N-Heterocyclic Carbenes in Late Transition Metal Catalysis

: 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

The Golden Age of Transfer Hydrogenation

Conventional oxidations of organic compounds formally transfer hydrogen atoms from the substrate to an acceptor molecule such as oxygen, a metal oxide, or a sacrificial olefin. In acceptorless dehydrogenation (AD) reactions, catalytic scission of C-H, N-H, and/or O-H bonds liberates hydrogen gas with no need for a stoichiometric oxidant, thereby providing efficient, nonpolluting activation of substrates. In addition, the hydrogen gas is valuable in itself as a high-energy, clean fuel. Here, we review AD reactions selectively catalyzed by transition metal complexes, as well as related transformations that rely on intermediates derived from reversible dehydrogenation. We delineate the methodologies evolving from this recent concept and highlight the effect of these reactions on chemical synthesis.

http://science.sciencemag.org/content/sci/341/6143/1229712.full.pdf

Applications of acceptorless dehydrogenation and related transformations in chemical synthesis.

N atom, thus providing carbenes derived from pyrazolium, isothiazolium, and even quinolinium salts that contain a stabilizing heteroatom in a remote position (G-J in Figure 1). Recently, carbenes such as K, which are comprised of only one heteroatom and lack delocalization through the heterocycle, have been discovered as versatile ligands, thus constituting another important class of carbenes with low heteroatom stabilization. Both the synthesis of the organometallic complexes of these ligands as well as the (catalytic) properties of the coordinated metal centers generally show distinct differences, compared to the more classical NHC complexes, such as C2-metallated imidazolylidenes. This review intends to describe such differences and highlights the chemical peculiarities of these types of N-heterocyclic carbene complexes. It introduces, in a qualitative manner, the synthetic routes that have been established for the preparation of such complexes, covering the literature from the very beginning of activities in this area up to 2008. While specialized reviews on some aspects of the present topic have recently appeared,7 a comprehensive overview of the subject has not been available thus far. Rather than just being descriptive, the present account is mainly directed toward the impact of these still unusual metal-carbene bonding modes on the electronic properties and on the new catalytic applications that have been realized by employing such new carbene complexes. As a consequence of our focus on complexes with less-stabilized heterocyclic ligands, systems comprising acyclic carbenes have not been included, and the interested reader is, instead, referred to the pioneering and

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Beyond Conventional N-Heterocyclic Carbenes: Abnormal, Remote, and Other Classes of NHC Ligands with Reduced Heteroatom Stabilization

Preparation, Structure, and Ethylene Polymerization Behavior of Bis(imino)pyridyl Chromium(III) Complexes

Osmium–carbon double bonds: Formation and reactions

Direct Access to POP-Type Osmium(II) and Osmium(IV) Complexes: Osmium a Promising Alternative to Ruthenium for the Synthesis of Imines from Alcohols and Amines

Hydride Is Not a Spectator Ligand in the Formation of Hydrido Vinylidene from Terminal Alkyne and Ruthenium and Osmium Hydrides: Mechanistic Differences

The preparation, structure, dynamic behavior in solution, and reactivity of polyhydride complexes of platinum group metals, described during the last three decades, are contextualized from both organometallic and coordination chemistry points of view. These compounds, which contain dihydrogen, elongated dihydrogen, compressed dihydride, and classical dihydride ligands promote the activation of B–H, C–H, Si–H, N–H, O–H, C–C, C–N, and C–F, among other σ-bonds. In this review, it is shown that, unlike other more mature areas, the chemistry of polyhydrides offers new exciting conceptual challenges and at the same time the possibility of interacting with other fields including the conversion and storage of regenerative energy, organic synthetic chemistry, drug design, and material science. This wide range of possible interactions foresees promising advances in the near future.

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Montserrat Oliván

Papers

Preparation, Structure, and Ethylene Polymerization Behavior of Bis(imino)pyridyl Chromium(III) Complexes

Osmium–carbon double bonds: Formation and reactions

Direct Access to POP-Type Osmium(II) and Osmium(IV) Complexes: Osmium a Promising Alternative to Ruthenium for the Synthesis of Imines from Alcohols and Amines

Hydride Is Not a Spectator Ligand in the Formation of Hydrido Vinylidene from Terminal Alkyne and Ruthenium and Osmium Hydrides: Mechanistic Differences

Polyhydrides of Platinum Group Metals: Nonclassical Interactions and σ-Bond Activation Reactions