catalysts

Article Alkanethiolate-Capped Palladium Nanoparticles for Regio- and Stereoselective Hydrogenation of Allenes

Ting-An Chen and Young-Seok Shon * Department of Chemistry and Biochemistry, California State University Long Beach, 1250 Bellflower Blvd., Long Beach, CA 90840, USA; [email protected] * Correspondence: [email protected]; Tel.: +1-562-985-4466



Received: 3 September 2018; Accepted: 25 September 2018; Published: 29 September 2018


Abstract: Colloidal Pd nanoparticles capped with octanethiolate ligands have previously shown an excellent selectivity toward the mono-hydrogenation of both isolated and conjugated dienes to internal alkenes. This paper reports an efficient stereoselective mono-hydrogenation of cumulated dienes (allenes) to either Z or E olefinic isomers, depending on the substitution pattern around C=C bonds. Kinetic studies indicate that the reaction progresses through the hydrogenation of less hindered C=C bonds to produce internal Z olefinic isomers. In the cases of di-substitued olefinic products, this initial hydrogenation step is followed by the subsequent isomerization of Z to E isomers. In contrast, the slow isomerization of Z to E isomers for tri-substituted olefinic products results in the preservation of Z stereochemistry. The high selectivity of Pd nanoparticles averting an additional hydrogenation is steered from the controlled electronic and geometric properties of the Pd surface, which are the result of thiolate-induced partial poisoning and surface crowding, respectively. The high activity of colloidal Pd nanoparticle catalysts allows the reactions to be completed at room temperature and atmospheric pressure.

Keywords: selective hydrogenation; catalysis; nanoparticle; cumulated diene; allene; ligand-capped; semi-heterogeneous

1. Introduction Selective hydrogenation of small alkynes and dienes is an important chemical process because such compounds are reactive monomers for polymerization that decreases the purity of pyrolysis petroleum products [1–3]. Compared to a variety of catalysts investigated for selective hydrogenation of alkynes and conjugated/isolated dienes, only a limited number of studies has been reported for the selective hydrogenation of allenes that have the unique orthogonal π orbital of cumulene. Besides the complete hydrogenation of two π bonds, the partial hydrogenation of allenes can involve either 1,2- or 2,3-hydrogenation. In addition, the products for selective hydrogenation of allenes are often stereoisomers (cis and trans), further complicating the catalysis results. The isomerization of allene groups to alkynes was also observed for several catalytic systems during the hydrogenation of allenes [4]. Earlier studies reported in the literature indicated that the selectivity of supported metal catalysts among different chemo-, regio-, and stereoselective hydrogenation products is generally low for this challenging allene hydrogenation reaction [5–10]. For example, palladium on alumina catalyst, which was synthesized by the hydrothermal method, converted allenes into alkenes, with a relatively low and time-dependent selectivity [9,10]. It has been shown that the pressure of the hydrogen gas would affect the catalytic selectivity of palladium on alumina, which has been correlated to the hydride concentration on the palladium surface. With the lower pressure of H2 and at the earlier stage of buta-1,2-diene hydrogenation, cis-but-2-ene was the major reaction product. However,

Catalysts 2018, 8, 428; doi:10.3390/catal8100428 www.mdpi.com/journal/catalysts Catalysts 2018, 8, 428 2 of 10

Catalysts 2018, 8, x FOR PEER REVIEW 2 of 10 with the increased hydrogen pressure above 100 torr or at the later stage of the catalytic reaction, reaction,the yields thefor yields butane, for a full butane, hydrogenation a full hydrogenation product, would product, greatly increasewould greatly with the increase formation with of some the formationtrans-but-2-ene of some [10]. trans During-but-2-ene the hydrogenation [10]. During reaction the hydrogenat of buta-1,2-diene,ion reaction the isomerizationof buta-1,2-diene, products, the isomerizationbut-1-yne and products, buta-1,3-diene, but-1-yne were and also buta-1,3-diene, observed [9]. were also observed [9]. SelectiveSelective mono-hydrogenationmono-hydrogenation of substitutedof substitu allenested allenes could produce could fourproduce different four stereoisomeric different stereoisomericalkenes depending alkenes on depending the regio- andon the stereoselective regio- and stereoselective addition of hydrogen, addition of as hydrogen, shown in as Scheme shown1. inMost Scheme heterogeneous 1. Most heterogeneouscatalysts, including catalysts, supported including Pd, supported Pt, Rh, and Pd, Ir, Pt, produced Rh, andcis Ir,-1,2-hydrogenation produced cis-1,2- hydrogenationproducts as major products products, as major with products, maximum with yieldsmaximum ranging yields from ranging 70% from to 98%, 70% to that 98%, are that highly are highlydependent dependent on the on reaction the reaction time and time hydrogen and hydrogen pressure pressure [5,6,11 [5,6,11].]. Most Most of these of these catalysts catalysts produced produced full fullhydrogenation hydrogenation products products as major as major products products after anafte extendedr an extended reaction reaction time. Hydrogenationtime. Hydrogenation of allenes of alleneswith homogeneous with homogeneous catalysts, catalysts, such assuch chlorotris(triphenylphosphine) as chlorotris(triphenylphosphine) rhodium, rhodium, allylpalladium allylpalladium (II), (II),and palladiumand palladium (bis(arylimino)acenaphthene) (bis(arylimino)acenaphthene) complexes, complexe also broughts, also about brought the cis about-1,2-hydrogenation the cis-1,2- hydrogenationreaction as its primaryreaction pathwayas its primary [12–14 pathway]. With the[12–14]. good With selectivity the good toward selectivity the cis -1,2-hydrogenationtoward the cis-1,2- hydrogenationproduct, the homogeneous product, the palladiumhomogeneous (bis(arylimino)acenaphthene) palladium (bis(arylimino)acenapht complex washene) used complex for the was selective used forhydrogenation the selective ofhydrogenation 1,2-allenyl phosphonates of 1,2-allenyl tophosphonates (Z)-1-alkenyl to phophonates (Z)-1-alkenyl [ 14phophonates]. [14].

R1H2C R2 R1 CH2R2 Mono- R2 R1 Hydrogenation H • H R2 R1

R1H2C CH2R2 SchemeScheme 1. 1.SelectiveSelective mono-hydrogenation mono-hydrogenation of substituted of substituted allenes produces allenes four produces different fourstereoisomeric different alkenes.stereoisomeric alkenes.

