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The Haloboration of Tri‐ tert ‐butylazadiboriridine NB 2 R 3 : Ring Opening versus NB 3 Cluster Formation
Author(s) -
Müller M.,
Müller J.,
Paetzold P.,
Radacki K.
Publication year - 2000
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/(sici)1521-3749(200006)626:6<1349::aid-zaac1349>3.0.co;2-q
Subject(s) - chemistry , isomerization , molecule , double bond , stereochemistry , ring (chemistry) , crystallography , nmr spectra database , cluster (spacecraft) , spectral line , catalysis , organic chemistry , physics , astronomy , programming language , computer science
The azadiboriridine [–BR–NR–BR–] ( 1 ; R = t Bu) is bromoborated at the B–B bond by alkyldibromoboranes R′BBr 2 to give the products Br–BR–NR=BR–BR′–Br ( 8 a – g : R′ = Me, Bu, i Bu, Bzl, CH 2 CHEt 2 , CH 2 Cy, CH 2 (4‐C 6 H 4 t Bu)). Two isomers of each of the products 8 a – g are formed and attributed to a cis / trans isomerism at the BN double bond; the isomerization is followed thermodynamically and kinetically by NMR methods with 8 a – d . The analogous chloroboration of 1 with BCl 3 yields Cl–BR–NR=BR–BCl 2 ( 8 h ), which at ambient temperature undergoes a degenerate exchange of the ligands Cl and BCl 2 along the B–N–B skeleton. At room temperature, the isomer Cl–BR–NR=BCl–BR–Cl ( 8 h ′) is slowly formed by an irreversible exchange of R and Cl along the B–B bond of 8 h . Different from BCl 3 , the chloroborane BH 2 Cl is simply added to the B–B bond of 1 under formation of the aza‐ nido ‐tetraborane NB 3 R 3 H 2 Cl ( 2 b ). The chloroborane BHCl 2 gives a mixture of 8 h ′ and 2 b upon addition to 1 , apparently according to a preceding dismutation into BCl 3 and BH 2 Cl. The configuration at the B3 atom of the nido ‐clusters NB 3 R 3 H 2 X (X = H, Cl) is discussed on the basis of the corresponding model molecules NB 3 Me 3 H 2 X, whose structure and NMR signals are computed by the B3LYP method. The boranes 8 b – g can be debrominated with Li in the presence of tmen on applying ultrasound. The products are found to be the B‐borylated azadiboriridines [–BR–NR–B(BRR′)–] ( 9 b – g ). The 2‐borylazadiboriridines NB 3 H 4 ( 9 h ) and NB 3 Me 4 ( 9 i ) were found as local minima on the energy hyperface by the B3LYP method, but minima for structural isomers with lower energy were also found; the tetrahedral clusters NB 3 R 4 give high‐energy minima with triplet ground states. Computations of the 11 B NMR shifts of 9 h and 9 i support the proposed structures of 9 b – g .