SYNTHESES OF NEW ORGANOBORON RINGS WITH 2 BORON ATOMS BY BORYLATION OF THE TRIMETHYLENEMETHANE DIANION

Borylation of Li2[C(CH2)3] (1) provides a versatile starting point for the synthesis of 5-, 6-, 7-, and 8-membered ring systems with two boron atoms and leads to 1,5-bis(dialkylamino)-3,7-dimethylene-1,5-diboracyclooctanes 2a, b (a: R = Et; b: R - iPr), 1,3-bis(dialkylamino)-5-methylene-1,3-diboracyclohexanes 8a, b, 1,3-bis(diethylamino)-5-methyl-1,3-dibora-4-cyclohexene (10), and 1,4-bis(dialkylamino)-6-methylene-1,4-dibora-2-cycloheptenes 11a, b. The compounds 2b, 8b, and the 2,3-biboratafulvene derivative [Li(TMEDA)]2[CH2C(CHB)2-(NIPr2)2] are characterized by X-ray diffraction analysis. It is shown that for trigonal boron B C(allyl) bond distances (typically 160 +/- 1 pm) are significantly larger than B C(alkyl) distances (typically 158 + 1 pm).