Synthesis and Decomposition Behavior of a C₂-Symmetrical Palladium(IV) Spirocyclic Complex

Abstract

A novel palladium(IV) complex consisting of a C 2-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.

High‐Oxidation‐State Palladium Catalysis: New Reactivity for Organic Synthesis

“…[46] Thermal treatment of an isolated Pd IV complex then led to the expected bisoxygenated compound, among other products (Scheme 12). [47] Although the strained cyclic carbon framework of the alkyl ligands cannot serve as a general model for alkyl substituents at palladium, this reaction proved that the reductive oxygenation of alkyl groups is indeed a feasible pathway for alkyl palladium(IV) complexes. It also lent weight to Bäckvalls earlier proposal of palladium(IV) intermediates in stoichiometric oxidation reactions of alkenes.…”

“…Mechanistic Basis for Reductive Elimination from s-Alkyl Palladium(IV) Catalysts Apart from the stoichiometric process in Scheme 12, few mechanistic details are known about the course of reductive elimination from s-alkyl palladium(IV) intermediates. [45,47] The high reactivity of monoalkyl palladium(IV) complexes has so far prevented their structural isolation and characterization, as indeed most catalysis involving monoalkyl palladium(IV) intermediates proceeds readily at room temperature. The high reactivity of these palladium(IV) intermediates is remarkable, especially if one considers that related salkyl palladium(II) complexes are usually stable towards any kind of CÀX reductive elimination.…”

Covalent d-Block Organometallics: Teaching Lewis Structures and sd/sd2 Hybridization Gives Students Additional Explanations and Powerful Predictive Tools

“…( Figure 11, B). 34 Lastly, Yamamoto's group reported the self-assembly of two unusual ('C,O') 2ligands around one palladium(IV) center, leading to the see-saw geometry 35 shown in Figure 11, C. 36 The structure makes complete sense, with the two carbanions binding at an almost ideal right angle with nothing trans to them, suggesting that these are 2c-2e bonds involving each their own sd 2 hybrid. The remaining sd 2 hybrid is utilized in a 3c-4e interaction with the two oxygen donors trans to each other.…”

Katalyse mit Palladium in hoher Oxidationsstufe: neue Reaktivität für die organische Synthese

“…vorgestellt, denen es gelang, Palladium(IV)‐Komplexe aus einer stöchiometrischen Alkenoxidation mit Tetrachlor‐1,2‐benzochinon ausgehend von Palladium(0)‐Quellen zu isolieren 46. In diesem Fall führte Erwärmung des isolierten Palladium(IV)‐Komplexes in Lösung zur erwarteten, dioxygenierten Verbindung, die neben anderen Produkten erhalten wurde (Schema ) 47. Das gespannte Kohlenstoffrückgrat kann zwar nicht als allgemeines Modell für Alkyl‐Liganden in Palladium‐Verbindungen fungieren, immerhin belegt diese Reaktion aber, dass reduktive Oxygenierungen von Alkylgruppen in der Tat ein gangbarer Reaktionsweg für Alkylpalladium(IV)‐Komplexe sind.…”

“…Abgesehen von der stöchiometrischen Umsetzung aus Schema sind wenige mechanistische Details zum Verlauf der reduktiven Eliminierung aus σ‐Alkyl‐Pd IV ‐Intermediaten bekannt 45. 47 Die hohe Reaktivität von Monoalkylpalladium(IV)‐Komplexen, die zumeist bereits bei Raumtemperatur abreagieren, hat ihre Isolierung und Charakterisierung bislang verhindert. Die hohe Reaktivität dieser Palladium(IV)‐Intermediate ist bemerkenswert, besonders wenn man bedenkt, dass die verwandten σ‐Alkyl‐Pd II ‐Komplexe zumeist gegen jede Art von reduktiver C‐X‐Eliminierung stabil sind.…”