Metalation of 2‐Propenylphenol

Abstract

AbstractIn order to generate 2‐propenylphenolate, PO−, as a potential ligand for oxomolybdenum compounds, the lithiation of the parent phenol derivative, POH, was investigated. Treatment of POH with BuLi in THF yielded a tetramer of the corresponding alkoxide “POLi” with a heterocubane structure in which the coordination spheres of the Li centres are completed by THF molecules, i.e. {Li(THF)[μ3‐OC6H4(CH=CH−CH3)‐2]}4 (1). Compound 1 proved to be rather unreactive and unsuitable as a starting material for the introduction of the corresponding aryloxide ligands into the coordination sphere of molybdenum by salt metathesis. The latter did occur, however, when “POLi” was synthesised in the presence of 12‐crown‐4 and subsequently treated with molybdenyl chloride. This led to an unidentified aryloxide compound as well as to a hitherto unknown chlorooxomolybdate anion in the complexes [Li(12‐crown‐4)][MoO2Cl3(THF)] (2) and [{Li(12‐crown‐4)}2Cl][MoO2Cl3(THF)] (2′) with an octahedral coordination sphere at the molybdenum centre in each case. An Mo(PO) complex was finally isolated for the first time when MoO2(OtBu)2 was employed as a starting material and treated with “POLi” prepared in situ in the presence of the crown ether. This led to the isolation of [Li(12‐crown‐4)2][MoO2(PO)3] (3), which represents a rare example of a five‐coordinate dioxomolybdenum(VI) complex as well as being the first example among these complexes with a square‐pyramidal ligand arrangement. Comparison of 2 with 3 suggests that the low coordination number of the 14‐electron compound 3 originates from the bulkiness of the PO− ligands. The crystal structures of all three compounds 1−3 are discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)