Filling The Gap in The Metallacrown Family: The 9-MC-3 Chromium Metallacrown.

Invited for the cover of this issue is the group of Eva Rentschler at the Johannes Gutenberg University Mainz. The image depicts a puzzle that represents the metallacrown family with the gap for the chromium metallacrown complex. Read the full text of the article at 10.1002/chem.202004947.

Filling the Gap in the Metallacrown Family: The 9-MC-3 Chromium Metallacrown.

In this work, we report on a long-sought missing complex in the metallacrown family. We synthesized and characterized the novel chromium metallacrown (MC) complex {CrIII (µ2 -piv)3 [9-MCCr(III)N(shi) -3](morph)3 }⋅MeOH (in which shi3- =salicyl hydroxamate, piv=pivalate, and morph=morpholine). The MC with a 9-MC-3 cavity of kinetically inert chromium(III) ions was synthesized by a solvothermal reaction. Magnetization measurements reveal a high spin ground state.

Unsymmetrical Iron P-NH-P' Catalysts for the Asymmetric Pressure Hydrogenation of Aryl Ketones.

The reductive amination of α-dialkylphosphine acetaldehydes with enantiopure ß-aminophosphines is a new, versatile route to unsymmetrical tridentate (pincer) ligands P-NH-P'. Four new ligands PR2 CH2 CH2 NHCHR'CHR''PPh2 (R=iPr, Cy, R'=Ph, CH(CH3 )2 , R''=Ph, H) prepared in this way are used to make the iron(II) complexes mer-FeCl2 (CO)(P-NH-P') and mer-FeCl(H)(CO)(P-NH-P'). The hydride complex with the rigid ligand with R'=R''=Ph is an efficient and highly enantioselective homogeneous asymmetric pressure hydrogenation (APH) catalyst. Prochiral aryl ketones are reduced under mild conditions (THF, 0.1 mol % catalyst, 1 mol % KOtBu, 5-10 bar, 50 °C) to the (S)-alcohols, usually in enantiomeric excess (ee) greater than 90 %. DFT calculations provided transition-state structures for the enantiodetermining hydride-transfer step.