The preparation of pentafluorophenyldihaloboranes from pentafluorophenylmercurials C6F5HgR and BX3: the dramatic dependence of the reaction direction on the ligand R

In search of convenient preparations of C 6 F 5 BX 2 (X = Cl, Br), reactions of C 6 F 5 HgR (R = C 6 F 5 , C 6 H 5 , C 2 H 5 , Br and Cl) with BX 3 were studied. Under the action of BCl 3 the order of the C–Hg bond cleavage is C 6 F 5 Hg–C 6 H 5 > C 6 F 5 –HgC 2 H 5 > C 6 F 5 –HgC 6 F 5 >> C 6 F 5 –HgCl. With more reactive BBr 3 the sequence is C 6 F 5 Hg–C 6 H 5 > C 6 F 5 –HgC 2 H 5 ~ C 6 F 5 Hg–C 2 H 5 > C 6 F 5 –HgC 6 F 5 ≥ C 6 F 5 –HgBr. During the study we found the simple way to alkyldibromoboranes which is presented by the preparation of C 2 H 5 BBr 2 from C 2 H 5 HgBr and BBr 3 . It is the second example of synthesis of alkylmercury derivative in an addition to the earlier reported formation of cyclopropylmercurials from di(cyclopropyl)mercury and BX 3 . Graphic abstract