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This feature article discusses the synthesis of new asymmetric Grubbs–Hoveyda II complexes with extended N-heterocyclic carbenes containing a bicyclic camphor-based framework. The new enantiopure complexes can be prepared in a short route from the chiral pool. The extended carbene-based catalyst shows high activity in olefin metathesis reactions. The new complexes exhibited enantioselectivity in an asymmetric ROCM desymmetrization. Depending on the substituents on the nitrogen atoms of the carbenes, the opposite enantiomer was formed in excess.

The presented work describes the synthesis of new six- and seven-membered haloamidinium salts and their reaction with different metals. The isolated metal complexes were tested in a catalytic reaction. Two different synthetic routes were applied to prepare five different salts. Chloroamidinium salts were very water-sensitive in comparison to their corresponding bromoamidinium salts. Hence, the preparation of the less sensitive bromoamidinium salts was higher prioritized. The formed salts were converted with metal sources to N-heterocyclic carbene (NHC) metal complexes through an oxidative insertion into the C–X bond. This type of formation is less examined for the synthesis of extended NHC metal complexes. Pd(PPh3)4and cobalt powder were applied as metal sources, whereby two palladium complexes were isolated, characterized, and their crystal and molecular structures determined. The palladium complexes were investigated in the Suzuki-Miyaura reaction and showed promising catalytic activity.

The synthesis of imidazolinium salts from low-cost amino alcohols incorporating different sterically demanding silyl groups is described. The new salts were analyzed and investigated as carbene precursors in a palladium-catalyzed asymmetric intramolecular α-arylation of an amide. The easily accessible carbene precursors gave enantiomeric excesses of up to 72% with nearly quantitative yields. The salts were also successfully applied as chiral solvating agents with the potassium salt of Mosher’s carboxylate and can therefore contribute to the field of chiral recognition.

In this work the synthesis of new asymmetric camphor-based carbene ligands from camphoric acid is described. The new carbenes can be prepared directly in high yields by the sequence: regioselective arylation of the less hindered primary amine group of (+)-cis-1,2,2-trimethylcyclopentane-1,3-diamine by Buchwald–Hartwig amination, treatment with trimethyl orthoformate, and finally treatment with a benzylic halide. The resulting carbenes, incorporating an aryl and a benzylic substituent, were successfully applied as ligands in a copper-catalyzed B2Pin2 [bis(pinacolato)diboron] addition to an unsaturated carbonyl compound. Depending on the substituents dual stereocontrol was observed and one enantiomer was obtained in up to 82% ee and the opposite enantiomer in up to 78% ee.

The unit cell of the title complex, [CoBr2(C18H20N2O)2], contains 1.5 formula units per asymmetric unit with one molecule sitting on a general site and a second one halved by a crystallographic twofold rotation axis passing through the CoIIcation. Both CoIIatoms are coordinated in a distorted tetrahedral manner by two Br−ligands and two O atoms of the pyrimidinone (OPyr) groups. The Br—Co—Br coordination angles are similar [115.46 (4) and 115.20 (5)°], while the O—Co—O angles differ slightly more [102.26 (18) and 98.1 (2)°]. Similarly, the Co—Br bond lengths are almost identical [2.3721 (9), 2.3757 (10) and 2.3809 (10) Å], with a larger difference between the Co—O bond lengths [1.929 (4), 1.926 (4) and 1.955 (4) Å]. The three independent OPyr groups present envelope conformations, with three C and two N atoms lying in well defined planes with maximum deviations from the least-squares planes of 0.047, 0.031 and 0.036 Å, and the external-most C atoms protruding by 0.654 (6), 0.643 (7) and 0.656 (6) Å out of the planes. The dihedral angles between the planar fractions of the OPyr planes are 50.5 (1)° for the nonsymmetric molecule and 49.7 (1)° for the symmetric one. Non-covalent interactions are of the C—H...Br type and they are weak, hardly shorter than van der Waals radii, with an H...Br distance range of 3.00–3.04 Å. The intermolecular interactions define chains parallel to [101].