Microwave‐Assisted Transfer Hydrogenation of Ketones by Ru(xantphos) Arene Complexes

A Ru‐catalyzed hydrogen transfer from 2‐propanol to acetophenone in the presence of the strong base KO t Bu afforded 1‐phenyl alcohol in >99 % yield within 5 min under microwave irradiation; no reaction occurred in the absence of the base. A series of catalysts was then prepared in situ from [RuCl 2 ‐η 6 ‐ p ‐cymene] 2 and xantphos family ligands, which were characterized by having natural bite angles ranging from 102.2 to 137.9°. The Ru(xantphos)arene catalyst was used for various substrates to give yields and turnover frequencies between 48 and 99 % and between ≥1431 and 2982 h −1 , respectively, for acetophenone derivatives and >99 % and ≥2982 h −1 for sterically bulky ketones (benzophenone, 9 H ‐fluoren‐9‐one, and α‐tetralone).