Experimentelle Beiträge zum Valenz‐Problem des Bors, IV.: Die Valenz‐Äußerungen des Bors im Tri‐benzyl‐, Tri‐ p ‐xylyl‐ und Tri‐α‐naphthyl‐bor

Synthetic Approaches to Triarylboranes from 1885 to 2020

“…To make the synthesis safer,B rown and co-workersu sed boron trifluoride etherate( BF 3 •OEt 2 )i nstead of gaseous boron trifluoride. Furthermore, they found that the triarylborane they synthesized was stable to air for more than one year.A st his finding was in contrast with the reports of Krause et al, [65] Brown et al had ac loser look into the geometry of the compound. They assigned the discrepancy between their and the earlier results to the existence of two possible rotational conformers, i.e.,s teric hindrance resulted in restricted rotationa roundt he BÀCb onds.…”

“…In 1930, Krause and co-workersa lso reported the synthesis of tri-p-xylylborane 9 and tri-a-naphthylborane 10,w hich were investigated similarly to the previousc ompounds 2 and 8. [65] For the isolation of 9 and 10,t he work up was slightly modified. Thus, to quench the remaining Grignard reagent, water was added and the resulting crude mixture was distilledw ith exclusion of air,a sn oneo ft he previously synthesized triarylboranes are stable to air.…”

“…This assumption was confirmed by elemental analysis of the reaction products. In 1930, Krause and co‐workers also reported the synthesis of tri‐ p ‐xylylborane 9 and tri‐α‐naphthylborane 10 , which were investigated similarly to the previous compounds 2 and 8 [65] . For the isolation of 9 and 10 , the work up was slightly modified.…”

Optimization of Aqueous Stability versus π‐Conjugation in Tetracationic Bis(triarylborane) Chromophores: Applications in Live‐Cell Fluorescence Imaging

“…The first studies in this field were done by Krause and co‐workers in 1924 . They found that BPh 3 was unstable in air, whereas tri‐α‐naphthylborane was almost air‐stable . Wittig and co‐workers synthesized tri‐( o ‐biphenyl)borane and tri‐4‐( N , N ‐dimethylamino)phenylborane, which were both found to be air‐stable for approximately one week .…”

“…[4] They found that BPh 3 was unstablei na ir,w hereas tri-a-naphthylboranew as almost air-stable. [5] Wittig and coworkers synthesizedt ri-(o-biphenyl)borane and tri-4-(N,N-dimethylamino)phenylborane, whichw ere both found to be airstable for approximately one week. [6] They explained the stabil-ity of the former compound by steric protection ando ft he latter by the electronic + +M effect of the amine substituents.I n 1957, Brown andD odson reported the synthesis of the first completely air-stable triarylborane, namely trimesitylborane (2,4,6-trimethylphenyl = mesityl = Mes), and concluded, after oxygen reactivity tests, that the stability increases with the "shielding of the boron atom by the surrounding aryl groups".…”