From N-Alkylimidazole Ligands at a Rhenium Center: Ring Opening or Formation of NHC Complexes

Abstract

Cationic rhenium tricarbonyl complexes with three N-alkylimidazole ligands undergo deprotonation of the central CH group upon reaction with 1 equiv of KN(SiMe3)2. For the tris(N-methylimidazole) complex, the metal fragment shifts from N to C, leaving an NHC complex with a nonsubstituted N atom. For compounds with at least one N-mesitylimidazole ligand, the intramolecular attack of the deprotonated carbon onto the central carbon of an N-mesitylimidazole ligand results in ring opening of the latter.

On the Electronic Impact of Abnormal C4‐Bonding in N‐Heterocyclic Carbene Complexes

“…Molecular structure of the cationic portions of complexes 10 (a) and 11 (b; ORTEP representation, 50 % probability, hydrogen atoms, non-coordinating BF 4 À anions and cocrystallized solvent molecules omitted for clarity). Selected bond lengths [] and angles [8]: for 10: Pd1ÀC1 1.955(4), Pd1ÀN3 2.071(4); C1-Pd1-C1a 83.2(2), C1-Pd1-N3 173.40 (15), C1-Pd1-N3a 4.70 (15), N3-Pd1-N3a 86.72 (19). For 11: Pd1ÀAg1 3.1120(10), Pd1ÀC1 1.970 (7), Pd1À C7 1.966 (7), Pd1ÀN5 2.075(6), Pd1ÀN6 2.082 (7), C1ÀC2 1.367(9), C6ÀC7 1.373 (10); C1-Pd1-C7 85.8(3), Ag1-Pd1-C1 64.6 (2), Ag1-Pd1-C7 64.68 (18).…”

“…[14] In contrast, normal NHCs possess alkyl or aryl substituents on both ortho-positions, that is, on the heteroatoms. [15] When comparing the two carbene bonding modes, hence, stereoelectronic effects often interfere with electronic alterations due to different substitution of the ortho positions.…”

A Labile and Catalytically Active Imidazol‐2‐yl Fragment System

“…[3] In these systems, with commonly used ancilliary NHC ligands that are substituted at nitrogen atom(s) by alkyl, aryl, or other groups, [2,3] all catalytic transformations take place at the metal center, which is stabilized and/or activated by the NHC ligand. However, transformations that may possibly involve both the metal center and at one ring nitrogen of the NHC ligand are much less common, [4, 5c,e-g] and are limited to protic NHC complexes [4][5][6] or their conjugated bases. Thus, the NÀH function of a protic NHC complex (A or D; Scheme 1) could behave as Brønsted acid, whereas the basic nitrogen atom in the imidazol-2-yl complex (B or C) may behave as a Brønsted base.…”

Deprotonation of Coordinated Phosphanes in a Rhenium Complex: CC Coupling with Diimine Coligands

“…Interligand CC coupling initiated by deprotonation of appropriately positioned CH groups has been demonstrated in a few examples. Thus, N ‐alkylimidazoles have been coupled with bipy or phen (1,10‐phenanthroline),1 other N ‐alkylimidazoles,2 nitriles, isonitriles,3 CO,4 and monodentate pyridines 5. Similar couplings of monodentate pyridines, followed by oxidation, afforded bipyridines 5b.…”