Donor Functionalized Iron(II) N‐Heterocyclic Carbene Complexes in Transfer Hydrogenation Reactions

Two piano‐stool iron(II) complexes bearing N‐heterocyclic carbene ligands outfitted with acetamide‐ and amine‐pendant arms [Cp*Fe(NHC R )(CO)I] {Cp* = η 5 ‐tetramethylcyclopentadienyl; R = CH 2 CONEt 2 ( 3 ), (CH 2 ) 2 NEt 2 ( 4 )}, have been prepared and fully characterized. Their catalytic activity in transfer hydrogenation (TH) of ketones using i PrOH as a hydrogen source and catalytic amounts of base (LiO t Bu) has been explored, along with that of previously reported [CpFe(NHC R )(CO)I] {R = n Bu ( 5 ), (CH 2 ) 2 OH ( 6 ), Et ( 7 ), and (CH 2 ) 3 OH ( 8 )} complexes containing hydroxyl and nonfunctionalized alkyl arms. Complex 3 displayed the highest catalytic activity of the whole series 3 – 8 , reaching a TOF 50 value of 533 h – 1 . NMR monitoring of the stoichiometric reaction of 3 with LiO t Bu, allowed the identification of a new species 3' containing a deprotonated amidate moiety, which has been fully characterized by 1 H, 13 C, and 15 N NMR. Finally, a green protocol for the reduction of ketones through TH using glycerol as a hydrogen source, under microwave irradiation in the presence of catalytic amounts of 3 and base has been developed.