An Empirical Study of Phosphine Ligands for the Methoxycarbonylation of Medium‐Chain Alkenes

Abstract

The methoxycarbonylation reaction provides ar oute to the synthesis of esters from medium-chain alkenes that may be used as fuel supplements. However,t he known productivec atalytic systems are expensive and/or unstablea te levated temperatures. Most of the data availableo nt he methoxycarbonylation of alkenes is derivedf rom ethylene and styrene as substrates. To broaden the scope, we conducted ac omparative study of ar ange of phosphine ligandsu nder comparable conditions fort he methoxycarbonylation of 1-octene. The results demonstrate that anumber of ligand structural motifs facilitate the process effectually.F urthermore, the critical importance of alkene isomerization and the acid/liganda nd Pd/ligand ratios are presented.Carbonylation reactions provide an efficient route to generate av ariety of functionalg roups from CÀCu nsaturation by using readily available carbon monoxidea nd other ancillary reagents.[1] Amongst others, these metal (Pd, Co, Ni, Rh, etc.) [2] catalyzed carbonylation reactions include the syntheses of aldehydes (hydroformylation), [3] carboxylic acids (hydrocarboxylation), [4] and esters (hydromethoxycarbonylation or methoxycarbonylation for short, Scheme 1). [5] Twom echanisms,n amely,P d ÀHa nd PdÀOMe, have been proposed for the methoxycarbonylationr eaction, each with much study and evidencei nits favor.[5b] However,m ost evidence collected thus far indicatesapreference for the PdÀH mechanism, as shown in Scheme 2. [5c,d] Despite the fact that long-chain esters play ac rucial role in the manufacture of lubricants and surfactants [6] and are eligible candidates for petroleum derivatives, these higher-carbonl inear aliphatic esters are typicallyp roduced by furtherm anipulations of the products of the hydroformylation reaction.[7] However,m uch effort is being devotedt oc atalytic methoxycarbonylation with respect to the utilization of renewable resources. [8] As South Africah as no naturals ource of liquid fuel, there is an opportunity and an eed to convert its (Sasol) FischerTropsch medium-chaino lefins into their correspondingm ethyl esters as substitutes for diesel fuels. Althoughanumber of catalytic systemsh ave been developed for the required methoxycarbonylation, industrial implementation with regard to medium-chain alkenes has not yet been realized. In addition to patent protection,t he known catalysts suffer from an umber of disadvantages, includingh igh cost. Most often, these systems comprise Pd 2 (dba) 3 (dba = dibenzylideneacetone)a nd the ligands( andt heir analogues) shown in Figure 1. [8, 9] The use of ligand A in the methoxycarbonylation of ethylene is aw ellknown industrial process (Lucite process).[10i]The requirements for ap otential industrial catalystw ould include low cost, efficiency in terms of reactionr ates and selectivity,h ight emperature stability, and the capability of recycling. The development of ac atalysts ystem of this kind can be expedited by ab etter understanding of the critical factors, in particular, ligand structure and reaction con...

Synthesis of Benzofuranones via Palladium‐Catalyzed Intramolecular Alkoxycarbonylation of Alkenylphenols

“…Based on our earlier reports on the alkoxy‐ and the thiocarbonylation of alkenes at ambient temperature, a modified Pd 0 ‐based catalytic system for lactonization was identified . We found that the combination of [Pd(dba) 2 ], ligand L1 (dppdtbpf; 1‐diphenylphosphino‐1′‐(di‐ tert ‐butylphosphino)‐ferrocene) and diphenylphosphoric acid (DPPA) that was previously used in the thiocarbonylation led to 81 % of 2 a (Table , entry 1). Whereas, the original alkoxycarbonylation conditions ( L2 , (dtbpx; bis(di‐ tert ‐butylphosphinomethyl)benzene)/BNPA (1,1′‐bi‐2‐naphthol phosphoric acid)) generated only 73 % yield (entry 2).…”

“…[4] The control of regioselectivity is one of the challenges of this transformation. [6] Better resultsw ere achieved by Manabe et al,w ho developed ac yclization of 2-vinyl aryl formatesu sing Ru 3 (CO) 12 under forcing reaction conditions (135 8C, 15 mol %o f[ Ru]). [5] Ag eneral methodf or the synthesis of benzofuran-2(3H)-ones (2)f rom alkenylphenols (1)p roved more difficult (Scheme 1).…”

“…[11] We found that the combination of [Pd(dba) 2 ], ligand L1 (dppdtbpf; 1-diphenylphosphino-1'-(di-tert-butylphosphino)-ferrocene) [12] and diphenylphosphoric acid (DPPA) that was previously used in the thiocarbonylation led to 81 %o f2a (Table 1, entry 1). [11] We found that the combination of [Pd(dba) 2 ], ligand L1 (dppdtbpf; 1-diphenylphosphino-1'-(di-tert-butylphosphino)-ferrocene) [12] and diphenylphosphoric acid (DPPA) that was previously used in the thiocarbonylation led to 81 %o f2a (Table 1, entry 1).…”

Cooperative Use of Brønsted Acids and Metal Catalysts in Tandem Isomerization Reactions of Olefins

“…On the other hand, Pd(II) salts such as Pd(OAc) 2 might undergo an acid‐base reaction leading to complex with replaced acetate anions. Furthermore, acid might accelerate the methanolysis by protonation of the acyl complex D …”

Hydroformylation of 2‐Alkynylanilines: Toward an Alternative Methodology for the Synthesis of 3‐Substituted Indoles

“…Coupled with our interestinmetal-catalysed carbonylation [17] and in the synthesis of indoles, [18] we were attracted to the possibility of am odification of the approacho fD onga nd Busacca [15a] to obtain 3-substitutedi ndoles that would avoid the use of substrates obtained through the Heck reaction. To this end, ah ydroformylation approach based on 2-alkynylanilines, produced throught he well-established Pd-catalysed Sonogashira coupling reaction, was envisaged (Scheme 2).…”