Reactions of Boron-Derived Radicals with Nucleophiles

Abstract

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.

Consecutive reduction, radical-cyclization, and oxidative-dehydrogenation reaction of ortho-substituted diboryl compounds

“…The bond length of B1 (B1')-C8 (C8') (1.635(8) Å) in 2 2is considerably shorter than that in 1 2due to the formation of above plane. Notably, the central Ring B moiety has a small BLA: the C7-C8 and C8-C9' bond lengths are 1.422 (8) and 1.400(6) Å, respectively, while C7-C9 bond length is 1.403 7Å. This small BLA illustrates the aromatization of 1,4-cyclohexadiene, which is consistent with the Nucleus-Independent Chemical Shifts (NICS) calculations.…”

“…Bourissou et al 7 displayed a Gomberg-type dimerization process of P-coordinated boryl radical (D, Scheme 1) through single-crystal X-ray diffraction. Stephan et al 8 described the reaction process of phenanthrenedione-and pyenedione-derived borocyclic radicals (E, Scheme 1), C n H 8 O 2 B(C 6 F 5 ) 2 • (n =14 or 16) with a variety of nucleophiles.…”

Stable Boron Dithiolene Radicals

“…Whereas compound 4 was routinely isolated as pale yellow‐green crystals (Scheme ), repeated attempts to isolate and characterize other side products from the thick residue were unsuccessful. Interestingly, Stephan and co‐workers recently reported that phenanthrenedione‐ (Figure d) and pyrenedione‐derived borocyclic radicals exhibit unique reactivity with nucleophiles (phosphines, carbenes, amines, and pyridines) …”

“…The C(2)−C(3) bond in 4 [1.365(2) Å] compares well with reported imidazole C=C double bonds . The four‐coordinate boron atom in 4 exhibits a 11 B NMR resonance at δ =18.9 ppm, which is comparable to the values reported for the zwitterions containing dioxoborocyclic moieties ( δ =10.2–11.1 ppm) . While comparing well to those [1.732(4)– 1.737(2) Å] in carbene‐stabilized sulfenyl cations, the C(1)−S(1) bond in 4 [1.7256(18) Å] is about 0.09 Å longer than that in 3 .…”

Zinc‐Containing Radical Anions via Single Electron Transfer to Donor–Acceptor Adducts

“…[23] However,t reatment of agreen C 6 D 5 Br solution of 4 with two equivalents of 4-dimethylaminopyridine (NC 5 H 4 NMe 2 )i mmediately produced al ight orange solution. These species were not found to react with tBu 3 P, in contrast to the closely related borocyclic radicals, for which the nucleophilic aromatic CÀHs ubstitutionw as seen.…”