is observed. A mechanism for the formation of the reaction products is proposed and supported by DFT calculations

Tuning the Catalytic Alkyne Metathesis Activity of Molybdenum and Tungsten 2,4,6-Trimethylbenzylidyne Complexes with Fluoroalkoxide Ligands OC(CF₃)_<i>n</i>Me_3–<i>n</i> (<i>n</i> = 0–3)

The molybdenum and tungsten 2,4,6-trimethylbenzylidyne complexes [MesCM­{OC­(CF₃)_<i>n</i>Me_3–<i>n</i>}₃] (M = Mo: <b>MoF0</b>, <i>n</i> = 0; <b>MoF3</b>, <i>n</i> = 1; <b>MoF6</b>, <i>n</i> = 2; <b>MoF9</b>, <i>n</i> = 3; M = W: <b>WF3</b>, <i>n</i> = 1; Mes = 2,4,6-trimethylphenyl) were prepared by the reaction of the tribromides [MesCMBr₃(dme)] (dme = 1,2-dimethoxyethane) with the corresponding potassium alkoxides KOC­(CF₃)_<i>n</i>Me_3–<i>n</i>. The molecular structures of all complexes were established by X-ray diffraction analysis. The catalytic activity of the resulting alkylidyne complexes in the homometathesis and ring-closing alkyne metathesis of internal and terminal alkynes was studied, revealing a strong dependency on the fluorine content of the alkoxide ligand. The different catalytic performances were rationalized by DFT calculations involving the metathesis model reaction of 2-butyne. Because the calculations predict the stabilization of metallacyclobutadiene (MCBD) intermediates by increasing the degree of fluorination, <b>MoF9</b> was treated with 3-hexyne to afford the MCBD complex [(C₃Et₃)­Mo­{OC­(CF₃)₃}₃], which was characterized spectroscopically

Tuning the Catalytic Alkyne Metathesis Activity of Molybdenum and Tungsten 2,4,6-Trimethylbenzylidyne Complexes with Fluoroalkoxide Ligands OC(CF₃)_<i>n</i>Me_3–<i>n</i> (<i>n</i> = 0–3)

The molybdenum and tungsten 2,4,6-trimethylbenzylidyne complexes [MesCM­{OC­(CF₃)_<i>n</i>Me_3–<i>n</i>}₃] (M = Mo: <b>MoF0</b>, <i>n</i> = 0; <b>MoF3</b>, <i>n</i> = 1; <b>MoF6</b>, <i>n</i> = 2; <b>MoF9</b>, <i>n</i> = 3; M = W: <b>WF3</b>, <i>n</i> = 1; Mes = 2,4,6-trimethylphenyl) were prepared by the reaction of the tribromides [MesCMBr₃(dme)] (dme = 1,2-dimethoxyethane) with the corresponding potassium alkoxides KOC­(CF₃)_<i>n</i>Me_3–<i>n</i>. The molecular structures of all complexes were established by X-ray diffraction analysis. The catalytic activity of the resulting alkylidyne complexes in the homometathesis and ring-closing alkyne metathesis of internal and terminal alkynes was studied, revealing a strong dependency on the fluorine content of the alkoxide ligand. The different catalytic performances were rationalized by DFT calculations involving the metathesis model reaction of 2-butyne. Because the calculations predict the stabilization of metallacyclobutadiene (MCBD) intermediates by increasing the degree of fluorination, <b>MoF9</b> was treated with 3-hexyne to afford the MCBD complex [(C₃Et₃)­Mo­{OC­(CF₃)₃}₃], which was characterized spectroscopically

Palladium(II) Complexes with Anionic N‑Heterocyclic Carbene–Borate Ligands as Catalysts for the Amination of Aryl Halides

A series of (allyl)­palladium­(II) complexes of anionic N-heterocyclic carbenes that contain a weakly coordinating borate moiety (WCA-NHC) were prepared by deprotonation of the carbene IPr with <i>n</i>-butyllithium in the 4-position, which was followed by addition of B­(C₆F₅)₃ and reaction of the resulting lithium carbene–borate with [(η³-allyl)­Pd­(μ-Cl)]₂ (allyl = 2-propenyl, 2-butenyl, 2-methyl-2-propenyl, 1-phenyl-2-propenyl). In polar solvents such as tetrahydrofuran, chloropalladate complexes of the type [Li­(THF)₃]­[(WCA-NHC)­PdCl­(η³-allyl)] were formed, whereas the reactions in toluene afforded neutral complexes of the type [(WCA-NHC)­Pd­(η³-allyl)], which exhibit an intramolecular interaction with the N-aryl groups of the carbene ligands. The allyl-palladium complexes were employed as catalysts for the Buchwald–Hartwig amination of various aryl halides with morpholine

Iridium(I) Complexes with Anionic N‑Heterocyclic Carbene Ligands as Catalysts for the Hydrogenation of Alkenes in Nonpolar Media

