Enantioenriched BoronC,N‐Chelates via Chirality Transfer

Abstract

Dedicated to Professor Andreas Pfaltz on the occasion of his 75th birthday.

Chirality Transfer of Stereogenic Boron Centers Enabled by a SN2-Type Mechanism

“…This coordination results in formation of the ( S ) B -configured C,N -chelate 4 from the ( S ) B - 5 (Scheme , Paths I–III). Furthermore, a preliminary investigation of the O,N -chelates 3 revealed a dynamic B–N bond . The associated equilibria of the dynamic B–N bond are depicted in Scheme , top, and similar equilibria have been reported for related boron chelates. − …”

“…Furthermore, a preliminary investigation of the O,Nchelates 3 revealed a dynamic B−N bond. 4 The associated equilibria of the dynamic B−N bond are depicted in Scheme 2, top, and similar equilibria have been reported for related boron chelates. 19−21 Starting from the different isomers of the B−N equilibrium, the chirality transfer might proceed through different reaction pathways.…”

“…The B–N bond barrier of C,N -chelate ( S ) B - 4b was determined by racemization kinetics as Δ G ‡ B–N = 125.1 kJ mol –1 and was higher than for all O,N -chelates ( R ) B - 3 . The stability of the B–N bond of 4 explains its chemical and configurational stability (Figure b).…”

“…1,15 Within this course, we developed a strategy for accessing enantioenriched boron C,N-chelates (S) B -4 via chirality transfer from aminoalcohol borinates (R) B -3 (Scheme 1b). 4 We chose a boron-attached phenylpyridine ppy as a chelate ligand given its interesting photophysical properties. These properties include thermally activated delayed fluorescence (TADF) 17 or photoisomerization reactions.…”

“…The structural study of O,N-chelates 3 commenced with a detailed investigation of the dynamic processes involving the B−N dative bond (Figure 1a). 4 This study should help one to better evaluate the equilibria precluding reaction paths I − III (Scheme 2). Previously, the dynamic behavior was studied by 1 1b).…”