WithWith the the emergence emergence of of the the α-amino-amino vinylphosphonate vinylphosphonate as as an an important important building building block block for for the the preparationpreparation of of biologically biologically active active molecules molecules [15], [15], the the research research on on developing developing heterogeneous heterogeneous catalysts catalysts forfor selectiveselective hydrogenationhydrogenation of ofα -aminoα-amino allenephosphonates allenephosphonates to α -aminoto α-amino vinylphosphonates vinylphosphonates has drawn has drawninterest interest [16]. The [16]. most The efficient most efficient heterogeneous heterogene catalystous catalyst for 1,2-hydrogenation for 1,2-hydrogenation was determined was determined to be the toPd/C be the (10 Pd/C wt.%) (10 in wt.%) the presence in the presence of quinoline. of quino Dependingline. Depending on the sizeon the and size functionality and functionality of the aminoof the aminogroup, group, however, however, the stereoselectivity the stereoselectivity between between Z and Z E and isomers E isomers varied varied dramatically, dramatically, ranging ranging from from58:42 58:42 to 96:4, to in96:4, favor in favor of Z isomers.of Z isomers. The yields The yields for 1,2-hydrogenation for 1,2-hydrogenation were aswere high as ashigh 97% as for 97%α-amino for α- aminoallenephosphonates, allenephosphonates, but also but as also low as as low 43% as for 43% bulkier for bulkier substrates. substrates. Recently,Recently, thethe firstfirst successful successful and and highly highly efficient effici 2,3-reductionent 2,3-reduction of substituted of substituted allenes wasallenes reported was reportedby Dong by et Dong al. [17 et]. al. The[17]. Rh-HThe Rh-H based based homogeneous homogeneous catalyst catalyst with with a a chiral chiral ligand ligand waswas able to to affordafford the the chemoselective chemoselective reduction, reduction, producing producing chir chiralal benzylic benzylic motifs motifs with with good good enantioselectivity. enantioselectivity. TheThe mechanistic studies using isotope labeling revealed that that the the hydride hydride is is added added directly directly to to the the branchedbranched position position (3-position) (3-position) of of allenes allenes for for 2,3-reduction. 2,3-reduction. DespiteDespite the the recent recent development, development, a facile a facile method method that produces that produces more th moreermodynamically thermodynamically stable E-alkenesstable E-alkenes directly from directly allenes from in allenesa single instep a is single currently step lacking is currently in the literature. lacking in Alkanethiolate- the literature. cappedAlkanethiolate-capped palladium nanoparticles palladium (PdNP) nanoparticles have shown (PdNP) a havehigh shownselectivity a high for selectivityboth isolated for bothand conjugatedisolated and dienes conjugated to form dienes mono-hyd to form mono-hydrogenationrogenation products products [18–20]. [ 18Pd/Al–20].2O Pd/Al3 coated2O3 coatedwith alkanethiolatewith alkanethiolate monolayers monolayers could couldselectively selectively hydrog hydrogenateenate unsaturated unsaturated fatty acids fatty with acids isolated with isolated diene groupsdiene groupsto monounsaturated to monounsaturated fatty acids fatty [21]. acids Betw [21].een Between two major two routes major routesfor the forconjugated the conjugated diene hydrogenation,diene hydrogenation, the 1,2- the and 1,2- 1,4-hydrogenation, and 1,4-hydrogenation, the thermodynamically the thermodynamically stable stableinternal internal alkenes alkenes were producedwere produced with high with selectivity high selectivity [20]. This [20]. was This due was to due the to strong the strong influence influence of the of thiolate the thiolate ligands ligands on theon chemical the chemical and electronic and electronic properties properties of the Pd of thesurface. Pd surface. The kinetic The study kinetic showed study that showed the direct that 1,4- the additiondirect 1,4-addition reaction supplemented reaction supplemented by the isomerizat by the isomerizationion of the 1,2-addition of the 1,2-addition products products was the was main the mechanismmain mechanism leading leading to the to internal the internal alkenes alkenes in hi ingh high yields. yields. This This article article presents presents the the catalytic catalytic hydrogenation of cumulated dienes using these PdNPs and the influence of surface capping ligands on their activity and selectivity.

