György Keglevich

Irina L. Odinets

László Kollár

Natalya M. Vinogradova

Tamás Kégl

Comptes Rendus Chimie

Full paper / MémoireCarbonylation reactions catalysed by rhodium(III)and palladium(II) complexes containing novel phosphine ligandsGyörgy Keglevich a,*, Tamás Kégl b, Irina L. Odinets c,Natalya M. Vinogradova c, László Kollár d,*a Department of Organic Chemical Technology, Budapest University of Technology and Economics, 1521 Budapest, Hungaryb Research Group for Petrochemistry of the Hungarian Academy of Sciences, H-8200 Veszprém, Hungaryc A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 119991 Moscow, Russian Federationd Department of Inorganic Chemistry, University of Pécs and Research Group for Chemical Sensorsof the Hungarian Academy of Sciences, 7624 Pécs, HungaryReceived 30 October 2003; accepted 19 February 2004Available online 24 July 2004AbstractRhCl2(Cp*)(monodentate P-ligand)- and trans-PdCl2(monodentate P-ligand)2-type complexes (where the P-ligand is eithera P-heterocyclic or a cyclopropane-based tertiary phosphine) have been used as catalyst precursors in hydroformylation andhydroalkoxycarbonylation reactions, respectively. The chemoselectivity of hydroformylation is excellent (higher than 99%) inall cases. A strong dependence of the regioselectivity on the P-substituents was found in the case of the P-heterocyclic ligands.While the P-phenyl substituent favours the formation of the branched aldehyde regioisomer (3-phenyl-propanal), the introduc-tion of ortho- and para-tolyl substituents resulted in the slightly preferred formation of linear aldehyde (2-phenyl-propanal). Atthe same time, the introduction of tolyl groups instead of the phenyl one caused an unexpectedly high increase in the catalyticactivity.An unprecedented feature of the system has been observed by using complexes with cyclopropyl-phosphine ligands. Theformation of the linear aldehyde regioisomer (3-phenyl-propanal) is favoured by the decrease of the temperature. To cite thisarticle: G. Keglevich et al., C. R. Chimie 7 (2004).© 2004 Académie des sciences. Published by Elsevier SAS. All rights reserved.RésuméLes complexes de type RhCl2(Cp*)(monodentate P-ligand) et trans-PdCl2(monodentate P-ligand)2 (où le ligand P est unephosphine tertiaire hétérocyclique ou cyclopropanique) ont été utilisés respectivement comme précurseurs catalytiques dans laréaction d’hydroformylation ou d’hydroalkoxycarbonylation. La chimioselectivité de l’hydroformylation est excellente(supérieure à 99%) dans tous les cas. La régiosélectivité est fortement influencée par la substitution sur le phosphore dans le casdes hétérocycliques. Tandis que le substituant phényl du phosphore favorise la formation de l’aldéhyde branché (2-phenyl-propanal), l’introduction d’un substituant tolyl en ortho- et en para- conduit, en plus faible proportion, à un aldéhyde linéaire(3-phenyl-propanal). En même temps, l’introduction de groupes tolyl à la place d’un groupe phenyl conduit à une augmentation* Corresponding author.E-mail address: gkeglevich@mail.bme.hu (G. Keglevich).C. R. Chimie 7 (2004) 779–784© 2004 Académie des sciences. Published by Elsevier SAS. All rights reserved.doi:10.1016/j.crci.2004.02.013inattendue de l’activité catalytique. Une caractéristique sans précédent du système a été observée en utilisant des complexespossédant des ligands cyclopropyl-phosphine. La formation d’un aldéhyde linéaire (3-phenyl-propanal) est favorisée par labaisse de température. Pour citer cet article : G. Keglevich et al., C. R. Chimie 7 (2004).