Synthesis and Decomposition Behavior of a <i>C</i>₂-Symmetrical Palladium(IV) Spirocyclic Complex

Abstract

A novel palladium(IV) complex consisting of a C2-symmetrical palladaspirocycle framework and an ether ligand was assembled only in a single step from commercially available Pd2(dba)3, tetrachloro-1,2-benzoquinone (o-chloranil), and norbornene. The solid-state structure was confirmed by X-ray analysis of a THF complex. The ligand exchange from diethyl ether to pyridine converted the trigonal-bipyramidal complex to a distorted-octahedral bis(pyridine) complex. Similar palladium(IV) spirocyclic complexes were also formed from the reaction of Pd2(dba)3 with o-chloranil and benzonorbornadiene. The benzonorbornadiene-derived complexes exhibited pronounced stability in both the solid state and solution. The complete decomposition of the mono(pyridine) complex required several hours in C6D6 at 70 °C, and the addition of extra pyridine retarded the decomposition rate. Benzonorbornadiene was obtained as the main organic product, together with two isomeric adducts between o-chloranil and benzonorbornadiene. On the other hand, the decomposition of the pyridine complex took place within 15 min even at −40 to −50 °C, upon exposure to HCl in a CDCl3 solution.