Three-Coordinate Halide and Methyl Complexes of Chromium, Manganese, Iron, Cobalt, and Nickel Enabled by an Imidazolin-2-iminato Ligand

Accessing low-coordinate halide and methyl complexes requires a bulky monodentate or bidentate ligand. Here, the synthesis and characterization of three-coordinate terminal halide and methyl complexes of the first-row transition metals are reported. The halide complexes could be accessed by the reaction of 1 molar equivalent (equiv) of M­(II) halides (M = Cr, Mn, Fe, Co, and Ni) and one equiv of the bulky imidazolin-2-iminato ligand NImDipp– (1,3-bis­(2,6-diisopropylphenyl)­imidazolin-2-iminato). Three-coordinate bridging (for Cr) and terminal (for Mn, Fe, and Co) methyl complexes could be synthesized by the reaction of [M­(μ2-NImDipp)­(X)]2 and LiCH3 or CH3MgCl in a 1:2 molar ratio. Single-crystal X-ray diffractometry (SC-XRD) revealed that Mn, Fe, and Co complexes have dimeric structures with terminal methyl ligands in the form of [M­(μ2-NImDipp)­(CH3)]2. In contrast, the Cr analog is a tetranuclear Cr4 cluster [Cr4(μ2-NImDipp)2(μ2-CH3)6] with both bridging NImDipp and CH3 ligands. Superconducting quantum interference device (SQUID) magnetometry studies of these methyl complexes showed that the metal ions are antiferromagnetically coupled. Furthermore, the catalytic activities of the methyl complexes and the nickel halide complex were also tested in Kumada cross-coupling reactions, and [Ni­(μ2-NImDipp)­(Cl)]2 was found to be the best catalyst among the complexes.