Metalation of 2‐Propenylphenol

In 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)[μ 3 ‐OC 6 H 4 (CH=CH−CH 3 )‐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)][MoO 2 Cl 3 (THF)] ( 2 ) and [{Li(12‐crown‐4)} 2 Cl][MoO 2 Cl 3 (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 MoO 2 (O t Bu) 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 ][MoO 2 ( 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)