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)­CF3.
The formation of 2 is accompanied by a white precipitate
determined to be a mixture of trans-Pd­(O2CCF3)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.