Beiträge zur Chemie des Bors, 209. 1,2‐Diboran(4)diyl‐ und 1,3‐Triboran(5)diyl‐ditosylate und ‐bis(triflate): Elektronenpräzise Polyboran‐Derivate mit aktiven Austrittsgruppen

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 RSO 3 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 B 2 (NMe 2 ) 2 (tos) 2 ( 1 ) reveals C 2 symmetry, and this also holds for B 2 (NMe 2 ) 2 (CCPh) 2 ( 7 ). While the two BNO planes in 1 include an angle of 80.8°, the two BNC planes in 7 are closer to orthogonality (84.6°). 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 B 2 (NH 2 ) 2 X 2 , 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.