Catalysts 2018, 8, 428 3 of 10

CatalystsCatalystsCatalystshydrogenation 2018Catalysts 2018Catalysts, 82018,, 8x, FOR2018x, 8FOR2018, x ,PEER 8FOR of,PEER 8x, cumulatedFORx PEERREVIEW FOR REVIEW PEER PEERREVIEW REVIEW REVIEW dienes using these PdNPs and the influence of surface capping3 of3 ligands of10 310 of 310 of3 of10 10 on their activity and selectivity. 2.2. Results Results2. Results2. 2. Resultsand Resultsand Discussionand Discussion and Discussionand Discussion Discussion 2. Results and Discussion TheThe Thecatalytic catalyticThe Thecatalytic catalytic hydrogenationcatalytic hydrogenation hydrogenation hydrogenation hydrogenation reaction reaction reaction reaction ofreaction of ester ofester ofester conjugated of conjugatedester esterconjugated conjugated conjugated cumulene cumulene cumulene cumulene cumulene 1 1with with1 with1C8 1C8with withPdNP C8PdNP C8 PdNPC8 was PdNP wasPdNP was was was performedperformedperformedperformedperformedThe at at catalyticroom roomat roomat temperatureat temperatureroom hydrogenation room temperature temperature temperature and and reaction atmosphericand atmospheric and atmosphericand ofatmospheric esteratmospheric pr conjugatedpressure.essure. pressure. pr prTheessure. Theessure. cumulene kineticThe kinetic The kineticThe study1kinetic studywithkinetic study of C8 studyof esterstudy PdNP esterof ester ofconjugated wasof conjugatedester esterconjugated performed conjugated conjugated cumulenecumulenecumuleneat roomcumulenecumulene 1 1showntemperature shown 1 shown 1 1inshown inshown Table Tablein and Tablein 1in atmospheric Table1 and Tableand 1 and Figure 1Figure 1and Figureand pressure.S1Figure S1Figure clearly S1clearly S1clearly S1 The indicatedclearly indicatedclearly kinetic indicated indicated indicatedthat studythat thatthe the ofthat mono-hydrogenatedthat theestermono-hydrogenated the mono-hydrogenatedthe conjugated mono-hydrogenated mono-hydrogenated cumulene cis- cis- cis- 1cis- cis- conjugatedconjugatedconjugatedshownconjugatedconjugated ester in ester Table esterproduct productester1 esterandproduct product Figure2 product 2is is 2the theis S12 primary the2 clearlyisprimary isthe primarythe primary indicated hydrogenationprimary hydrogenation hydrogenation hydrogenation thathydrogenation the product product mono-hydrogenated product product during productduring during theduring theduring early theearly cis-conjugated the early thestage stageearly early stage of ofstage thestage theof ester theof of the the catalyticcatalyticcatalyticproductcatalytic hydrogenation.catalytic hydrogenation. 2hydrogenation.is hydrogenation. the hydrogenation. primary It Itis is hydrogenationreasonableIt reasonable is It reasonable Itis isreasonable reasonable to to infer product inferto infertoth toth atinferat during infertheth theat thsteric thethatsteric theat the steric theeffect early effectsteric steric effect stageof ofeffect the effect theof of substituted the theofsubstituted of the substituted catalyticthe substituted substituted ester ester hydrogenation. estergroup group ester estergroup group group waswas thewasIt the is wasmain reasonablethewasmain the main causethe cause main main cause for to forcause inferthecause forthe initial for thattheinitial for the initial the thepreferential initialpreferential stericinitial preferential preferential effect preferential form form of formation theation form substituted formation of of ationcis ationcis of isomers cisisomers of of estercisisomers cis isomersafter isomers groupafter aftermono-hydrogenation, mono-hydrogenation, after was aftermono-hydrogenation, themono-hydrogenation, mono-hydrogenation, main cause as for as the as as as shownshownshowninitial inshown in shownScheme Scheme preferentialin Scheme in in Scheme2 Scheme2[22]. [22]. 2 formation[22].After 2After [22].2 [22].After the the After 2After of the2h hreaction, cisthe 2reaction, theh isomers 2reaction, h2 hreaction, thereaction, the after yields theyields the mono-hydrogenation,yields the for yieldsfor yieldsthe forthe cis for thecis for product theproductcis the cisproduct cis product 2 product2reached as reached 2 shown reached 2 reached2over reachedover in over84%. Scheme 84%. over over 84%.This This 84%.2[ 84%.This 22 This]. This resultresultAfterresult at resultat theresult thetheat early 2 theatearly hat the reaction, early thestage stageearly early stage of theofstage thestage yieldstheof catalytic theof catalyticof for the catalyticthe thecatalytic reactioncatalytic cisreaction productreaction reaction wasreaction was2 wascomparablereached comparable was wascomparable comparable overcomparable to 84%.to those thoseto This thoseto ofto resultthoseof otherthose otherof atotherof metalof themetalother other earlymetal based metalbased metal stage based based ofbased hydrogenationshydrogenationshydrogenationsthehydrogenations catalytichydrogenations discussed reactiondiscussed discussed discussed wasdiscussedin in the comparable thein introduction theinintroduction in the introduction the introduction tointroduction those that that ofproducethat produce otherthat producethat produce metal cisproduce cis products cisproducts based cisproducts cis products hydrogenations productsas as major majoras majoras productsas majorproducts major products discussed products products[22,23]. [22,23]. [22,23]. in [22,23]. the[22,23]. TheThe completeTheintroduction completeThe completeThe complete completeconsumption consumption thatconsumption consumption produce consumption of of the cisthe of substrate products thesubstrateof of the substrate the substrate substrate1 as 1required majorrequired 1 required 1 1required products onlyrequired only only3 3h, only [h, 22at only3 at ,h,which23 3which at ].h,3 Theh,which at theat whichthe completewhich isomerization theisomerization the isomerization the isomerization consumption isomerization of of the the of cis thecisof of the cis the cis cis isomerisomerisomersubstrate 2isomer 2toisomer to the 2 the to1 trans2 required the transto2 to the trans isomerthe isomer trans onlytrans isomer 3isomer 3started isomer h,started 3 at started which3 tostarted3 to startedtake take to the placetake to isomerizationplace to take placetake more moreplace place more rapidly. rapidly. more more of rapidly. the rapidly.This rapidly. cisThis isomerThissuggests suggests This suggestsThis2 suggeststo thatsuggests that the thethat transthe thatadsorption thethatadsorption isomer the adsorption the adsorption adsorption3 ofstarted of of of of thethe substrate thetosubstrate takethe substratethe substrate place substrate1 1is is more more1 more is 1 more isfavorable1 rapidly. favorable ismore more favorable favorable This favorablethan than suggests thanthat that than ofthanthat of the that the ofthat cis the thecisof isomerof the isomercisadsorption the cisisomer cis 2isomer .2 Onceisomer. Once 2. of Once 2the the .the 2Once. reactantOnce substrate thereactant the reactant the reactant 1 reactant 1was wasis 1 more consumed,was consumed,1 was1 consumed, favorablewas consumed, consumed, the the than the the the coordinationcoordinationcoordinationthatcoordination ofcoordination the of of cis the the isomerof cis thecisof isomerof the cisisomer 2the. cisisomer Once cis 2isomer 2 followedisomer thefollowed 2 followed reactant 2 followed2 byfollowed by the1 thebywas addition thebyaddition by consumed, the addition the addition of addition of hydrogen hydrogen of the hydrogen of coordination of hydrogen hydrogen produced produced produced produced of produced the the the mono- cis themono- isomerthe mono- theσ mono- σbonded mono-bonded2σfollowed bondedσ σbonded bonded σ PdPd alkyl Pdbyalkyl thePdalkyl intermediatePd intermediate alkyl addition alkyl intermediate intermediate intermediate of (Scheme hydrogen (Scheme (Scheme (Scheme 2). (Scheme produced2). After After2). After2). the 2). theAfter the σAfter the σbond mono- bond the σ the bond rotationσ rotationσbondbonded bond rotation rotation to rotationto release Pd release to alkyl releaseto to therelease intermediate therelease steric thesteric the steric