title: Dehydrocoupling reactions of borane-secondary and -primary amine adducts catalyzed by group-6 carbonyl complexes: formation of aminoboranes and borazines.
abstract: Photoirradiation of a solution of BH(3).NHR(2) (1a: R = Me, 1b: R = 1/2C(4)H(8), 1c: R = 1/2C(5)H(10), 1f: R = Et) containing a catalytic amount of a group-6 metal carbonyl complex, [M(CO)(6)] (M = Cr, Mo, W), led to dehydrogenative B-N covalent bond formation to produce aminoborane dimers, [BH(2)NR(2)](2) (2a-c, f), in high yield. During these reactions a borane sigma complex, [M(CO)(5)(eta(1)-BH(3).NHR(2))] (3), was detected by NMR spectroscopy. Similar catalytic dehydrogenation of bulkier amineboranes, BH(3).NH(i)Pr(2) (1d) and BH(3).NHCy(2) (1e, Cy = cyclo-C(6)H(11)), afforded monomeric products BH(2) horizontal lineNR(2) (4d, e). The reaction mechanism of the dehydrocoupling was investigated by DFT calculations. On the basis of the computational study, we propose that the catalytic dehydrogenation reactions proceed via an intramolecular pathway and that the active catalyst is [Cr(CO)(4)]. The reaction follows a stepwise mechanism involving NH and BH activation. Dehydrocoupling of borane-primary amine adducts BH(3).NH(2)R (1g: R = Me, 1h: R = Et, 1i: R = (t)Bu) gave borazine derivatives [BHNR](3) (5g-i).
authors.affiliation: Department of Basic Science, Graduate School of Arts and Sciences, University of Tokyo, Meguro-ku, Tokyo 153-8902, Japan. ckawano1@mail.ecc.u-tokyo.ac.jp
authors.forename: Yasuro
authors.initials: Y
authors.lastname: Kawano
authors.forename: Mikio
authors.initials: M
authors.lastname: Uruichi
authors.forename: Mamoru
authors.initials: M
authors.lastname: Shimoi
authors.forename: Seitaro
authors.initials: S
authors.lastname: Taki
authors.forename: Takayuki
authors.initials: T
authors.lastname: Kawaguchi
authors.forename: Taeko
authors.initials: T
authors.lastname: Kakizawa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ogino