R–Ph–B(FMes)2 compounds exhibit low reduction potentials, bright emission, a TICT state and unusual long-lived phosphorescence at low temperature.

Aromatic hydrogenation is a challenging transformation typically requiring alkali or transition metal reagents and/or harsh conditions to facilitate the process. In sharp contrast, the aromatic heterocycle 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene is shown to be reduced under 4 atm of H2 to give [3.1.0]bicylo reduction products, with the structure of the major isomer being confirmed by X-ray crystallography. NMR studies show this reaction proceeds via a reversible 1,4-H2 addition to generate an intermediate species, which undergoes an irreversible suprafacial hydride shift concurrent with P-P bond formation to give the isolated products. Further, para-hydrogen experiments confirmed the addition of H2 to triphosphabenzene is a bimolecular process. Density functional theory (DFT) calculations show that facile distortion of the planar triphosphabenzene toward a boat-conformation provides a suprafacial combination of vacant acceptor and donor orbitals that permits this direct and uncatalyzed reduction of the aromatic molecule.

The synthesis of indoles via the metal-catalyzed cross-coupling of ammonia is reported for the first time; the developed protocol also allows for the unprecedented use of methylamine or hydrazine as coupling partners. These Pd/Josiphos-catalyzed reactions proceed under relatively mild conditions for a range of 2-alkynylbromoarenes.

Inter- and intramolecular P/B frustrated Lewis pairs are shown to react with an N-sulfinylamine to form PNSOB linakages. These species can be regarded as phosphinimine-borane-stabilized sulfur monoxide complexes, and indeed these species act as sources of SO, effecting the oxidation of PPh3 and delivering SO to [RhCl(PPh3)3] and an N-heterocyclic carbene.

The synthesis and isolation of stable main group radicals remains an ongoing challenge. Here we report the application of frustrated Lewis pair chemistry to the synthesis of boron-containing radicals. H2 activation with polyaromatic diones and B(C6F5)3 leads to radical formation in good yields. These radicals are robust; they do not decompose on silica gel or react with O2 and are stable at 35 °C under N2 indefinitely. The mechanism of formation is explored experimentally, with support from DFT calculations. EPR and UV/vis spectroscopy as well as cyclic voltammetry data are provided, and the radicals are shown to react with cobaltocenes in one-electron chemical reductions to their corresponding borate anions.

An improved methodology for the synthesis of F-BODIPYs from dipyrrins and bis(dipyrrin)s is reported. This strategy employs lithium salts of dipyrrins as intermediates that are then treated with only 1 equiv of boron trifluoride diethyletherate to obtain the corresponding F-BODIPYs. This scalable route to F-BODIPYs renders high yields with a facile purification process involving merely filtration of the reaction mixture through Celite in many cases.

A series of alkyl-substituted ketones are shown to activate hydrogen in the presence of B(C6F5)3, affording the corresponding borinic esters RR'CHOB(C6F5)2. The mechanism is shown to proceed via H2 activation, hydride delivery and protonation of a C6F5 group. The aliphatic aldehyde Et2CHCHO reacts with B(C6F5)3 or BPh3 to give boron enolates Et2C[double bond, length as m-dash]CH(OBAr2) (Ar = C6F5, Ph). These latter species are amenable to FLP-catalyzed reduction to the corresponding borinic esters.

Reactions of phenanthrenedione- and pyrenedione-derived borocyclic radicals, CHOB(CF) (n = 14 (1), 16 (3)), with a variety of nucleophiles have been studied. Reaction of 1 with P(t-Bu) affords the zwitterion 3-(t-Bu)PCHOB(CF) (5) in addition to the salt [HP(t-Bu)][CHOB(CF)] (6). In contrast, the reaction of 1 with PPh proceeds to give two regioisomeric zwitterions, 1-(PhP)CHOB(CF) (7a) and 3-(PhP)CHOB(CF) (7b), as well as the related boronic ester CHOB(CF) (2). In a similar fashion, 3 reacted with PPh to give 3-(PhP)CHOB(CF) (8a), 1-(PhP)CHOB(CF) (8b), and boronic ester CHOB(CF) (4). Reactions of secondary phosphines PhPH and tBuPH with 3 yield 3-(RPH)CHOB(CF) (R = Ph (9), t-Bu (10)). The reaction of 1 with N-heterocyclic carbene IMes afforded 3-(IMes)CHOB(CF) (11) and [IMesH][CHOB(CF)] (12), while the reactions with quinuclidine and DMAP afforded the species 3-(CHN)CHOB(CF) (13) and [H(NCH)][CHOB(CF)] (14), and the salt [9,10-(DMAP)CHOB(CF)][CHOB(CF)] (15), respectively. These products have been fully characterized, and the mechanism for the formation of these products is considered in the light of DFT calculations.