The Effect of Chloride Ions on the Mechanism of the Oxidative Addition of Cyclic Allylic Carbonates to Pd⁰ Complexes by Formation of Neutral[(η¹‐allyl)PdClL₂] Complexes

The reversible oxidative addition of a cyclic allylic carbonate cis ‐ 1 to palladium(0) complexes ligated by PPh 3 is affected by chloride ions in DMF or chloroform. In the presence of chloride ions, the oxidative addition may become irreversible and the rate of isomerization of cis ‐ 1 to trans ‐ 1 is slowed down. This is a consequence of a slower isomerization of the cationic complex [(η 3 ‐allyl)Pd(PPh 3 ) 2 ] + ( cis ‐ 2 + ) to trans ‐ 2 + due to the formation of neutral [(η 1 ‐allyl)PdCl(PPh 3 ) 2 ] ( cis ‐ 3 / trans ‐3 ) complexes. Such complexes are formed instead of the cationic cis ‐ 2 + and trans ‐ 2 + whatever the source of chloride ions, i.e., whether voluntarily added to the cationic complexes cis ‐ 2 + and trans ‐ 2 + , voluntarily added in the oxidative addition of cis ‐ 1 with Pd 0 complexes ligated to PPh 3 , or introduced in the dimeric complexes [(η 3 ‐allyl)Pd(μ‐Cl)] 2 ( cis‐ 5 / trans ‐ 5 ). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)