On the mechanism of the cyclopalladation reaction of benzyl-benzylidene-amine with palladium(II) acetate in acetic acid

The reaction of benzyl-benzylidene-amine of formula C6H5CHNCH2C6H5 (1) and palladium(II) acetate in a one-to-one molar ratio in monodeuterated acetic acid (CH3CO2D) at 60 °C (reaction b) produced deuterium-enriched cyclopalladated compounds of formula (μ-OAc)2[Pd{C6H4CHNCH22,6-(H1−xDx)2C6H3}]2 (2d), whose deuterium atoms were located at the ortho positions of the benzyl groups and whose deuterium content slowly increased with the time of reaction b. In addition, treatment of the cyclopalladated compound of formula (μ-OAc)2[Pd(C6H4CHNCH2C6H5)]2 (2) in monodeuterated acetic acid at 60 °C for 24 h, led to compound 2d with a deuterium content [expressed as percentage of occupation by deuterium atoms of the ortho positions of its benzyl groups] of ca. 10%. However, reaction b after 24 h of reaction yielded a compound 2d with a deuterium content of ca. 40%. In addition, the solution formed, when 1 and palladium(II) acetate in a one-to-one molar ratio were dissolved in a solution of CDCl3 in perdeuterated acetic acid in a one-to-two volume ratio, contained as major compounds benzaldehyde, C6H5CH2ND2 and Pd(OAc-d3)2 a few minutes after its formation. However, after 2 weeks at room temperature, its major compounds were benzaldehyde and the cyclopalladated compounds (μ-OAc-d3)2[Pd(C6H4CH2ND2)]2 and (μ-OAc-d3)2[Pd(C6H4CHNCH2C6H5)]2. These results led to the proposal of a set of reactions that produced 2, when 1 and palladium(II) acetate reacted in acetic acid.