Synthesis and Reactivity of Poly(propyleneimine) Dendrimers Functionalized with Cyclopentadienone N-Heterocyclic-Carbene Ruthenium(0) Complexes

Abstract

Ligand design in metal chemistry is a fundamental step when pursuing compounds with specific reactivity. In this paper, the functionalization of the OH group in the lateral chain of the N-heterocyclic-carbene (NHC) ligand bound to a bis-carbonyl cyclopentadienone NHC ruthenium(0) complex allowed the decoration of five generations of poly(propyleneimine) (PPIs) dendrimers with up to 64 organometallic moieties. The coupling was achieved by employing carbonyldiimidazole and the formation of carbamate linkages between dendritic peripheral NH2 and lateral OH groups on ruthenium complexes. The synthetic procedure, chemical purification, and spectroscopic characterization of the five generations of dendrimers (3g1–5) are here described. The ruthenium-modified dendrimers were activated as catalysts in the transfer hydrogenation of the model compound 4-fluoroacetophenone in the presence of cerium ammonium nitrate as their mononuclear congeners. The catalytic activity, being similar for the five generations, shows a decrease if compared to mononuclear complexes. This detrimental effect might be ascribed to the –CH2NH– functionalization, largely present in dendrimer skeleton and that can compete with the hydrogen transfer mechanism, but also partially to a dendritic effect caused by steric encumbrance.

Molecular Ruthenium Cyclopentadienone Bifunctional Catalysts for the Conversion of Sugar Platforms to Hydrogen

“…The obtained results, reported in Table 1, showed that the best performance in terms of hydrogen production was achieved with Shvo catalyst 1 (entry 1, glucose conversion=15.2 %). Although at this temperature all the catalysts should have been activated, this behavior could be ascribed both to the easier activation of Shvo complex 1 in comparison with 2 [70,71,72] and 3 , [63] and to its higher efficiency in transfer hydrogenation (see below).…”

Synthesis of functionalized iron N-heterocyclic carbene complexes and their potential application as flame behavior modifier in cross linked epoxy resins

“…. [36][37][38][39][40] Another class of ligands that can provide stability to the corresponding complexes are variously functionalized cyclopentadienones. [41][42][43][44][45][46][47][48][49][50] As above cited, our group has recently developed a straightforward synthetic procedure that combine NHC and cyclopentadienone as ligands in stable iron(0) complexes.…”

Iron integrated carbon nitride: A recoverable heterogeneous catalyst for the construction of bis (hetero/homoarylidene)cycloalkanones

“…37 Generally, in order to heterogenize iron catalysts, a solid matrix including silica, alumina, or polymers have been employed. [38][39][40][41][42][43][44][45][46][47][48] However, inorganic metal oxides are hard and heavy when compared with soft organic support materials. In an organic solvent, an organic catalyst powder can mix better than inorganic material.…”

“…Hence, homogeneous catalyst is not favored towards industrial applications 37 . Generally, in order to heterogenize iron catalysts, a solid matrix including silica, alumina, or polymers have been employed 38–48 . However, inorganic metal oxides are hard and heavy when compared with soft organic support materials.…”