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-ray
study 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. 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)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 that
contain coordinated dimethylaniline, with which free aniline does not exchange readily on
the 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 be
as stable as in the oxygen ligand system. Zr and Hf 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 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 at
room temperature, and neither will polymerize ethylene readily at 1 atm and 25 °C. It is
proposed that a solvated five-coordinate cation must lose the solvent in order to react with
an olefin and that β-hydride elimination in the four-coordinate cation limits chain length.
