Electronic Push–Pull Modulation by Peripheral Substituents in Pentaaryl Boroles

Abstract

Establishing access to a bulky tetraaryl dilithiobutadiene (Ph*C)4Li2 (Ph*=3,5‐tBu2(C6H3)) allowed for the synthesis of five‐membered heterocycles with incorporated main‐group elements. Along with an amino borole, a set of substituted pentaaryl boroles (Ph*C)4BAr has been synthesized. The examination of their absorption spectra and computational studies by means of DFT granted insight into the influence of peripheral substituents on the electronic features of the parent pentaphenyl borole (PhC)4BPh. Introduction of the more electron‐rich Ph* residue at the carbon atoms increases the HOMO energy, redshifting the visible π/π*‐absorption bands compared with the parent pentaphenyl borole. The influence on the frontier orbitals of three different boron‐bound aryls with electronically modulating substituents in the remote 3,5‐positions Ar=3,5‐R2‐C6H3 (R=Me, H, CF3) was studied. The substituents were found to increase (+I effect, Me) or decrease (−I effect, CF3) the LUMO energy, thus directly affecting the visible absorption spectra. This represents the first study on HOMO–LUMO‐gap adjustments by a combined push–pull approach of a substituted pentaphenylborole.

2,5-Bis-trimethylsilyl substituted boroles

“…47,83 We are eager to extend the library of accessible free boroles with regards to the substituents attached to boron and carbon atoms of the central moiety and to study the electronic impacts of each individual substituent. 84 Here we report on the synthetic access to 2,5-bis-trimethylsilyl substituted boroles.…”

A Neutral “Aluminocene” Sandwich Complex: η1‐ versus η5‐Coordination Modes of a Pentaarylborole with ECp* (E=Al, Ga; Cp*=C5Me5)

“…We recently reported the synthesis of a set of novel, highly soluble tert ‐butyl‐decorated pentaphenyl boroles (Ph*C) 4 BR [Ph*=3,5‐ t Bu 2 (C 6 H 3 )] . We are interested in further expanding the chemical scope of boroles as ligands to the p‐block elements.…”

“…We recently reported the synthesis of aset of novel, highly soluble tert-butyl-decorated pentaphenyl boroles (Ph*C) 4 BR [Ph* = 3,5-tBu 2 (C 6 H 3 )]. [12] We are interested in further expanding the chemical scope of boroles as ligands to the pblock elements.T oc ircumvent salt metathesis reactions,w e treated borole (Ph*C) 4 BXyl F (A)w ith the established, potentially reductive monovalent Group 13 reagents (AlCp*) 4 and GaCp* (Scheme 1).…”

Ein neutraler “Aluminocen”‐Sandwich‐Komplex: η1‐ vs. η5‐Koordination eines Pentaarylborols mit ECp* (E=Al, Ga; Cp*=C5Me5)

“…Wenngleich nur wenige Kommentare diesbezüglich in der Literatur zu finden sind, liegt diese Seltenheit insbesondere von p‐Block‐Verbindungen vermutlich daran, dass Boroldiidsalze in Metathesereaktionen mit Hauptgruppenhalogeniden nicht als Ligandenquelle, sondern als Reduktionsmittel reagieren. Wir berichteten unlängst von der Synthese einiger substituierter Pentaphenylborole (Ph*C) 4 BR [Ph*=3,5‐ t Bu 2 (C 6 H 3 )] mit ausgeprägter Löslichkeit in unpolaren Lösungsmitteln . Wir beschäftigen uns mit der Erweiterung der Koordinationschemie von Borolen als Liganden auf die Hauptgruppenelemente.…”

“…Wirberichteten unlängst von der Synthese einiger substituierter Pentaphenylborole (Ph*C) 4 BR [Ph* = 3,5-tBu 2 (C 6 H 3 )] mit ausgeprägter Lçslichkeit in unpolaren Lçsungsmitteln. [12] Wirbeschäftigen uns mit der Erweiterung der Koordinationschemie von Borolen als Liganden auf die Hauptgruppenelemente.…”