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Reactions of Boron-Derived Radicals with Nucleophiles

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journal contribution
posted on 30.11.2016, 00:00 by Lauren E. Longobardi, Pavel Zatsepin, Roman Korol, Lei Liu, Stefan Grimme, Douglas W. Stephan
Reactions of phenanthrenedione- and pyrenedione-derived borocyclic radicals, CnH8O2B­(C6F5)2 (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-(t-Bu)3PC14H7O2B­(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), and boronic ester C16H8O2B­(C6F5) (4). Reactions of secondary phosphines Ph2PH and tBu2PH 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]­[C14H8O2B­(C6F5)2] (12), while the reactions with quinuclidine and DMAP afforded the species 3-(C7H13N)­C14H7O2B­(C6F5)2 (13) and [H­(NC7H13)2]­[C14H8O2B­(C6F5)2] (14), and the salt [9,10-(DMAP)2C14H8O2B­(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.