β-Diiminato Complexes of VIII and TiIII – Formation and Structure of Stable Paramagnetic Dialkylmetal Compounds
✍ Scribed by Peter H. M. Budzelaar; A. Bart van Oort; A. Guy Orpen
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 281 KB
- Volume
- 1998
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Polymerizations / Diimine / Dialkylmetal compounds (Mono-β-diiminato)titanium(III) and -vanadium(III) dichlo-The corresponding dialkyltitanium(III) compounds are less stable; only the dimethyl derivatives could be obtained in rides LMCl 2 [L = ArNC(R)CHC(R)NAr -] are easily accessible from the metal trichlorides and LLi in THF. The crystal pure form (from LTiCl 2 and MeMgI), and only for ligands bearing 2,6-disubstituted aryl groups. The structure of structures of LVCl 2 (Ar = 2,6-iPr 2 C 6 H 3 , R = Me) and LTiCl 2 (Ar = 2,4,6-Me 3 C 6 H 2 , R = Me and Ar = 2,4,6-Me 3 C 6 H 2 , R =
LTiMe 2 (Ar = 2,4,6-Me 3 C 6 H 2 , R = Me) is also similar to that of the dichloride. Reaction of LTiMe 2 with B(C 6 F 5 ) 3 produces tBu) reveal tetrahedral metal environments. Treatment of LVCl 2 with alkyllithium reagents affords surprisingly stable a catalyst for α-olefin polymerization, but the corresponding V III derivatives are inactive. dialkylvanadium(III) compounds; the structure of LV(nBu) 2 (Ar = 2,6-iPr 2 C 6 H 3 , R = Me) is similar to that of the dichloride. sition alkylmetal compounds. Neutral dialkylmetal comgands in selected cases. [4] pounds, in particular, are of great importance as precursors of catalytically active cationic monoalkyl species. Most of the work in this area has concentrated on diamagnetic d 0 complexes of group-III and -IV metals. It is still unclear whether d 1 or d 2 complexes can be as efficient in olefin polymerization as their d 0 analogues, and this lack of insight is Ligand Syntheses at least partly due to the unavailability of suitable catalyst precursors. However, work by Theopold on d 3 chromium
The two main routes for the synthesis of β-diimines are systems demonstrates that well-defined paramagnetic summarized in Scheme 1. The most convenient route (A) is homogeneous polymerization catalysts are certainly poscondensation of a β-diketone with an (aromatic) amine. [5] sible. [1] The second route (B) is especially useful for very bulky di-We report herein on the preparation of Ti III (d 1 ) and V III imines, [6] where the route A condensation is very sluggish. (d 2 ) complexes containing a β-diiminato ancillary ligand.
Route B is also applicable to the synthesis of asymmetri-The β-diimine ligand has not been widely used in orcally substituted diimines (different Ar groups). The ligands ganometallic chemistry. Some Pd II and Ni II complexes have used in the present work were all prepared by one of these been prepared recently; in comparison with related α-diimtwo methods. Lappert has reported a more exotic synthesis ine complexes they showed a much lower activity in Brookof silyl-substituted diiminates from bis(trimethylsilyl)methhart-type olefin polymerization. [2] Collins has recently reyllithium and nitriles. [7] ported the synthesis of several Zr IV complexes of β-diimines. [3] One advantage of β-diimines is that ligand variation, in Dichloride Complexes both the ligand backbone and the substituent at the nitrogen atom, is relatively easy. This has allowed us to probe the Complexes LMCl 2 (M ϭ Ti III , V III ; L L 4 or L 6 ) are consequences of steric effects in the present study (Scheme 1 conveniently prepared by reaction in THF of MCl 3 (THF) 3 with the lithium salt of the β-diimine (prepared in situ from [ ] Present address: Department of Inorganic Chemistry, Univerthe free diimine and nBuLi).