ABSTRACT
The field of supported catalysis has experienced increased attention with respect to the development of novel architectures for immobilizing catalytic species, aiming to maintain or enhance their activity while facilitating the easy recovery and reuse of the active moiety. Dendrimers have been identified as promising candidates capable of imparting such properties to catalysts through selective functionalization. The present study details the synthesis of two polyphosphorhydrazone (PPH) dendrons, each incorporating azide or acetylene groups at the core for subsequent coupling through "click" triazole chemistry. Employing this methodology, a novel PPH Janus dendrimer was successfully synthesized, featuring ten polyethylene glycol (PEG) chains on one side of the structure and ten Ru(p-cymene) derivatives on the other. This design was intended to confer dual properties, influencing solubility modulation, and allowing the presence of active catalytic moieties. The synthesized dendrimer underwent testing in the isomerization of allyl alcohols in organic solvents and biphasic solvent mixtures. The results demonstrated a positive dendritic effect compared with model monometallic and bimetallic species, providing a proof-of-concept for the first PPH Janus dendrimer with tested applications in catalysis.
ABSTRACT
Dendrimers, being highly branched monodispersed macromolecules, predominantly exhibit identical terminal functionalities within their structural framework. Nonetheless, there are instances where the presence of two distinct surface functionalities becomes advantageous for the fulfilment of specific properties. To achieve this objective, one approach involves implementing Janus dendrimers, consisting of two dendrimeric wedges terminated by dissimilar functionalities. The prevalent method for creating these structures involves the synthesis of dendrons that possess a core functionality that complements that of a second dendron, facilitating their coupling to generate the desired dendrimers. In this comprehensive review, various techniques employed in the fabrication of phosphorus-based Janus dendrimers are elucidated, displaying the different coupling methodologies employed between the two units. The advantages of phosphorus dendrimers over classic dendrimers will be shown, as the presence of at least one phosphorus atom in each generation allows for the easy monitoring of reactions and the confirmation of purity through a simple technique such as 31P NMR, as these structures typically exhibit easily interpretable patterns.
ABSTRACT
Herein, we describe a study of the synthesis, characterization, and catalytic properties of a cis-dichlorido seleno-chelated Hoveyda-Grubbs type complex (Ru8). Such a complex has been obtained through a straightforward and high-yielding synthetic protocol in three steps from the commercially available 2-bromobenzaldehyde in good overall yield (54%). The catalytic profile, especially the latency of this complex, has been probed through selected olefin metathesis reactions such as ring-closing metathesis (RCM), self-cross-metathesis (self-CM) and ring-opening metathesis polymerization (ROMP). In addition to its high latency, the selenium Hoveyda-type complex Ru8 exhibits a switchable behavior upon thermal activation. Of interest, while the corresponding sulfur-chelated Hoveyda type catalyst is reported to be only activated by heat, the selenium analogue was found to be active upon both heat and light irradiation.
