Ruthenium Carbene–Diether Ligand Complexes: Catalysts for Hydrogenation of Olefins

Abstract

A series of carbene–diether ligands were prepared and the corresponding Ag salts used to prepare the complexes RuHCl(PPh3)2(Im(OR)2) (Im(OR)2 = C3H2(NCH2CH2OR)2; R = Me (4a), t-Bu (4b), tert-hexyl (4c), Ph (4d), 2,6-i-Pr2C6H3 (4e)). In an analogous fashion the species RuHCl(PPh3)2(Y2Im(OMe)2) (Y2Im(OMe)2 = Y2C3(NCH2CH2OMe)2; Y2 = C6H4 (4f), Y = Cl (4g), Me (4h)) were also synthesized. Similarly RuHCl(CO)(PPh3)2(Im(OMe)2) (5) was prepared and readily converted to RuHCl(CO)(SIMes)(Im(OMe)2) (6) via treatment with SIMes. The reaction of 4a with SIMes afforded RuHCl(SIMes)(Im(OMe)2)(PPh3) (7), which reacts subsequently with Na[BPh4] to give [RuH(Im(OMe)2)(SIMes)][(η6-Ph)BPh3] (8). In a series of tests, the species 4a–h, 5, 6, and 8 were shown to catalyze the hydrogenations of 1-hexene, cyclohexene, and dimethyl itaconate. From the activity of 4a–h it is clear that the capability of the carbene–ether substituents to coordinate to the metal as well as electron-donating substituents on the carbene fragment enhances catalytic activity. Other variations such as in 5, 6, and 8 resulted in terminal-olefin-selective hydrogenation catalysts, although the zwitterionic species 8 showed significantly enhanced activity.

Bis(ether-functionalized NHC) Nickel(II) Complexes, Trans to Cis Isomerization Triggered by Water Coordination, and Catalytic Ethylene Oligomerization

“…Several ether N-functionalized NHC complexes have been reported in the literature with various transition metals; they were synthesized by transmetalation from a precursor NHC Ag­(I) complex or by deprotonation of an imidazolium salt with either an external base prior to metalation , or an internal base directly incorporated as a ligand into the precursor metal complex. ,,,,, …”

Rate-Limiting Steps in the Intramolecular C–H Activation of Ruthenium N-Heterocyclic Carbene Complexes

“…Since then, other but structurally similar complexes bearing either one or two NHCs have been synthesized and used in hydrogenation (see Figure ). − …”

Ruthenium-Catalyzed [2 + 2] Cycloadditions between Norbornene and Propargylic Alcohols or Their Derivatives

“…The development of ruthenium-catalyzed chemical processes has become an emerging field over the past decade. − With their wide range of oxidation states (from −2 to +8) and several coordination geometries, ruthenium catalysts can form a variety of intermediates such as (π-allyl)ruthenium, ruthenium–carbene, and ruthenacycle species . Among various ruthenium complexes, CpRu(COD)Cl and Cp*Ru(COD)Cl have been found to be the catalysts of choice in many reactions such as [2 + 2 + 2] cycloadditions, − conjugate additions, bis-Diels–Alder cycloadditions, Alder-ene reactions, , cross-benzannulations, and many others. , We and other groups have been largely involved in the preparation of cyclobutene rings via ruthenium-catalyzed [2 + 2] cycloadditions. − …”

“…The development of ruthenium-catalyzed chemical processes has become an emerging field over the past decade. 1−4 With their wide range of oxidation states (from −2 to +8) and several coordination geometries, ruthenium catalysts can form a variety of intermediates such as (π-allyl)ruthenium, 5 ruthenium− carbene, 6 and ruthenacycle species. 7 Among various ruthenium complexes, CpRu(COD)Cl and Cp*Ru(COD)Cl have been found to be the catalysts of choice in many reactions such as [2 + 2 + 2] cycloadditions, 8−10 conjugate additions, 11 bis-Diels− Alder cycloadditions, 12 Alder-ene reactions, 13,14 cross-benzannulations, 15 and many others.…”