Highly Efficient Synthesis and Solid-State Characterization of 1,2,4,5-Tetrakis(alkyl- and arylamino)benzenes and Cyclization to Their Respective Benzobis(imidazolium) Salts

Abstract

[reaction: see text] New synthetic methodology to a variety of 1,2,4,5-tetraaminobenzenes and their corresponding benzobis(imidazolium) salts has been accomplished. Palladium-catalyzed coupling of various 1,2,4,5-tetrabromo- or 1,2,4,5-tetrachlorobenzenes with aryl- or tert-alkylamines afforded the respective tetrakis(N-substituted)aminobenzenes in excellent yields. This enabled comparative solid-state structural analyses of this elusive class of electron-rich arenes with their oxidized derivatives. The tetraamines were found to undergo formylative cyclization to the corresponding benzobis(imidazolium) salts in good to excellent yields.

Synthesis and Study of 5,5′‐Bibenzimidazolylidenes and Their Bimetallic Complexes

“…Unfortunately, 5e failed to form under these conditions, consistent with the failure of 1,2,4,5-tetra(mesitylamino)-benzene to undergo formylative cyclization. [15] The 1 H NMR signals for the benzimidazolium protons in 5 were found between 8.9 and 10.5 ppm ([D 6 ]DMSO), which was within the range expected for 1,3-disubstituted benzimidazolium salts.…”

“…Collectively, these results were similar to those we obtained with various 1,2,4,5-tetraaminobenzenes prepared using an analogous fourfold aryl amination methodology from tetrachloro-or tetrabromobenzene. [15] Comprehensive structural analyses of 1,2,4,5-tetraaminobenzenes analogous to 4 revealed that the nitrogen lone pairs were rotated into the planes of their respective arene rings. [15] To determine if the bisarenes 4 exhibited similar structural characteristics, single crystals of 4a were grown by slowly cooling a saturated solution in toluene from reflux to ambient temperature and then analyzed by X-ray diffraction.…”

“…[15] Comprehensive structural analyses of 1,2,4,5-tetraaminobenzenes analogous to 4 revealed that the nitrogen lone pairs were rotated into the planes of their respective arene rings. [15] To determine if the bisarenes 4 exhibited similar structural characteristics, single crystals of 4a were grown by slowly cooling a saturated solution in toluene from reflux to ambient temperature and then analyzed by X-ray diffraction. [20] As shown in Figure 2, the tert-butyl groups on two of the nitrogen atoms were positioned above and below the planes of the arene rings with torsion angles of approximately 130°.…”

“…Four-fold aryl amination of 1,2,4,5-tetrabromo-or chlorobenzene afforded the respective tetraaminobenzenes bearing large N-substituents (R = tertiary alkyl, aryl) in excellent yields (typically Ͼ90 %). [15] After subsequent formylative cyclization and deprotonation, this methodology enabled isolation of the respective stable bis(NHC)s 1. [8] Although the physical and electronic properties of 1 can be tuned by modification of the N-substituents using the aforementioned synthetic approaches, [11] we desired methodology that would enable the incorporation of other aromatic linkers into bis(NHC) scaffolds, in particular biphenyl, leading to derivatives such as 2 (see Figure 1).…”

Quinobis(imidazolylidene): Synthesis and Study of an Electron‐Configurable Bis(N‐Heterocyclic Carbene) and Its Bimetallic Complexes

“…[20] Presumably, the acute N-C-N angle observed in 1 reflects the smaller steric bulk of mesityl versus tertiary alkyl groups. [80] Given the similar N-C-N angles in 1 and 1,3-dimesitylimidazolylidene (IMes) of 102.3(3) and 101.4(3)8, respectively, [81] the QBI could be viewed as two IMes fragments annulated by p-quinone.…”