© 2004 Académie des sciences. Published by Elsevier SAS. All rights reserved.Keywords: Hydroformylation; Hydroalkoxycarbonylation; Rhodium; Palladium; Phosphine; Homogenous catalysisMots clés : Hydroformylation ; Hydroalkoxycarbonylation ; Rhodium ; Palladium ; Phosphine ; Catalyse homogène1. IntroductionAmong the carbonylation reactions, hydroformyla-tion has been playing an outstanding role for somedecades [1]. Several phosphorus containing mono- anddiphosphines, phospholes, and heterobidentate ligandshave already been tested in cobalt, rhodium andplatinum-catalysed hydroformylation reactions andhave been referenced recently [2]. Both the hydro-formylation of simple substrates like propene and theasymmetric hydroformylation (e.g., that of vinylaro-matics resulting in a-phenylpropanals, the precursorsof a-aryl-propionic acids, which are of pharmacologi-cal importance [3]) hold an enormous potential insynthesis. Due to their high practical importance, hy-droformylation catalysts have received particular at-tention.The synthesis of esters from alkenes via carbonyla-tion reactions has also a potential in synthetic organicchemistry. In the hydroalkoxycarbonylation (‘hydroes-terification’) reaction, carbon monoxide and an alcoholare added to an alkene [4]. The reaction has an obviousrelation to hydroformylation, where alcohol is usedinstead of hydrogen. Hydroalkoxycarbonylation of alinear olefin resulted in the predominant formation ofthe linear ester, both in the presence of palladium [5]and platinum [6] bimetallic catalysts.A double hydroalkoxycarbonylation of conjugateddienes like butadiene provides a direct route to di-esters, like dialkyl adipates [7].In spite of examples aimed at the synthesis of morecomplicated structures of biological importance[8–13], the palladium-catalysed hydroalkoxycarbony-lation of simple vinyl aromatics like styrene still re-mains the most important reaction. These compoundsmay serve not only as model derivatives, but the pre-dominantly formed branched esters containing a ste-reogenic centre in position a can be considered asuseful intermediates. Therefore, the enantioselectivehydroalkoxycarbonylation is of special interest[14,15].To find an appropriate balance of chemo- and regi-oselectivities, as well as a satisfactory catalytic activ-ity, the search for efficient catalysts is a never-endingstory. In the present work, we describe the applicationof novel phosphorus ligands either with an endo- orwith an exocyclic phosphorus atom [16,17] in therhodium-catalysed hydroformylation and in thepalladium-catalysed hydroalkoxycarbonylation of sty-rene. Our systematic work on the fine tuning of thesteric and electronic properties of the phospholeligands [18] made available novel cyclic P-ligands, aswell as ligands possessing a cyclopropane moiety(Fig. 1).2. Results and discussionThe most active complexes used in hydroformyla-tions have the general formula HxMy(CO)zLn, whereM = cobalt and rhodium. We wished to test the activityof Rh(III) complexes lacking a CO moiety in the coor-dination sphere. It was also a challenge for us to inves-tigate the properties of catalysts with novel P-ligands.Styrene (8) displaying a relatively high reactivityamong the alkenes was chosen as the model substratethat was reacted with CO/H2 (1/1) at 40–100 °C and ata pressure of 100 bar (Table 1) in the presence of one ofthe RhCl2(Cp*)(L)-type precursors (where L = 1–7,Fig. 1).780 G. Keglevich et al. / C. R. Chimie 7 (2004) 779–784(1)PhCH = CH28→CO⁄H2PhCH(CHO)CH39+ PhCH2CH2CHO10+ PhCH2CH311In addition to the formyl regioisomers 9 and 10,some hydrogenation product 11 is also expected. Sur-prisingly, by