Premium
Aza‐ nido ‐dodecaboranes and ‐borates from Aza‐ closo ‐dodecaboranes by the Addition of Neutral or Anionic Bases: Mechanism
Author(s) -
Paetzold Peter,
Lomme Petra,
Englert Ulli
Publication year - 2002
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/1521-3749(200203)628:3<632::aid-zaac632>3.0.co;2-8
Subject(s) - chemistry , adduct , stereochemistry , crystallography , boron , hydrogen bond , nmr spectra database , nuclear magnetic resonance spectroscopy , molecule , spectral line , organic chemistry , physics , astronomy
The addition of neutral (L = py, NEt 3 , NHEt 2 , NH 2 tBu) and anionic Lewis bases (X ‐ = OH ‐ , Br ‐ , N 3 ‐ , Me ‐ , NHBu ‐ , NH t Bu ‐ , [FeCp(CO) 2 ] ‐ ) to aza‐ closo ‐dodecaboranes RNB 11 H 11 ( 1 ) or to derivatives thereof with boron bound non‐hydrogen ligands yields nido ‐clusters RNB 11 H 11 L or [RNB 11 H 11 X] ‐ or derivatives thereof, respectively, the non‐planar pentagonal aperture N—B4—B9—B8—B5 of which hosts a B8—B9 hydrogen bridge. The base is either bound to B8 ( 3 )or B4 ( 5 )or B2( 7 ). The structures of these adducts are concluded from 1 H and 11 B NMR including 2D‐NMR spectra, and in the case of MeNB 11 H 11 (NHEt 2 ) (type 3 ) also by a crystal structure analysis. With two of the adducts MeNB 11 H 11 L (L = py, NHEt 2 ), isomers of the type 3 , 5 , and 7 , and with two of the adducts, MeNB 11 H 11 (NH 2 t Bu) and {MeNB 11 H 11 [FeCp(CO) 2 ]} ‐ , isomers of the type 3 and 7 could be identified. The position of boron‐bound ligands during the addition of bases to 1 shows, that only vertices of the ortho ‐belt of 1 are involved in the opening process. A mechanism is made plausible that starts by the attack of the base at B2 of 1 and opening of the N‐B2 bond, denoted as a [3c, 1c]‐collocation, to give 2 with an endo ‐H atom, whose migration into an adjacent bridge position and opening of a second B—N bond, denoted as a [3c, 2c]‐translocation, gives 3 ; this isomer can be transformed into 7 by a sequence of [3c, 2c]‐translocations via the isomers 4 , 5 , and 6 . The chiral type 3 species MeNB 11 H 11 L with L = NHEt 2 , NH 2 t Bu undergo a rapid enantiomerization, for whose mechanism the exchange of the bridging and the amine‐H atom has been made plausible.