Synthesis and Structures of Low-Valent Tungsten Complexes Bearing Chiral Oxazoline-Derived Ligands
2014
Lloyd-Jones, Guy C. | Pfaltz, Andreas
The synthesis of low-valent tungsten (0 and II) complexes bearing chiral bidentate phosphino- oxazoline or bisoxazoline ligands is described. The structures of four of the complexes have been determined by single crystal X-ray analyses. Tungsten(II)-allyl complexes of the type [W(CO)₂(PN)(C₃H₅)Cl] (PN = phosphino-oxazoline) are fluxional in solution, but can be crystallized as single diastereoisomers. The complex [W(CO)₃(PN)(CH₃CN)], which also crystallizes as a single diastereoisomer, is readily oxidized in solution and solid state, in stark contrast to analogous compounds bearing four carbonyl ligands [W(CO)₄(PN)] or [W(CO)₄(NN)] (NN = bisoxazoline) which were found to be stable. [W(CO)₃(PN)(CH₃CN)] functions as a highly enantioselective catalyst in allylic substitution reactions with dimethyl sodiomalonate, whereas complexes of the type [W (CO)₂(PN)(Z -C₃H₄)X)] (Z = H, Ph; X = Cl, Br) failed to yield allylic alkylation products.
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