Homobimetallic Ruthenium Vinylidene, Allenylidene, and Indenylidene Complexes: Synthesis, Characterization, and Catalytic Studies

Abstract

Four homobimetallic ruthenium-(pcymene) complexes bearing a tricyclohexylphosphine ligand and polyunsaturated carbon-rich fragments were obtained via a vinylidene-allenylidene-indenylidene cascade pathway from the ethylene complex. All the products were isolated and fully characterized by IR and NMR spectroscopies. The molecular structure of the indenylidene complex 11 was determined by X-ray crystallographic analysis. The catalytic activity of the four complexes was probed in various types of olefin metathesis reactions and compared with those of a related homobimetallic ruthenium-benzylidene complex, as well as first, second, and third generation monometallic Grubbs catalysts. In the ring-closing metathesis (RCM) of diethyl di-A C H T U N G T R E N N U N G allylmalonate, the homobimetallic ruthenium-indenylidene complex 11 outperformed all the rutheniumbenzylidene complexes under investigation and was only slightly less efficient than its monometallic parent. Cross-metathesis experiments with ethylene showed that deactivation of ruthenium-benzylidene or indenylidene complexes was due to the rapid bimolecular decomposition of methylidene active species into ethylene complex 7a. Vinylidene and allenylidene complexes were far less efficient catalyst precursors for ring-opening metathesis polymerization (ROMP) or RCM and remained inert under an ethylene atmosphere. Their catalytic activity was, however, substantially enhanced upon addition of an acidic co-catalyst that most likely promoted their in situ transformation into indenylidene species. Due to its straightforward synthesis and high metathetical activity, homobimetallic ruthenium-indenylidene complex 11 is a valuable intermediate for the preparation of the Hoveyda-Grubbs catalyst A C H T U N G T R E N N U N G [Cl 2 RuA C H T U N G T R E N N U N G (PCy 3 )(=CH-o-O-i-PrC 6 H 4 )] via stoichiometric cross-metathesis with 2-isopropoxystyrene. The procedure did not require any sacrificial phosphine and the transition metal not incorporated into the final product was easily recovered and recycled at the end of the process.

O,N‐Bidentate Ruthenium Azo Complexes as Catalysts for Olefin Isomerization Reactions

“…(Scheme 1). Filtering the solid and recrystallization using ethyl acetate/hexane (1:8) yielded 38 % of HL 6 . C 14 …”

“…[3][4][5][6] Except for isomerization, the catalytic properties of these complexes have been investigated in various fields ranging from hydrogen transfer [7][8][9][10][11] to ring-closing metathesis, [4,[12][13][14] etc. The extension of the catalytic activities towards isomerization depends on the metal itself and its structure.…”

Synthesis and Organocatalytic Applications of Imidazol(in)ium‐2‐thiocarboxylates

“…[11][12][13] Such NHC·CO 2 zwitterions are rather labile in solution and act as convenient surrogates to air-and moisture-sensitive free carbenes in organometallic synthesis [14] and organocatalysis. [15] For instance, we have successfully used imidazol(in)ium-2-carboxylates as NHC ligand precursors in the synthesis of various second-generation ruthenium-alkylidene catalysts in olefin metathesis, [16] whereas other groups have developed several new major organocatalytic processes based on these zwitterions for carbon dioxide fixation reactions. [17] Scheme 1.…”

Ruthenium in Catalysis

“…1) was synthesized and tested in RCM reactions [215]. However, later investigations revealed that the final catalysts formed were actually phenylindenylideneruthenium complexes rather than allenylidene analogs [216][217][218]. This latter homobimetallic ruthenium allenylidene complex was finally synthesized along with other ruthenium homobimetallic complexes and they were tested as catalysts in olefin metathesis [219].…”