Mono- and Bis-Phosphine Promoted Incorporation of Boron, Nitrogen, and Phosphorus into Heterocycles via Staudinger Reactions of Borafluorene Azides.

We report the synthesis and characterization of a series of BNP-incorporated borafluorenate heterocycles formed via thermolysis reactions of pyridylphosphine and bis(phosphine)-coordinated borafluorene azides. The use of diphenyl-2-pyridylphosphine (PyPhP), trans-1,2-bis(diphenylphosphino)ethylene (PhP(H)C═C(H)PPh), and bis(diphenylphosphino)methane (PhPC(H)PPh) as stabilizing ligands resulted in Staudinger reactions to form complex heterocycles with four- (BNP, BNPC, PN) and five-membered (BNPC and BNPC) rings, which were successfully isolated and fully characterized by multinuclear NMR and X-ray crystallography. However, when bis(diphenylphosphino)benzene (PhP-Ph-PPh) was used as the ligand in a reaction with 9-bromo-9-borafluorene (BF-Br), due to the close proximity of the donor P atoms, the diphosphine-stabilized borafluoronium ion with an unusual borafluorene dibromide anion was formed.

Unveiling Three Interconvertible Redox States of Boraphenalene.

Neutral 1-boraphenalene displays the isoelectronic structure of the phenalenyl carbocation and is expected to behave as an attractive organoboron multi-redox system. However, the isolation of new redox states have remained elusive even though the preparation of neutral boron(III)-containing phenalene compounds have been extensively studied. Herein, we have adopted an N-heterocyclic carbene ligand stabilization approach to achieve the first isolation of the stable and ambipolar 1-boraphenalenyl radical .

Air- and photo-stable luminescent carbodicarbene-azaboraacenium ions.

Substitution of a C=C bond by an isoelectronic B-N bond is a well-established strategy to alter the electronic structure and stability of acenes. BN-substituted acenes that possess narrow energy gaps have attractive optoelectronic properties. However, they are susceptible to air and/or light.

Bis(9-Boraphenanthrene) and Its Stable Biradical.

Selective and site-specific boron-doping of polycyclic aromatic hydrocarbon frameworks often give rise to redox and/or photophysical properties that are not easily accessible with the analogous all-carbon systems. Herein, we report ligand-mediated control of boraphenanthrene closed- and open-shell electronic states, which has led to the first structurally characterized examples of neutral bis(9-boraphenanthrene) (-) and its corresponding biradical (). Notably, compounds and show intramolecular charge transfer absorption from the 9-boraphenanthrene units to -quinodimethane, exhibiting dual (red-shifted) emission in solution due to excited state conjugation enhancement (ESCE).

Photochemically and Thermally Generated BN-Doped Borafluorenate Heterocycles via Intramolecular Staudinger-Type Reactions.

A series of BN-incorporated borafluorenate heterocycles, bis(borafluorene-phosphinimine)s (-), have been formed via molecular Staudinger-type reactions. The reactions were promoted by light or heat using monodentate phosphine-stabilized 9-azido-9-borafluorenes (RP-BF-N; -) and involve the release of dinitrogen (N), migration of phosphine from boron to nitrogen, and oxidation of the phosphorus center (P to P). Density functional theory (DFT) calculations provide mechanistic insight into the formation of these compounds.