Synthesis, Coupling, and Condensation Reactions of 1,2‐Diborylated Benzenes: An Experimental and Quantum‐Chemical Study

Abstract

1,2-Bis(pinacolboryl)benzene (1,2-C(6)H(4) (Bpin)(2), 2) was synthesized in preparatively useful yields from 1,2-C(6)H(4)Br(2), iPrO-Bpin, and Mg turnings in the presence of 1,2-C(2)H(4)Br(2) as an entrainer. Compound 2 is a versatile starting material for the synthesis of (un)symmetrically substituted benzenes (i.e., 1,2-C(6)H(4)(Ar(1))(Ar(2))) through sequential Suzuki-Miyaura coupling reactions. Alternatively, it can be transformed into bis-borate Li(2)[1,2-C(6)H(4)(BH(3))(2)] (3) through reduction with Li[AlH(4)]. In the crystal lattice, the diethyl ether solvate 3·OEt(2) establishes a columnar structure that is reinforced by an intricate network of B-(μ-H)-Li interactions. Hydride-abstraction from compound 3 with Me(3)SiCl leads to the transient ditopic borane 1,2-C(6)H(4)(BH(2))(2), which can either be used in situ for subsequent hydroboration reactions or trapped as its stable NMe(2)Et diadduct (6). In SMe(2) solution, the putative diadduct 1,2-C(6)H(4)(BH(2)·SMe(2))(2) is not long-term stable but rather undergoes a condensation reaction to give 9,10-dihydro-9,10-diboraanthracene, HB(μ-C(6)H(4))(2)BH, and BH(3). 9,10-Dihydro-9,10-diboraanthracene was isolated from the reaction mixture as its SMe(2) monoadduct (7), which dimerizes in the solid state through two B-H-B bridges ((7)(2), elucidated by X-ray crystallography). In contrast, hydride-abstraction from compound 3 in THF or CH(2)Cl(2) provides the unique exo-adduct H(2)B(μ-H)(2)B(μ-C(6)H(4))(2)B(μ-H)(2)BH(2) (8, elucidated by X-ray crystallography). Quantum-chemical calculations on various conceivable isomers of [1,2-C(6)H(4)(BH(2))(2)](2) revealed that compound 8 was the most stable of these species. Moreover, the calculations confirmed the experimental findings that the NMe(2)Et diadduct of 1,2-C(6)H(4)(BH(2))(2) is significantly more stable than the corresponding SMe(2) complex and that the latter complex is not able to compete successfully with borane-dimerization and -condensation. The reaction cascade in SMe(2), which proceeds from 1,2-C(6)H(4)(BH(2))(2) to the observed adducts of HB(μ-C(6)H(4))(2)BH, has been elucidated in detail and the important role of B-C-B-bridged intermediates has been firmly established.

Control of Excited‐State Conformations in B,N‐Acenes

“…Bidentate interaction of lithium o ‐phenylbisborate 1 (Li 2 [1,2‐C 6 H 4 (BH 3 ) 2 ]) with hydrazine 2 a (R=Ph) provided 2,3,1,4‐benzodiazadiborinane 3 a in a one‐step process (Scheme ). The reaction was optimized, revealing toluene as the best solvent and a temperature of 60 °C for 6 h as the most suitable conditions (see the Supporting Information for details).…”

How Boron Doping Shapes the Optoelectronic Properties of Canonical and Phenylene‐Containing Oligoacenes: A Combined Experimental and Theoretical Investigation

“…The substituents R and R′ provide useful set‐screws to tailor the properties of 1 for a given purpose. The parent compound (R=R′=H) can readily be derivatized through hydroboration reactions to furnish brightly luminescent, yet air‐ and moisture‐sensitive products . 9,10‐Dimesityl‐9,10‐dihydro‐9,10‐diboraanthracene ( DBA ; Figure ) is long‐term stable, even under ambient conditions; a similarly stabilizing effect can be achieved through the introduction of 9‐anthryl substituents at the boron centers or by applying the concept of structural constraint .…”

Metal‐Free Ammonia–Borane Dehydrogenation Catalyzed by a Bis(borane) Lewis Acid

“…When the reaction was conducted at room temperature,n oH 2 evolution was observed (entry 5). Furthermore,a ryl bis(borohydride) 6 [28] was tested as acatalyst (entry 10). When methyl-substituted bis(boron) catalysts 3 [26] and 5 [27] were used, less H 2 evolution was observed (entries 7a nd 9).…”