Synthesis of an ortho‐Methyl‐N,N′‐bis(triptycenyl) N‐Heterocyclic Carbene Ligand and Its Metal Complexes

Abstract

A new N,N′-bis(triptycenyl)-NHC ligand with methyl groups in the ortho position has been synthesized starting from 2,3-dimethyltriptycene-1,4-quinone. The respective metal complexes [ML(NHC)] [ML = CuBr, AuCl, PdCl(allyl), RhCl(cod), IrCl(cod), RhCl(CO) 2 , IrCl(CO) 2 , and RuCl 2 (=CHC 6 H 4 OiPr)] were [a]

Bispentiptycenyl‐N‐Heterocyclic Carbene (NHC) Gold Complexes: Highly Active Catalysts for the Room Temperature Hydration of Alkynes

“…[AuCl(NHC)] complex 1 contains two triptycenyl‐substituents. The NHC ligand in complex 2 is bulkier than in complex 1 since the respective two ortho‐positions of the triptycene units contain methyl groups instead of hydrogen atoms. Complex 2 is a mixture of syn‐ and anti‐isomers, with the latter isomer being a mixture of two enantiomers.…”

Facile Synthesis of Triptycene‐Azolium Salts and NHC‐Metal Complexes

“…This step requires 60 d under reflux (step d) in Scheme 2) for triptycene quinones derived from plain anthracene and is even more sluggish for triptycene quinones derived from substituted anthracenes. [8] However, the ortho-methyl group next to the nitrogen is essential for the stability of the envisaged catalytically active NHC-metal complexes, which otherwise tend to decompose via ortho-metalation of the sp 2 -CH group. [9] The new approach presented here relies on commercially available 2-methyl-p-aminophenol (or p-aminophenol), which is reacted with 4-nitrobenzenesulfonylchloride (nosylchloride) to provide the respective nosylated aminophenol, which is then oxidized with ammonium cerium(IV)-nitrate to obtain the respective nosylated quinone-imine (Scheme 3).…”

“…Synthesis of Amino‐triptycenes . Previously, we reported on the synthesis of triptycene‐anilines with an ortho‐methyl group, which were prepared in a five‐step procedure starting from 2,3‐dimethylbenzoquinone and anthracene [8] . An additional reaction step is the etherification of the −OH‐group with a long alkyl chain, which is attached at a later stage of the synthesis to improve solubility.…”

“…A critical step in the previous approach is the introduction of the nitrogen atom using hydroxylamine via oxime formation, which is slowed down by the presence of the two methyl groups. This step requires 60 d under reflux (step d) in Scheme 2) for triptycene quinones derived from plain anthracene and is even more sluggish for triptycene quinones derived from substituted anthracenes [8] . However, the ortho‐methyl group next to the nitrogen is essential for the stability of the envisaged catalytically active NHC‐metal complexes, which otherwise tend to decompose via ortho‐metalation of the sp 2 ‐CH group [9] …”

Bi- and trimetallic complexes with macrocyclic xanthene-4,5-diNHC ligands

“…Finally, the complexes [(MCl(cod)) 2 ( 9)] (M = Rh, Ir) were obtained from the reaction of the free carbene (generated with sodium amylate and diimidazolium salt 9•2HCl) with [(MCl(cod)] 2 (M = Rh, Ir). Normally, [MCl (cod)(NHC)] complexes are very stable, 29,[48][49][50] however, [RhCl(cod) (9)] turned out to be labile and purification was difficult since the complex suffers from very significant decomposition during chromatographic purification. The closely related iridium complex [(IrCl(cod)) 2 (9)] is slightly more stable and chromatographic purification affords pure complex, albeit in moderate yield since again a significant amount of the complex decom-poses during chromatographic purification.…”