Synthesis and Characterization of a Sterically Encumbered Unsymmetrical 9-Borafluorene, Its Pyridine Adduct, and Its Dilithium Salt

Abstract

The reaction of 2,6-(4-t-BuC 6 H 4 ) 2 C 6 H 3 Li with BH 2 Cl‚SMe 2 in hexane or Et 2 O solution affords the terphenyl-substituted unsymmetrical 9-borafluorene 1-(4-tert-butylphenyl)-7-tertbutyl-9-(bis-2,6-(4-tert-butylphenyl)phenyl)-9-borafluorene (1) in good to moderate yields. Addition of pyridine gives the colorless crystalline adduct 1‚py. Compound 1 is readily reduced to the deep red heteroaromatic dianionic (µ 2 -η 5 ,η 5 -1-(4-tert-butylphenyl)-7-tert-butyl-9-(bis-2,6-(4-tert-butylphenyl)phenyl)-9-borafluorenyl)bis(diethyl ether)dilithium ( 2) with excess lithium powder in Et 2 O solution. Reactions of the dianionic 2 with various metal salts leads to reduction of these salts, and bright yellow 1 is recovered in essentially quantitative yields. Compounds 1, 1‚py, and 2 were characterized by 1 H, 13 C, and 11 B NMR spectroscopy and compounds 1‚py and 2 also by single-crystal X-ray diffraction.

The Pentaphenylborole–2,6‐Lutidine Adduct: A System with Unusual Thermochromic and Photochromic Properties

“…The BÀN bond in 1 b (1.6567 (3) ) is considerably longer than that in the chloroborole 4-picoline adduct (1.6022(3) ), [9b] and the sterically highly hindered borafluorene systems (1.638 (3) ). [10] In fact, the value in 1 b is much more comparable to that observed in the aforementioned FLP of B(C 6 F 5 ) 3 and 2,6-lutidine, which dissociates at room temperature in solution. [11] In comparison with PPB, the molecular structure of 1 b reveals significant strain, as shown by the torsion angles of the borole.…”

2,6-Di(4-t-butylphenyl)phenyl-group 13 organometallic compounds

“…It has been shown that this ligand has the tendency for facile intramolecular C-H bond activation of the ortho position of the outer phenyl ring, which may serve as a mechanism to form an in situ generated bidentate ligand that provides robust steric protection for the metal center [9]. The literature reveals a paucity of reports of 2,6-di(4-t-butylphenyl)phenyl based group 13 compounds [10,11]. The reactivity of RLi (R = 2,6-(4-t-BuC 6 H 4 ) 2 C 6 H 3 ) with group 13 metals was of interest, as to ascertain the stability and structural properties of the ligand-metal complexes.…”

(Hetero)arene-fused boroles: a broad spectrum of applications

“…Besides these three widely applied approaches, which can assemble 9-aryl-9-borauorenes in one step, the Wehmschulte group synthesized two unsymmetric 9-borauorenes (2a and 2b, Scheme 3, path h) in one step by using H 2 ClB$SMe 2 as the boron source. 75,76 The formation of the borole ring takes place via a facile intramolecular C-H activation process, but the requirement of bulky terphenyl precursors limits its further application.…”