374074-89-2Relevant academic research and scientific papers
Synthesis, characterization and ethylene polymerization activity of zirconium complexes containing nonsymmetric diamido ligands derived from 2-aminobenzylamine
Gauvin, Regis M.,Lorber, Christian,Choukroun, Robert,Donnadieu, Bruno,Kress, Jacky
, p. 2337 - 2346 (2007/10/03)
Several N,N′-bis(trialkylsilyl)-substituted diamines of the general formula [(SiR3)2-ABA]H2 [ABA = 2-amidobenzylamido, SiR3 = SiMe3 (1a), SiMePh2 (1b), SiMe2tBu (1c) or SiiPr3 (1d)], together with related compounds in which the substituents of the two nitrogen atoms are different, e.g. [(SiMePh2)(SiMe3)-ABA]H2 (1g), have been synthesized. Their reaction with 2 equiv. of nBuLi afforded the dilithiated derivatives, which reacted with ZrCl4 to yield metallaspirocyclic complexes of the type Zr[(SiR3)2-ABA]2. Protonolysis of Zr(NMe2)4 with 1 equiv. of the parent diamines led to the monosubstituted complexes Zr[(SiR3)2-ABA](NMe2)2 [SiR3 = SiMe3 (4a), SiMePh2 (4b) or SiMe2tBu (4c)] and Zr[(SiMePh2)(SiMe3)-ABA](NMe2)2 (4g) in high yield, and subsequent reaction with excess SiMe3Cl afforded the dichlorides Zr[(SiMe3)2-ABA]Cl2 (5a), Zr[(SiMe2tBu)2-ABA]Cl2 (5c), and Zr[(SiMePh2)(SiMe3)-ABA]Cl2 (5g). The X-ray crystal structure of 5c shows that it forms dimers via two Zr-Cl bridges; moreover, a bonding interaction between the zirconium centre and the aryl ipso-carbon atom linked to the anilinic nitrogen atom is evident. A hydrochlorinated derivative of 5c, Zr[(SiMe2tBu)2(H)-ABA]Cl3 (6c), was also analysed by X-ray diffraction and shown to exhibit analogous structural characteristics. Low-temperature NMR studies revealed all these complexes to be fluxional and permitted an insight into the molecular structures in solution. The ABA framework undergoes a rocking motion about the corresponding ZrN2 plane, whose activation energy is between 37 and 43 kJ mol-1. Compounds 3 and 5 exist as several stereoisomers that interconvert by this process. On activation with MAO, the dichloride complexes of type 5 polymerize ethylene at both room temperature and pressure to yield linear high molecular mass polyethylenes with a broad molecular mass distribution.
