Zirconium complexes incorporated with asymmetrical tridentate pincer type mono- and di-anionic pyrrolylligands: mechanism and reactivity as catalytic precursors

Abstract

The reactions of Zr(NR₂)₄ (1, R = Me; 2, R = Et) with an asymmetrical tridentate pincer type pyrrole ligand precursor [C₄H₂NH(2-CH₂NH^tBu)(5-CH₂NMe₂)] and treatment of the derivatives with either PhNCS or PhNCO have been carried out and characterized. Reacting Zr(NR₂)₄ (1, R = Me; 2, R = Et) with [C₄H₂NH(2-CH₂NH^tBu)(5-CH₂NMe₂)] generates Zr[C₄H₂N(2-CH₂N^tBu)(5-CH₂NMe₂)](NR₂)₂ (3, R = Me; 4, R = Et) in high yield along with the elimination of 2 equiv of dimethylamine or diethylamine, respectively. Interestingly, while changing the solvent from Et₂O to CH₂Cl₂, the complex Zr[C₄H₂N(2-CH₂N^tBu)(5-CH₂NMe₂)][C₄H₂N(2-CH₂NH^tBu)(5-CH₂NMe₂)]Cl (5) is produced by undergoing C–Cl bond cleavage. Furthermore, reaction of either 3 or 4 with 1 or 2 equiv of PhNCS or PhNCO yields Zr[C₄H₂N(2-CH₂N^tBu)(5-CH₂NMe₂)](NMe₂)[PhNC(NMe₂)S] (6), Zr[C₄H₂N(2-CH₂N^tBu)(5-CH₂NMe₂)](NEt₂)[PhNC(NEt₂)O] (7) and Zr[C₄H₂N(2-CH₂NH^tBu)(5-CH₂NMe₂)][PhNC(NEt₂)O]₃ (8), respectively. All the aforementioned complexes were characterized by ¹H and ¹³C NMR spectrometry and the molecular structures of 5, 6, and 8 have been determined by single-crystal X-ray diffractometry. Complexes 4, 5, and 7 initiated the ethylene polymerization in the presence of MAO as the co-catalyst.