Redox- and Charge-State Dependent Trends in 5, 6, and 7-Membered Boron Heterocycles: A Neutral Ligand Coordination Chemistry Approach to Boracyclic Cations, Anions, and Radicals.

ConspectusBoron heterocycles represent an important subset of heteroatom-incorporated rings, attracting attention from organic, inorganic, and materials chemists. The empty p orbital at the boron center makes them stand out as quintessential Lewis acidic molecules, also serving as a means to modulate electronic structure and photophysical properties in a facile manner. As boracycles are ripe for extensive functionalization, they are used in catalysis, chemical biology, materials science, and continue to be explored as chemical synthons for conjugated materials and reagents.

Synthesis and Ring-Opening Metathesis Polymerization of a Strained -Silacycloheptene and Single-Molecule Mechanics of Its Polymer.

The - and -isomers of a silacycloheptene were selectively synthesized by the alkylation of a silyl dianion, a novel approach to strained cycloalkenes. The -silacycloheptene (-SiCH) was significantly more strained than the isomer, as predicted by quantum chemical calculations and confirmed by crystallographic signatures of a twisted alkene. Each isomer exhibited distinct reactivity toward ring-opening metathesis polymerization (ROMP), where only -SiCH afforded high-molar-mass polymer under enthalpy-driven ROMP.

Approaching Dianionic Tetraoxadiborecine Macrocycles: 10-Membered Bora-Crown Ethers Incorporating Borafluorenate Units.

The addition of non-benzenoid quinones, acenapthenequinone or aceanthrenequinone, to the 9-carbene-9-borafluorene monoanion (1) affords the first examples of dianionic 10-membered bora-crown ethers (2-5), which are characterized by multi-nuclear NMR spectroscopy ( H, C, B), X-ray crystallography, elemental analysis, and UV/Vis spectroscopy. These tetraoxadiborecines have distinct absorption profiles based on the positioning of the alkali metal cations. When compound 4, which has a vacant C B O cavity, is reacted with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate, a color change from purple to orange serves as a visual indicator of metal binding to the central ring, whereby the Na ion coordinates to four oxygen atoms.

Systematic Electronic and Structural Studies of 9-Carbene-9-Borafluorene Monoanions and Transformations into Luminescent Boron Spirocycles.

The impact of the exact spatial arrangement of the alkali metal on the electronic properties of 9-carbene-9-borafluorene monoanions is assessed, and a series of [K][9-CAAC-9-borafluorene] complexes (-) have been isolated (CAAC = cyclic(alkyl)(amino) carbene, (2,6-diisopropylphenyl)-4,4-diethyl-2,2-dimethyl-pyrrolidin-5-ylidene). Compound , which contains [B]-K(THF) interactions, is compared to charge-separated -, which were prepared by capturing the potassium cations with 18-crown-6, 2.2.