Synthesis and structure of hypervalent boron (10-B-5) compounds bearing a 2,6-(p-tolyloxymethyl)benzene tridentate ligand

Abstract

Several organoboron compounds having a tridentate ligand based on 2,6-bis(p-tolyloxymethyl)benzene (5) were prepared. X-ray crystallography revealed that the distances between the central boron and both oxygen atoms of the tridentate ligand varied from 2.50 Å to 3.16 Å . The boron atom of the pinacolato derivative (5a) was found to be tricoordinated, whereas those of the diphenyl (5b) and the catecholato derivative (5c) were pentacoordinated, although these molecular structures were unsymmetrical. Compound 5c was found to have the strongest BÀ ÀO interactions among this series because the BÀ ÀO distances of 5c (av. 2.60 Å ) are shorter than those for 5b (av. 2.65 Å ), and this could mainly come from the electronic effect of the substituents at the boron atom.

A Hypervalent Pentacoordinate Boron Compound with an N−B−N Three-Center Four-Electron Bond

“…Since the former smaller basis set seemed to be sufficient for obtaining structural parameters similar to those for the X-ray structure, we decided to use it for further computations. Furthermore, the B3PW91 functional has been found to be more superior to the B3LYP functional for reproducing structural parameters of X-ray structures for analogous hypervalent carbon and boron compounds bearing neutral oxygen donors at the apical positions with only a slight overestimation of the bond lengths (deviation: 0.1% to 1.2%). ,− Thus, this functional was adopted in a combination with the 6-31G(d) basis set. Selected structural parameters of the two states deduced with the B3PW91/6-31G(d) method are shown in Table alongside the experimental data.…”

“…Since the capability to form short hypervalent bonds would require the apical donor groups to be attached to a more flexible backbone, carbon compounds 3 and boron compounds 4 using a van Koten-type tridentate ligand with oxygen donor sites were examined (Figure ) . X-ray electron-density analyses and DFT calculations suggested that these compounds ( 3 and 4 ) were also hypervalent compounds.…”

Synthesis and Characterization of Terpyridine-Supported Boron Cations: Evidence for Pentacoordination at Boron

“…However, by deployment of the sterically rigid 1,8-dimethoxy-9-anthracenyl ligand framework (Chart , C ), Akiba and co-workers have successfully prepared, and structurally characterized, a raft of pentacoordinate boron compounds. The geometry about the central boron atom in each case is a result of a variety of factors including the inflexible ligand backbone, the pendant donor atoms in the 1 and 8 positions, and the nature of the substituents at the boron atom.…”

Generation of triplet carbenes by oxidation of an allene compound

“…The geometries and relative stabilities of the singlet and triplet states of 8a (A = S) and 8b (A = NMe) were calculated at the B3PW91/6‐31G(d) level . The triplet states ( 8a T and 8b T , respectively) were found to be favored over the corresponding closed‐shell singlet states ( 8a CS and 8b CS , respectively) for both compounds (Δ E ST = E CS − E T = 12.6 and 14.0 kcal/mol for 8a and 8b , respectively).…”