Synthesis, Structure, and Polymerization Activity of a Titanium Complex with a Chelating [(Hydroxy‐κO)amino‐κN]phenolato(2−)‐κO Ligand

Abstract

Dedicated to Professor Giambattista Consiglio on the occasion of his 65th birthday A novel titanium complex with a chelating nitroxide ligand, dichloro-2-{[(hydroxy-kO)phenylaminokN)phenylmethyl}phenolato(2À)-2kO}(tetrahydrofuran)titanium (1), was synthesized and characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray crystallography. In the presence of methylaluminoxane (MAO), 1 displayed moderate activity for the polymerization of propylene.Introduction. -The past two decades have witnessed major advances in olefin poly-A C H T U N G T R E N N U N G merizations utilizing well-defined metallocene complexes [1 -4]. These advances have led to new insights on the role of catalyst structure on the polymerization behavior of transition-metal catalysts [5 -7] We have recently demonstrated that hydroxylaminato ligands derived from stable nitroxide radicals (R 2 A C H T U N G T R E N N U N G NÀO · ) are an intriguing class of hemi-labile ancillary ligands for early transition metals [37 -43]. These ligands adopt both h 2 and h 1 (i.e., kN, kO and kO) coordination modes, depending on the nature of the hydroxylamine ligand and the ancillary ligation at the Ti-atom. For example, the X-ray structure of [TiCl 3 (tempo) (tempo = 2,2,6,6-tetramethylpiperidin-1-yloxy) reveals an h 2 coordination of the tempo group to the Ti-atom, while in the complexes [TiCl 2 (Cp)(tempo)] and [TiCl(Cp) 2 A C H T U N G T R E N N U N G (tempo)], (Cp = cyclopentadienyl), tempo adopts an h 1 coordination to the metal [39] [40]. The solution measurements indicate that the h 1 ! h 2 interconversion of [TiCl 3 (tempo)] is facile at room temperature [38]. Mono(cyclopentadienyl)titanium derivatives such as [Ti(Cp*)Me 2 A C H T U N G T R E N N U N G (ONEt 2 )]/Ph 3 A C H T U N G T R E N N U N G C[B(C 6 F 5 ) 4 ] (Cp*= pentamethylcyclopentadienyl) exhibit very high activities for propylene polymerization, generating high-molecular-mass atactic polypropylenes [43]. Herein, we report the synthesis, structure, and polymerization behavior of a novel Ti complex with a chelating nitroxide ligand.

Group 4 Metal Olefin Polymerization Catalysts Stabilized by Bidentate O,P Ligands

“…Although simple group 4 metal bis-phenoxide catalysts are active, additional neutral donors are often incorporated into the ligand frame to occupy sites of coordinative unsaturation not needed for chain growth – ,, Such additional donors may also help to “rigidify” the structure of the complex and open up the possibility for stereoselective polymerizations using prochiral olefins.…”

“…In group 4 metal complexes, the phenoxide donors tend to be matched with relatively hard first-row nitrogen- – and oxygen-based c,f−i, c,h, donors. However, there is growing evidence that softer second-row donors may offer beneficial stabilization of the highly reactive metal center …”