Preparation and Characterization of an Isometallabenzene with the Structure of a 1,2,4-Cyclohexatriene

The elongated dihydrogen complex [Os{C6H4C(O) CH3}(eta2-H2)(H2O)(PiPr3)2]BF4 reacts with phenylacetylene and HBF4.OEt2 to give the unsaturated compound [Os{(E)-CH=CHPh}(CCPh)(CCH2Ph)(PiPr3)2]BF4 containing alkenyl, alkynyl, and carbyne ligands. The addition of sodium chloride to this compound leads to the cyclic allene Os{=C=C(Ph)CH(Ph)CH=C(CH2Ph)}Cl(PiPr3)2, which is the first isometallabenzene with the structure of a 1,2,4-cyclohexatriene.