The reductive amination of α-dialkylphosphine acetaldehydes with enantiopure β-aminophosphines is a new, versatile route to unsymmetrical tridentate (pincer) ligands P-NH-P'. Four new ligands PR CH CH NHCHR'CHR''PPh (R=iPr, Cy, R'=Ph, CH(CH ) , R''=Ph, H) prepared in this way are used to make the iron(II) complexes mer-FeCl (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.
Spin-flip inelastic tunneling spectroscopy (SF-IETS) at low temperatures allows the electrical characterization of surface magnetism, particularly for molecule/ substrate systems which can be interesting for molecular spintronics. Here, SF-IETS was used to explore the competing character of intramolecular superexchange interactions on a device-compatible metallic substrate. For this purpose, the multinuclear metallacrown system CuFe4, [Cu(ii)(DMF) 2 Cl 2 [12-MC Fe(III)N(Shi) -4](DMF) 4 •2DMF], on Au(111) and its resulting "surface" spin ground state were studied. After the deposition of CuFe4 molecules by a solution-based technique onto a Au(111) surface, the CuFe4 system exhibits an evident hallmark of inelastic tunneling, that is, step-like features on the differential conductance spectra, which we attribute to spin-flip excitations. By analyzing the experimental curve with a second-order electron transport model simulation, we determined the exchange coupling constants and the spin ground state. Our results are compared with those spin ground states published in the literature for this compound based on the broken-symmetry density functional theory calculations and temperature-dependent magnetic susceptibility measurements.
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.
Chromium(III)‐based Metallacrowns complete this class of compounds important in molecular recognition, catalysis, and magneto chemistry. While metallacrowns are usually built via self‐assembly reactions, the solvothermal reaction paves the way for new kinetically and thermodynamically stable metallacrowns. More information can be found in the Communication by E. Rentschler et al. on page 4283.
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.
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