The chemistry of heterocyclic carbenes has experienced a rapid development over the last years. In addition to the imidazolin-2-ylidenes, a large number of cyclic diaminocarbenes with different ring sizes have been described. Aside from diaminocarbenes, P-heterocyclic carbenes, and derivatives with only one, or even no heteroatom within the carbene ring are known. New methods for the synthesis of complexes with N-heterocyclic carbene ligands such as the oxidative addition or the metal atom template controlled cyclization of β-functionalized isocyanides have been developed recently. This review summarizes the new developments regarding the synthesis of N-heterocyclic carbenes and their metal complexes.

Heterocyclic Carbenes: Synthesis and Coordination Chemistry

: 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

Organocatalytic Reactions Enabled by N-Heterocyclic Carbenes.

Lead halide perovskite materials have attracted significant attention in the context of photovoltaics and other optoelectronic applications, and recently, research efforts have been directed to nanostructured lead halide perovskites. Collodial nanocrystals (NCs) of cesium lead halides (CsPbX3, X = Cl, Br, I) exhibit bright photoluminescence, with emission tunable over the entire visible spectral region. However, previous studies on CsPbX3 NCs did not address key aspects of their chemistry and photophysics such as surface chemistry and quantitative light absorption. Here, we elaborate on the synthesis of CsPbBr3 NCs and their surface chemistry. In addition, the intrinsic absorption coefficient was determined experimentally by combining elemental analysis with accurate optical absorption measurements. 1H solution nuclear magnetic resonance spectroscopy was used to characterize sample purity, elucidate the surface chemistry, and evaluate the influence of purification methods on the surface composition. We fi...

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Highly Dynamic Ligand Binding and Light Absorption Coefficient of Cesium Lead Bromide Perovskite Nanocrystals

Quantification and variation of characteristic properties of different ligand classes is an exciting and rewarding research field. N-Heterocyclic carbenes (NHCs) are of special interest since their electron richness and structure provide a unique class of ligands and organocatalysts. Consequently, they have found widespread application as ligands in transition-metal catalysis and organometallic chemistry, and as organocatalysts in their own right. Herein we provide an overview on physicochemical data (electronics, sterics, bond strength) of NHCs that are essential for the design, application, and mechanistic understanding of NHCs in catalysis.

The Measure of All Rings—N‐Heterocyclic Carbenes

Synthesis, Structure, and Reactivity of a 1sigma(4),3sigma(2)-Diphosphaallene We are grateful to the French Embassy in Japan for a grant to T.K., and to the CNRS for financial support of this work.

Novel stable phosphastannapropene derivatives. Synthesis and characterization

Free and Supported Phosphorus Ylides as Strong Neutral Broensted Bases.

κ-(BETS) 8 (Cu 2 Cl 6 )(CuCl 4 ) ( 1 ), θ-(BETS) 2 (CuCl 2 ) ( 2 ), (BETS) 2 (CuCl 4 ) ( 3 ) (BETS = bis(ethylenedithio)tetraselenafulvalene) have been prepared by diffusion-electrocrystallisation of BETS and (AsPh 4 ) 2 (Cu 2 Cl 6 ) solutions in chlorobenzene–ethanol. 2 has also been obtained by simple diffusion of BETS and (AsPh 4 ) 2 (Cu 2 Cl 6 ) solutions. 1 and 2 exhibit metal-like behaviour, down to 40 K for 1 and 4 K for 2 . 3 behaves as an insulator. The crystal structures of 1 , 2 , and 3 are determined by X-ray diffraction methods. The structures of 1 (at 140 and 25 K) and 2 are characterised by a strong disorder of their respective anions. The crystal structure of 3 shows an unusual packing of the BETS molecules, consisting of slipped stacked (BETS) 2 dimers, leading to insulating properties. Based on the structures of 1 (at 140 and 25 K), 2 and 3 , molecular and band structure calculations are carried out for the interpretation of the physical behaviours of these phases.

Structure and properties of BETS salts: κ-(BETS)8(Cu2Cl6)(CuCl4), θ-(BETS)2(CuCl2) and (BETS)2(CuCl4)

A new tetrapyridyl ligand (BDPEA) and the corresponding di-iron(III) μ-oxo complex were synthesized. The iron complex structure, determined by X-ray crystallography, exhibited the dinuclear core [Fe2III(BDPEA)2(μ-O)(NO3)2](NO3)2 (1). With monopersulfate as oxidant, this complex catalyzed the conversion of 2,4,6-trichlorophenol and catechol, with a better activity and an enhanced life-time compared to the previously reported complex [FeIII(BDPMA)](NO3)3 (2) (BDPMA: bis[di(2-pyridyl)methyl]amine) which contained two fragile benzylic C–H bonds on the tetrapyridyl ligand.

Heinz Gornitzka

Papers

Synthesis, Structure, and Reactivity of a 1sigma(4),3sigma(2)-Diphosphaallene We are grateful to the French Embassy in Japan for a grant to T.K., and to the CNRS for financial support of this work.

Novel stable phosphastannapropene derivatives. Synthesis and characterization

Free and Supported Phosphorus Ylides as Strong Neutral Broensted Bases.

Structure and properties of BETS salts: κ-(BETS)8(Cu2Cl6)(CuCl4), θ-(BETS)2(CuCl2) and (BETS)2(CuCl4)

Second generation of a polypyridine ligand to mimic enzymes containing non-heme iron centers