Amido- and imido-ethylpyridine titanium complexes. Crystal structure of {Ti[NCH2CH2py]Cl2(THF)}2

doi:10.1016/S0022-328X(01)00837-3

Journal of Organometallic Chemistry

Volume 632, Issues 1–2, 24 August 2001, Pages 17-26

https://doi.org/10.1016/S0022-328X(01)00837-3 Get rights and content

Abstract

Compounds of general formula N(R₁)(R₂)CH₂CH₂py (py=C₅H₄N; R₁=R₂=SiMe₃, 1a; R₁=H, R₂=Si^tBuMe₂, 1b; R₁=SiMe₃, R₂=Si^tBuMe₂, 1c; R₁=SiMe₃, R₂=Ph, 5) were synthesised. They readily reacted with TiCl₄ to afford the corresponding amidoaminotrichlorides {Ti[N(R₂)(CH₂CH₂py)]Cl₃} (R₂=SiMe₃, 2a; R₂=Si^tBuMe₂, 2b; R₂=Ph, 6). The related imido derivatives {Ti[N(CH₂CH₂py)]Cl₂}_n (3b) and {Ti[N(CH₂CH₂py)](L)Cl₂}₂ (L=THF, 3c; PMe₃, 3d) were isolated upon heating and reaction with L, respectively. Reaction of 6 with THF afforded the corresponding adduct, {Ti[N(Ph)(CH₂CH₂py)](THF)Cl₃} (7). Compound 3b reacted with LiNMe₂ to give asymmetrical {Ti₂[N(CH₂CH₂py)][N(CH₂CH₂py)]′Cl₄} (4a). Compound {CpTi[N(CH₂CH₂py)]Cl}_n (4b), was formed when 3b reacted with NaCp. Analogous studies with 2a and 6 led to Cp₂TiCl₂. {Cp₂Ti₂[μ-N(Ph)]Cl₂} (8) was isolated as the product of CpTiCl₃ and Na[N(Ph)CH₂CH₂py]. The molecular structure of 3c was determined by X-ray single crystal diffraction.

The syntheses of 2′-aminoethyl pyridine derivatives and 2′-aminoethyl-2-pyridine titanium complexes are described. The reactions of py(CH₂)₂N(SiMe₃)R (R=SiMe₃, SiMe₂^tBu, Ph) with TiCl₄ readily afford the corresponding amido complexes. The cleavage of the NR bonds (R=SiMe₃, SiMe₂^tBu) led to bridging imido ligands and the synthesis of binuclear complexes as {Ti[NCH₂CH₂py]Cl₂(THF)}₂ that was characterised by X-ray diffraction. The formation of imido complexes was also observed when R=Ph leading to [TiCl₂(μ-NPh)]₂.

Introduction

Nitrogen-based ligands offer a great diversity of structural frameworks that have been used as ancillary ligands in several studies of organometallic chemistry [1], [2], [3], [4], [5], [6], [7], including Group 4 metal complexes with activity in olefin polymerisation [8], [9], [10], [11]. Relevant results include bis(amido)titanium (IV) complexes that carry out the living polymerisation of olefins [12], [13], [14].

The amido/amine donor set has attracted the interest of several researchers. Pyridyl-substituted 1-azaallyl ligands have been successfully co-ordinated to zirconium to give octahedral complexes that show high activity in ethylene polymerisation [15], [16]. Recent studies on Group 4 aminopyridinato complexes emphasise the importance of the amido nitrogen substituents on the control of metal–ligand stoichiometry and reactivity [5], [15], [17], [18].

The particular features that dictate the performance of polyfunctional nitrogen compounds as catalysts are still not fully understood [10], [19]. Thus, the study of Group 4 complexes with ancillary N-donor ligands is a topic of current interest [20], [21], [22], [23], [24]. We report the synthesis, characterisation and reactivity of new Ti(IV) complexes containing amido- and imido-ethylpyridine ligands.

Section snippets

Results and discussion

Silylated amine derivatives are useful reagents as they are easy to synthesise and because they react with metal chlorides to give R₃SiCl which, being volatile, are easily eliminated from the reaction media. These features, associated with efficient steric bulk, partially explain their extensive use in synthesis and the large number of co-ordination compounds containing such ligands [1], [5], [9], [25], [26]. Silylated derivatives of 2′-aminoethyl-2-pyridine are no exception. Compounds 1a–1c

Conclusions

N(SiMe₃)(R)(CH₂CH₂)py reacts readily with TiCl₄ to give the corresponding trichlorides, {Ti[N(R)(CH₂CH₂)py]Cl₃}. The study of their chemistry is hampered by the high reactivity of the NR bond that often leads to the formation of N-bridged imido complexes, and by the inability of amidoethylpyridine ligands to offer steric protection to the metal centres. The lack of rigidity conferred by the C₂ chain does not impose a constrained co-ordination mode of the ligand, a feature that may be crucial

Experimental

All manipulations, except stated otherwise, were carried out under N₂, using either standard Schlenk-line or dry-box techniques. Solvents were pre-dried using 4 Å molecular sieves and refluxed over sodium-benzophenone (Et₂O, THF and C₆H₅CH₃) or CaH₂ (CH₂Cl₂, 1,2-dichloroethane and n-hexane) under an atmosphere of N₂, and collected by distillation. Deuterated solvents were dried with molecular sieves and freeze–pump–thaw–degassed prior to use. ¹H- and ¹³C-NMR spectra were recorded in a Varian

Supplementary material

Experimental details, atomic coordinates, bond lengths and angles for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC no. 157363 for compound 3c. Copies of data may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (Fax: +44-1223-336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).

Acknowledgements

This work was supported by Program PRAXIS XXI (PRAXIS/C/QUI/12224/98) Fundação para a Ciência e Tecnologia, (Lisbon, Portugal). I.E. and M.J.F. are grateful to Fundação para a Ciência e Tecnologia, (Lisbon, Portugal) for financial support.

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Amido- and imido-ethylpyridine titanium complexes. Crystal structure of {Ti[NCH2CH2py]Cl2(THF)}2

Abstract

Introduction

Section snippets

Results and discussion

Conclusions

Experimental

Supplementary material

Acknowledgements

J. Organomet. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

J. Organomet. Chem.

Coord. Chem. Rev.

J. Organomet. Chem.

J. Am. Chem. Soc.

Organometallics

Organometallics

Inorg. Chem.

Chem. Commun.

Organometallics

J. Chem. Soc. Dalton Trans.

Chem. Commun.

Angew. Chem. Int. Ed. Engl.

J. Am. Chem. Soc.

J. Am. Chem. Soc.

Organometallics

Inorg. Chem.

Chem. Ber. Rec.

Chem. Commun.

Amido- and imido-ethylpyridine titanium complexes. Crystal structure of {Ti[NCH₂CH₂py]Cl₂(THF)}₂