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1,1‐Carboboration of Dialkynyltin Compounds using Triorganoboranes of Greatly Different Lewis Acid Strength. 1,4‐Stannabora‐cyclohexa‐2,5‐dienes and Characterization of Zwitterionic Intermediates
Author(s) -
Wrackmeyer Bernd,
Thoma Peter,
Marx Simone,
Glatz Germund,
Kempe Rhett
Publication year - 2013
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/zaac.201300007
Subject(s) - chemistry , reactivity (psychology) , intramolecular force , electrophile , lewis acids and bases , nuclear magnetic resonance spectroscopy , tin , stereochemistry , adduct , medicinal chemistry , catalysis , organic chemistry , medicine , alternative medicine , pathology
Abstract. Triorganoboranes B R 3 , Et‐9‐BBN, BPh 3 , and B(C 6 F 5 ) 3 , were compared in their reactivity towards various dialkynyl(diorgano)tin compounds ( R 1 2 Sn(C≡C– R 2 ) 2 with R 1 2 = –(CH 2 ) 5 –, R 2 = H ( a ), R 1 = n Bu, R 2 = H ( b ), R 1 = Ph, R 2 = H ( c ), R 1 = R 2 = n Bu ( d )). 1,1‐Carboboration took place readily in two consecutive steps (inter‐ and intramolecular), leading either to stannoles or to 1,4‐stannabora‐cyclohexa‐2,5‐dienes, or mixtures thereof. The weakest Lewis‐acidic triorganoboranes BEt 3 and Et‐9‐BBN afford selectively stannoles with diethynyltin compounds, whereas the strongly electrophilic B(C 6 F 5 ) 3 leads selectively to 1,4‐stannabora‐cyclohexa‐2,5‐dienes for all dialkynyltin compounds studied. In several cases, zwitterionic intermediates could be detected by multinuclear magnetic resonance spectroscopy ( 1 H, 11 B, 13 C, and 119 Sn NMR), and the molecular structure of such an intermediate as well as that of the final product, an 1,4‐stannabora‐cyclohexa‐2,5‐diene, could be determined by X‐ray crystallography.