Synthesis and Structure of (η⁵-cyclohexadienyl)Mn(CO)₃ and Cationic (η⁶-arene)Mn(CO)₃ Complexes Comprising a Double Bond Conjugated to the π System

Abstract

Addition of a Grignard reagent to keto-substituted (η5-cyclohexadienyl)Mn(CO)3 complexes leads to the corresponding alcohols in very good yields. After acidic treatment, dehydration occurs, which gives rise to the formation of unprecedented (η5-cyclohexadienyl)Mn(CO)3 complexes substituted by a double bond conjugated to the π system as the major compounds, along with uncoordinated trienones due to the rearrangement of the intermediate carbocation. The structure of one of these η5 complexes has been determined by X-ray crystallography as well as one of the corresponding cationic (η6-arene)Mn(CO)3 complexes formed upon hydride abstraction.