theinteraction interactionsteric steric (Schemeinteraction interaction interaction of 2of ).the the Afterof cis thecisof of thethe cis the cis cis σ α isomer,isomer,isomer,bond isomer,the isomer,the subsequent rotation thesubsequent the subsequent the subsequent to subsequent release α -hydrogenα-hydrogen α the-hydrogen α -hydrogen stericα-hydrogen elimination elimination interaction elimination elimination elimination resulted ofresulted the resulted cisresulted in resulted isomer,in the thein formation theinformation thein the formation the subsequent formation formation of of the theof trans theoftrans-hydrogen of the trans isomerthe isomertrans trans isomer elimination 3isomer , 3 isomerthe, the 3 , the3 , 3 the, the thermodynamicallythermodynamicallythermodynamicallyresultedthermodynamicallythermodynamically in the formation more more more stable stable more ofmore stable theprod stableprod stable trans product.uct. prod isomerEven product. Evenuct. Even uct.with 3with Even, theEven withthe the thermodynamicallywith extended with theextended theextended the extended extendedreac reaction reaction reac moretime,tion reac time,tion time, tion stablea avery time, very time, a product.verysmall asmall verya verysmall amount amountsmallEven small amount amount with amount ofof the ofthe full theoffull extendedof the hydrogenationfull thehydrogenation full hydrogenationfull reactionhydrogenation hydrogenation product, time,product, product, aproduct, veryaproduct, asaturated saturated smalla saturateda asaturated amount saturatedester ester ester4 of4esterthat thatester the4 thatforms 4 full forms 4that thatforms hydrogenation via formsvia forms the viathe viadi- theviadi- σ the σ di-bondedthe product,bonded σdi- di-bondedσ σ bonded Pd-alkyl bondedPd-alkyl a saturatedPd-alkyl Pd-alkyl Pd-alkyl σ intermediate,intermediate,intermediate,esterintermediate,intermediate,4 that was was forms wasgenerated generated was viageneratedwas thegenerated generated [24,25]. di- [24,25]. [24,25].bonded [24,25].The [24,25].The isomerizThe Pd-alkylisomeriz The isomerizThe isomerized isomeriz intermediate,ed alkyne, edalkyne, edalkyne,ed alkyne,ethyl alkyne,ethyl wasethyl 2-butynoate, 2-butynoate,ethyl generated ethyl 2-butynoate, 2-butynoate, 2-butynoate, [was24 was,25 wasnot]. not Thewas observednotwas observed isomerizednot observednot observed observed fromfromfromalkyne, any anyfrom from ofany of the ethylany the ofany kinetic theofkinetic 2-butynoate, of thekinetic the study.kinetic study. kinetic study. The study. wasThe study. carbonylThe carbonyl not The carbonylThe observed carbonyl groupcarbonyl group group fromwas groupwas group not anywas not washydrogenated ofnot washydrogenated the not hydrogenated not kinetic hydrogenated hydrogenated study.at at all all at during The duringall at at duringall carbonyl all theduring theduring C8 theC8 PdNP groupthe C8PdNP the C8PdNP C8 was PdNP PdNP catalysiscatalysiscatalysisnotcatalysis hydrogenatedreaction,catalysis reaction, reaction, reaction, indicatingreaction, indicating atindicating allindicating indicating duringa agood good a thegood achemoselectivity achemoselectivitygood C8good chemoselectivity PdNP chemoselectivity chemoselectivity catalysis toward toward reaction,toward towardthe towardthe C=C the indicatingC=C the C=Cbondthe bond C=C C=Cbond over a overbond goodbond overthe theover chemoselectivity C=Oover theC=O the C=Obondthe bondC=O C=Obond bond bond hydrogenationshydrogenationshydrogenationstowardhydrogenationshydrogenations the [18,19]. C=C [18,19]. [18,19]. bond The[18,19]. The[18,19]. over resultThe result The theresultThe also alsoresult C=O result showedalso showed bondalso showedalso showedth hydrogenations showedthatat theth theat thmono-hydrogenation thethmono-hydrogenationatat the mono-hydrogenation the mono-hydrogenation [mono-hydrogenation18,19]. The resultof of terminal terminal of also terminalof of terminal showed C=Cterminal C=C C=Cin in the thatC=C the C=Cin thein in the the allenealleneallenemono-hydrogenation group allenegroupallene group is groupis muchgroup much is much is more ismuchmore much more offavored favored terminalmore more favored favoredover favoredover C=C overeither either over in overeither thethe eitherthe either allenemono-hydrogenation themono-hydrogenation themono-hydrogenation the group mono-hydrogenation mono-hydrogenation is much of more of conjugated conjugatedof favored conjugatedof of conjugated conjugated C=C overC=C C=Cor eitheror C=Cthe theC=Cor theor or the the doubledoubledoublemono-hydrogenation hydrogenationdouble hydrogenationdouble hydrogenation hydrogenation hydrogenation of of both of both of conjugated bothalleneof alleneof both bothallene C=C alleneC=C C=Callene C=Cbonds. bonds. C=C or C=Cbonds. the After bonds. After doublebonds. After 24 24After h hydrogenationAfter hof24 of reaction, h24 reaction, of24 h reaction,hof of reaction, esterreaction, ester of bothesterconjugated conjugated ester esteralleneconjugated conjugated conjugated C=C cumulene cumulene bonds.cumulene cumulene cumulene 1After 1 1 1 1 waswas was24converted converted hwas ofwasconverted reaction,converted converted to to mono-hydrogenated mono-hydrogenatedto ester mono-hydrogenatedto to conjugatedmono-hydrogenated mono-hydrogenated cumulene conjugated conjugated conjugated 1conjugated wasconjugated ester convertedester esterproducts productsester esterproducts to products mono-hydrogenated products(~96%, (~96%, (~96%, 2(~96%, 2(~96%,and and2 and3 2), 3 2 ),andwith conjugatedand3with), 3 with ),a3 ),awithhigh highwitha esterhigha ahigh high selectivityselectivityselectivityproductsselectivityselectivity toward toward (~96%, toward transtoward transtoward2 andtrans conjugated conjugated trans3 trans ),conjugated with conjugated conjugated aester highester esterproduct selectivityproduct ester esterproduct product 3, product3, with toward with 3, with a3, a yield 3,with yield trans witha yield of a conjugatedof yielda~69%. yield~69%. of ~69%. of With of ~69%.With ~69%. ester With an an With increased product With increasedan increasedan an increased3, increasedreaction withreaction reaction a reactionyield reaction timetime timeofto to ~69%.36time 36 timeto h, h, 36 theto With the to h,36 yields 36 the yieldsh,an h, theyields increasedthe for yieldsfor yieldstrans fortrans fortrans conjugated reactionfor conjugated trans trans conjugated conjugated time conjugated ester ester to 36 esterproduct product h, ester theesterproduct yieldsproduct 3 product3further further 3 for further 3 transincreasedfurther3 increasedfurther increased conjugated increased increasedto to ~86%, ~86%, toester ~86%, to while to ~86%,while product~86%, while the thewhile whileyield the3yieldfurther the yield the yield yield forfor the forincreasedthe forfull theforfull the hydrogenationfull thehydrogenation tofull hydrogenation ~86%,full hydrogenation hydrogenation while product product the product yield product 4 product 4remained for remained4 the remained4 4 fullremained remainedmostly hydrogenationmostly mostly mostlythe themostly same thesame the productsame the(from (fromsame same (from 4% 4 (from4% remained(from to 4%to 6%). 4% 6%).to4% 6%).to mostly The to The6%). 6%).Theresults results theThe Theresults same results results confirmedconfirmed(fromconfirmedconfirmedconfirmed a 4% higha high to a 6%).highselectivity aselectivity higha high Theselectivity selectivity resultsselectivity for for mono-hydrogenation formono-hydrogenation confirmed formono-hydrogenation for mono-hydrogenation mono-hydrogenation a high selectivity products products products products for overproducts over mono-hydrogenation overfull full over hydr overfull hydr full hydrogenation fullogenation hydr hydrogenationogenationogenation product, products product, product, product, with product, overwith with full with with a atrans/cis trans/cisahydrogenation trans/cisa trans/cisa selectivity trans/cis selectivity selectivity selectivity product,selectivity of of up up of to upto withof10.7. of 10.7.upto up a10.7. to trans/cis to 10.7. 10.7. selectivity of up to 10.7.

