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Tridentate Lewis Acids Based on 1,3,5‐Trisilacyclohexane Backbones and an Example of Their Host–Guest Chemistry
Author(s) -
Weisheim Eugen,
Reuter Christian G.,
Heinrichs Peter,
Vishnevskiy Yury V.,
Mix Andreas,
Neumann Beate,
Stammler HansGeorg,
Mitzel Norbert W.
Publication year - 2015
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201501683
Subject(s) - chemistry , lewis acids and bases , hydroboration , stereochemistry , crystal structure , nuclear magnetic resonance spectroscopy , crystallography , indium , gallium , metalation , medicinal chemistry , catalysis , organic chemistry
Abstract Directed tridentate Lewis acids based on the 1,3,5‐trisilacyclohexane skeleton with three ethynyl groups [CH 2 Si(Me)(C 2 H)] 3 were synthesised and functionalised by hydroboration with HB(C 6 F 5 ) 2 , yielding the ethenylborane {CH 2 Si(Me)[C 2 H 2 B(C 6 F 5 ) 2 ]} 3 , and by metalation with gallium and indium organyls affording {CH 2 Si(Me)[C 2 M(R) 2 ]} 3 (M=Ga, In, R=Me, Et). In the synthesis of the backbone the influence of substituents (MeO, EtO and i PrO groups at Si) on the orientation of the methyl group was studied with the aim to increase the abundance of the all ‐cis isomer. New compounds were identified by elemental analyses, multi‐nuclear NMR spectroscopy and in some cases by IR spectroscopy. Crystal structures were obtained for cis‐trans‐ [CH 2 Si(Me)(Cl)] 3 , all ‐cis‐ [CH 2 Si(Me)(H)] 3 , all‐ cis‐ [CH 2 Si(Me)(C 2 H)] 3 , cis ‐ trans ‐[CH 2 Si(Me)(C 2 H)] 3 and all ‐cis ‐[CH 2 Si(Me)(C 2 SiMe 3 )] 3 . A gas‐phase electron diffraction experiment for all‐ cis‐ [CH 2 Si(Me)(C 2 H)] 3 provides information on the relative stabilities of the all‐equatorial and all‐axial form; the first is preferred in both solid and gas phase. The gallium‐based Lewis acid {CH 2 Si(Me)[C 2 Ga(Et) 2 ]} 3 was reacted with a tridentate Lewis base (1,3,5‐trimethyl‐1,3,5‐triazacyclohexane) in an NMR titration experiment. The generated host–guest complexes involved in the equilibria during this reaction were identified by DOSY NMR spectroscopy by comparing measured diffusion coefficients with those of the suitable reference compounds of same size and shape.