Reactions of Boron-Derived Radicals with Nucleophiles

Reactions of phenanthrenedione- and pyrenedione-derived borocyclic radicals, CnH8O2B(C6F5)(2)(center dot) (n = 14 (1), 16 (3)), with a variety of nucleophiles have been studied. Reaction of 1 with P(t-Bu)(3) affords the zwitterion 3-(tBu)(3)PC14H7O2B(C6F5)(2) (5) in addition to the salt [HP(t-Bu)(3)][C14H8O2B(C6F5)(2)] (6). In contrast, the reaction of 1 with PPh3 proceeds to give two regioisomeric zwitterions, 1-(Ph3P) C14H7O2B (C6F5)(2) (7a) and 3-(Ph3P)C14H7O2B(C6F5)(2) (7b), as well as the related boronic ester C14H8O2B(C6F5) (2). In a similar fashion, 3 reacted with PPh3 to give 3(Ph3P)C16H7O2B(C6F5)(2) (8a), 1-(Ph3P)C16H7O2B(C6F5)(2) (8b), C16H8O2B(C6F5) (4). Reactions of secondary phosphines Ph2PH and tBu(2)PH with 3 yield 3-(R2PH)C16H7O2B(C6F5)(2) (R = Ph (9), t -Bu (10)). The reaction of 1 with N -heterocyclic carbene IMes afforded 3-(IMes)C14H7O2B(C6F5)(2) (11) and [IMesH] [Ci(4)H(8)O(2)B(C6F5)(2)] (12), while the reactions with quinuclidine and DMAP afforded the species 3-(C7H13N)C14H7O2B(C6F5)(2) (13) and [H(NC7F13)(2)][CI4H8O2B(C6P5)(2)] (14), and the salt [9,10-(DMAP)(2)C-14}H8O2B(C6F5)(2)][C14H8O2B(C6F5)(2)] (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.