The striking influence of solubility on the nuclearity of cobalt NCN pincer complexes

The synthesis and characterization of two Co(II) complexes stabilized by NCN pincer ligands are described. The paramagnetic Co(II) complex [Co(κ³NCN-NCN^CH2-iPr)Br] is obtained via a transmetalation protocol from CoBr₂ and NC(C–Br)N^CH2-iPr in THF. Surprisingly, the dinuclear complex [Co₂(κ³NCN-μ₂-NCN^CH2-iPr)(μ-Cl)(Cl)₂] was synthesized following the same synthetic protocol but using an ultrasonicated CoCl₂ suspension instead of CoBr₂ in the same solvent. Both complexes are paramagnetic species exhibiting solution magnetic moments of 1.9(1) and 5.8(3) μ_B, respectively. This corresponds to low-spin and high-spin d⁷ configurations featuring one and three unpaired electrons at the metal centers. X-ray structures of both complexes are presented.