Syntheses and Reactions of a Stable 1,2‐Dichloro‐1,2‐diborolane and Aromatic Tetraboranes

Abstract

The 1,2-dichloro-1,2-diborolane 1b was isolated in good yield after the reaction of the 1,2-bis(dimethylamino)-1,2-diborolane 2c with BCl 3 . We prepared 2c from 1,2-bis(dimethylamino)-1,2-dichlorodiborane(4) (3) and TMEDA-free [1,3-bis(trimethylsilyl)allyl]lithium (5a·Li), which is accessible by deprotonation of 1,3-bis(trimethylsilyl)propene (4a) with nbutyllithium in diethyl ether. Upon its reaction with lithium in THF, the 1-allyl-2-chlorodiborane(4) 6a obtained in the first step undergoes an unprecedented ring closure with 1,2-migration of a trimethylsilyl substituent to yield the boronstabilized carbanion 7a. Reaction of 7a with either chlorotrimethylsilane or HCl gives 2c or 2d, respectively. The latter

Synthesis and Structure of a Carbene‐Stabilized π‐Boryl Anion

“…[2] Chemical reduction of haloboranes with KC 8 or Na/K alloy generally yields products from radical reactions, that is, C À H bond insertion, [3] homocoupling, and rearrangement. [4,5] In 2006, the groups of Nozaki and Yamashita isolated the first structurally characterized boryllithium reagent of type A by reduction of the corresponding 2-halo-1,3,2-diazaborole.…”

1,2‐Diboracyclopentanes without Strong Donor Substituents: Synthesis, Reactions, and Computational Analysis

“…Reaction of the 1,2-dichloro-1,2-diboracyclopentane 1c [2] with duryllithium afforded 1a in 90 % yield (Scheme 2). Upon melting of 1a or heating solutions of 1a at reflux in benzene, a mixture of compounds was obtained from which nonclassical diborirane 5a could be isolated as the main product (55-60 %).…”

“…The structure of 1a ( Figure 1) resembles that of 1c, [2] differences can be explained by increased steric hindrance and reduced hyperconjugation in 1a relative to those in 1c. Compound 1a deviates strongly from C s symmetry in the solid state mainly due to the positions of the duryl moieties.…”

“…1,2-Diboracyclopentanes with strong donor substituents at the boron centers [1,2] do not show any tendency to form nonclassical isomers. The latter have been computed to be preferred energetically in case of unsubstituted prototype 1u (Scheme 1): monohomoaromatic 2u and bishomoaromatic 3u are lower in energy than 1u by 2.5 and 18.9 kcal mol -1 , respectively, at the MP2/6-31G* level of theory.…”

Complexes with Sterically Bulky Allyl Ligands: Insights into Structure and Bonding

“…[33] The dimeric complex has Li1-O1 and Li2-O2 bond lengths that are indistinguishable at 1.87 Å, and the C-C allyl bonds are slightly more delocalized (∆ = 0.052 Å) than in {Li [1,1Ј,3- Figure 3). [42] The π-bonded allyl ligands are at an angle of 60-62°from the major chain axes, and the Li-C distances range from 2.16 Å to 2.35 Å. The average distance of 2.26 Å is considerably shorter than the corre-sponding separation in the polymeric {Li[1,3-Ph 2 C 3 H 3 ]· OEt 2 } ϱ (2.42 Å), [43] which reflects the presence of the coordinated ethers in the latter complex.…”