Abstract: In search of convenient preparations of C6F5BX2 (X = Cl, Br), reactions of C6F5HgR (R = C6F5, C6H5, C2H5, Br and Cl) with BX3 were studied. Under the action of BCl3 the order of the C–Hg bond cleavage is C6F5Hg–C6H5 > C6F5–HgC2H5 > C6F5–HgC6F5 >> C6F5–HgCl. With more reactive BBr3 the sequence is C6F5Hg–C6H5 > C6F5–HgC2H5 ~ C6F5Hg–C2H5 > C6F5–HgC6F5 ≥ C6F5–HgBr. During the study we found the simple way to alkyldibromoboranes which is presented by the preparation of C2H5BBr2 from C2H5HgBr and BBr3. 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 BX3. Graphic abstract: [Figure not available: see fulltext.].