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Reactions at the B–B Bond of Tri‐ tert ‐butylazadiboriridine NB 2 R 3 : Ring Extensions
Author(s) -
Luckert S.,
Eversheim E.,
Englert U.,
Wagner T.,
Paetzold P.
Publication year - 2001
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(200108)627:8<1815::aid-zaac1815>3.0.co;2-k
Subject(s) - chemistry , cyclopentadiene , double bond , ring (chemistry) , medicinal chemistry , trimethylsilyl , stereochemistry , allene , yield (engineering) , isomerization , octane , propene , polymer chemistry , organic chemistry , catalysis , materials science , metallurgy
The OCO carboxylate unit of pivalic acid adds to the B–B bond of the azadiboriridine NB 2 R 3 ( 1 a , R = t Bu) to give the chiral heterocyclohexadiene 2 a ; the enantiomers of 2 a are transformed into one another by a [1,3] sigmatropic hydride transfer along the B–N–B ring fragment. The azadiboracyclopentanes 3 a – e are formed from 1 a and the alkenes ethene, propene, isobutene, (trimethylsilyl)ethene, and 2,3‐dimethyl‐1‐butene. Only one double bond of cyclopentadiene and 1,3‐butadiene reacts in the same way to give 3 f , g , respectively, and both of the double bonds of 1,3‐butadiene react with an excess of 1 a to give 3 h , which is obtained in a 9 : 1 mixture of racemate and meso ‐isomer; the meso ‐isomer crystallizes in the space group P 2 1 / n . The corresponding diazadiboracyclopentane 3 i and the triazadiboracyclopentane 3 j are formed from 1 a and N ‐phenyl benzaldimine or azobenzene, respectively. Ethyne and 1 a give either the azadiboracyclopentene 4 a (1 : 1) or the diazatetraborabicyclo[3.3.0]octane 3 k (1 : 2). The phosphaalkyne P≡C– t Bu and 1 a analogously yield the heterocyclopentene 4 c . The insertion of Si t Bu 2 into 1 a to give the azasiladiboracyclobutane 5 a is achieved by applying Li powder and t Bu 2 SiCl 2 . The hitherto unknown azadiboriridines BN 2 R 2 R′ (R = t Bu; R′ = 1‐ i Pr, 2‐Mes, 2‐CMe 2 Et: 1 b – d ) were synthesized by the chloroboration of the iminoboranes RB≡N i Pr and RB≡NR with RBCl 2 , MesBCl 2 , and (EtMe 2 C)BCl 2 , respectively, and subsequent dechlorination of the isolated and characterized diborylamines Cl–BR–N i Pr–BR–Cl ( 6 a ), Cl–BR–NR–BMes–Cl ( 6 b ), and Cl–BR–NR–B(CMe 2 Et)–Cl ( 6 c ), respectively, with lithium (Mes = mesityl).The azadiboriridine 1 b dimerizes to give the diaza‐ nido ‐hexaborane 7 a , whereas 1 c and 1 d are storable at room temperature. The product 1 c crystallizes as a racemate in the space group P 2 1 / c ; its ring geometry differs from that of the known N ‐mesityl isomer.