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 (LFe)-Fe-tBu(NMP)Cl (L-tBu = bulky beta-diketiminate ligand). The X-ray crystal structure of Fe3Cl6(NMP)(8) shows an octahedral Fe(NMP)(6)(2+) cation and two tetrahedral FeCl3(NMP) anions. H-1 NMR spectra show that the NMP ligands are labile, exchanging rapidly on the NMR time scale. The beta-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. (C) 2009 Elsevier B.V. All rights reserved.