Density functional study of possible intermediates in the mechanism of olefin cyclopropanation catalyzed by metal carboxylates

The structures of several complexes arising from the interaction between me thylene and palladium and rhodium diformates were optimized through density functional calculations. For palladium, mono-, di-, and trimeric complexes were considered. The results obtained show that in all cases the most stab le structures correspond to complexes in which methylene has inserted in on e of the M-O bonds, while metal-carbene complexes are energy minima only fo r monomeric palladium diformate and for rhodium diformate. Trimeric palladi um formate is thermodynamically stable upon fragmentation. However, when it reacts with methylene, fragmentation becomes favorable, The role of the re sulting monomeric complex in the olefin cyclopropanation mechanism catalyze d by palladium dicarboxylates is discussed.