Palladium Schiff Base Complexes: Potential catalysts for C-C bond reactions

The catalytic activities of two palladium complexes [Pd₄(dbbs)₄] (1) and [Pd(dpbs)Cl] (2) (where (dbbs)₂ = N,N'-(1,1'-dithio-bis(phenylene))-bis(salicylideneimine) and (dpbs)₂ = o,o’-(N,N’-dipicolinyldene)diazadiphenyl disulfide) were evaluated in the formation of C-C bond in Michael Addition, Heck and Suzuki reactions.  The formation of the coupling products were monitored using GC-MS.  The two palladium complexes were found to be ineffective catalyst towards Michael Addition reactions. However, both catalytic systems exhibited comparable activities in the Heck reaction with good to excellent yields of the desired products (> 99 %) even though complex 1 is tetranuclear and complex 2 is mononuclear.  The yields of the products were found to depend upon other parameters such as reaction time, catalyst loading, base, solvent and substrates. Preliminary investigations were also carried out in Suzuki reaction, where the cross-croupling product was obtained in the range of 60-99 %.  These two complexes are promising supramolecular skeleton for the construction of highly active catalysts.