using RhCl2(Cp*)(ligand) catalytic pre-cursors, the formation of 11 was negligible (less than0.5% and, in most cases, less than the detection limit).The hydroformylation activity of RhCl2(Cp*)(1)and RhCl2(Cp*)(2) catalysts is moderate and the con-versions are nearly the same (Table 1, entries 1 and 3).Higher activities have been observed with the cyclo-propyl ligands 5 and 6 bearing an exocyclic phospho-rus atom (Table 1, entries 11 and 15). Moreover, forlonger reaction times, the latter ligand proved to beactive even at 40 °C (Table 1, entry 16). Note that theintroduction of a methyl substituent in the cyclopro-pane ring in trans position to the phosphorus atom(ligand 7) resulted in a spectacular decrease of thecatalytic activity (Table 1, entries 11 and 17).The catalysts formed with ligands possessingo-tolyl and p-tolyl substituents (3 and 4) can be consid-ered as inactive at low temperatures, but the rhodium-Cp* type complexes of both ligands provided excellentconversions at 100 °C in comparison with the catalystcontaining ligand 1 with similar structure, but bearinga phenyl group at the phosphorus atom (Table 1, entries6–10). Thus, the introduction of tolyl groups instead ofthe phenyl one caused an unexpectedly high increase inactivity.It is worth noting that the chemoselectivity of thehydroformylations is excellent in all cases, where thecatalyst is active at all. Ethylbenzene could be detectedby immediate GC–MS analysis only in traces (videsupra).As far as the regioselectivity is concerned, a dra-matic drop in regioselectivity has been observed in theligand series 1, 3, 4 going from 1 to 3–4. The introduc-tion of o- and p-tolyl substituents (3 and 4) caused apronounced decrease of the regioselectivity from 85%to 33% and 42%, respectively (Table 1, entries 1, 7 and9).A further feature has been observed by the applica-tion of the cyclopropane-based ligands 5 and 6, i.e. theregioselectivity towards the branched aldehyde (9)seems to be significantly influenced by the basicity ofthe phosphorus ligands. The use of the more basicphosphine 6 results in lower regioselectivities. More-over, the selectivity changes in favour of the linearaldehyde (10) (Table 1, entries 11 and 15, respec-tively). Going from ligand 5 to ligand 7, the regioselec-Fig. 1. Compounds 1 to 7.781G. Keglevich et al. / C. R. Chimie 7 (2004) 779–784tivity again decreased (Table 1, entries 11 and 17). It isnoteworthy that the activity and the regioselectivity ofthe hydroformylation in the presence of 5–7 are chang-ing in the opposite direction.It has been shown that the lower the temperaturewas, the lower regioselectivities towards the branchedaldehyde 9 were detected, i.e. a decrease in tempera-ture favours the formation of the linear aldehyde 10(Table 1, entries 11 and 12). This tendency is oppositeto that observed with well-known preformed (e.g.,HRh(CO)(PPh3)3) or in situ prepared rhodium–PPh3systems [19]. Similar regioselectivity-temperature de-pendence has been observed for the analogousHRh(CO)(dppe) system.The application of widely used in situ systemsformed from [Rh(COD)Cl]2 or [Rh(CO)2Cl]2 precur-sors in the presence of conventional PPh3 or a,x-bis(diphenylphosphino)alkanes resulted in regioselec-tivities towards 9 up to 96% [20].Considering the whole ligand series (1–7) investi-gated, it turned out that using the catalytic systemcontaining sterically slightly more bulky (and morebasic) ligands (3, 4, and 6) the activity increases, whilethe regioselectivity towards branched aldehyde dropssubstantially. It is explained by the formation of a moreactive