Two-electron reduction of carbene-supported 9bromo-9-borafluorenes with excess KC 8 , Na, or Li-naphthalenide affords six N-heterocyclic carbene (NHC)-or cyclic-(alkyl)(amino) carbene (CAAC)-stabilized borafluorene anions (3-8)-the first isolated and structurally authenticated examples of the elusive 9-carbene-9-borafluorene monoanion. The electronic structure, bonding, and aromaticity of the boracyclic anions were comprehensively investigated via computational studies. Compounds 5 and 8 react with metal halides via salt elimination to give new B-E (E = Au, Se, Ge)containing materials (9-12). Upon reaction with diketones, the carbene ligand cleanly dissociates from 5 or 8 to yield new B-O containing spirocycles (13-14) that cannot be easily obtained using "normal" valent borafluorene compounds. Collectively, these results support the notion that carbene-stabilized monoanionic borafluorenes may serve as a new platform for the onestep construction of higher-value boracyclic materials.

The first examples of pyrene-fused Janus-type N-heterocyclic germylenes (NHGe) are reported.

Because of their rigidity,polycyclic aromatic hydrocarbons (PAHs) have become as ignificant building block in molecular materials chemistry.F usion or doping of boron into PAHs is known to improve the optoelectronic properties by reducing the LUMO energyl evel.H erein, we reporta comprehensive study on the syntheses, structures, and photophysical properties of an ew class of fused N-heterocyclic boranes (NHBs), pyrene-and benzene-linked in a" Janustype" fashion (2-4, 6-9,and 11). Remarkably,these examples of fused NHBs display fluorescent properties, and collectively their emission spans the visible spectrum.T he pyrene-fused NHBs all display blue fluorescence, as the excitationsa re dominated by the pyrene core. In notable contrast, the emission properties of the benzene-fused analogues are highly tunable and are dependent on the electronicso ft he NHB fragments (i.e.,t he functional group directly bound to the boron atoms). Pyrene-fused 2-4 and 11 represent the only molecules in whicht he K-region of pyrene is functionalized with NHB units,a nd while they exhibit distorted (twisted or stair-stepped) pyrene cores, benzene-fused 6-9 are planar. The electronic structure and optical properties of these materials were probed by computational studies, including an evaluation of aromaticity,e lectronic transitions, and molecular orbitals.