Electrophilic nitration of phenylboron dichloride with nitronium tetrafluoroborate and N-nitro-2,4,6-collidinium tetrafluoroborate was investigated in nitromethane solution. The reactions give 10-18% ortho, 67-69% meta, and 15-21% para isomer. NMR studies of the systems also show the formation of PhBFCl and PhBF2 by fluoride exchange as well as their intermediate complexes with the BF4- anion. The high meta content is attributed to the nitration of uncomplexed phenylboron dihalides with the -BX2 group exhibiting an -I effect which directs the nitration significantly to the meta position. High para isomer content was obtained when the phenylboron dihalides were mostly complexed by the BF4- anion, thereby reducing the -I effect of -BX2 group. The nitration of iodobenzene dichloride gave essentially only nitroiodobenzenes due to the dissociation of PhICl2 and the much faster nitration of Phi as compared to PhICl2. Attempted nitration of PhPCl2 with NO2+BF4- in CH3NO2 led only to oxidation. The oxidation could not be prevented even when trimethyl phosphate was used as solvent or the milder nitrating agent MeONO2/BF3. © 1990, American Chemical Society. All rights reserved.