catalytic species, HRh(CO)2(L) rather than pen-tacoordinated HRh(CO)2(L)2 18-electron species thatmight form the R(CO)Rh(CO)2(L)2 acyl intermediatethat does not react with hydrogen because of the lack ofa vacant coordination site for molecular hydrogen toundergo oxidative addition [21]. It has to be mentionedthat the oxidative addition of molecular hydrogen toRh complexes possessing phosphine and diphosphineligands is considered as the rate-determining step ofhydrogenation. Kinetic studies revealed, however, thatthe rate-determining step depends on the nature of theligand and in some cases alkene insertion into Rh-hydride bond becomes the slowest step [22]. The factTable 1Hydroformylation (HF) and hydroethoxycarbonylation (HEC) of styrene with rhodium–Cp*–(phosphorus ligand) and palladium–(phosphorusligand) (ligand = 1–7) complexes, respectively aEntry Complex Reaction Temp.(°C)Reactiontime (h)Conv.(%)TOFe(h–1) Rcb(%)Rbrc(%)1 RhCl2(Cp*)(1) HF 100 12 19 63 96 852 RhCl2(Cp*)(1) HF 70 24 28 40 > 99.5 863 RhCl2(Cp*)(2) HF 100 11 25 91 98 834 RhCl2(Cp*)(2) HF 70 24 2 3 > 99.5 955 RhCl2(Cp*)(2) HF 40 22 0 — — —6 RhCl2(Cp*)(3) HF 40 14 0 — — —7 RhCl2(Cp*)(3) HF 100 4 > 99.5 1000 > 99.5 338 RhCl2(Cp*)(3) HF 40 72 0 — — —9 RhCl2(Cp*)(4) HF 100 4 99.3 993 > 99.5 4210 RhCl2(Cp*)(4) HF 40 70 0 — — —11 RhCl2(Cp*)(5) HF 100 9 97 431 > 99.5 6812 RhCl2(Cp*)(5) HF 70 24 > 99 167 > 99.5 2713 RhCl2(Cp*)(5) HF 40 16 0 — — —14 RhCl2(Cp*)(5) HF 40 26 2 3 > 99.5 3915 RhCl2(Cp*)(6) HF 100 4 99.5 995 > 99.5 3416 RhCl2(Cp*)(6) HF 40 70 52.5 30 > 99.5 517 RhCl2(Cp*)(7) HF 100 4 15 150 > 99.5 2418 RhCl2(Cp*)(7) HF 40 70 0 — — —19 trans-PdCl2(2)2 HEC 90 48 2 2 > 99d >9920 trans-PdCl2(5)2 HEC 90 48 21 17 > 99d 98a Reaction conditions: 100 bar CO/H2 = 1/1; Rh/styrene = 1:4000; solvent: toluene (HF); 90 bar CO; Pd/styrene = 1:4000; solvent:toluene/ethanol (HEC).b Chemoselectivity (9+10)/(9+10+11) × 100 (HF); (12+13)/(12+13+oligomers) × 100 (HEC).c Regioselectivity towards branched regioisomer 9/(9+10)*100 (HF); 12/(12+13) × 100 (HEC).d Oligomerisation (dimerisation) of styrene as side reaction.e Turnover frequency: mmol converted substrate/(mmol catalyst × reaction time).782 G. Keglevich et al. / C. R. Chimie 7 (2004) 779–784that the less hindered (and less basic) ligand decreasesthe reaction rate, but increases the regioselectivity to-wards the branched aldehyde, indicates that the regi-oselectivity is determined in the alkyl–Rh formationstep from the p-olefin Rh complex [23].Due to the great variety of rhodium–ligand systemsused in the hydroformylation of styrene, we focused onthose catalysts formed from Rh–Cp precursors. Byusing P-ligand-free (Cp)Rh(CO)2 catalyst, nearlyequal amount of linear (10) and branched (9) aldehydewas formed. The application of Rh–Cp complexes con-taining ester functionalities on the Cp ring slightlyincreased regioselectivity. Upon addition of PPh3, ex-cellent branched-to-linear aldehyde ratios towardsbranched aldehydes were, however, obtained. Thepresence of a phosphine ligand in these rhodium-Cpsystems seems to be essential to achieve regioselectivi-ties of practical importance [24].In those cases, when sterically demanding phospho-rus ligands (3, 4, and 6) are used, good to excellentturnover frequencies (TOFs) up to 1000 have beenobtained referring to the determining role of coordina-tively unsaturated HRh(CO)2(L) species of high activ-ity. It is worth noting that the high activity was accom-panied by practically complete chemoselectivitiestowards aldehydes.The palladium-catalysed hydroalkoxycarbonyla-tion of styrene (Eq. (2)) resulted in much lower cata-lytic activities than the rhodium catalysts (containingthe same ligands) in hydroformylation. The palladiumprecursor containing cyclopropanyl ligand 5 formed amore active catalyst than the analogous trans-PdCl2(2)2 complex. In both cases, the formation of thechiral branched ester 12 is highly favoured (Table 1,entries 19 and 20).