Koichiro Mikami

A two-coordinate boron cation featuring C–B+–C bonding

Two-coordinate boron cations (R2B(+)), referred to as borinium ions, are chemical species in which the boron bears only four valence electrons, and that are isoelectronic with hypothetical carbon dications (R2C(2+)). Although lone-pair-donating substituents such as amino groups have enabled the isolation of several borinium ions, diarylated and dialkylated borinium derivatives remain entirely unexplored. Here, we present the synthesis, structure and reactivity of the dimesitylborinium ion, which displays unexpectedly high thermal stability. X-ray crystallography and (11)B NMR spectroscopy, supported by density functional theory calculations, reveal that the borinium ion adopts a linear two-coordinate structure in both the solid state and in solution. The boron centre is stabilized by pπ bonding from the mesityl groups and is free from coordination by the counterion or solvent molecules. This diarylborinium ion possesses exceptional Lewis acidity, accepting a pair of electrons from CO2 to cause an unusual deoxygenation reaction.

Helicity Induction in Three π‐Conjugated Chromophores by Planar Chirality of Calixamide

Shall we twist? Three-dimensional arrangement of π-conjugated chromophores with triple-stranded helicity was achieved by using the planar chirality of m-calix[3]amide. Based on spectroscopic data and theoretical calculations, the dynamic and preferred helical characters of bithiophene units embedded in the tubular molecule were elucidated, and the absolute configuration was determined.

Catalyst-dependent intrinsic ring-walking behavior on π-face of conjugated polymers

We show that ring-walking behavior on the π-face of conjugated polymers is catalyst-dependent, and this significantly affects the composition of the products in catalyst-transfer condensation polymerization (CTCP). Systematic mechanistic study by means of density functional calculations combined with experimental verification revealed that the activation energy of the ring-walking process on the π-face and the stability of the oxidative addition state (C–M–X) are key determinants of catalyst mobility. Our findings offer a rational basis for designing innovative catalysts and monomers for CTCP.