a Table 1. Catalytic reaction of ethyl buta-2,3-dienoatea 1 . TableTableTable 1. 1.CatalyticTable CatalyticTable 1. Catalytic 1. 1.Catalytic reaction Catalytic reaction reaction ofreaction of reactionethyl ethyl of ethylbuta-2,3-dienoate of buta-2,3-dienoate of ethyl ethylbuta-2,3-dienoate buta-2,3-dienoate buta-2,3-dienoate 1 a1. . 1 a. 1 a1. a.

SubstrateSubstrateSubstrateSubstrateSubstrateSubstrate

ProductProductProductProductProduct CompositionProduct Composition Composition Composition Composition Composition

1 1 1 1 1

ReactionReactionReactionReaction TimeReaction Time Time Time Reaction Time 1 1 1 1 1 2 2 2 2 2 3 3 3 3 3 4 4 4 4 4 0.50.50.5 h 0.5h 0.5h 0.5 h h 86% 86% 86% 86% 86% 86% 13% 13% 13% 13% 13% 13% 1% 1% 1% 1% 1% 0% 0% 0% 0% 0% 1 1 h h 1 h 1 h1 h 71% 71% 71% 71% 71% 71% 26% 26% 26% 26% 26% 26% 3% 3% 3% 3% 3% 0% 0% 0% 0% 0% 2 h 10% 84% 6% 0% 2 h 10% 84% 6% 0% 23 h 2 h 2 h2 h 10% 0% 10% 10% 10% 84% 84% 76% 84% 84% 6% 6% 24% 6% 6% 0% 0% 0% 0% 34 3 h h 3 h 3 h3 h 0% 0% 0% 0% 0% 0% 76% 76% 76% 67% 76% 76% 24% 24% 24% 24% 30% 24% 0% 0% 0% 0% 0%3% 244 4h h h 4 h 4 h4 h 0% 0% 0% 0% 0% 0% 67% 67% 67% 27% 67% 67% 30% 30% 30% 30% 69% 30% 3% 3% 3% 3% 3%4% 243624 h h24 h24 24 h h 0% 0% 0% 0% 0% 0% 27% 27% 27% 8% 27% 27% 69% 69% 69% 69% 86% 69% 4% 4% 4% 4% 4%6% a 3636Reaction h h36 h36 condition:36 h h 0.5 0% mmol0% 0% substrate, 0% 0% 5 mol 8% 8% % Pd8% catalyst 8% 8% (0.025 86% 86% mmol 86% Pd),86% 86% 2.5 mL CDCl 6% 6%3 , 16% atm 6% H6% 2. a a a a Reaction Reaction Reactiona Reactioncondition: condition:Reaction condition: condition: 0.5 condition: 0.5 mmol mmol0.5 mmol0.5 substrate, 0.5substrate, mmol mmol substrate, substrate, 5 substrate, mol5 mol 5 % mol % Pd 5 Pd mol 5 %catalyst mol catalystPd % %catalystPd Pd(0.025 catalyst (0.025 catalyst (0.025 mmol mmol (0.025 (0.025 mmol Pd), Pd), mmol 2.5mmol Pd), 2.5 mL Pd), mL2.5 Pd), CDCl mL2.5CDCl 2.5 mLCDCl3, mL13, atmCDCl1 atm3CDCl, 1 H atm 3H2, .1 32, . atm 1H atm2. H 2H. 2.

Catalysts 2018, 8, 428 4 of 10 Catalysts 2018, 8, x FOR PEER REVIEW 4 of 10

Scheme 2. The proposedproposed catalyticcatalytic reactionreaction mechanism mechanism of of ethyl ethyl buta-2,3-dienoate buta-2,3-dienoate1 for1 for the the formation formation of bothof both cis cis and and trans trans alkenes. alkenes.

To investigate the the influence influence of of substrate substrate structur structuree on on the the catalytic catalytic activity activity and andselectivity, selectivity, the thecatalytic catalytic reactionsreactions of various of various allenes allenes using using C8 PdNP C8 PdNP were were attempted attempted (Table (Table 2 and2 and Figures Figures S2–S9). S2–S9). The Thecatalytic catalytic hydrogenation hydrogenation of ester of ester conjugated conjugated cumulene cumulene 5 also5 alsoproduced produced almost almost the same the same results results as that as thatof 1.of This1. This indicates indicates that that the thepresence presence of the of the phenyl phenyl ring ring in in the the ester ester functional functional group group of of cumulene cumulene 5 wouldwould notnot affect affect the the catalytic catalytic reactivity reactivity of C8of PdNP.C8 Pd TheNP. presenceThe presence of the of methyl the methyl group atgroup the C4 at position the C4 ofposition internal of cumulatedinternal cumulated diene 9 seemed diene 9 to seemed enhance to theenhance cis to the trans cis isomerization. to trans isomerization. Hence, the Hence, catalytic the reactioncatalytic ofreaction9 produced of 9 produced trans conjugated trans conjugated ester 11 as ester the major 11 as productthe major without product yielding without cis yielding conjugated cis esterconjugated10 after ester the 10 extended after the equilibrium extended equilibrium between two between conjugated two conjugated stereoisomers. stereoisomers. However, the However, further reductionthe further of reduction internal cumulated of internal diene cumulated9 to fully diene hydrogenated 9 to fully esterhydrogenated seemed to ester be also seemed facilitated to be based also onfacilitated the increased based yield on the of saturated increased ester yield12 .of This saturated is because ester the cis12. toThis trans is isomerizationbecause the ofcis isomer to trans10 withisomerization a large ethyl of isomer substituent 10 with could a be large sterically ethyl moresubstituent inhibited, could facilitating be sterically the addition more ofinhibited, second hydrogenfacilitating to the the addition mono-σ-bonded of second Pd-alkyl hydrogen intermediate to the mono- formedσ-bonded after the Pd-alkyl addition intermediate of the first hydrogen formed toafter the the adsorbed addition C=C of the bond first of thehydrogen cis isomer to the10 .adsorbed These three C=C results bond indicated of the cis that isomer C8 PdNP10. These promotes three theresults selective indicated hydrogenation that C8 PdNP of conjugated promotes allenes the se tolective thermodynamically hydrogenation stableof conjugated trans-isomers allenes with to goodthermodynamically stereo- and regioselectivity. stable trans-isomers with good stereo- and regioselectivity. For the the reaction reaction of of ester ester conjugated conjugated cumulene cumulene 13, the13, methyl the methyl group group on C2 on (αC C2 from (αC ester from group) ester group)of the substituted of the substituted cumulene cumulene eliminated eliminated the full the hydrogenation full hydrogenation of the allene of the allenegroup, group, resulting resulting in the inquantitative the quantitative formation formation of the mono-hydroge of the mono-hydrogenatednated Z and E conjugated Z and E conjugated ester products, ester 14 products, and 15. 14However,and 15. the However, selectivity the selectivitybetween Z betweenand E isomers Z and was E isomers reversed was for reversed the reaction for the of ester reaction conjugated of ester conjugatedcumulene 13 cumulene in comparison13 in comparisonto those of two to those less sterically of two less hindered sterically substrates, hindered 1 substrates,and 5, and 1alsoand di-5, andsubstituted also di-substituted internal cumulene internal cumulene9. After the9. Afterformation the formation of kinetically of kinetically favored favored Z isomer Z isomer 14, the14, theisomerization isomerization of Zof to Z E toisomer E isomer (15) (requires15) requires the adsorption the adsorption of Z isomer of Z isomer and the and Pd-H the Pd-Haddition addition to the tomore the sterically more sterically bulky C=C bulky bond. C=C It bond. appears It appearsthat the thatsubstituted the substituted methyl gr methyloup at groupthe C2 at position the C2 positionhindered hindered this process this processand slowed and slowedthe isomerization the isomerization down, producing down, producing the Z isomer the Z isomer14 as the14 asmajor the majorproduct product even evenafter afterthe prolonged the prolonged reaction reaction time. time. For For the the catalytic catalytic hydrogenation hydrogenation of of the the diester substrate 1717,, thethe kineticallykinetically favoredfavored product,product, thethe ZZ isomerisomer 18 waswas againagain thethe majormajor product,product, with a selectivity over 90%. The adsorption and hydrogen addition occurs via the lessless stericallysterically hinderedhindered coordination complex. The presence of large esterester groupsgroups preventedprevented thethe additionaladditional adsorptionadsorption and hydrogen addition, inhibiting both the isomerization of Z isomer 18 to E isomer 19 and the secondsecond hydrogenation to the saturatedsaturated esterester productproduct 2020.. The extended reaction time did not changechange thethe selectivity for the finalfinal mono-hydrogenated conjugatedconjugated esterester products,products, 1818 andand 1919.. TheThe overall results clearly demonstrated that C8 PdNP synthesized using the thiosulfate protocol has the unique catalytic property to form the Z mono-hydrogenated conjugated esters from ester conjugated

