Early Transition Metal Complexes Bearing a C-Capped Tris(phenolate) Ligand Incorporating a Pendant Imine Arm: Synthesis, Structure, and Ethylene Polymerization Behavior

The ligand 3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-(2,6-diisopropyl)phenylimine] (L 1 H3) was reacted with MCl4 (M = Ti, Zr) or MCl5 (M = Nb, Ta) to give complexes of the type [MCl2( L 1 H2)2] (M = Ti ( 1 ); Zr ( 2 )), [NbCl3( L 1 H)] ( 3 ), or [TaCl4( L 1 H2)] ( 4 ), respectively. Single crystal X-ray diffraction of 1 - 4 revealed common “iminium” species resulting in zwitterionic complexes. Reaction of [V(Np-tol)(On-Pr)3] with L 1 H3 afforded [{(VNp-tol)( L 1 H)}2(µ-On-Pr)2] ( 5 ), and a second complex [(VO)2(µ-O)( L 3 H)2] ( 6 ) ( L 3H being derived from 3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-p-tolylimine]). The condensation reaction between 3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butyl-2-hydroxybenzaldehyde] ( L 0 H3) and o-phenylenediamine (1,2-diaminobenzene) afforded two products: a pseudo-16-membered hydrogen bonded macrocyclic structure {1,2-bis-3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-benzyldiimine]} ( L 5 H6), or the benzimidazolyl bearing ligand ( L 6 H3). The reaction of L 5 H6 or L 6 H3 with [VO(On-Pr)3] under varying conditions produced the complexes [(VO)( L 5 H4)] ( 7 ), [(VO)2( L 5 H)] ( 8 ), or [VO( L 6 H2)2] ( 9 ). L 0 H3 was reacted with a number of anilines to give the proligands {3-[2,2'-methylenebis(4,6-di-tert-butylphenol)-5-tert-butylsalicylidene-R-imine]}, where R = NC6H5 ( L 2 H3), NC6H4-Me ( L 3 H3), and NC6H2-Me3 ( L 4 H3). Reactions of these ligands with [VO(On-Pr)3] formed bischelating complexes of the form [(VO)( L 2-4 H2)2] ( 10 , 11 , and 12 , respectively). The reaction of L 1 H3 with trimethylaluminum led to a bis-aluminum complex {(AlMe2)[AlMe(NCMe)] L 1 } ( 13 ). The ability of complexes 1-12 to polymerize ethylene in the presence of an organoaluminum cocatalyst was investigated. Procatalysts 1 and 2 were found to produce negligible activities in the presence of dimethylaluminum chloride (DMAC) and the reactivator ethyltrichloroacetate (ETA), whereas 3 and 4 were found to be completely inactive for polymerization using a variety of different organoaluminum cocatalysts. Using the combination of DMAC and ETA, complexes 5-12 were found to be highly active catalysts; in all cases, the polymer formed was of high molecular weight linear polyethylene

"Imine-based Vanadium Catalysts for alpha-olefin Polymerization"

Advances over the last decade in the development of vanadium-based pro-catalysts bearing ligands containing the imine functionality are discussed in terms of their synthesis, characterization and their ability to oligmerize/polymerize a-olefins. The chapter is organized by ligand type, considering initially ligands which chelate (bi- and tri-dentate) only through nitrogen centres, before discussing those binding via nitrogen and oxygen (bi-, tri- and tetra-dentate), those with nitrogen, oxygen and sulfur donors (penta- and hexa-dentate) and finally a number of ligand systems which are either mono-dentate or for which the term imine can be more loosely applied, such as the heterocycle pyridine

EPR Monitoring of Vanadium(IV) Species Formed upon Activation of Vanadium(V) Polyphenolate Precatalysts with AlR2Cl and AlR2Cl/Ethyltrichloroacetate (R = Me, Et)

Reactions of the vanadyl polyphenolate complexes {VO[p-tert-butylcalix[4]arene(O)3(OMe)]} ( 1 ) and [VO(OArCH2Ar'CH2OAr)]2 (Ar = 4,6-tert-butylphenol; Ar' = 4-tert-butylphenol) ( 2 ) with AlR3 and AlR2Cl, in the absence and in the presence of reactivator (ethyltrichloroacetate, ETA), were monitored by EPR (R = Me, Et). It was shown, that vanadium(IV) complexes with proposed structures L1VIVR(AlR3) and L1VIVR(AlR2Cl) are formed upon interaction of 1 with AlR3 and AlR2Cl, respectively (20 °C, L1 is the initial oxo-calix[4]arene ligand). Similarly, vanadium(IV) complexes with proposed structures L2VIVR(AlR3) and L2VIVR(AlR2Cl) are formed upon interaction of 2 with AlR3 and AlR2Cl (L2 is the initial ligand of 2 ). The growth of the concentration of L1VIVR(AlR2Cl) and L2VIVR(AlR2Cl) correlates with the increase of the ethylene polymerization activity of the catalyst systems 1 , 2 /AlR2Cl/ETA. It is proposed therefore that vanadium(IV) species of the type L1VIVR(AlR2Cl) and L2VIVR(AlR2Cl) can be the active species (or their immediate precursors) of the catalyst system 1 , 2 /AlR2Cl/ETA