Coordination of N-methylpyrrolidone to iron(II)

The use of NMP (N-methylpyrrolidone) as a cosolvent has been shown to improve the yield of iron-catalyzed cross-coupling reactions, but surprisingly there are no iron complexes of NMP in the literature. This paper reports two novel NMP complexes of iron(II): Fe3Cl6(NMP)8 and LtBuFe(NMP)Cl (LtBu = bulky β-diketiminate ligand). The X-ray crystal structure of Fe3Cl6(NMP)8 shows an octahedral Fe(NMP)62+ cation and two tetrahedral FeCl3(NMP)− anions. 1H NMR spectra show that the NMP ligands are labile, exchanging rapidly on the NMR time scale. The β-diketiminate complex has a trigonal pyramidal geometry with the NMP in an axial position. The use of NMP improves the yield of the catalytic cross-coupling of methyl 4-chlorobenzoate and 1-hexylmagnesium bromide using these and other iron complexes as precatalysts.

Graphical abstractN-Methylpyrrolidone coordinates to two iron(II) chloride complexes. In each case, O-coordination of NMP is shown by X-ray crystallography. Iron catalysts with NMP give higher yields in catalytic cross-coupling reactions.Figure optionsDownload full-size imageDownload as PowerPoint slide