Chiral Complexes of a New Diazaallyl Ligand:  Group 4 Aminooxazolinates

Abstract

A new biaryl-bridged bis(iminooxazolidine) proligand H 2 L is prepared in good yield from 2,2-diamino-6,6′-dimethylbiphenyl. The direct reaction of H 2 L with [Ti(CH 2 Ph) 4 ] leads via deprotonation of the ligand to the C 2 -symmetric dibenzyl complex [LTi(CH 2 Ph) 2 ] (85%) containing diazaallyl ligation. The analogous group 4 complexes [LZr(CH 2 Ph) 2 ] (79%) and [LHf(CH 2 Ph) 2 ] (91%) are similarly obtained. Molecular structures of these three compounds indicate C 2 -symmetry in all cases and that the chirality of the backbone is well expressed in the coordination sphere. Reaction of H 2 L with Ti(NMe 2 ) 4 gives the amide [LTi(NMe 2 ) 2 ] (90%), which on reaction with SiMe 3 Cl gives the chloride [LTiCl 2 ] (78%). The dichloride [LZr-(NMe 2 H)Cl 2 ] is prepared via treatment of H 2 L with Zr(NMe 2 ) 2 Cl 2 (THF) 2 (86%). The direct reaction of H 2 L with TiCl 4 (THF) 2 gives the adduct [(H 2 L)TiCl 4 ] (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(CH 2 Ph)][B(C 6 F 5 ) 3 (CH 2 Ph)] were consistent with tight ion pairing on the NMR chemical shift time scale.

Recent progress in transition metal catalysed hydrofunctionalisation of less activated olefins

“…In this amidate system, far greater flexibility in terms of the binding mode is possible compared to the earlier reported complexes of Zirconium or Titanium (Fig. 19 b and c) [52,53] (Fig. 19) (Fig.…”

Diazaallyls of group 4 metals based on trans-1,2-diaminocyclohexane

“…With regard to the design of chiral tetradentate ligands based on aminothiazolinates and the analogous aminooxazolinates [11,12] we note that the cyclohexyl unit in L 2 has a small but significant effect on the coordination arrangement in the region of co-ligand sites (Fig. 5), the thiazolinyl 4-methyl groups at (a) are oriented away from the coordination sphere while those at (b) are oriented towards it.…”

“…We were interested in what effects the constrained ligand geometry would have on structure and stability in comparison to, e.g., complexes of the Schiff-base ligand system III [9,10]. We have also taken opportunity here to explore the possibility of synthesis of the related proligands based on our recently reported aminooxazolinato unit IV (E = O) [11,12] and the hitherto unknown ligand type aminothiazolinato IV (E = S). The formal negative charge on these latter diazaallyl systems should be more extensively delocalised than it is in aminopyridinato ligands and hence, like the amidinates, they may be suitable for coordination to a much wider range of metals.…”

Bis[N,N′-bis(trimethylsilyl)benzamidinato]diethylhafnium(IV)

“…The only other complex that comes close to this binding mode is a zirconacyclopentane compound that possesses -H atoms, although -hydride elimination is hampered by the cyclic nature of the ligand (Hagadorn & Arnold, 1997). All the other structurally characterized derivatives show benzyl (Bazinet et al, 2003;Munslow et al, 2004;Hagadorn, 2001;Duncan et al, 2001;Walther et al, 1996;Coles & Hitchcock, 2003;Ong et al, 2003;Westmoreland et al, 2004) or methyl (Hagadorn & Arnold, 1997;Littke et al, 1998) groups attached to the group 4 metal.…”