Synthesis and Structures of Low-Valent Tungsten Complexes Bearing Chiral Oxazoline-Derived Ligands

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)(C 3 H 5 )Cl] (PN = phosphino-oxazoline) are fluxional in solution, but can be crystallized as single diastereoisomers. The complex [W(CO) 3 (PN)(CH 3 CN)], 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)(CH 3 CN)] functions as a highly enantioselective catalyst in allylic substitution reactions with dimethyl sodiomalonate, whereas complexes of the type [W (CO) 2 (PN )(Z -C 3 H 4 )X)] (Z = H, Ph; X = Cl, Br) failed to yield allylic alkylation products.