| Abstract
| - Compounds of the type (ArylNHCH2CH2)2O (Aryl = 2,6-Me2C6H3 (H2[1a]), 2,6-Et2C6H3(H2[1b]), 2,6-i-Pr2C6H3 (H2[1c])) can be prepared by treating (TsOCH2CH2)2O (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-raystudy of [1a]Ti(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. AnX-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 structurehalfway between type A and type B, i.e., a distorted square pyramid with one alkyl in theapical position. Analogous compounds were also prepared that contain a sulfur donor insteadof oxygen, i.e., [(2,6-Me2C6H3NHCH2CH2)2S] (H2[2a]), [(2,6-i-Pr2C6H3NHCH2CH2)2S] (H2[2c]),[2a,c]Zr(NMe2)2, [2a,c]ZrCl2, [2a,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 thatcontain coordinated dimethylaniline, with which free aniline does not exchange readily onthe NMR time scale at 60 °C. Addition of excess ether to {[1a]MMe(NMe2Ph)}[B(C6F5)4](M = Zr, Hf) 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 beas stable as in the oxygen ligand system. Zr and Hf dimethyl complexes that contain anoxygen donor or a sulfur donor ligand can be activated with [Ph3C][B(C6F5)4] to yield efficientcatalysts for polymerization of 1-hexene, although the molecular weight of the poly(1-hexene)chains is limited to ∼20 000−∼25 000 under the conditions employed. Neither {[1c]ZrMe(ether)}[B(C6F5)4] nor {[1c]HfMe(ether)}[B(C6F5)4] will polymerize 1-hexene in C6D5Br atroom temperature, and neither will polymerize ethylene readily at 1 atm and 25 °C. It isproposed that a solvated five-coordinate cation must lose the solvent in order to react withan olefin and that β-hydride elimination in the four-coordinate cation limits chain length.
- Dialkyl Ti, Zr, and Hf compounds that contain ligands of the type [(ArylNCH2CH2)2D]2- (Aryl = 2,6-Me2C6H3, 2,6-Et2C6H3, 2,6-i-Pr2C6H3; D = O, S) adopt various structures between two different types of trigonal bipyramids on the basis of steric interactions within the five-coordinate complex. Dialkyl complexes can be activated with [PhNMe2H][B(C6F5)4], and monoalkyl cations that contain coordinated dimethylaniline can be observed. Zr and Hf dimethyl complexes can be activated with [Ph3C][B(C6F5)4] to yield efficient catalysts for polymerization of 1-hexene.
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