New and reliable procedures for the preparation of both enantiomers of 2,2‘-bipiperidine have been
developed. Chiral imidazolinium salts derived from 2,2‘-bipiperidine and partially reduced biisoquinoline
were prepared in high yields. Rhodium and iridium complexes of new chiral N-heterocyclic carbenes
were obtained by transmetalation from corresponding silver(I) complexes. The structures of these
complexes were verified by X-ray diffraction. The novel carbenes seem to range between the very electron-rich bis(amido)carbenes and the imidazole-derived carbenes with regard to the electronic ligand properties
(IR evidence). Rhodium and iridium complexes were applied to a variety of catalytic asymmetric reactions.
Modest enantioselectivities of up to 28% ee were observed.
A chiral C
2-symmetric diamine was prepared from (S)-3-phenyl-3,4-dihydroisoquinoline by the virtue
of asymmetric transformation. Rhodium and iridium complexes of chiral N-heterocyclic carbenes with
restricted flexibility derived from 3,3‘-substituted partially reduced biisoquinoline were obtained by
transmetalation from the corresponding silver(I) complexes. Unexpected double-bond formation in the
carbene ligand has occurred during a transmetalation step. The structures of these complexes were verified
by X-ray diffraction. Metal complexes of these N-heterocyclic carbenes were applied to the asymmetric
hydrogenation of methyl 2-acetamidoacrylate. Good enantioselectivities of up to 67% ee were achieved.
New methods for the preparation of NHC-metal complexes have been developed. It was shown that a nitrile group in Reissert analogous compounds can act as a good leaving group in thermal elimination, resulting in carbene formation. Moreover potassium carbonate was introduced as a highly efficient and mild reagent for the generation of N-heterocyclic carbene complexes in good to excellent yields, even in water, as the most environmentally friendly medium.
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