Capped-Tetrahedrally Coordinated Fe(II) and Co(II) Complexes Using a “Click”-Derived Tripodal Ligand: Geometric and Electronic Structures

The ‘Click’-derived tripodal ligand tris­[(1-benzyl-1<i>H</i>-1,2,3-triazole-4-yl)­methyl]­amine, tbta, was used to synthesize the complexes [Fe­(tbta)­Cl]­BF₄, <b>1</b>, and [Co­(tbta)­Cl]­BF₄, <b>2</b>. Both complexes were characterized by ¹H NMR spectroscopy and elemental analysis. Single-crystal X-ray structural determination of <b>2</b> shows a 4 + 1 coordination around the cobalt­(II) center with a rather long bond between Co­(II) and the central amine nitrogen atom of tbta. Such a coordination geometry is best described as capped tetrahedral. <b>1</b> and <b>2</b> are thus the first examples of pseudotetrahedral coordinated Fe­(II) and Co­(II) complexes with tbta. A combination of SQUID susceptometry, EPR spectroscopy, Mössbauer spectroscopy, and DFT calculations was used to elucidate the electronic structures of these complexes and determine the spin state of the metal center. Comparisons are made between the complexes presented here with related complexes of other ligands such as tris­(2-pyridylmethyl)­amine, tmpa, hydrotris­(pyrazolyl) borate, Tp, and tris­(2-(1-pyrazolyl)­methyl)­amine, amtp. <b>1</b> and <b>2</b> were tested as precatalysts for the homopolymerization of ethylene, and both complexes delivered distinctly different products in this reaction. Blind catalyst runs were carried out with the metal salts to prove the importance of the tripodal ligand for product formation