(2)PhCH = CH28→CO⁄EtOHPhCH(COOEt)CH312+ PhCH2CH2COOEt133. ExperimentalAll reactions were carried out under argon usingstandard Schlenk tube techniques. Toluene was dis-tilled from sodium in the presence of benzophenone.Styrene was freshly distilled before use. The phos-phine ligands were prepared by a known deoxygen-ation reaction of the corresponding precursors bearingP=O moiety by trichlorosilane [25]. The rhodium(III)and Pd(II) complexes used as catalytic precursors wereprepared as described earlier [16,17].3.1. Hydroformylation experimentsIn a typical hydroformylation experiment a solutionof 0.00125 mmol RhCl2(Cp*)(L) catalyst in 1.5 ml oftoluene containing 5 mmol of styrene was transferredinto a 20-ml stainless steel autoclave under argon. Thereaction vessel was pressurised to 100-bar total pres-sure with CO/H2 (1:1) and the magnetically stirredmixture was heated in an oil bath. The pressure wasmonitored throughout the reaction. After cooling andventing of the autoclave, the solution was immediatelyanalysed by gas chromatography.3.2. Hydroethoxycarbonylation experimentsIn a typical experiment, a solution of 0.00125 mmolPdCl2(L)2 catalyst in 1.5 ml of toluene containing5 mmol of styrene and 0.5 ml of ethanol was trans-ferred into a 20-ml stainless steel autoclave under ar-gon. The reaction vessel was pressurised with CO to90 bar and the magnetically stirred mixture was heatedin an oil bath. The pressure was monitored throughoutthe reaction. After cooling and venting of the auto-clave, the solution was immediately analysed by gaschromatography.AcknowledgementsK.L. and G.K. thank the OTKA funds (No. T035047and T 042479, respectively), while I.O. acknowledgesthe partial support from the Russian Basic ResearchFoundation (grant No. 02-03-33073).References[1] H. Brunner, W. Zettlmeier, Handbook of EnantioselectiveCatalysis with Transition Metal Compounds, VCH, Wein-heim, Germany, 1993.783G. Keglevich et al. / C. R. Chimie 7 (2004) 779–784[2] (a) I. Ojima, C.-Y. Tsai, M. Tzamarioudaki, D. Bonafoux, in:L.E. Overman, et al. (Eds.), The hydroformylation reaction,56, 2000, pp. 1–354 Org. React (Ch. 1) and references citedtherein; (b) C.D. Frohning, C.W. Kohlpainter, in: B. Cornils,W.A. Herrmann (Eds.), Applied Homogeneous Catalysis withOrganometallic Compounds, 1, VCH, Weinheim, 1996, p. 29.[3] (a) C. Botteghi, S. Paganelli, A. Schionato, M. Marchetti,Chirality 3 (1991) 355; (b) C. Botteghi, M. Marchetti, S.Paganelli, in: M. 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Finke, Prin-ciples and Applications of Organotransition Metal Chemistry,University Science Books, Mill Valley, California, 1987,p. 621.[24] M. Costa, F.S. Dias, G.P. Ciusoli, G.L. Gazzola, J. Organomet.Chem. 488 (1995) 47.[25] R. Engel, in: R. Engel (Ed.), Handbook of OrganophosphorusChemistry, Marcel Dekker, Inc, NewYork, 1992, Ch. 5, p. 193.784 G. Keglevich et al. / C. R. Chimie 7 (2004) 779–784

Carbonylation reactions catalysed by rhodium(III) and palladium(II) complexes containing novel phosphine ligands

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Carbonylation reactions catalysed by rhodium(III) and palladium(II) complexes containing novel phosphine ligands

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