Catalysts 2018, 8, 428 5 of 10 clearly demonstrated that C8 PdNP synthesized using the thiosulfate protocol has the unique catalytic CatalystsCatalystsCatalystsCatalysts 2018 2018 2018 ,2018 8, 8x, , ,8 FOR x8, ,xFOR x FOR FORPEER PEER PEER PEER REVIEW REVIEW REVIEW REVIEW 5 of5 5of105 of 10of 10 10 CatalystsCatalystsCatalystsCatalystsCatalysts 20182018 2018 2018 2018,20182018, 88,,, x8x,, , ,, 8FOR 8 FORx8x8,, , ,xFOR xFOR xx FOR FOR FORFOR PEERPEER PEERPEER PEER PEER PEERPEER REVIEWREVIEW REVIEWREVIEW REVIEW REVIEW REVIEWREVIEW 55 ofof5 5of 5101055 of of of of10 10 10 1010 propertyCatalystsCatalystsCatalystsCatalysts 2018 to 2018 2018 form,2018, 8,, 8xx, , , 8 FOR FORx8x, the, xFOR FORx FOR FOR PEERPEER Z PEERPEER PEER mono-hydrogenatedPEER REVIEWREVIEW REVIEWREVIEW REVIEW REVIEW conjugated esters from ester conjugated cumulenes5 of5 5of105 of of10 10 10 in the earlycumulenescumulenescumulenes stagecumulenes of in reactionsin thein inthe the earlythe early early early stage and stage stage stage thenof of reactionsof ofreactions furtherreactions reactions and isomerizeand and andthen then then then further further further thefurther Zisomerize isomerize alkene isomerize isomerize tothe the thethe Zthe Zalkene EZ Zalkene alkene alkene to to theto oftothe the Ethe conjugated Ealkene E alkeneE alkene alkene of of of of esters cumulenescumulenescumulenescumulenescumulenes inin in thethe inin the the theearlyearly early earlyearly stagestage stage stagestage ofof of reactionsreactions ofof reactions reactionsreactions andand and andand thenthen then thenthen furtherfurther further furtherfurtherfurtherfurther isomerizeisomerize isomerize isomerize isomerizeisomerizeisomerize thethe the the the theZtheZ Zalkenealkene Z Z ZZalkene alkene alkenealkenealkene toto to the the to toto tothe the the theEtheE Ealkenealkene E EEEalkene alkene alkenealkenealkene ofof of of ofof of dependingconjugatedcumulenesconjugatedcumulenesconjugatedcumulenescumulenesconjugated on inesters estersin the the inesters in estersthe thethedependingearly structure dependingearly depending earlyearlydepending stage stage stagestage ofonof onof the reactionsonthe ofonof reactionsthe reactionsthe reactions substrate,structurethe structure structure structure and and and andof then of especially thethenof thenofthethen the furthersubstrate,the furthersubstrate, furthersubstrate, furthersubstrate, isomerize the isomerize especially isomerizeisomerize degreeespecially especially especially the the ofthe the theZ the substitution Zthealkene degreethe Z Z alkenedegree alkenedegreealkene degree to of to of the tosubstitutiontoof theofsubstitution the atsubstitutiontheE substitution Ealkene the E Ealkene alkenealkene C2 ofat positionatof ofat of at conjugatedconjugatedconjugatedconjugatedconjugated estersesters esters esters esters dependingdepending depending depending depending onon on theon theon the the structurethestructure structure structure structure ofof of the theof of the the substrate,thesubstrate, substrate, substrate, substrate, especiallyespecially especially especially especially thethe the the degreethedegree degree degree degree ofof of substitution substitutionof of substitution substitution substitution atat at at at conjugatedtheconjugatedconjugatedconjugatedthe C2 C2 position position esters esters esters esters (mono-substituteddepending (mono-substituteddepending depending depending on on onthe on the the thestructure at structure atstructureC2: structure C2: E alkene,E of alkene,of theof of the the thesubstrate, di-substituted substrate, di-substitutedsubstrate, substrate, especially especially especially especially at atC2: C2: the Z the the alkene).Zthedegree alkene).degree degree degree of of substitutionof of substitution substitution substitution at at at at (mono-substitutedthethethethethe the C2theC2theC2 C2 C2C2position positionpositionC2C2 position position position positionposition (mono-substituted(mono-substituted(mono-substituted (mono-substituted at(mono-substituted (mono-substituted (mono-substituted(mono-substituted C2: E alkene, atatat di-substitutedat C2: C2: C2:at at at atC2: C2: C2: C2:EC2:EE Ealkene,alkene, E E Ealkene,E alkene, alkene, di-substituteddi-substituted atdi-substituted di-substituted di-substituted C2: Z alkene). atat at C2: C2:at at C2: C2: C2:ZZ Zalkene).alkene). Z Zalkene). alkene). alkene). thethethethe C2the C2C2 C2 positionC2 positionposition position position (mono-substituted (mono-substituted(mono-substituted (mono-substituted (mono-substituted at at atC2: at at C2:C2: C2: C2:E EEalkene, E alkene,E alkene, alkene, di-substituted di-substituted di-substituted di-substituted at at C2: at atC2: C2: C2:Z Zalkene). Z Zalkene). alkene). alkene). a a TableTableTableTable 2. 2.Catalytic 2. Catalytic2. Catalytic Catalytic reaction reaction reaction reaction of of conjugated of ofconjugated conjugated conjugated ester ester ester ester functionalized functionalized functionalized functionalized allenes allenes allenes allenes aa. a. a .a . a TableTableTableTableTableTable 2.2. 2.CatalyticCatalytic 2. 2.Catalytic Catalytic Catalytic reactionreaction reactionreaction reaction reaction ofof of conjugatedconjugated of ofconjugated conjugated conjugated conjugated esterester ester ester esterester functionalizedfunctionalized functionalized functionalized functionalized allenesallenes allenes allenes allenes allenes a.. a.. a a.a. .. . TableTableTableTable 2. 2.Catalytic 2. 2.Catalytic Catalytic Catalytic reaction reaction reaction reaction of of conjugated of ofconjugated conjugated conjugated ester ester ester ester functionalized functionalized functionalized functionalized allenes allenes allenes allenes a.. a.. a.a . ProductProductProductProduct Composition Composition Composition Composition SubstrateSubstrateSubstrateSubstrate Reaction Reaction Reaction Reaction Time Time Time Time ProductProductProductProductProductProduct CompositionComposition Composition CompositionComposition Composition Conv.Conv.Conv.Conv. SubstrateSubstrateSubstrateSubstrateSubstrate Reaction Reaction Reaction Reaction Reaction Time Time Time Time Time ciscis orciscis or Z or orZ Z Z ProductProductProductProduct trans trans transComposition trans Compositionor Composition Compositionor E or orE E E Full FullFull FullHydrogenation Hydrogenation Hydrogenation Hydrogenation Conv.Conv. Conv.Conv.Conv. Conv. SubstrateSubstrateSubstrateSubstrate Reaction Reaction Reaction Reaction Time Time Time Time cisciscis orciscisorciscis or Z Z or or Z Z Z trans trans trans trans trans oror or E Eor or E E E FullFullFullFullFull HydrogenationHydrogenation Hydrogenation Hydrogenation Hydrogenation Conv. Conv.Conv.Conv. ciscis orciscis or Z or orZ Z Z trans trans trans trans or or E or orE E E FullFullFullFull Hydrogenation Hydrogenation Hydrogenation Hydrogenation

