Converting Caffeine to Electronically Different N-Heterocyclic Carbenes with a Hypoxanthine Backbone
摘要:
The synthesis of the new mixed amino amido N-heterocyclic carbene 2, featuring a hypoxanthine structural unit, starting from caffeine via the hypoxanthinium precursor 4 is described. NHC 2 forms adducts with group 6 elements, coordinates to L2ClRh fragments (L-2 = COD, (CO)(2)), or dimerizes to yield olefin 8. The donor properties of NHC 2 were evaluated by IR spectroscopic assessment of its TEP value (2058 cm(-1)), which is typical for an amino amido NHC. Dicarbenes are also easily obtained by converting the imidazole moieties of the hypoxanthinium cation 4 or the olefin 8 into NHC functions. X-ray structure determinations of a Rh complex of carbene 2 and the olefinic dicarbene precursor 13 are presented.
The synthesis of the new mixed amino amido N-heterocyclic carbene 2, featuring a hypoxanthine structural unit, starting from caffeine via the hypoxanthinium precursor 4 is described. NHC 2 forms adducts with group 6 elements, coordinates to L2ClRh fragments (L-2 = COD, (CO)(2)), or dimerizes to yield olefin 8. The donor properties of NHC 2 were evaluated by IR spectroscopic assessment of its TEP value (2058 cm(-1)), which is typical for an amino amido NHC. Dicarbenes are also easily obtained by converting the imidazole moieties of the hypoxanthinium cation 4 or the olefin 8 into NHC functions. X-ray structure determinations of a Rh complex of carbene 2 and the olefinic dicarbene precursor 13 are presented.