Structure of the carrier of the cross-polarization magic angle spinning carbon-13 nuclear magnetic resonance signal assigned to 3,4-dimethylenethiophene. Multiple position-labeling and chemical trapping in annealed glasses

Orbital Decomposition of the Carbon Chemical Shielding Tensor in Gold(I) N-Heterocyclic Carbene Complexes

The good performance of N‐heterocyclic carbenes (NHCs), in terms of versatility and selectivity, has called the attention of experimentalists and theoreticians attempting to understand their electronic properties. Analyses of the Au(I)–C bond in [(NHC)AuL]^+/0 (L stands for a neutral or negatively charged ligand), through the Dewar–Chatt–Duncanson model and the charge displacement function, have revealed that NHC is not purely a σ‐donor but may have a significant π‐acceptor character. It turns out, however, that only the σ‐donation bonding component strongly correlates with one specific component of the chemical shielding tensor. Here, in extension to earlier works, a current density analysis, based on the continuous transformation of the current density diamagnetic zero approach, along a series of [(NHC)AuL]^+/0 complexes is presented. The shielding tensor is decomposed into orbital contributions using symmetry considerations together with a spectral analysis in terms of occupied to virtual orbital transitions. Analysis of the orbital transitions shows that the induced current density is largely influenced by rotational transitions. The orbital decomposition of the shielding tensor leads to a deeper understanding of the ligand effect on the magnetic response properties and the electronic structure of (NHC)‐Au fragments. Such an orbital decomposition scheme may be extended to other magnetic properties and/or substrate‐metal complexes.

The chemistry of bisallenes

This review describes the preparation, structural properties and the use of bisallenes in organic synthesis for the first time. All classes of compounds containing at least two allene moieties are considered, starting from simple conjugated bisallenes and ending with allenes in which the two cumulenic units are connected by complex polycyclic ring systems, heteroatoms and/or heteroatom-containing tethers. Preparatively the bisallenes are especially useful in isomerization and cycloaddition reactions of all kinds leading to the respective target molecules with high atom economy and often in high yield. Bisallenes are hence substrates for generating molecular complexity in a small number of steps (high step economy).