Metal basicity and cooperative effects in the reactions of dinuclear pyrazolato rhodium complexes

The complex [ { Rh(p-Pz)(CNBut)2)2] (1) acts as a supernucleophile due to the strong basicity induced by the isocyanide ligands. It reacts rapidly with halocarbons (RX) such as PhCH2Cl or Me1 to give the cationic dirhodium(II1) complexes of formula [ { Rh(p-Pz)(R)(CNBut)2)2(p-X)]X. These reactions are stereoselective since the single stereoisomer formed presents both organic groups ( P h C H 2 or Me) outside the p o c k e t of the complexes. However g e m dichloroderivatives, RCHC12, react with 1 to give functionalised methylene bridged complexes [ { Rh(p-Pz)(C1)(CNBut)2}2(p-CHR)]. The latter reactions involve an unusual three-fragment four-electron addition process. Bridged chloroalkyl [ { Rh(pPz)(Cl)(CNBut)2J;?(p-CClR)] complexes are also formed by reaction of 1 with gemtrichoroderivatives without P-hydrogen, but for 1 , 1 , 1 -trichloroethane, which contains P-hydrogen, a further dehydrohalogenation reaction takes place to give the bridging vinylidene complex [{Rh(p-Pz)(CI)(CNBut)2}2(p-C=CH2)J. The latter reacts with 0 2 in acid media to give the cationic dinuclear acyl-derivative [{Rh(pPz)(CNBU~)~)~(~-CI)CI(~~-COCH~)]BF~. These reactions could be a model for the degradation of alkyl chloro derivatives which are exogenous environmental pollutants.