Two-Coordinate First Row Transition Metal Complexes with Short Unsupported Metal−Metal Bonds

A series of first row transition metal complexes with unsupported M−Fe bonds, (3,5-iPr2-Ar*)MFe(η5-C5H5)(CO)2 (M = Fe (1), Mn (2), Cr (3), 3,5-iPr2-Ar* = -C6H-2,6-(C6H2-2,4,6-iPr3)2-3,5-iPr2), was synthesized by salt metathesis. They were characterized by 1H NMR, UV−vis spectroscopy, X-ray crystallography, and SQUID magnetic measurements. Two distinct Fe atoms in 1 were confirmed by Mössbauer spectroscopy. All three compounds feature short metal−metal bond distances (Fe−Fe, 2.3931(8) Å (1); Mn−Fe, 2.4512(5) Å (2); Cr−Fe, 2.4887(5) Å (3)). Their DFT computed structures were in excellent agreement with the experimental data and revealed a dative bonding interaction between the metals.