Synthesis of group 4 complexes that contain the tridentate diamido/donor ligands [(ArylNCH2CH2)2O]2- and zirconium complexes that contain [(ArylNCH2CH2)2S]2- and an evaluation of their activity for the polymerization of 1-hexene

Compounds of the type (ArylNHCH(2)CH(2))(2)O (Aryl= 2,6-Me2C6H3 (H-2[1a]), 2,6-Et2C6H3 (H-2[1b]), 2,6-i-Pr2C6H3 (H-2[1c])) can be prepared by treating (TsOCH2CH2)(2)O (TsO = tosylate) with the lithium anilides in THF. [1a,b]TiCl2, [1a,b]TiMe2, [1a]Ti(CH2Ph)(2), [1a-c]M(NMe2)(2) (M = Zr or Hf), [1a-c]MCl2, and [1a-c]MR2 (R = Me, Et, i-Bu) were prepared. An X-ray study of [1aTi](CH2Ph)(2) revealed the structure to be a distorted trigonal bipyramid (type B) in which the two amido nitrogens and one benzyl Ligand occupy equatorial positions. An X-ray study of [1a]ZrMe2 showed it to be a distorted trigonal bipyramid that contains "axial" amido groups (type A), while an X-ray study of [1c]HfEt2 revealed it to have a structure halfway between type A and type B, i.e., a distorted square pyramid with one alkyl in the apical position. Analogous compounds were also prepared that contain a sulfur donor instead of oxygen, i.e., [(2,6-Me2C6H3NHCH2CH2)(2)S] (H-2[2a]), [(2,6-i-Pr2C6H3NHCH2CH2)(2)S] (H-2[2c]), [2a,c]Zr(NMe2)(2), [Ba,c]ZrCl2, [2Ba,c]ZrMe2,and [2c]Zr(CH2CHMe2)(2). An X-ray study of [2a]-ZrMe2 revealed it to be closest to a type B structure. Addition of 1 equiv of [PhNMe2H]-[B(C6F5)(4)] in C6D5X (X = Br, Cl) to [1a,c]MMe2 (M = Zr, Hf) gave cationic complexes that contain coordinated dimethylaniline, with which free aniline does not exchange readily on the NMR time scale at 60 degrees C. Addition of excess ether to {[1a]MMe(NMe2Ph)}[B(C6F5)(4)] (M = Zr, I-If) led to {[1a]MMe(ether)}[B(C6F5)(4)] (M = Zr, Hf) complexes in high yield. Analogous cations can be prepared in the sulfur ligand system, but they do not appear to be as stable as in the oxygen ligand system. Zr and I-If dimethyl complexes that contain an oxygen donor or a sulfur donor ligand can be activated with [Ph3C][B(C6F5)(4)] to yield efficient catalysts for polymerization of l-hexene; although the molecular weight of the poly(l-hexene) chains is limited to similar to 20 000 - similar to 25 000 under the conditions employed. Neither {[1c]ZrMe-(ether)}[B(C6F5)(4)] nor {[1c]HfMe(ether)}[B(C6F5)(4)] will polymerize I-hexene in Ce6D6 Br at room temperature, and neither will polymerize ethylene readily at 1 atm and 25 degrees C. It is proposed that a solvated five-coordinate cation must lose the solvent in order to react with an olefin and that beta-hydride elimination in the four-coordinate cation limits chain length.