Synthesis of Iron P‑N-P′ and P‑NH-P′ Asymmetric Hydrogenation Catalysts
datasetposted on 17.12.2015 by Jessica F. Sonnenberg, Alan J. Lough, Robert H. Morris
Datasets usually provide raw data for analysis. This raw data often comes in spreadsheet form, but can be any collection of data, on which analysis can be performed.
Complexes of the type mer,trans-[Fe(P-N-P′)(CO)2Br]BF4 are known to be precatalysts for the asymmetric direct hydrogenation of ketones and imines. Employing related ligand scaffolds, we successfully generated and tested the series of three new precatalysts [Fe(PCy2CH2CHNCH(R)CH2PPh2)(CO)2Br]BF4 with chirality derived from (S)-amino alcohols with phenyl, benzyl, and isopropyl substituents (R), yielding fairly active and selective systems. For the reduction of acetophenone to (S)-1-phenylethanol turnover frequencies up to 920 h–1 and up to 74% enantiomeric excess at 50 °C and 5–25 atm of H2 were obtained. We found, however, that placing these large groups R next to nitrogen was found to be deleterious to catalytic activity. Extending the scope of the ligand structure, we then developed a series of six P-N-P and five P-NH-P′ systems starting with o-diphenylphosphinobenzaldehyde and the phosphine-amines PPh2CHR1CHR2NH2 (R1 = H, Ph, CH2Ph, iPr with R2 = H or R1 = Me, Ph with R2 = Ph) as well as their corresponding [Fe(P-N-P′)(NCMe)3][BF4]2 and [Fe(P-NH-P′)(NCMe)3][BF4]2 complexes, which were not catalytically active. Finally, we made the new achiral iron complex mer,cis-Fe(PPh2(o-C6H4)CHNCH2CH2PPh2)(CO)Br2, which was active for the direct hydrogenation of acetophenone, achieving turnover frequencies of 800 h–1 at 50 °C and 25 atm of H2.