Crowded bis ligand complexes of TtzPh,Me with first row transition metals rearrange due to ligand field effects: structural and electronic characterization (TtzPh,Me = tris(3-phenyl-5-methyl-1,2,4-triazolyl)borate)

Abstract

The tris(3-phenyl-5-methyl-1,2,4-triazolyl)borate (Ttz^Ph,Me) ligand provides intermediate steric bulk and forms predominantly bis(ligand) complexes of the form M(Ttz^Ph,Me)₂ with first row divalent transition metals (1_M, M = Zn, Cu, Ni, Co, Fe, Mn). Due to ligand field effects that are greatest with Ni and Cu, ligand rearrangement is favored with these metals and Cu(Ttz^Ph,Me*)₂ (1_Cu*) and (Ttz^Ph,Me*)Ni(Ttz^Ph,Me) (1_Ni*) were isolated by selective recrystallization and fully characterized (* indicates a rearranged Ttz ligand with Ph and Me in swapped positions in one triazole ring). For comparison with Co(Ttz^Ph,Me)₂, the less bulky analogs (Ttz^H,H)₂Co (4) and (Ttz^Me,Me)₂Co (5) were studied by NMR and EPR spectroscopy, and 5 was crystallographically characterized. These complexes allow for a study of how slight changes in structure and electron donor properties (for Ni and Cu), as well as dramatic changes in steric bulk (for Co), influence the physical properties; specifically there are significant changes in the UV-Vis, EPR and NMR spectra. Bis(ligand) complexes predominate with all metals, but (Ttz^Ph,Me)Ni(OH₂)Cl (2) and (Ttz^Ph,Me)ZnBr (3) were also isolated and these show that Ttz^Ph,Me is coordinatively flexible.