Low-Valent Ene–Amido Iron Complexes for the Asymmetric Transfer Hydrogenation of Acetophenone without Base

Abstract

Examination of the role of base in the activation of our previously reported iron(II) complexes having the general formula [Fe(CO)(Br)(PNNP)][BPh(4)] revealed a five-coordinate iron(II) complex in which the tetradentate PNNP ligand had been doubly deprotonated. The new iron(II) complexes were used in the transfer hydrogenation of acetophenone in isopropanol in the absence of added base, and certain analogues showed catalytic activity.

The Golden Age of Transfer Hydrogenation

“…If the ethyl group on phosphorus of 46 was replaced by bulky Cy or iPr substituents, the corresponding complexes were inactive for TH, which was attributed to the inactivity of their parent compounds. 279 The same research group also reported that when activation of the 282 This result suggested that partial ligand reduction is the key for high catalytic activity and that an outer-sphere mechanism is more probable for iron−PNNP promoted TH.…”

C–H Activation at a Ruthenium(II) Complex – The Key Step for a Base‐Free Catalytic Transfer Hydrogenation?

“…[23] However, this catalyst is generated by first reacting a precursor with a strong base, isolating it and finally applying it in catalysis. [23] However, this catalyst is generated by first reacting a precursor with a strong base, isolating it and finally applying it in catalysis.…”

Exploring the decomposition pathways of iron asymmetric transfer hydrogenation catalysts

“…28 Upon addition of DCl (4 equiv.) to 3a in Et2O, the homogeneous red solution turned into a yellow slurry immediately.…”

“…One of the key discoveries in this area was the isolation and characterization of bis-eneamido intermediates that form upon the treatment of the second-generation catalysts (second-generation refers to iron carbonyl ATH precatalysts with two imine donors, and a methylene linker between the imine and phosphorus moieties) with base ( Figure 1). 28 The bis-eneamido species were not active catalysts themselves, but gave a well-defined entry point into the activation process, which lead to catalytically active species. 30 Understanding the activation process, in turn, lead to the development of a more active third-generation of catalysts, where one of the imine donors has been reduced to an amino group.…”