Chemistry of Boryllithium: Synthesis, Structure, and Reactivity

Evidence for extensive single-electron-transfer chemistry in boryl anions: isolation and reactivity of a neutral borole radical

Despite the synthesis of a boryl anion by Yamashita et al. in 2006, compounds that show boron-centered nucleophilicity are still rare and sought-after synthetic goals. A number of such boryl anions have since been prepared, two of which were reported to react with methyl iodide in apparent nucleophilic substitution reactions. One of these, a borolyl anion based on the borole framework, has now been found to display single-electron-transfer (SET) reactivity in its reaction with triorganotetrel halides, which was confirmed by the isolation of the first neutral borole-based radical. The radical was characterized by elemental analysis, single-crystal X-ray crystallography, and EPR spectroscopy, and has implications for the understanding of boron-based nucleophilic behavior and the emergent role of boron radicals in synthesis. This radical reactivity was also exploited in the synthesis of compounds with rare B-Sn and B-Pb bonds, the latter of which was the first isolated and structurally characterized compound with a "noncluster" B-Pb bond.

Heavy metal boryl chemistry: complexes of cadmium, mercury and lead

Synthetic routes to the first boryl complexes of cadmium and mercury are reported via transmetallation from boryllithium; the syntheses of related group 14 systems highlight the additional factors associated with extension to more redox-active post-transition elements.

Half-sandwich scandium boryl complexes bearing a silylene-linked cyclopentadienyl-amido ligand

A boryl scandium complex supported by the silylene-linked cyclopentadienyl-amido ligand was synthesized for the first time.

An efficient synthetic route to stable bis(carbene)borylenes [(L1)(L2)BH]

Two unsymmetrically substituted bis(carbene)borylene adducts [(L₁)(L₂)BH] and a radical cation [(L₁)(L₂)BH˙⁺, X⁻] are prepared by two- and one-electron reduction, respectively.

BN isosteres of indole

Indole is a heterocycle of great importance to biological systems and materials applications. Synthesis of indole and its derivatives has been a major focus of research for over a century. BN/CC isosterism is an emerging strategy for expanding the structural diversity of indole-based compounds. Two classes of BN indoles have been reported to date: the well-studied "external" BN indoles (or 1,3,2-benzodiazaborolines), and the recently reported "fused" BN indoles. This perspective presents the history of both classes of indole isosteres, with a general overview of their synthesis, functionalization, and properties.

Synthesis of a ruthenium bis(diisopropylamino(isocyano)borane) complex from the activation of an amino(cyano)borane

The reactivity of the amino(cyano)borane (i)Pr(2)NBH(CN) (2) towards [RuH(2)(η(2)-H(2))(2)(PCy(3))(2)] (3) was investigated. Our study reveals that the formation of the bis(isocyanoborane) ruthenium complex [RuH(CN)(CN-BHN(i)Pr(2))(2)(PCy(3))(2)] (6) occurs via the intermediacy of the bis(σ-B-H) ruthenium complex [RuH(CN)(H(2)BN(i)Pr(2))(PCy(3))(2)] (5). This transformation involves BCN linkage isomerisation in 2. The diisopropylaminoborane ligand in 5 can be displaced to ultimately produce the bis(σ-borane) complex [RuH(2)(η(2):η(2)-H(2)BN(i)Pr(2))(PCy(3))(2)] (4) as a by-product.

Oxidative geminal functionalization of organoboron compounds

Excellent tolerance: Stable acylboronates equipped with N-methyliminodiacetyl (MIDA) boryl groups ([B]) were prepared by using a sequence of oxidative manipulations at the boron-bound carbon center (green in scheme). Chemoselective transformations of these acylated organoboron building blocks yielded a range of multifunctionalized boron derivatives and supplied access to valuable borylated heterocycles (see scheme).

Disclosing the structure/activity correlation in trivalent boron-containing compounds: a tendency map

Most trivalent boron reagents are electrophiles owing to the vacancy for two electrons to fill the outer orbital of boron; however, interestingly, trivalent boron compounds can change their electrophilic character to a nucleophilic character by only changing the nature of the substituents on the boron atoms. With the help of computational tools, we have analyzed the structural- and electronic properties of boryl fragments that were either bonded to main-group metals or coordinated to transition-metals/rare-earth-metals and we have designed a map that might help to identify certain trends. This trend map will be useful for selecting an appropriate trivalent boron compound, depending on the sought reactivity.

Alkali-metal mediated reactivity of a diaminobromoborane: mono- and bis-borylation of naphthalene versus boryl lithium or hydroborane formation

Reaction of lithium with PDABBr [PDA = C(6)H(4)-1,2-(NTripp)(2), Tripp = 2,4,6-Pr(i)(3)C(6)H(2)] and naphthalene afforded 2- and 2,6-borylated naphthalenes; conversely, use of high-sodium lithium (0.5% Na) afforded the lithium boryl [(PDAB)Li(THF)(2)]; this work establishes that main group reagents can achieve selective borylations of fused polycyclic aromatics under mild conditions in good yields.

Nucleophilic boron strikes back

It has been demonstrated that the interaction of a simple Lewis base with tetraalkoxydiboranes generates an unusual nucleophilic character in one of the boryl moieties. The interaction of amines, N-heterocyclic carbenes (NHCs), and alkoxides with a diboron reagent results in the formation of a Lewis acid–base adduct, in which the formally intact sp2 boryl moiety becomes nucleophilic. We describe in this work the application of this new type of nucleophilic boron synthon in the selective preparation of organoboranes through β-boration and diboration reactions.

Luminescence properties of C-diazaborolyl-ortho-carboranes as donor-acceptor systems

Seven derivatives of 1,2-dicarbadodecaborane (ortho-carborane, 1,2-C(2)B(10)H(12)) with a 1,3-diethyl- or 1,3-diphenyl-1,3,2-benzodiazaborolyl group on one cage carbon atom were synthesized and structurally characterized. Six of these compounds showed remarkable low-energy fluorescence emissions with large Stokes shifts of 15100-20260 cm(-1) and quantum yields (Φ(F)) of up to 65% in the solid state. The low-energy fluorescence emission, which was assigned to a charge-transfer (CT) transition between the cage and the heterocyclic unit, depended on the orientation (torsion angle, ψ) of the diazaborolyl group with respect to the cage C-C bond. In cyclohexane, two compounds exhibited very weak dual fluorescence emissions with Stokes shifts of 15660-18090 cm(-1) for the CT bands and 1960-5540 cm(-1) for the high-energy bands, which were assigned to local transitions within the benzodiazaborole units (local excitation, LE), whereas four compounds showed only CT bands with Φ(F) values between 8-32%. Two distinct excited singlet-state (S(1)) geometries, denoted S(1)(LE) and S(1)(CT), were observed computationally for the benzodiazaborolyl-ortho-carboranes, the population of which depended on their orientation (ψ). TD-DFT calculations on these excited state geometries were in accord with their CT and LE emissions. These C-diazaborolyl-ortho-carboranes were viewed as donor-acceptor systems with the diazaborolyl group as the donor and the ortho-carboranyl group as the acceptor.