Synthesis, crystal structure, and reactivity of a four-coordinate iron(II) chloride complex bearing the sterically demanding tert-butyl-tris(3-isopropylpyrazolyl)borato ligand

The salt elimination reaction between FeCl₂(THF)_1.5 and the sterically hindered thallium tert-butyl-tris(3-isopropylpyrazolyl)borate, Tl[t-BuTp^i-Pr], affords the new air and moisture-sensitive, high-spin, four-coordinate complex Fe[t-BuTp^i-Pr]Cl (1) in 52% yield. Compound 1 has been characterized by elemental analysis, paramagnetic ¹H NMR, and X-ray crystal structure determination. Fe[t-BuTp^i-Pr]Cl is monomeric, and the homoscorpionate ligand is κ³-coordinated. The Fe(II) ion lies in a trigonally distorted tetrahedral environment with average N-Fe-N and N-Fe-Cl angles of 89.4(2)° and 125.7(2)°, respectively. Upon reactions with methyllithium followed by carbonylation, the six-coordinate acetyl-dicarbonyl derivative Fe[t-BuTp^i-Pr](CO)₂{C(O)Me} was identified by IR spectroscopy. The reaction of 1 with ethylmagnesiumbromide furnished a mixture of mononuclear Grignard complexes Mg[t-BuTp^i-Pr]X (X = Et, Cl, Br), resulting formally from a facile and quantitative replacement of the [Fe-Cl]⁺ fragment by [Mg-X]⁺.