CONTRIBUTIONS TO THE CHEMISTRY OF BORON .209. 1,2-DIBORANE(4)DIYL AND 1,3-TRIBORANE(5)DIYL DITOSYLATE AND BIS(TRIFLATE) - ELECTRON-PRECISE POLYBORANE DERIVATIVES WITH ACTIVE LEAVING GROUPS

Introduction of the tosylate or triflate group into dimethylamino polyboranes gives electron-precise polyborane derivatives of high reactivity. Five representatives 1-4 of these types of compounds are reported. The RSO3 groups strengthen the B-N bond while they are good leaving groups as shown by alkylation reactions when using LiR compounds. The X-ray structure of B2(NMe2)2(tos)2 (1) reveals C2 symmetry, and this also holds for B2(NMe2)2(C = CPh)2 (7). While the two BNO planes in 1 include an angle of 80.8-degrees, the two BNC planes in 7 are closer to orthogonality (84.6-degrees). In contrast, the bis(9-fluorenyl)diborane 10 reveals different structures in solution and the solid state. Experimental results correspond fairly well with MNDO calculations on model compounds B2(NH2)2X2, particularly with B-B and B-N bond lengths and conformations. They also suggest that nucleophilic substitutions at 1-4 may proceed by a dissoziative process.