Synthesis and Reactivity Studies of Square Pyramidal Complexes on Group 5 and 6 Metals for Nitrogen and Small Molecule Fixation

I have completed work in the Lavoie Group which has resulted in the synthesis of new square pyramidal complexes supported by the tert-butyl-substituted (ethenediylidene)tetraphenoxide “TPO” ligand system. Complexes 6, 2,2',2",2"'-(1,2-ethenediylidene)tetrakis[4-tert-butylphenoxo] tantalum(V) ethoxide and 7, 2,2',2",2"'-(1,2-ethenediylidene)tetrakis[4-tert-butylphenoxo] tantalum(V) dimethylamide were synthesized and structurally characterized. Crystal structures confirmed that the geometry of complexes 6 and 7 is square pyramidal with the TPO ligand coordinating to tantalum slightly below the xy plane on which the metal resides. In addition, the ethoxo and dimethylamido ligands coordinate to tantalum on the z axis. Analyzing the X-ray structures gives valuable insight into pi-interactions between the metal center and the apical ligands. Bond lengths and angles from the structures indicate significant double bond character between the metal and the apical ligand. Reaction of (TPO)Ta(OEt) (6) and (TPO)Ta(NMe2) (7) with trimethylaluminum gave the methyl complex (TPO)Ta(CH3) (8). Bonding on complex 7 was further explored using density functional theory calculations.