Arene complexes of transition metals in reactions with nucleophilic reagents: XXX. Reaction of π-halomesitylene [Tetramethyl(ethyl)cyclopentadienyl]rhodium(II) complexes with anions derived from CH acids

Reactions of fluoro-and chloromesitylene π-complexes [(η6-1-Hlg-2,4,6-Me3C6H2)(η5-C5EtMe4)Rh]-(BF4)2 (Hlg = F, Cl) with diethyl malonate anion in THF or acetone-d6 at 20°C initially (within the first 5–30 min) involve nucleophile addition at unsubstituted carbon atom in the arene ligand with formation of π-cyclohexadienyl complexes {[η5-1-(EtOCO)2CH-1-H-3-Hlg-2,4,6-Me3C6H2](η5-C5EtMe4)Rh}(BF4). The subsequent replacement of the halogen atom yields {[η6-1-(EtOCO)2CH-2,4,6-Me3C6H2](η5-C5EtMe4)Rh}(BF4)2, where the arene ligand is readily withdrawn from π-coordination by the action of chloride ion or the solvent. Dimethyl mesitylmalonate was isolated in 76% yield. Likewise, the reactions with anions derived from malononitrile and ethyl cyanoacetate gave 25–38% of the corresponding derivatives 1-R-2,4,6-Me3C6H2 where R = (NC)2CH or EtOCO(NC)CH.