Synthesis of a Palladium Dimer Supported by a C-Bound Trifluoroacetonate Bridge Formed by Cleavage of a Hexafluoroacetylacetonate Ligand.

Palladium(II) hexafluoroacetylacetonate (Pd(Hfacac) 2 ) is known to form adducts of bases, such as lutidine (2,6-dimethylpyridine). When treated with approximately 3 equiv of lutidine, Pd(Hfacac) 2 yields a 1:1 complex as reported in the literature, Pd( O , O -Hfacac)( C -Hfacac)(lutidine), 1 . However, when the amount of excess lutidine is increased, a new complex, 2 , is formed. A single-crystal X-ray structure of 2 proves it is a rare example of a dimeric palladium complex containing two Pd(Hfacac)(lutidine) fragments bridged by a dianionic trifluoroacetonate ligand, μ-CHC(O)CF 3 . The formation of 2 is accompanied by a white precipitate determined to be a mixture of trans -Pd(O 2 CCF 3 ) 2 (lutidine) 2 ( 3 ), confirming the fate of the missing trifluoroacetate fragment from the cleavage of the Hfacac ligand, and [lutidinium][Hfacac] ( 4 ). Subsequent experiments revealed the determinative role that water played in this reaction. The mechanism of cleavage of the Hfacac ligand was explored by DFT methods.