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First N‐Heterocyclic Carbenes Relying on the Triazolone Structural Motif: Syntheses, Modifications and Reactivity
Author(s) -
Jonek Markus,
Diekmann Janina,
Ganter Christian
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.201502685
Subject(s) - motif (music) , structural motif , chemistry , reactivity (psychology) , stereochemistry , combinatorial chemistry , philosophy , biochemistry , medicine , alternative medicine , pathology , aesthetics
Abstract 4‐Phenylsemicarbazide and 1,5‐diphenylcarbazide are suitable starting materials for the syntheses of N‐heterocyclic carbene (NHC) compounds with new backbone structures. In the first case, cyclisation and subsequent methylation leads to a cationic precursor whose deprotonation affords the triazolon‐ylidene 2 , which was converted to the corresponding sulfur and selenium adducts and a range of metal complexes. In contrast, cyclisation of diphenylcarbazide affords a neutral betain‐type NHC‐precursor 7 , which is not in equilibrium with its carbene tautomer 7a . Precursor 7 can either be deprotonated to give the anionic NHC 8 or methylated at the N or O atom of the backbone resulting in two isomeric cationic species 16 and 20 . Deprotonation of the latter two provides neutral NHC compounds with a carboxamide or carboximidate backbone, respectively. The ligand properties of the new NHC compounds were evaluated by IR and 77 Se NMR spectroscopy. Tolman electronic parameter (TEP) values range from 2050 to 2063 cm −1 with the anionic NHC 8 being the best overall donor.