Twisting the arm: structural constraints in bicyclic expanded-ring N-heterocyclic carbenes

A series of diaryl, mono-aryl/alkyl and dialkyl mono- and bicyclic expanded-ring N-heterocyclic carbenes (ER-NHCs) have been prepared and their complexation to Au( i ) investigated through the structural analysis of fifteen Au(NHC)X and/or [Au(NHC) 2 ]X complexes. The substituted diaryl 7-NHCs are t...

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Bibliographic Details
Published in:Dalton transactions : an international journal of inorganic chemistry 2019-02, Vol.48 (5), p.185-1858
Main Authors: Sampford, Katharine R, Carden, Jamie L, Kidner, Edward B, Berry, Abigail, Cavell, Kingsley J, Murphy, Damien M, Kariuki, Benson M, Newman, Paul D
Format: Article
Language:English
Subjects:
Aromatic compounds
Carbenes
Crystallography
NMR
Nuclear magnetic resonance
Single crystals
Structural analysis
Twisting
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Summary:A series of diaryl, mono-aryl/alkyl and dialkyl mono- and bicyclic expanded-ring N-heterocyclic carbenes (ER-NHCs) have been prepared and their complexation to Au( i ) investigated through the structural analysis of fifteen Au(NHC)X and/or [Au(NHC) 2 ]X complexes. The substituted diaryl 7-NHCs are the most sterically encumbered with large buried volume (% V B ) values of 40-50% with the less flexible six-membered analogues having % V B values at least 5% smaller. Although the bicyclic systems containing fused 6- and 7-membered rings (6,7-NHCs) are constrained with relatively acute NCN bond angles, they have the largest % V B values of the dialkyl derivatives reported here, a feature related to the fixed conformation of the heterocyclic rings and the compressional effect of a pre-set methyl substituent. Bicyclic expanded ring carbenes show increased sterics compared to similar monocyclic derivatives. The enhancement is a consequence of an impacting methyl substituent.
ISSN:1477-9226
1477-9234
DOI:10.1039/c8dt04462g