exo,endo and exo,exo isomers of 6,9-(PMe2Ph)2-arachno-B10H12 and its halogenated derivatives. Molecular structures of exo,endo- and exo,exo-6,9-(PMe2Ph)2-arachno-B10H12 and exo-6,endo-9-(PMe2Ph)2-2-Br-arachno-B10H11

Abstract

Reaction of PMe₂Ph with nido-B₁₀H₁₄ at ca. 200 K gave exo,exo and exo,endo isomers of 6,9-(PMe₂Ph)₂-arachno-B₁₀H₁₂ which were separated chromatographically. Both forms were confirmed crystallographically. The compounds 2-Br-nido-B₁₀H₁₃ and 2,4-Cl₂-nido-B₁₀H₁₂ gave exclusively exo,endo forms at ca. 200 K with the 2-Br product consisting of equal amounts of 6-endo-9-exo and 6-exo-9-endo-(PMe₂Ph)₂ isomers, demonstrating no directional control by the 2-Br substituent. The relative configurations of the two brominated isomers were confirmed by a crystallographic study of the 6-exo-9-endo species. Both the monobrominated exo,endo isomers gave the exo,exo counterpart on heating, but the 2,4-Cl₂ species is more robust, with apparent decomposition on extended heating, and no evidence for the formation of exo,exo-6,9-(PMe₂Ph)₂-2,4-Cl₂B₁₀H₁₀.