The new N-heterocyclic carbene 1-(2,6-diisopropylphenyl)-3,4,5-trimethylimidazolin-2-ylidene (IPrMe) (3) was prepared in three steps from methyl isothiocyanate and 2,6-diisopropylaniline, affording N-methyl-NЈ-2,6-diisopropylthiourea (1). Reaction of 1 with 3-hydroxybutanone gave the imidazolin-2-thione (IPrMe)S (2), which was reduced with elemental potassium to the carbene IPrMe (3). Treatment of 3 with trimethylsilyl azide (Me 3 SiN 3 ) in boiling toluene, followed by desilylation in methanol, gave the imidazolin-2-imine (IPrMe)NH (4). The ethylene-bridged diimine ligand N, diisoprop-* Prof. Dr. M. Tamm 2204 ylphenyl)-3,4,5-trimethylimidazolin-2-ylidene]-1,2-ethanediamine, (IPrMe)NCH 2 CH 2 N(IPrMe) (5) was prepared by reaction of 4 with 1,2-ethyleneditosylate and subsequent deprotonation with KOtBu. The reaction of 5 with metal dichlorides furnished the tetrahedral complexes [(5)MCl 2 ] [M = Fe (6), M = Ni (7), M = Zn (8)] and the squareplanar complex [(5)PdCl 2 ] (9), as revealed by X-ray diffraction analyses. The X-ray crystal structures of 2, 3, and 4 were also established. Complex 8 and related zinc(II) bis(imidazolin-2-imine) complexes were tested in the polymerization of d,l-lactide.the ligands BL R,RЈ (Scheme 1), with the contribution of the dipolar mesomeric form increasing significantly upon coordination to transition metal complex fragments. As a conse-Scheme 1. Mesomeric structures (A, B) for bis(imidazolin-2-imine) ligands BL R,RЈ (BL Me : R = RЈ = Me; BL iPr : R = RЈ = iPr; BL Dipp,Me : R = 2,6-diisopropylphenyl, RЈ = Me); schematic presentation of C 2symmetric bis(imidazolin-2-imine) metal complexes (box). Journal of Inorganic and General Chemistry Zeitschrift für anorganische und allgemeine Chemie www.zaac.wiley-vch.de
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Dedicated Clusterquence of this charge separation, the imidazole rings in the resulting metal complexes usually adopt a perpendicular orientation relative to the N-M-N plane, precluding any significant π-interaction with the metal-bound nitrogen atoms.Accordingly, bis(imidazolin-2-imine) ligands with a symmetric N,NЈ-substitution pattern (R = RЈ), such as BL Me and BL iPr , usually form C s -or C 2v -symmetric chelate complexes with four magnetically equivalent nitrogen substituents. [1] The introduction of unsymmetric imidazolin-2-ylidene moieties with nitrogen substituents of distinctly different size, however, might afford BL R,R' ligands (R = BIG ϶ RЈ = small) that are able to form chiral C 2 -symmetric complexes by adopting a conformationally stable anti-orientation of the R and RЈ pairs of substituents as illustrated in Scheme 1 (box). In principle, this would allow the synthesis of chiral complexes for applications in asymmetric catalysis such as transfer hydrogenation. [4c,4f,4g] A similar concept was developed for related αdiimine ligands and their respective nickel(II) and palladium(II) complexes, which serve as catalysts for the production of highly branched polyethylene. [6] To test this hypothesis, we report herein the preparation of the bis(imidazolin-2-im...
