Tunable Ligand Effects on Ruthenium Catalyst Activity for Selectively Preparing Imines or Amides by Dehydrogenative Coupling Reactions of Alcohols and Amines

5 years ago

Tunable Ligand Effects on Ruthenium Catalyst Activity for Selectively Preparing Imines or Amides by Dehydrogenative Coupling Reactions of Alcohols and Amines

Haruki Nagae, Takafumi Higuchi, Atsuhiro Iimuro, Kazushi Mashima, Shoko Akiyama, Risa Tagawa

Selective dehydrogenative synthesis of imines from a variety of alcohols and amines was developed by using the ruthenium complex [RuCl2(dppea)2] (6 a: dppea=2-diphenylphosphino-ethylamine) in the presence of catalytic amounts of Zn(OCOCF3)2 and KOtBu, whereas the selective dehydrogenative formation of amides from the same sources was achieved by using another ruthenium complex, [RuCl2{(S)-dppmp}2] [6 d: (S)-dppmp=(S)-2-((diphenylphosphenyl)methyl)pyrrolidine], in the presence of catalytic amounts of Zn(OCOCF3)2 and potassium bis(trimethylsilyl)amide (KHMDS). Our previously reported ruthenium complex, [Ru(OCOCF3)2(dppea)2] (8 a), was the catalyst precursor for the imine synthesis, whereas [Ru(OCOCF3)2{(S)-dppmp}2] (8 d), which was derived from the treatment of 6 d with Zn(OCOCF3)2 and characterized by single-crystal X-ray analysis, was the pre-catalyst for the amide formation. Control experiments revealed that the zinc salt functioned as a reagent for replacing chloride anions with trifluoroacetate anions. Plausible mechanisms for both selective dehydrogenative coupling reactions are proposed based on a time-course study, Hammett plot, and deuterium-labeling experiments. Time for a tune: Tunable ligand effects on ruthenium catalyst activity for selective synthesis of imines and amides by dehydrogenative coupling reaction is reported. Plausible mechanisms for both selective dehydrogenative coupling reactions are proposed based on a time-course study, Hammett plot, and deuterium-labeling experiments.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701342