A series of lithium complexes of anionic N-heterocyclic carbenes that contain a weakly coordinating borate moiety (WCA-NHC) was prepared in one step from free N-heterocyclic carbenes by deprotonation with <i>n</i>-butyl lithium followed by borane addition. The reaction of the resulting lithium-carbene adducts with [M­(COD)­Cl]₂ (M = Rh, Ir; COD = 1,5-cyclooctadiene) afforded zwitterionic rhodium­(I) and iridium­(I) complexes of the type [(WCA-NHC)­M­(COD)], in which the metal atoms exhibit an intramolecular interaction with the N-aryl groups of the carbene ligands. For M = Rh, the neutral complex [(WCA-NHC)­Rh­(CO)₂] and the ate complex (NEt₄)­[(WCA-NHC)­Rh­(CO)₂Cl] were prepared, with the latter allowing an assessment of the donor ability of the ligand by IR spectroscopy. The zwitterionic iridium–COD complexes were tested as catalysts for the homogeneous hydrogenation of alkenes, which can be performed in the presence of nonpolar solvents or in the neat alkene substrate. Thereby, the most active complex showed excellent stability and activity in hydrogenation of alkenes at low catalyst loadings (down to 10 ppm)

Ni–Fe and Pd–Fe Interactions in Nickel(II) and Palladium(II) Complexes of a Ferrocene-Bridged Bis(imidazolin-2-imine) Ligand

The bis­(imidazolin-2-imine) ligand <i>N</i>,<i>N</i>′-bis­(1,3-diisopropyl-4,5-dimethyl­imidazolin-2-ylidene)-1,1′-ferrocene­diamine, fc­(NIm)₂ (<b>1</b>) was prepared. Its reaction with [NiCl₂(dme)] (dme = 1,2-dimethoxyethane) or [PdCl₂(MeCN)₂] afforded the tetrahedral, paramagnetic complex [(<b>1</b>-κ²<i>N</i>,<i>N</i>′)­NiCl₂] (<b>6a</b>) or the diamagnetic, square-planar complex [(<b>1</b>-κ²<i>N</i>,<i>N</i>′)­PdCl₂] (<b>6b</b>), respectively. For the latter, slow rearrangement to the ionic complex [(<b>1</b>-κFe,κ²<i>N</i>,<i>N</i>′)­PdCl]­Cl, [<b>7</b>]­Cl, was observed, which was followed by ¹H NMR and UV/vis spectroscopy. Treatment of [<b>7</b>]Cl with NaBF₄ afforded [<b>7</b>]­BF₄; the palladium atoms in both cations adopt square-planar environments with short Fe–Pd bonds (ca. 2.65 Å). In addition, a series of dicationic complexes of the type [(<b>1</b>-κFe,κ²<i>N</i>,<i>N</i>′)­ML]­(BF₄)₂ (<b>8a</b>: M = Ni, L = MeCN; <b>8b</b>: M = Pd, L = MeCN; <b>9a</b>: M = Ni, L = PMe₃; <b>9b</b>: M = Pd, L = PMe₃) was prepared from <b>6a</b> (M = Ni) or [<b>7</b>]­BF₄ by chloride abstraction with NaBF₄ or AgBF₄ in the presence of acetonitrile or trimethylphosphine, respectively. In the presence of triphenylphosphine, the palladium­(II) complex [(<b>1</b>-κFe,κ²<i>N</i>,<i>N</i>′)­Pd­(PPh₃)]­(BF₄)₂ (<b>10</b>) was isolated. Iron–nickel and iron–palladium bonding in these complexes was studied experimentally by NMR, UV/vis, and Mössbauer spectroscopy and by cyclic voltammetry. Detailed DFT calculations were carried out for the cations [(<b>1</b>-κFe,κ²<i>N</i>,<i>N</i>′)­M­(MeCN)]²⁺ in the <b>8a</b>/<b>8b</b> couple, with Bader’s atoms in molecules theory revealing the presence of noncovalent, closed-shell metal–metal interactions. Potential energy surface scans with successive elongation of the Fe–M bonds allow an estimation of the iron–metal bond dissociation energies (BDE) as BDE­(Fe–Ni) = 11.3 kcal mol^–1 and BDE­(Fe–Pd) = 24.3 kcal mol^–1

Advances in molecular quantum chemistry contained in the Q-Chem 4 program package

A summary of the technical advances that are incorporated in the fourth major release of the Q-Chem quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation theories, methods for electronically excited and open-shell species, tools for treating extended environments, algorithms for walking on potential surfaces, analysis tools, energy and electron transfer modelling, parallel computing capabilities, and graphical user interfaces. In addition, a selection of example case studies that illustrate these capabilities is given. These include extensive benchmarks of the comparative accuracy of modern density functionals for bonded and non-bonded interactions, tests of attenuated second order Møller–Plesset (MP2) methods for intermolecular interactions, a variety of parallel performance benchmarks, and tests of the accuracy of implicit solvation models. Some specific chemical examples include calculations on the strongly correlated Cr2 dimer, exploring zeolite-catalysed ethane dehydrogenation, energy decomposition analysis of a charged ter-molecular complex arising from glycerol photoionisation, and natural transition orbitals for a Frenkel exciton state in a nine-unit model of a self-assembling nanotube