J. Appl. Cryst.の発刊に際して

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Recent Developments in the Preparation and Chemistry of Metallacycles and Metallacages via Coordination

https://www.pnas.org/content/pnas/90/5/1635.full.pdf

Supramolecular chemistry.

In this contribution, we provide a comprehensive overview of C-H activation methods promoted by NHC-transition metal complexes, covering the literature since 2002 (the year of the first report on metal-NHC-catalyzed C-H activation) through June 2019, focusing on both NHC ligands and C-H activation methods. This review covers C-H activation reactions catalyzed by group 8 to 11 NHC-metal complexes. Through discussing the role of NHC ligands in promoting challenging C-H activation methods, the reader is provided with an overview of this important area and its crucial role in forging carbon-carbon and carbon-heteroatom bonds by directly engaging ubiquitous C-H bonds.

N-Heterocyclic Carbene Complexes in C–H Activation Reactions

Ruthenium-Catalyzed C–H Activation of Salicylaldehyde and Decarboxylative Coupling of Alkynoic Acids for the Selective Synthesis of Homoisoflavonoids and Flavones

Diethylene glycol-functionalized imidazo[1,5-a]pyridin-3-ylidenes (DEG-ImPy) have been developed as bifunctional N-heterocyclic carbene ligands. The DEG-ImPy Cu(I) complexes efficiently catalyzed the direct C–H carboxylation of benzoxazole with CO2, showing higher isolated yields than those with the N,N′-(2,6-diisopropylphenyl)imidazolylidene Cu catalyst.

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Bifunctional N-heterocyclic carbene ligands for Cu-catalyzed direct C–H carboxylation with CO2

A family of heteroleptic iridium(III) cyclometalates, [4-(2-RCB)ppy]2Ir(acac) (3c–3g; CB = o-carboran-1-yl; ppy = 2-phenylpyridinato-C2,N; acac = acetylacetonate; R = iPr (3c), iBu (3d), Ph (3e), CF3C6H4 (3f), C6F5 (3g)) with various 2-R substituted o-carboranes at the 4-position in the phenyl ring of the ppy ligand, were prepared. The X-ray crystal structure of all complexes, including 3a (R = H) and 3b (R = Me), showed that while the carboranyl C–C bond distance increases with the increasing steric effect of the 2-R substituent (3a–3d), the bond distance is more likely to be influenced by the electronic effect of the substituent for the 2-aryl substituted complexes (3e–3g). The absorption and emission bands of all complexes were red-shifted with respect to those of the parent (ppy)2Ir(acac) (4). While 3a–3d exhibited intense green phosphorescence with good quantum efficiency in toluene (ΦPL = 0.17–0.47), the complexes were poorly emissive in THF (ΦPL < 0.004). In a PMMA film, however, 3a–3d became substantially emissive (ΦPL = 0.11–0.14, 8 wt% Ir), albeit less emissive than 4 (ΦPL = 0.15). In contrast, the 2-aryl substituted 3e–3g were almost non-emissive in both the solution and solid states. All complexes underwent facile carborane-centered, electrochemical reduction (Eonset = −2.01 to −1.22 V). The potential values of these reductions increased with increases in the electron accepting ability of the 2-R group (H < alkyl < aryl) and were largely shifted anodically with respect to those of 4 and 5-carborane substituted complexes. This reduction behavior of 3a–3g implies that the LUMO contribution of 2-R-o-carborane units increases through the substitution at the 4-position of the ppy ligand and is influenced by the nature of the 2-R group, which may be responsible for facile carboranyl C–C bond variation leading to efficient quenching of the emissive excited states.

The substituent effect of 2-R-o-carborane on the photophysical properties of iridium(III) cyclometalates

Ethylene tetramerization catalyst systems comprising a Cr(III) complex containing PNP ligands and methylaluminoxane (MAO) are useful for the production of 1-octene. However, a concern with these systems is the use of expensive MAO in excess. Herein, we report a catalytic system that avoids the use of MAO. Metathesis of CrCl3(THF)3 and [(CH3CN)4Ag]+[B(C6F5)4]− afforded [L4CrIIICl2]+[B(C6F5)4]− (L = CH3CN or tetrahydrofuran (THF)), which was converted to [(PNP)CrCl2L2]+[B(C6F5)4]−, where PNP is iPrN(PPh2)2 (1) or [CH3(CH2)16]2CHN(PPh2)2 (2). The molecular structures of [(THF)4CrIIICl2]+[B(C6F5)4]− and [1-CrCl2(THF)2]+[B(C6F5)4]− were unambiguously determined by X-ray crystallography. The cationic (PNP)CrIII complexes paired with [B(C6F5)4]− anions, that is, [(PNP)CrCl2(CH3CN)2]+[B(C6F5)4]−, exhibited high activity in chlorobenzene when activated with common trialkylaluminum species (Me3Al, Et3Al, and iBu3Al). The activities and selectivity were comparable to those of the original MAO-based Sasol system (1-C...

Methylaluminoxane-Free Chromium Catalytic System for Ethylene Tetramerization.

The self-assembly of Cs-symmetric tetrapyridyl cobalt–metalloligand 2 with three half-sandwich diruthenium acceptors, 3–5, led to the formation of A4D2 (A = acceptor, D = donor) metallacages 6–8, as shown by ESI mass spectrometry, NMR spectroscopy, and X-ray crystallography. The solid-state structures of 6–8 revealed that the length of the acceptor unit greatly influences the molecular packing of these metallacages. Hence, in the solid state, 6–8 can be considered to have waterwheel-shaped, tweezer-shaped, and butterfly-like architectures, respectively.

Ji Yeon Ryu

Papers

Ruthenium-Catalyzed C–H Activation of Salicylaldehyde and Decarboxylative Coupling of Alkynoic Acids for the Selective Synthesis of Homoisoflavonoids and Flavones

Bifunctional N-heterocyclic carbene ligands for Cu-catalyzed direct C–H carboxylation with CO2

The substituent effect of 2-R-o-carborane on the photophysical properties of iridium(III) cyclometalates

Methylaluminoxane-Free Chromium Catalytic System for Ethylene Tetramerization.

Ruthenium–Cobalt Bimetallic Supramolecular Cages via a Less Symmetric Tetrapyridyl Metalloligand and the Effect of Spacer Units