Très BN: The introduction of a BN dipole into the internal positions of pyrene (see scheme) provides a novel platform for heterocyclic fluorescent species. Comparisons of the photophysical and redox properties between the CC and BN analogues reveal both similarities and differences.

[structure: see text]. Phenanthrene analogues with internalized B-N moieties were found to afford blue light emission with good quantum efficiencies, whereas the isomeric species with peripheral B-N moieties displayed only UV emission behavior, like the all-carbon framework.

A series of alkyl (1-3), aryl (6), and benzo-annulated (4, 5) heteroaromatic triphenylene analogues with B(2)N(2)C(2) cores have been synthesized via chelation of pyridazine derivatives using difunctional Lewis acidic diborabiphenyl precursors. In contrast to triphenylene, NICS(1) calculations on 1 suggested high aromaticities for the central (-11.3 ppm) and outer borabenzene rings (-7.7 ppm), along with nonaromatic behavior for the pyridazine ring (-0.7 ppm). Crystal structure analyses supported this analysis. When the a- and c-faces of the pyridazine moiety were free of substitution (1, 3), planar structures resulted, but upon substitution, a twisted B(2)N(2)C(2) core was observed due to steric repulsion of neighboring hydrogen atoms (e.g., 5). The increase of steric bulk from H (1) to (i)Pr (3) in the planar species was found to result in a dimeric, head-to-tail herringbone packing motif, held together by close intermolecular B...N interactions of 3.39 Angstrom. One-electron reduction by Cp(2)Co was found to afford the radical anions of 3 and 5, which were characterized by broad, featureless singlets in the EPR spectra; [3](.)(-)[Cp(2)Co](+) was characterized by X-ray crystallography. While the planar structures (1-4) were observed to possess weak fluorescence (Phi(F) = 0.02-0.08) with either yellow-orange (ca. 555 nm) or green emission (521 nm), the twisted structures (5, 6) were found to be nonfluorescent.

Fluoride abstraction from a BODIPY dye gives a well defined borenium ion which can be converted to a borenium hydride via treatment with DIBAL-H.

A theoretical calculation of the aromaticity of benzene relative to (benzene)Cr(CO)3 (1) based on the exaltation of magnetic susceptibility criterion was carried out using ab initio MO theory. As others have also found, benzene exhibits a diamagnetic susceptibility exaltation, Λcalc = −15.1 ppm cgs, Λexp = −13.7 ppm cgs, and is aromatic. In contrast, (benzene)Cr(CO)3 (1) has a positive susceptibility exaltation, Λcalc = 12.3 ppm cgs, characteristic of an antiaromatic compound. The validity of susceptibility exaltation as an aromaticity indicator for organometallic compounds was also tested for (cyclobutadiene)Fe(CO)3 (16), which proved to be aromatic (Λcalc = −6.10 ppm cgs). The validity of the calculations was further supported by a comparison of the calculated isotropic susceptibility χav of 1 (−109.3 ppm cgs) with an experimental result (−113 ± 22 ppm cgs). The related NMR calculations for 1 reproduce very well the 13C solid state results of Waugh and also the experimental isotropic upfield shift of ca. 2 ppm seen in the 1H NMR spectra of complex 1 relative to benzene. Contrary to the usual assumptions, the in-plane shieldings of the complexed benzene ring are more important than the perpendicular (ring current) counterparts. As expected, the present theoretical study reproduces very well the experimental geometries, energies, and harmonic frequencies of the purely organic compounds, but there is also very good agreement in the calculated properties of the organometallic compounds, where such data are available for comparison. The present study is based on GIAO, CSGT, and IGAIM NMR calculations performed on the optimized geometry of the most stable conformation at the B3LYP/6-311+G** level for the 12 organic and organometallic compounds needed directly or indirectly for the “group increment” magnetic susceptibility exaltation determinations. The organometallic structures include Cr(CO)6 (10), (ethylene)Cr(CO)5 (11), (1,3-butadiene)Cr(CO)4 (12), (benzene)Cr(CO)3 (1), Fe(CO)5 (13), (ethylene)Fe(CO)4 (14), (1,3-butadiene)Fe(CO)3 (15), and (cyclobutadiene)Fe(CO)3 (16).