Rational Synthesis and Electronic Structure of Functionalized Trinuclear Pd Metal Sheet Sandwich Complexes

In this article we
present the rational synthesis and full characterization
of molecular Pd3 clusters sandwiched by imidazolium- and
pyridinium-functionalized cycloheptatrienide ligands, of general formula
[Pd3Br3(C7H6R)2]+. From functionalized η3-cycloheptatrienide
Pd complexes as starting materials, PdBr2(η3-C7H6R), a number of synthetic routes were
tested and a generally applicable strategy was developed on the basis
of the formation of dimeric “preclusters”, [{PdBr­(η3-C7H6R)}2(μ-Br)]+, which exhibit a Pd–Pd interaction. Spectroscopic
and electrochemical results indicate a noninteger, common oxidation
state of Pd in the trinuclear clusters, and crystallographic analysis
reveals distinct differences in the binding properties of the Pd atoms
in the solid state, suggesting that in certain environments there
are even two discernible oxidation states, which is supported by computational
analysis of the charge distribution.