Chiral Complexes of a New Diazaallyl Ligand: Group 4 Aminooxazolinates

A new biaryl-bridged bis(iminooxazolidine) proligand H2L is prepared in good yield from
2,2-diamino-6,6‘-dimethylbiphenyl. The direct reaction of H2L with [Ti(CH2Ph)4] leads via
deprotonation of the ligand to the C2-symmetric dibenzyl complex [LTi(CH2Ph)2] (85%)
containing diazaallyl ligation. The analogous group 4 complexes [LZr(CH2Ph)2] (79%) and
[LHf(CH2Ph)2] (91%) are similarly obtained. Molecular structures of these three compounds
indicate C2-symmetry in all cases and that the chirality of the backbone is well expressed in
the coordination sphere. Reaction of H2L with Ti(NMe2)4 gives the amide [LTi(NMe2)2] (90%),
which on reaction with SiMe3Cl gives the chloride [LTiCl2] (78%). The dichloride [LZr(NMe2H)Cl2] is prepared via treatment of H2L with Zr(NMe2)2Cl2(THF)2 (86%). The direct
reaction of H2L with TiCl4(THF)2 gives the adduct [(H2L)TiCl4] (83%), which is shown by
X-ray crystallography to contain intramolecular NH···Cl hydrogen bond contacts. The
complexes were tested as precatalysts for the polymerization of ethene and 1-hexene using
a range of cocatalysts and were found to display low activity. Correspondingly, NMR studies
on a presumed active species [LZr(CH2Ph)][B(C6F5)3(CH2Ph)] were consistent with tight ion
pairing on the NMR chemical shift time scale.

以2,2'-二氨基-6,6'-二甲基联苯为原料，以优异收率合成了联芳基桥联双（亚氨基恶唑烷）前配体（biaryl-bridged bis(iminooxazolidine) proligand）H₂L。将H₂L与[Ti(CH₂Ph)₄]直接反应，经配体脱质子过程得到具有二氮烯丙基配位的C₂对称二苄基配合物[LTi(CH₂Ph)₂]（收率85%）。类似地，可制备得到第4族金属配合物[LZr(CH₂Ph)₂]（收率79%）与[LHf(CH₂Ph)₂]（收率91%）。上述三种化合物的分子结构均显示其具有C₂对称性，且骨架手性在配位环境中得到充分体现。将H₂L与Ti(NMe₂)₄反应可得到酰胺配合物[LTi(NMe₂)₂]（收率90%），该配合物与三甲基氯硅烷（SiMe₃Cl）反应后可得到氯化物配合物[LTiCl₂]（收率78%）。二氯化物配合物[LZr(NMe₂H)Cl₂]通过H₂L与Zr(NMe₂)₂Cl₂(四氢呋喃, THF)₂反应制得，收率为86%。将H₂L与TiCl₄(四氢呋喃, THF)₂直接反应可得到加合物[(H₂L)TiCl₄]（收率83%），经X射线晶体学（X-ray crystallography）表征证实其存在分子内NH···Cl氢键相互作用。将上述配合物作为预催化剂，在多种助催化剂作用下用于乙烯与1-己烯的聚合反应，结果显示其催化活性较低。相应地，对推测的活性物种[LZr(CH₂Ph)][B(C₆F₅)₃(CH₂Ph)]的核磁共振（NMR）研究表明，该物种在核磁共振化学位移时间尺度上表现为紧密离子对。