BOROLE DERIVATIVES .21. 2,5-DIPHENYL-2,5-DIHYDRO-1H-BOROLES - STRUCTURES OF TERT-BUTYL-2,5-DIPHENYL-2,5-DIHYDRO-1H-BOROLE AND OF BIS(TMEDA)LITHIUM 2,5-DIPHENYL-2,4-DIHYDRO-1H-BOROLEDIIDE

The magnesium reagent Mg(C(4)H(4)Ph(2))(THF)(3) derived from (E,E)-1,4 -diphenyl-1,3-butadiene reacts with boron dihalides BCl2(NR(2)) (R=Me, Et,Pr-i) and (t)BuBF(2) to give 2,5-dihydro-2,5-diphenyl-1H-boroles 2 ,5-Ph(2)C(4)H(4)BNR(2) (la-lc) and 2,5-Ph(2)C(4)H(4)B(t)Bu (Id) as mix tures of cis-trans isomers. cis-ld possesses a classical structure wit h a ring folding of 8 degrees along the line C-2,C-5 of the C4B ring. The dimethylamino compounds la undergo metallation when treated with L DA in THF. After addition of TMEDA, the product can be crystallized fr om hexane-THF (2:1) as [Li(TMEDA)](2)[2,5-Ph(2)C(4)H(2)BNMe(2)] (3). T he structure of 3 is that of a contact ion triple with a triple-decker -like arrangement of the borole ring and two [Li(TMEDA)](+) units.