Donor Functionalized Iron(II) N‐Heterocyclic Carbene Complexes in Transfer Hydrogenation Reactions. Issue 1 (20th October 2020)

• Record Type: Journal Article
• Authors: Lopes, Rita; Raya‐Barón, Álvaro; Robalo, M. Paula; Vinagreiro, Carolina; Barroso, Sónia; Romão, Maria J.; Fernández, Ignacio; Pereira, Mariette M.; Royo, Beatriz
• Is Part Of: European journal of inorganic chemistry. Issue 1(2021)
• Page Start: 22
• Page End: 29
• Publication Date: 2020-10-20
• Subjects: Iron -- Carbene ligands -- Transfer hydrogenation -- Reduction -- Ketones -- Microwave irradiation; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.202000868
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract : 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 = CH2 CONEt2 (3 ), (CH2 )2 NEt2 (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 ), (CH2 )2 OH (6 ), Et (7 ), and (CH2 )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 TOF50 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. Abstract : The catalytic activity of bifunctional piano‐stool Fe(II) complexes bearing NHC ligands functionalized with alkyl, hydroxyl, acetamide, and amine groups in transfer hydrogenation of carbonyl groups has been studied. The iron complex bearing the acetamide group, displayed the best catalytic performance. The formation of an intermediate species bearing a deprotonated amidate moiety is demonstrated by NMR spectroscopy.