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

Selective dehydrogenative synthesis of imines from a variety of alcohols and amines was developed by using the ruthenium complex [RuCl 2 (dppea) 2 ] ( 6 a : dppea=2‐diphenylphosphino‐ethylamine) in the presence of catalytic amounts of Zn(OCOCF 3 ) 2 and KO t Bu, whereas the selective dehydrogenative formation of amides from the same sources was achieved by using another ruthenium complex, [RuCl 2 {( S )‐dppmp} 2 ] [ 6 d : ( S )‐dppmp=( S )‐2‐((diphenylphosphenyl)methyl)pyrrolidine], in the presence of catalytic amounts of Zn(OCOCF 3 ) 2 and potassium bis(trimethylsilyl)amide (KHMDS). Our previously reported ruthenium complex, [Ru(OCOCF 3 ) 2 (dppea) 2 ] ( 8 a ), was the catalyst precursor for the imine synthesis, whereas [Ru(OCOCF 3 ) 2 {( S )‐dppmp} 2 ] ( 8 d ), which was derived from the treatment of 6 d with Zn(OCOCF 3 ) 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.