Phosphacarborane Chemistry: The 7,8,9,11-, 7,9,8,10- and 7,8,9,10-Isomers ofnido-P2C2B7H9—Diphosphadicarbaborane Analogues of 7,8,9,10-C4B7H11

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Abstract
The reaction between the carborane arachno‐4,6‐C2B7H13 (1) and PCl3 in dichloromethane in the presence of a “proton sponge” (PS=1,8‐dimethylaminonaphthalene) resulted in the isolation of the eleven‐vertex nido‐diphosphadicarbaboranes 7,8,9,11‐P2C2B7H9 (2) and 3‐Cl‐7,8,9,11‐P2C2B7H8 (3‐Cl‐2) in yields of 54 and 7 %, respectively. Replacement of the PS by NEt3 in the same reaction gave diphosphadicarbaboranes 2 and 3‐Cl‐2 together with the isomeric species nido‐7,9,8,10‐P2C2B7H9 (3) in yields of 28, 15 and 3 %, respectively. The reaction between the isomeric carborane arachno‐4,5‐C2B7H13 (4) and PCl3 in dichloromethane in the presence of PS gave the asymmetrical isomer, nido‐7,8,9,10‐P2C2B7H9 (5), along with the chloro derivatives 4‐Cl‐7,8,9,10‐P2C2B7H8 (4‐Cl‐5) and 11‐Cl‐7,8,9,10‐P2C2B7H8 (11‐Cl‐5) (yields of 21, 1 and 13 %, respectively). The structures of the chlorinated derivatives 3‐Cl‐2 and 11‐Cl‐5 were determined by X‐ray diffraction analysis. In addition, the structures of all compounds isolated were geometry‐optimised and confirmed by comparison of experimental 11B chemical shifts with those calculated by the GIAO‐SCF/II//RMP2(fc)/6‐31G* method. The calculations also include the structure and 11B NMR shifts of the isomer nido‐7,10,8,9‐P2C2B7H9 (6) which has not yet been isolated.