Boron-Doped Pentacenes: Isolation of Crystalline 5,12- and 5,7-Diboratapentacene Dianions.

The syntheses, molecular structures, reactivities, and computational assessment of dipotassium diboratapentacene isomers are described ( and ). These compounds represent the first examples of aromatized diboraacenes where the boron atoms are spatially separated in different rings of the acene framework. Both and react with carbon dioxide (CO) via diastereoselective carboxylation of the pentacene backbone that likely proceeds by a frustrated Lewis pair-like mechanism.

Enhancing the Antiaromaticity of -Indacene through Naphthothiophene Fusion.

Addressing the instability of antiaromatic compounds often involves protection with bulky groups and/or fusion of aromatic rings, thus decreasing paratropicity. We report four naphthothiophene-fused -indacene isomers, one of which is more antiaromatic than parent -indacene. This surprising result is examined computationally through nucleus-independent chemical shift XY calculations and experimentally via nuclear magnetic resonance spectroscopy, X-ray crystallography, ultraviolet-visible spectrophotometry, and cyclic voltammetry, with the latter two indicating that this molecule possesses the lowest highest occupied molecular orbital-lowest unoccupied molecular orbital energy gap observed for heterocycle-fused -indacene.

Monoradicals and Diradicals of Dibenzofluoreno[3,2-]fluorene Isomers: Mechanisms of Electronic Delocalization.

The preparation of a series of dibenzo- and tetrabenzo-fused fluoreno[3,2-]fluorenes is disclosed, and the diradicaloid properties of these molecules are compared with those of a similar, previously reported series of anthracene-based diradicaloids. Insights on the diradical mode of delocalization tuning by constitutional isomerism of the external naphthalenes has been explored by means of the physical approach (dissection of the electronic properties in terms of electronic repulsion and transfer integral) of diradicals. This study has also been extended to the redox species of the two series of compounds and found that the radical cations have the same stabilization mode by delocalization that the neutral diradicals while the radical anions, contrarily, are stabilized by aromatization of the central core.

Serendipitous Rediscovery of the Facile Cyclization of Z,Z-3,5-Octadiene-1,7-diyne Derivatives to Afford Stable, Substituted Naphthocyclobutadienes.

The serendipitous isolation of very small amounts of two naphthocyclobutadiene (NCB) derivatives has led to the computational re-examination of the electrocyclization of Z,Z-3,5-octadiene-1,7-diyne as well as the experimental and computational study of diethynylindeno[2,1-a]fluorene derivatives that contain the 3,5-octadiene-1,7-diyne motif as part of a larger π-framework. In both cases the calculated potential energy surface strongly implicates two successive electrocyclic reactions to afford the antiaromatic products. With the octadienediyne fragment locked in the reactive conformation, the postulated diethynylindeno[2,1-a]fluorene intermediates afford the NCBs in modest to good yields.

Exploiting the Hydrogen Bond Donor/Acceptor Properties of PN-Heterocycles: Selective Anion Receptors for Hydrogen Sulfate.

We describe two novel hybrid receptors combining a phosphorus-/nitrogen-containing (PN) phosphonamidate heterocycle with urea recognition units in an arylethynyl backbone. Structural, spectroscopic and computational studies reveal that the origin of superior binding for hydrogen sulfate (HSO ) anion is correlated with the formation of strong hetero-complementary hydrogen bonds with the phosphonamidate motif. We further demonstrate that the hybrid host system is capable of capturing/transporting the HSO anion from an aqueous, biphasic system.

One-Step Conversion of Potassium Organotrifluoroborates to Metal Organoborohydrides.

This letter describes the one-step conversion of heteroatom-substituted potassium organotrifluoroborates (KRBF) to metal monoorganoborohydrides (MRBH) using alkali metal aluminum hydrides. The method tolerates a variety of functional groups, expanding MRBH diversity. Hydride removal with MeSiCl in the presence of dimethylaminopyridine (DMAP) affords the organoborane·DMAP (RBH·DMAP) adducts.