Bis-Cyclometalated Indazole and Benzimidazole Chiral-at-Iridium Complexes: Synthesis and Asymmetric Catalysis

A new class of bis-cyclometalated iridium(III) catalysts containing two inert cyclometalated 6-tert-butyl-2-phenyl-2H-indazole bidentate ligands or two inert cyclometalated 5-tert-butyl-1-methyl-2-phenylbenzimidazoles is introduced. The coordination sphere is complemented by two labile acetonitriles, and a hexafluorophosphate ion serves as a counterion for the monocationic complexes. Single enantiomers of the chiral-at-iridium complexes (>99% er) are obtained through a chiral-auxiliary-mediated approach using a monofluorinated salicyloxazoline and are investigated as catalysts in the enantioselective conjugate addition of indole to an α,β-unsaturated 2-acyl imidazole and an asymmetric Nazarov cyclization.

The spectra of Δ-IrInd are identical and will not be shown. The spectra of Δ-IrBim are identical and will not be shown.

Single Crystal X-Ray Diffraction
X-ray data were collected either with a STOE STADIVARI diffractometer or with a BRUKER D8 QUEST diffractometer.

Conditions using the STOE STADIVARI diffractometer:
Data was collected with a STOE STADIVARI diffractometer equipped with CuKa radiation, a graded multilayer mirror monochromator (λ = 1.54178 Å) and a DECTRIS PILATUS 300K detector using an oil-coated shock-cooled crystal at 100(2) K. Absorption effects were corrected semi-empirical using multiscanned reflexions (STOE LANA, absorption correction by scaling of reflection intensities.). The number of observed reflections of the data collection used for cell constant refinement is pictured in table S1 (cell determination). The structure was solved by direct methods by using the program XT V2014/1 (Bruker AXS Inc., 2014) and refined by full matrix least squares procedures on F 2 using SHELXL-2018/3 (Sheldrick, 2018). The non-hydrogen atoms have been refined anisotropically, carbon bonded hydrogen atoms were included at calculated positions and refined using the 'riding model' with isotropic temperature factors at 1.2 times (for CH3 groups 1.5 times) that of the preceding carbon atom.
CH3 groups were allowed to rotate about the bond to their next atom to fit the electron density.

Conditions using the BRUKER D8 QUEST diffractometer:
Data was collected with a Bruker D8 QUEST area detector diffractometer equipped with MoKα radiation, a graded multilayer mirror monochromator (λ = 0.71073 Å) and a PHOTON-100 CMOS detector using an oil-coated shock-cooled crystal at 100(2) K. Absorption effects were corrected semiempirical using multiscanned reflexions (SADABS-2016/2 -Bruker AXS area detector scaling and absorption correction). The number of observed reflections of the data collection used for cell constant refinement is pictured in table S1 (cell determination). The structure was solved by direct methods by using the program XT V2014/1 (Bruker AXS Inc., 2014) and refined by full matrix least squares procedures on F 2 using SHELXL-2018/3 (Sheldrick, 2018). The non-hydrogen atoms have been refined anisotropically, carbon bonded hydrogen atoms were included at calculated positions and refined using the 'riding model' with isotropic temperature factors at 1.2 times (for CH3 groups 1.5 times) that of the preceding carbon atom. CH3 groups were allowed to rotate around the bond to their next atom to fit the electron density.
Single crystals suitable for X-ray diffraction were prepared from a concentrated solution of the respective iridium(III)-complex (about 1.5 mg) in MeCN, which was transferred to a regular NMR tube.
THF (about 0.1 mL) was added and the mixture obtained was carefully layerd with Et2O (about 3.0 mL), the tube was sealed and the biphasic mixture was left standing at room temperature over night to allow the diffusion of layers. If no formation of suitable crystals was observed after that time, the NMR-tube S18 was laid down horizontally for another 12 h. Crystal structures, data and details of the structure determination are presented in figure S27 and in table S1. Figure S23: Crystal structures of Λ-IrInd, rac-IrBim and Λ-(S)-3b (from left to right). Solvent molecules, hydrogen atoms and PF6-counterions are omitted for clarity. ORTEP drawing with 30% probability of thermal ellipsoids.