Ruthenium‐Catalyzed Hydroformylation of Alkenes by using Carbon Dioxide as the Carbon Monoxide Source in the Presence of Ionic Liquids

Abstract

Dedicated to the memory of Prof. Roberto F. Souza, one of the pioneers of ionic liquid phase organometallic catalysisThe reaction of [BMI·Cl] (BMI = 1-butyl-3-methylimidazolium) or [BMMI·Cl] (BMMI = 3-butyl-1,2-dimethylimidazolium) with Ru 3 (CO) 12 generates Ru-hydride-carbonyl-carbene species in situ that are efficient catalysts for a reverse water gas shift/ hydroformylation/hydrogenation cascade reaction. The addition of H 3 PO 4 increased the catalytic activity of the first step (i.e., the hydrogenation of CO 2 to CO). Under the optimized reaction conditions [120 8C and 6.0 MPa CO 2 /H 2 (1:1) for 17 h], cyclohexene and 2,2-disubstituted alkenes were easily functionalized to alcohols through sequential hydroformylation/carbonyl reduction.Carbon dioxide sequestration and its use as a feedstock in industrial processes are major challenges in the development of alternative greener and sustainable processes. [1] Indeed, several catalytic processes are under investigation, and they include the incorporation of CO 2 through the addition to epoxides to generate organic carbonates, diols, and polycarbonates by using either organic or metal-based catalysts. [2] However, the substitution of carbon monoxide (CO) by carbon dioxide (CO 2 ) in carbonylation reactions [3][4][5][6] may allow for new applications with broader use for this important and abundant but poorly reactive substrate. Indeed, at the industrial scale, the hydroformylation [7,8] of alkenes is one of the most important applications of homogeneous catalysis, and over 9 million tons of socalled oxo products, such as aldehydes and alcohols, are produced each year. [9] Rh-modified systems are the catalysts of choice for this reaction, as they are highly active and selective for the formation of aldehydes, [7,8] as well as for cascade reactions involving hydroformylation/Witting, [10] hydroaminomethylation sequences, [11,12] and hydroformylation/cyclization reactions. [13][14][15][16] Other metals, such as Pt and Ru, have been much less studied owing to their high hydrogenation activity, which results in the formation of large amounts of alkanes as byproducts. [17][18][19][20] However, the use of Rh-Ru bimetallic systems is of interest for the production of alcohols by hydroformylation/hydrogenation se-quences. [21][22][23][24][25] The differences in selectivity could be easily understood if we look at the hydroformylation and hydrogenation mechanisms catalyzed by Rh I and Ru 0 systems, as the active catalytic species under hydroformylation conditions are the RhÀH and the RuÀ(H) 2 species. [7][8][9]26] The accepted mechanism for the formation of MÀ(H) 2 is the homolytic cleavage of the HÀH bond, as the formation of MÀH occurs either by intramolecular (ligands) or intermolecular (external base) heterolysis of the HÀH bond, which favors the formation of MÀH species. [12,27,28] For instance, cationic [RuÀH] + species species are described as the catallytically active species in the Ru-catalyzed hydrogenation of acids, cyclic carbonates, and CO 2 to alcohol. [...

Acid‐Promoted Hydroformylative Synthesis of Alcohol with Carbon Dioxide by Heterobimetallic Ruthenium‐Cobalt Catalytic System

“…Cationic counterion of chloride additive and bromide anion subtly impacted on catalytic activity and chemoselectivity (entries 14–21). Although the previous reports indicated the formation of Ru‐carbene complex between Ru 3 (CO) 12 and [Bmim]Cl via the oxidative addition of a C−H imidazolium bond to Ru 0 center, as well the deprotonation of imidazolium to generate N ‐heterocyclic carbine ligand in the presence of base,– the formation of Ru‐carbene complex from [Ru(CO) 3 Cl 3 ] − with [Bmim]Cl was less probable due to high oxidation state of Ru and acidic reaction conditions. The performances of four simple cobalt salts were tested, but none of them was superior to Co 2 (CO) 8 (details see Figure S2 in SI).…”

Telomerization of 1,3‐Butadiene with Carbon Dioxide: A Highly Efficient Process for δ‐Lactone Generation

“…entries 13 and 18, Table ), which blocks the formation of carbenes at the active C2 position. This supports the hypothesis of the formation of these carbene species in the case of ionic liquids that are unsubstituted at the C2 position …”

“…This supports the hypothesis of the forma-tion of these carbene species in the case of ionic liquids that are unsubstituted at the C2 position. [31,32]…”

Carbon Dioxide Transformation in Imidazolium Salts: Hydroaminomethylation Catalyzed by Ru‐Complexes

“…[32] Generally,s ophisticated ligandsa re required to control the reactivity of [Ru-H] + species andt oi mprove both catalytic activity and selectivity. [24][25][26]29] However, it was reported that the RWGS/hydroformylation path may be favoredi nt he absence of extra ligandsi ft he reaction is performed in the presence of imidazolium salt-based ionic liquids (IL) [30] that can generate in situ abnormal Ru-carbene species( Scheme2) [33] The catalytic speciesg enerated by dissolving Ru 3 (CO) 12 in the ionic liquids1 -n-butyl-3-methyl-imidazolium chloride or 1-nbutyl-2,3-dimethyl-imidazolium chloride are efficient multifunctional catalysts for:( a) reverse water-gas shift, (b) hydroformylation of alkenes, and (c) reductive amination of aldehydes. Thus the reaction of alkenes with primary or secondary amines (alkene/amine, 1:1) under CO 2 /H 2 (1:1) affords the hydroaminomethylations products in high alkene conversions (up to 99 %) and selectivities (up to 96 %).…”

“…[28] However, 31 PNMR experiments revealed that this apparent ligand effect wasc aused by the formation of phosphoric acid (H 3 PO 4 )u nder our reaction conditions. [33] It is reasonable to assume, that even in the case of reactions involving CO 2 /H 2 in imidazolium salt IL media, it will be possible to shift the selectivity towards the CO path by fine-tuning the reaction conditions. We report herein that the hydroaminomethylation can be easily performed with the simple catalytic system (i.e.,i midazolium chloride IL/Ru 3 CO 2 / H 3 PO 4 ).…”