1 1 11 2 2 22 3 3 33 4 4 44 11 1 11 2 2 22 3 3 3 33 4 4 44 4 24124 h241 24 h11 h h 27%2 27% 27%2 27% 22 69%3 69% 69%3 69% 33 4%4 4% 4 4% 4%4 4 100% 100% 100% 100% 242424 h h2424 h h h 27% 27% 27% 27% 27% 69% 69% 69% 69% 69% 69% 4% 4% 4% 4% 4% 4% 100% 100% 100% 100% 100% 100% 36243624 h362424 36h h h 27% 8% 27% 8% 27% 8%27% 8% 86%69% 86%69% 86%69% 69%86% 6%4% 6%4% 6%4% 4%6% 100% 100% 100% 100% 363636 h h3636 h h h 8% 8% 8% 8% 8% 86% 86% 86% 86% 86% 86% 6% 6% 6% 6% 6% 6% 100% 100% 100% 100% 100% 100% 3636 h3636 h h h 8% 8% 8% 8% 86% 86% 86% 86% 6% 6% 6% 6% 100% 100% 100% 100%

5 5 55 6 6 66 7 7 77 8 8 88 55 5 55 66 6 66 77 7 7 77 88 8 88 8 24524 h245 24 h55 h h 26%6 26% 26%6 26% 66 70%7 70% 70%7 70% 77 4%8 4% 8 4% 4%8 8 100% 100% 100% 100% 242424 h h2424 h h h 26% 26% 26% 26% 26% 70% 70% 70% 70% 70% 70% 4% 4% 4% 4% 4% 4% 100% 100% 100% 100% 100% 100% 36243624 h362424 36h h h 14%26% 14%26% 14%26% 26%14% 82%70% 82%70% 82%70% 70%82% 4% 4% 4% 4% 100% 100% 100% 100% 363636 h h3636 h h h 14% 14% 14% 14% 14% 82% 82% 82% 82% 82% 82% 4% 4% 4% 4% 4% 4% 100% 100% 100% 100% 100% 100% 3636 h3636 h h h 14% 14% 14% 14% 82% 82% 82% 82% 4% 4% 4% 4% 100% 100% 100% 100%

9 9 99 1010 10 10 1111 11 11 1212 12 12 99 9 99 101010 1010 111111 11 1111 121212 1212 12 24924 h249 24 h99 h h 20%10 20%10 20% 20%1010 71%11 71%11 71% 71%1111 9%12 9%12 9%12 9%12 100% 100% 100% 100% 100% 242424 hh2424 h h h 20% 20% 20% 20% 20% 71% 71% 71% 71% 71% 9% 9% 9% 9% 9% 100% 100% 100% 100% 100% 48244824 h 482424 48h h h 20% 0% 20% 0% 20% 0%20% 0% 82%71% 82%71% 82%71% 71%82% 18% 9% 18% 9% 18% 9%18% 9% 100% 100% 100% 100% 100% 484848 hh4848 h h h 0% 0% 0% 0% 0% 82% 82% 82% 82% 82% 18% 18% 18% 18% 18% 100% 100% 100% 100% 100% 4848 h4848 h h h 0% 0% 0% 0% 82% 82% 82% 82% 18% 18% 18% 18% 100% 100% 100% 100%

1313 13 13 1414 14 14 1515 15 15 1616 16 16 131313 1313 141414 1414 151515 1515 161616 1616 241324 h 13 24 2413h13 h h 86%14 86%14 86% 86%1414 14%15 14%15 14% 14%1515 0%16 0%16 0%16 0%16 100% 100% 100% 100% 100% 242424 hh2424 h h h 86% 86% 86% 86% 86% 14% 14% 14% 14% 14% 0% 0% 0% 0% 0% 100% 100% 100% 100% 100% 36243624 h 362424 36h h h 73%86% 73%86% 73%86% 86%73% 27%14% 27%14% 27%14% 14%27% 0% 0% 0% 0% 100% 100% 100% 100% 100% 363636 hh3636 h h h 73% 73% 73% 73% 73% 27% 27% 27% 27% 27% 0% 0% 0% 0% 0% 100% 100% 100% 100% 100% 3636 h3636 h h h 73% 73% 73% 73% 27% 27% 27% 27% 0% 0% 0% 0% 100% 100% 100% 100%

