Base-Promoted Tautomerization of Imidazole Ligands to N-Heterocyclic Carbenes and Subsequent Transmetalation Reaction

Abstract

Imidazole complexes of manganese(I) are transformed into their corresponding N-heterocyclic carbene derivatives by means of acid−base treatments; the subsequent sequential transmetalation reaction of the carbene to gold(I) proceeds through isolable heterometallic intermediate species.

Imidazole to NHC Rearrangements at Molybdenum Centers: An Experimental and Theoretical Study

“…[24] The Mo1ÀN1 distance of 2.219 (8) , is similar to other molybdenum(II) imidazole distances previously reported.…”

“…[6,7] In 2007 Ruiz and Perandones published the transformation of an imidazole Mn I compound into an NHÀNHC complex by a deprotonation/ protonation sequence (see Scheme 1a). [8] About at the same time, we found that the deprotonation reaction of the analogous rhenium compounds, [ReA C H T U N G T R E N N U N G (bipy)(CO) 3 A C H T U N G T R E N N U N G (N-RIm)]OTf (R = methyl, mesityl; OTf = triflate), led to a completely different kind of product. [9] As shown in Scheme 1b, the re-A C H T U N G T R E N N U N G action of the rhenium species with a strong base deprotonated the imidazole C2 À H group, and the so formed carbeniate attacked a C ortho of the adjacent 2,2'-bipyridine ligand.…”

“…[8] The theoretical calculations have shown that the reaction mechanism recently found for Mn complexes involving an initial attack onto a cis-CO ligand, [10] is the preferred route for molybdenum species as well, suggesting that this new and un-A C H T U N G T R E N N U N G expected "carbonyl mechanism" can be quite general for related transformations.…”

Heterocyclic Carbenes: Synthesis and Coordination Chemistry

“…Subsequent attempts to deprotonate the C 2 carbon atom led to an intermediate which upon protonation with NH 4 PF 6 reacted to give the complex with a C 2 metalated NH,NPh-stabilized carbene ligand. [358] This base-catalyzed tautomerization [359] of an imidazole complex into an NHC complex could be of general applicability for the preparation of NHC complexes. Similar complexes with NH,NR-stabilized benzimidazolin-2-ylidene ligands have been obtained from N-alkylbenzimidazole (Scheme 97).…”

Cationic Protic Imidazolylidene NHC Complexes of Cp*IrCl+ and Cp*RhCl+ with a Pyridyl Tether Formed at Ambient Temperature

“…For example, in some syntheses of NHC complexes, free NHCs are made by deprotonating imidazolium salts; this route is precluded in making PNHCs, because the most acidic proton on the imidazolium salt precursor would be that on one of the nitrogens. Some PNHC complexes are made by coordination of a 1-alkylimidazole to a metal fragment, followed by deprotonation with the appropriate base at C-2, migration of the metal fragment to C-2, followed by protonation with the appropriate acid [3][4][5]. A variant on this scheme starts with C-2 deprotonation, installation of the metal at C-2, and protonation [6][7][8].…”