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Shaping and Enforcing Coordination Spheres: The Implications of C3 and C1 Chirality in the Coordination Chemistry of 1,1,1-Tris(oxazolinyl)ethane (Trisox)

Gade, Lutz H., Marconi, Guido, Dro, Clemence, Ward, Benjamin David, Poyatos, Macarena, Bellemin-Laponnaz, Stephane, Wadepohl, Hubert, Sorace, Lorenzo and Poneti, Giordano 2007. Shaping and Enforcing Coordination Spheres: The Implications of C3 and C1 Chirality in the Coordination Chemistry of 1,1,1-Tris(oxazolinyl)ethane (Trisox). Chemistry - A European Journal 13 (11) , pp. 3058-3075. 10.1002/chem.200601651

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A key feature of tris(oxazolinyl)ethane (“trisox”) ligands, which have shown broad scope in asymmetric catalysis, is the orientation and steric demand of their oxazoline substituents. This, along with the modularity of their synthesis determines their coordination chemistry. The possibility to combine oxazolines, in which the stereogenic centers adjacent to the N-donor atoms have different absolute configuration, whilst retaining their ability to coordinate as tripodal ligands, has been demonstrated by the synthesis of the enantiomerically pure C3-symmetric iPr-trisox(S,S,S) and C1-symmetric iPr-trisox(S,S,R) and their reaction with [Mo(CO)3(NCMe)3] yielding [Mo{iPr-trisox(S,S,S)}(CO)3] (1 a) and [Mo{iPr-trisox(S,S,R)}(CO)3] (1 b), respectively. The non-autocomplementarity of two homochiral trisox ligands at one metal center has been demonstrated by reaction of rac-C3iPr-trisox with one equivalent of [Co(ClO4)2]6 H2O, giving the centrosymmetric heterochiral complex [Co(iPr-trisox)2](ClO4)2 (3), whereas an analogous reaction with the enantiopure ligand yielded a mixture of CoII complexes, which is characterized by the total absence of a [(trisox)2Co]+/2+ ion. The scope of the trisox ligand in terms of facial coordination to both early and late transition metals was demonstrated by the synthesis and structural characterization of the mononuclear complexes [ScCl3(iPr-trisox)] (4), [Fe(tBu-trisox)(NCMe)3](BF4)2 (5), and [Ru(η6-p-cymene)(iPr-trisox)](PF6)2 (6). The facial coordination of their three ligating atoms to a metal center may be impeded if the transition-metal center stereoelectronically strongly favors a non-deltahedral coordination sphere, which is generally the case for the heavier d8-transition-metal atoms/ions. Reaction of iPr-trisox with [Rh(cod)2]BF4 led to the formation of the 16-electron d8-configured complex [Rh(iPr-trisox)(cod)](BF4) (7), which is oxidized by CsBr3 to give the RhIII complex [RhBr3(iPr-trisox)] (8) possessing a C3-symmetric structure with a κ3-N-trisox ligand. The crystalline salts [M2(μ-Cl3)(iPr-trisox)2](PF6) (M=FeII: 9, CoII: 10, NiII: 11), were prepared by addition of one molar equivalent of iPr-trisox and an excess of KPF6 to solutions of the anhydrous (FeCl2) or hydrated metal halides (CoCl26 H2O, NiCl26 H2O). All dinuclear complexes display weak magnetic coupling. For the mononuclear species [CuCl2(iPr-trisox)] (12) the removal of a chloride anion and thus the generation of a dinuclear chloro-bridged structure failed due to Jahn–Teller destabilization of a potential octahedral coordination sphere.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Uncontrolled Keywords: C3 symmetry; chirality; coordination chemistry; transition-metal complexes; trisoxazolines; X-ray diffraction
Publisher: Wiley-Blackwell
ISSN: 1521-3765
Last Modified: 04 Jun 2017 01:40

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