Mononuclear Four-Coordinate Bis-Fluoride Bis-NHC Complexes of Chromium(II), Iron(II), and Cobalt(II)

The reaction between silylamido complexes of Cr(II), Fe(II), and Co(II) and IMes2HF salt in the presence of IMes (IMes = 1,3-dimesitylimidazol-2-ylidene) led to isolation of Cr(IMes)(2)F-2 (2-Cr), Fe(IMes)(2)F-2 (2-Fe), and Co(IMes)(2)F-2 (2-Co). X-ray structural studies revealed that 2-Cr adopts square planar geometry, while 2-Fe and 2-Co have distorted tetrahedral geometry. Magnetic susceptibility studies of 2-Cr, 2-Fe, and 2-Co were consistent with high-spin complexes, S = 2 for 2-Cr/2-Fe and S = 3/2 for 2-Co. We demonstrated that fluoride can be successfully exchanged for cyanide and azide using trimethylsilyl cyanide and trimethylsilyl azide (3-Fe and 4-Fe). DFT studies suggest that the preference of 2-Cr to adopt square planar geometry over tetrahedral is due to its d(4) metal center, where four electrons fill the lower-lying d-orbitals.

Automated summary

The reaction between silylamido complexes of Cr(II), Fe(II), and Co(II) with IMes2HF salt resulted in the isolation of corresponding metal complexes. X-ray structural studies revealed that the Cr complex adopted a square planar geometry, while the Fe and Co complexes exhibited distorted tetrahedral geometries. Magnetic susceptibility studies demonstrated that the Cr and Fe complexes were high-spin complexes, while the Co complex had a slightly different spin state.