Optimised synthesis of monoanionic bis(NHC)-pincer ligand precursors and their Li-complexes

Abstract

A straightforward preparation of bis(imidazol)carbazole 4 from carbazole, its transformation to various bis(imidazolium) salts and their deprotonation to Li carbene complexes is presented.

The Fascinating Flexibility and Coordination Modes of a Pentamethylene Connected Macrocyclic CNC Pincer Ligand

“…In the 13 C NMR spectrum, the carbene signal of the free NHC moiety would be expected at around 215 ppm. In our case, the signal at 204.5 ppm is characteristic for a coordination of the carbene moiety to lithium ions as it has been reported for other Li(bimca) complexes [ 13 ]. However, typically, the carbene signals of lithium complexes are shifted by about 20 ppm to higher field compared to the respective free carbenes.…”

“…When we reported on the improved synthesis of the so-called bimca ligand [ 15 ] (1,8- b is( im idazolin-2-ylidene)-3,8-di- tert -butyl ca rbazolide), a monoanionic CNC ligand, we also showed that a still relatively concentrated reaction mixture of 1,8-bis(imidazol-1-yl)-3,8-di- tert -butylcarbazol and 1,5-dibromopentane leads selectively to the bisimidazolium macrocycle 1a (Hbimca C5 )·2HBr [ 13 ]. However, until now, the coordination chemistry of this proligand remained unexplored.…”

“…Tethered CNC pincer complexes with smaller ring sizes are scarce [ 9 ], although potential ligand precursors are well known [ 10 , 11 , 12 , 13 , 14 ]. The interaction with the metal center should become stronger and influence its reactivity by steric restrictions.…”

The crystal structure of 1,1′-(9-ethyl-9H-carbazole-3,6-diyl)bis(3-ethyl-1H-imidazol-3-ium) bis(hexafluorophosphate(IV)), C24H27N5F12P2

“…Imidazolium salts are best known for their applications in catalysis [6,7], the field of ionic liquids [8][9][10], and antimicrobial properties [11,12]. Many NHC precursor has been put on designing [13][14][15], but the NHC precursor containing carbazole are quite rare [16,17]. There are two cations and four anions in the asymmetric unit.…”

Synthesis and Catalytic Activity of Rhodium(I) and Iridium(I) 4,5-Dibrominated N-Heterocyclic Carbenes

“…N-heterocyclic carbenes (NHCs) have become ubiquitous in transition metal chemistry, 1-3 catalysis [4][5][6] and for the stabilisation of reactive main group complexes. [7][8][9] Numerous studies over the last 30 years have expanded the structural and electronic diversity of NHCs, in an effort to fine-tune their properties. 1,4 Among the possibilities for derivatisation is the modification of the 4,5-position of the imidazole ring, which has been shown to impart an increase in aerobic stability, 10,11 an important step to achieving 'bottleable' NHCs.…”