Double reduction of the THF adduct of 9H‐9‐borafluorene (1⋅THF) with excess alkali metal affords the dianion salts M2[1] in essentially quantitative yields (M=Li–K). Even though the added charge is stabilized through π delocalization, [1]2− acts as a formal boron nucleophile toward organoboron (1⋅THF) and tetrel halide electrophiles (MeCl, Et3SiCl, Me3SnCl) to form B−B/C/Si/Sn bonds. The substrate dependence of open‐shell versus closed‐shell pathways has been investigated.

Subvalent boron compounds contain boron atoms with oxidation numbers lower than +III. Over the last decades, the development of isolable derivatives has relied heavily on the use of specially designed ligands capable of stabilizing the electron‐rich boron centers electronically or through steric protection. Herein, we are exclusively reviewing anionic organo(hydro)boranes largely devoid of stabilizing ligands or heteroatom substituents. The restriction to these subvalent species is intended to minimize the risk of ligand artifacts being included when carving out the characteristic properties of the respective boron centers, such as nucleophilic or carbenoid behavior. The scope of this review encompasses triorganoborane radical monoanions ([·BR3]–) along with closed‐shell dianions ([:BR3]2–), boryl anions ([:BR2]–), as well as B–B single‐bonded diborane(6) dianions ([R3B–BR3]2–) and diborane(5) monoanions ([R2B–BR3]–), and finally B=B double‐bonded diborane(4) dianions ([R2B=BR2]2–). We are showing how these species are related to each other and comment on their bonding situations from an experimentalist's perspective.

9,10‐Dihydro‐9,10‐diboraanthracenes (DBAs) have low‐energy LUMOs and narrow HOMO–LUMO gaps and are thus attractive electron‐transporting and light‐emitting materials in optoelectronic devices. A systematic series of ten C‐halogenated 9,10‐(Mes)2‐DBAs was synthesized and studied by cyclic voltammetry, UV/Vis absorption and emission spectroscopy, and quantum‐chemical calculations (Mes=mesityl). We probed the influence of the nature of the halogen atoms and the halogen substitution patterns on key optoelectronic properties of the DBAs. All 9,10‐(Mes)2 derivatives can be reversibly reduced at the DBA cores and at electrode potentials between E1/2Red1=−1.84 and −1.26 V (vs. FcH/FcH+). The most bathochromic UV/Vis absorption and the fluorescence emission of each DBA correspond to an ICT transition between the Mes rings and the DBA core. Br substituents lower the DBA LUMO energy and narrow the energy gap to the highest degree along the series F

The mixed heteroadamantanes Si6Ge4 and Si6Sn4 are readily accessible from Me2ECl2/Si2Cl6/cat. Cl– (4 × EMe2, 2 × SiCl2, 4 × Si–SiCl3 vertices; E = Ge, Sn). Different from Si6Ge4, two...

9,10-Diboratatriptycene salts M2[RB(μ-C6H4)3BR] (R = H, Me; M+ = Li+, K+, [n-Bu4N]+) have been synthesized via [4+2] cycloaddition between doubly reduced 9,10-dihydro-9,10-diboraanthracenes M2[DBA] and benzyne, generated in situ from C6H5F...

The thermal decomposition from 50 to 250" of lauroyl, decanoyl, and octanoyl peroxides in solution in a high molecular weight hydrocarbon was studied. These peroxides are convenient sources of C-11, C-9, and C-7 straight-chain aliphatic free radicals, whose reactions may be considered as models for the higher molecular weight radicals formed during thermal cracking of polyolefins.The ratio of disproportionation to combination for these radicals is about 0.2, which is very similar to the values obtained for lower alkyl radicals in the gas phase. This ratio appears to be relatively independent of temperature. Intramolecular chain transfer, which results in the isomerization of the radical, occurs at the higher temperatures, and the process has an apparent activation energy of about 2 kcal per mole.The product distribution indicates that at reaction temperatures up to 250" a statistically random distribution of alkyl radicals is never achieved in solution. Since the radicals are formed in pairs, they tend to react with each other rather than with radicals formed from other peroxide molecules. This is demonstrated by the near absence of cross-combination products when two different peroxides are decomposed in the same solution simultaneously at 70". At 250", some cross-product is formed but less than one-fifth of the amount expected if the radicals were uniformly distributed in the solution. The activation energy for the formation of cross-product is of the same order as that for diffusion. The significance of these results in terms of the classical picture of "cage reactions" is discussed.

The B-nucleophilic 9H-9-borafluorene dianion reacts with 9-chloro-9-silafluorene to afford air-and moisture-stable silylborate salts M[Ar 2 (H)BÀ Si(H)Ar 2 ] (M[HBSiH], M = Li, Na). Li[HBSiH] and Me 3 SiCl give the BÀ pyridine adduct Ar 2 (py)BÀ Si-(H)Ar 2 ((py)BSiH) or the chlorosilane Li[Ar 2 (H)BÀ Si(Cl)Ar 2 ] (Li[HBSiCl]) in C 6 H 6 -pyridine or THF. In both cases, the first step is H À abstraction at the B center. The resulting free borane subsequently binds a py or thf ligand. While the py adduct is stable at room temperature, the thf adduct undergoes a 1,2-H shift via the cyclic B(μ-H)Si intermediate BHSi, which is afterwards attacked at the Si atom by a Cl À ion to give Li[HBSiCl]. DFT calculations were employed to support the proposed reaction mechanism and to characterize the electronic structure of BHSi. Treatment of Li[HBSiCl] with the N-heterocyclic carbene IMe introduces the neutral donor at the Si atom and leads to Ar 2 (H)BÀ Si(IMe)Ar 2 (HBSi(IMe)), a donor-acceptor-stabilized silylene.

Diboration and silaboration reactions are prominent tools to introduce valuable functional groups into organic substrates. To date, most diboranes(4) and silylboranes used for this purpose are electronically and/or kinetically stabilized...