Synthesis and characterization of titanium ketimide complexes Ti(N C t Bu 2 ) n Cl 4n (n = 1, 2): Ethylene polymerization studies M. Joa ˜o Ferreira, Ine ˆs Matos, M. Teresa Duarte, M. Merce ˆs Marques, Ana M. Martins * Centro de Quı ´mica Estrutural, Instituto Superior Te ´cnico, Av. Rovisco Pais, 1, 1049-001 Lisboa, Portugal Available online 30 January 2008 Abstract Compounds [Ti(N C t Bu 2 )Cl 3 ] 2 , 1, [Ti(N C t Bu 2 ) 2 Cl 2 ] 2 , 2, [Ti(N C t Bu 2 )(CH 2 Ph) 3 ], 3, [Ti(N C t Bu 2 ) 2 (CH 2 Ph) 2 ], 4, [Ti(N C t- Bu 2 )(CH 2 Ph) 2 (m-CH 2 PhB(C 6 F 5 ) 3 ], 5 and [Ti(N C t Bu 2 ) 2 (CH 2 Ph) (m-CH 2 PhB(C 6 F 5 ) 3 ], 6, are described. 1 was obtained from the reaction of TiCl 4 and Me 3 SiN C t Bu 2 and used as starting material for the preparation of 2 and 3. Complex 4 was obtained by reaction of 2 with PhCH 2 MgCl. Complexes 5 and 6 were prepared by addition of B(C 6 F 5 ) 3 to 3 and 4, respectively. The NMR spectra of 5 and 6 reveal that these complexes exist in solution as zwitterions with one benzyl ligand bridging the titanium and boron centres. Complexes 1 and 2 are ethylene polymerization catalysts when activated with MAO, displaying activities of 217.1 and 794.6 kg/(mol(Ti[E]) h), respectively. # 2007 Elsevier B.V. All rights reserved. Keywords: Titanium ketimide; Ethylene polymerization; MAO 1. Introduction The diversity of Group 4 metal complexes that display extremely high activity, productivity and selectivity in a-olefin polymerization catalysis rose exponentially in recent years due to a deeper understanding of the reactions mechanisms [1–8]. It is currently recognised that the ability to modulate and control homo- and co-polymer synthesis is intrinsically associated to ligand modifications that determine stereochemical and/or electronic aspects. Subtle interactions as agostic hydrogen bonding [9], ion pairing [10,11] and aggregation levels [12], for instance, proved to be extremely important in the catalysts performance through the stabilization of the Lewis acidic metal centres that are the actual polymerization catalysts. Among several types of support ligands extensively used in Group 4 metal olefin polymerization catalysts are nitrogen- based ligands as benzamidinates [13–15], amidos [16–18] and, more recently, phosphinimides [19,20] and ketimides [21]. Compounds of the type Cp 0 Ti(N C t Bu 2 )Cl 2 , patented by Nova Chemicals [22], have proven to be extremely active catalysts in a-olefin homopolymerizations [23–26], and are capable of copolymerizing ethylene with polar [23] and apolar monomers [24,26]. Particularly noteworthy is the ethylene–styrene copolymerization that was obtained in a living manner by Nomura [26]. The cationic complexes [TiCp 0 (N CR 1 R 2 )Me] + , which are accepted as the active species in olefin polymeriza- tion catalysis, have been studied by Piers et al. [27,28]. We have recently reported that the titanium tris(ketimide) complex Ti(N C t Bu 2 ) 3 Cl is a good ethylene polymerization catalysts when activated by MAO [29] and carried out reactivity studies relevant to the understanding of their behaviour as ethylene polymerization catalysts [30]. We present now the syntheses and characterization of mono- and bis-ketimide titanium complexes of general formula Ti(N C t Bu 2 ) n X 4n (n = 1, 2; X = Cl, PhCH 2 ) and reactivity studies that include ethylene polymerization. 2. Experimental All manipulations, except stated otherwise, were carried out under nitrogen, using either standard Schlenk-line or dry-box techniques. Solvents were pre-dried using 4 A ˚ molecular sieves and refluxed over sodium-benzophenone (diethyl ether, tetrahydro- furan and toluene) or calcium hydride (dichloromethane, acetonitrile and n-hexane) under an atmosphere of nitrogen, and collected by distillation. Deuterated solvents were dried with molecular sieves and freeze–pump–thaw–degassed prior to use. www.elsevier.com/locate/cattod Available online at www.sciencedirect.com Catalysis Today 133–135 (2008) 647–653 * Corresponding author. Tel.: +351 218419172; fax: +351 218464457. E-mail address: ana.martins@ist.utl.pt (A.M. Martins). 0920-5861/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2007.11.054