Simply mixing the complex [{RuCl2(1,3,5‐C6H3iPr3)}2] (1) with PCy3 is sufficient to generate a catalyst suitable for highly efficient atom‐transfer radical addition and polymerization reactions at exceptionally low temperatures (see scheme). The steric congestion at the metal caused by the bulky ligands is thought to be essential for the reactivity of the catalyst.
Abstract:The bimetallic ruthenium complex [(1,3,5-i-Pr 3 C 6 H 3 )Ru(m-Cl) 3 RuCl(C 2 H 4 )(PCy 3 )] has been synthesized by reaction of [(1,3,5-i-Pr 3 C 6 H 3 )RuCl 2 )] 2 with one equivalent of PCy 3 in the presence of ethylene. It can be used as a catalyst precursor for the controlled atom transfer radical polymerization of methacrylates at 35 8C. The resulting polymers show low polydispersities.Keywords: acrylates; bimetallic complex; polymerization; radical reaction; ruthenium Starting with seminal publications in the mid 1990s, [1] transition metal-catalyzed atom transfer radical polymerizations (ATRP) have become ubiquitous in modern macromolecular chemistry.[2] For most applications, Cu(I) complexes with amine-based ligands are used as the catalysts.[3] Nevertheless, there are a number of other transition metals which are known to catalyze ATRP reactions.[2] Among those, ruthenium complexes are of special interest because some of them were found to display very high activities. [4,5] In continuation of our efforts to develop new catalysts for ruthenium-catalyzed radical reactions, [5a,6] we have recently described the homobimetallic complex [(cymene)Ru(m-Cl) 3 RuCl(C 2 H 4 )(PCy 3 )] (1). [7] This complex shows an outstanding catalytic activity in atom transfer radical addition (ATRA) reactions. Since ATRP and ATRA are mechanistically closely related, [2] we were interested to see whether complex 1 can also be used for the controlled polymerization of acrylates. Unfortunately, complex 1 showed a very limited solubility in the monomer-toluene starting mixtures. We therefore investigated possibilities to increase the solubility of complex 1. A modification of the p-ligand appeared to be a suitable strategy because the catalytically relevant RuCl 2 (C 2 H 4 )(PCy 3 ) fragment would not be directly affected. Consequently, the well-soluble dimer [(1,3,5-i-Pr 3 C 6 H 3 )RuCl 2 ] 2 (2) [8] was chosen as the starting material. When a solution of complex 2 in isooctane was heated to 50 8C with one equivalent of PCy 3 in the presence of an atmosphere of ethylene, the desired bimetallic complex 3 was formed (Scheme 1). The product precipitates from solution and can be isolated by filtration (yield: 90%).The new complex was comprehensively characterized by 1 H and 13 C NMR spectroscopy, elemental analysis and single-crystal X-ray crystallography. The 13 C NMR spectrum of 3 in CD 2 Cl 2 showed two signals of equal intensity for the methyl groups of the i-Pr 3 C 6 H 3 p-ligand. This can be explained by the fact that complex 3 is chiral and configurationally stable on the NMR time scale. The methyl groups are thus diastereotopic. In the 1 H NMR spectrum, however, the difference between the two CH 3 groups was not resolved and only one doublet was observed at d ¼ 1.39 ppm. In order to avoid partial dissociation of the labile ethylene ligand, all spectra were recorded under an atmosphere of C 2 H 4 . Analysis of complex 3 by X-ray crystallography confirmed the expected dinuclear structure with three chloro bridges (Fi...
Einfaches Mischen des Komplexes [{RuCl2(1,3,5‐C6H3iPr3)}2] (1) mit PCy3 liefert einen Katalysator, der bei außergewöhnlich niedrigen Temperaturen Atomtransfer‐Radikalpolymerisationen und ‐additionen hoch effizient katalysiert (siehe Schema). Die sterische Überladung am Metall als Folge der sperrigen Liganden wird als entscheidend für die Reaktivität des Katalysators gesehen.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.