Synthesis of Novel Group 4 Complexes Bearing the Tropidinyl Ligand:  Investigations of Dynamic Behavior, Reactivity, and Catalytic Olefin Polymerization

Abstract

A new class of group 4 complexes bearing the tropidinyl (Trop) ligand were synthesized. This novel anionic ligand, easily derived from the natural product tropine, is regarded as an analogue of the well-studied Cp ligand (Cp ) cyclopentadienyl) and features a bicyclic ring system in which an allyl function donates 4π electrons and an amine function donates 2σ electrons to the metal center. The synthesis of the group 4 complexes involved transmetalation of a stannylated allyl functionality with a group 4 metal halide with concomitant elimination of Me 3 SnCl. Reaction of endo-stannylated tropidine (1) and ZrCl 4 , CpZrCl 3 , or CpTiCl 3 afforded the complexes (Trop) 2 ZrCl 2 (2), (Cp)(Trop)ZrCl 2 (3), and (Cp)-(Trop)TiCl 2 (4), respectively. These dihalide complexes were alkylated using methyllithium to generate (Trop) 2 ZrMe 2 (5), (Cp)(Trop)ZrMe 2 ( 6), (Cp)(Trop)TiMe 2 (7), or benzylmagnesium chloride to give (Trop) 2 ZrBn 2 ( 8) and (Cp)(Trop)ZrBn 2 (9). Complexes 2, 3, 5, and 8 were characterized by X-ray crystallography. Complexes 5 and 6 were observed to undergo protonolysis with various acids (HA) to give mixed [Zr]MeA complexes. Reaction of complex 6 with isonitriles (ArNC) gave the η 2 -iminoacyl complex (Cp)(Trop)ZrMe[N(Ar)CMe] (13), whose structure was confirmed by X-ray crystallography. All the complexes displayed dynamic behavior, and the various exchange processes were investigated by variabletemperature NMR spectroscopy. The dihalide complexes 2, 3, and 4 in the presence of modified methylaluminoxane (MMAO) were active catalysts for the polymerization of ethylene. The catalyst system 3/MMAO displayed a very high ethylene polymerization activity and was similar to that observed for Cp 2 ZrCl 2 /MMAO. High molecular weight polypropylene was generated using 4/MMAO, and polypropylene oligomer was obtained using 3/MMAO. The cationic complex [(Cp)(Trop)ZrMe][MeB(C 6 F 5 ) 3 ] (14) was formed upon reaction of the dimethyl complex 6 with B(C 6 F 5 ) 3 and was shown to be an active ethylene polymerization catalyst.

A new series of zirconium metallocenes derived from partially alkylated s-indacene with potential applications in the polymerization of ethylene

“…The experimental angles and bond lengths for these new zirconium compounds are similar to other previously reported group IV complexes [42,43]. All intramolecular Zr-C distances concerning those to the s-indacene ligand as well as the Cp or Cp ⁄ ligand vary from 2.2 to 2.6 Å, ratifying the g 5 hapticity of Zr in both complexes.…”

Synthesis and reactivity of zirconium and hafnium complexes incorporating chelating diamido-N-heterocyclic-carbene ligands

“…The 1 H NMR spectrum of 26 shows a C s symmetric species in solution with a Hf-CH 3 resonance at d 0.19, which is similar to previously described complexes [31].…”

Group 4 metal complexes for homogeneous olefin polymerisation: a short tutorial review

“…Catalysts supported by these ligands can give productivities similar to their Cp analogues. Tropidinyl ligands have been utilised by Bergman et al [83] as a Cp mimic in complexes such as 13 despite having separate r and p systems. An alternative ligand that can be used in place of Cp is the monoanionic tris(pyrazol)borate (Tp) [84][85][86].…”