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 pi-complexes [(eta(6)-1-Hlg-2,4,6-Me3C6H2)(eta(5) -C5EtMe4)Rh]-(BF4)(2) (Hlg = F, Cl) with diethyl malonate anion in THF or acetone-d(6) at 20 degrees C initially (within the first 530 min) involve nucleophile addition at unsubstituted carbon atom in the arene ligand with formation of pi-cyclohexadienyl complexes {[eta(5)-1-(EtOCO)(2)CH-1-H-3-Hlg-2,4,6-Me3C6H2](eta(5)-C5EtMe4)Rhj(BF4)(2), The subsequent replacement of the halogen atom yields {[eta(6)-1-(EtOCO)(2)CH-2,4,6-Me3C6H2](eta(5) -C5EtMe4)Rh}(BF4)(2), where the arene ligand is readily withdrawn from pi-coordination by the action of chloride ion or the solvent.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)(2)CH or EtOCO(NC)CH.