1717 17 17 1818 18 18 1919 19 19 2020 20 20 171717 1717 181818 1818 191919 1919 202020 2020 2424 h 24 2417&h h 17& 48h 17& 17 48& h 48 48h h h 90%18 90%18 90% 90%1818 10%19 10%19 10% 10%1919 0%20 0%20 0%20 0%20 100% 100% 100% 100% 100% 242424 hh2424 &h& h & h4848 & &48 h h48 48 h h h 90% 90% 90% 90% 90% 10% 10% 10% 10% 10% 0% 0% 0% 0% 0% 100% 100% 100% 100% 100% a aa a24a 24 h2424 &h h &h48 & &48 h48 48 h hh 90% 90% 90% 90% 10% 10% 10% 10% 0% 0% 0% 0% 100% 100% 100% 100% a Reactiona ReactionaReaction aReaction Reaction condition, condition, condition,condition, condition, 0.5 0.5 mmol0.5 0.5 mmol mmol mmol substrate, substrate, substrate, substrate, 5 mol5 5mol 55 mol mol%mol %Pd % %Pd catalystPd Pd catalyst catalyst catalyst (0.025 (0.025 (0.025 (0.025 mmol mmol mmol mmol mmol Pd), Pd), Pd), Pd),2.5 Pd), 2.5 mL2.5 2.5 2.5mL mL CDClmL mLCDCl CDCl CDCl CDCl3, 13, atm31,3 ,1atm 31 ,atm H 1atm atm2H. H 2H. 2. H2 . 2. a Reactiona Reactionaaa Reaction Reaction condition, condition, condition, condition, 0.5 0.5 mmol0.5 0.5 mmol mmol mmol substrate, substrate, substrate, substrate, 5 mol5 5mol 5 mol mol% % Pd % %Pd catalystPd Pd catalyst catalyst catalyst (0.025 (0.025 (0.025 (0.025 mmol mmol mmol mmol Pd), Pd), Pd), Pd),2.5 2.5 mL2.5 2.5 mL mL CDClmL CDCl CDCl CDCl33, 13, atm313,3 ,1atm 1 atm atmH 2H2. H 2H. 22.2 . a ReactionReactiona ReactionReactiona aReaction ReactionReaction condition,condition, condition,condition, condition, condition,condition, 0.50.5 0.50.5 mmolmmol0.5 0.50.5 mmolmmol mmol mmolmmol substrate,substrate, substrate,substrate, substrate, substrate,substrate, 55 mol mol55 5 mol mol55 mol mol%mol% %%PdPd % %%PdPd catalystcatalystPd PdPd catalystcatalyst catalyst catalystcatalyst (0.025(0.025 (0.025(0.025 (0.025 (0.025(0.025 mmolmmol mmolmmol mmol mmolmmol Pd),Pd), Pd),Pd), Pd), Pd),Pd),2.52.5 2.52.5 mLmL2.5 2.52.5 mLmL mL CDClCDClmLmL CDClCDCl CDCl CDClCDCl3,, 113, , atm atm311,3 , , 1 atm atm11 atm atmHatmH 2HH.. H 2HH.. 2.2 .. Reaction Reaction Reaction Reaction condition, condition, condition, condition, 0.5 0.5 mmol0.5 0.5 mmol mmol mmol substrate, substrate, substrate, substrate, 5 mol5 5 mol5 mol mol% %Pd % %Pd catalystPd Pd catalyst catalyst catalyst (0.025 (0.025 (0.025 (0.025 mmol mmol mmol mmol Pd), Pd), Pd), Pd),2.5 2.5 mL2.5 2.5 mL mL CDClmL CDCl CDCl CDCl3, 13, atm31,3 , 1 atm1 atm atmH 2H. H 2H. 2.2 . ToToTo examine ToexamineTo examine examine examine the the the therole role role role role of ofof theof ofthe the theconjugated conjugated conjugatedconjugated conjugated ester ester ester ester ester grou grou grou group group pduringp duringp during during during the the the thecatalytic catalytic catalytic thecatalytic catalyticreaction reaction reaction reaction of reactionof allenes,of ofallenes, allenes, allenes, the of the the allenes,the ToToTo ToexamineexamineTo examine examineexamine thethe the the therolerole role rolerole ofof of the theofof the the theconjugatedconjugated conjugated conjugatedconjugated esterester ester esterester grougrou grou grougroupp pduringduringp pduring duringduring thethe the the thecatalyticcatalytic catalytic catalyticcatalytic reactionreaction reaction reactionreaction ofof of allenes, allenes,ofof allenes, allenes,allenes, thethe the the the thekinetic kinetickinetickineticToTo investigation Toexamine Toinvestigation investigationexamineinvestigation investigationexamineexamine the the the theofrole of role theof role ofrole the ofof the hydrogentheof the theofhydrogenof thehydrogen hydrogen the theconjugated hydrogenationconjugated conjugatedconjugatedationationationation of esterof 1-cyclohexylpropa-1,2-dieneofester of ester1-cyclohexylpropa-1,2-dieneester 1-cyclohexylpropa-1,2-diene 1-cyclohexylpropa-1,2-dienegrou ofgrou grougrou 1-cyclohexylpropa-1,2-dienep pduringp pduring duringduring the the the thecatalytic catalytic catalyticcatalytic 21 21 reactionwas21 21 reactionwas reactionwasreaction was performed performed performed ofperformed 21of allenes, ofof allenes,was allenes,allenes, (Table (Table performed(Table the(Table the the the kinetickinetickinetickinetickinetic investigationinvestigation investigation investigationinvestigation ofof of thethe ofof the the thehydrogenhydrogen hydrogen hydrogenhydrogenationationationationation ofof of 1-cyclohexylpropa-1,2-diene1-cyclohexylpropa-1,2-diene ofof 1-cyclohexylpropa-1,2-diene 1-cyclohexylpropa-1,2-diene1-cyclohexylpropa-1,2-diene 2121 21 was 21was21 was was waswaswas performedperformed performed performed performedperformedperformed (Table(Table (Table (Table (Table(Table(Table (Table3,kinetic 3,kineticFigure3,kinetic kinetic3,Figure3 Figure, Figure Figureinvestigation investigationS10). investigationS10).investigation S10). S10). The S10). The The Theresults resultsof Theresults resultsof the ofof theshowed resultsthe thehydrogenshowed showed hydrogenshowed hydrogenhydrogen that showed that ationthat that theation ationtheation the reactanttheof reactant thatof reactant1-cyclohexylpropa-1,2-diene ofreactantof 1-cyclohexylpropa-1,2-diene 1-cyclohexylpropa-1,2-diene1-cyclohexylpropa-1,2-diene the consumption consumption consumption reactantconsumption consumptionof of 21of of21 is21 21 isslower is isslower 21slower slower21 was2121 thanwas of wasthanwas performedthan than 21 performedthat performed performedthat isthat that of slower of theof of the(Table the esterthe(Table (Tableester(Table thanester ester that 3,3, 3, FigureFigure3, 3,Figure Figure Figure S10).S10). S10). S10). S10). TheThe The The The resultsresults results results results showedshowed showed showed showed thatthat that that thatthatthat thethe the the the reactantthethereactant reactant reactant reactant reactantreactant consumptionconsumption consumption consumption consumption consumptionconsumption ofof of 21 21of of of of21 isis21 21 is slowerslower is is isisslower slower slower slowerslower thanthan than than than thanthan thatthat that that that thatthat ofof of the theof of of ofthe the the esterthetheester ester ester ester esterester conjugated3,conjugated 3,Figureconjugated3, 3,conjugatedFigure Figure Figure S10). S10).cumulene S10). S10).cumulene Thecumulene cumulene The The The results results results 1results . 1In .1 1showedIn. .addition, In showed In addition,showed showedaddition, addition, that1 thatthe that that thethe the hydrogenationthe the hydrogenationthereactant hydrogenation reactanthydrogenation reactant reactant consumption consumption consumption consumption selectivity selectivity selectivity selectivity of of for 21of of for21 for is21 thefor21 istheslower is the isslowerterminalthe slowerslowerterminal terminal terminal than than than thanC=C thatC=C C=Cthat C=Cthat thatbond of bond of bond theof bondof the ofthe the esterof theesterof ofester theester the the ofconjugatedconjugated theconjugatedconjugatedconjugated ester conjugated cumulenecumulene cumulene cumulenecumulene 11. cumulene. 1 In In. 1 1In. . . .addition,addition, In InInIn addition, addition, addition,addition,addition, . thethe In the the the thehydrogenationthe addition,hydrogenation hydrogenation hydrogenation hydrogenationhydrogenationhydrogenation the hydrogenationselectivityselectivity selectivity selectivity selectivityselectivityselectivity forfor for for fortheforthefor the selectivity the the theterminaltheterminal terminal terminal terminalterminalterminal C=CC=C C=C for C=C C=CC=CC=C bondbond the bond bond bondbondbond terminal ofof of thethe of ofof ofthe the the thethe C=C alleneconjugatedalleneconjugatedalleneconjugatedconjugatedallene group group group group cumulene wascumulene cumulenewascumulene was was much much much much 1. lower1In .1lower 1In. .lower addition, InlowerIn addition, addition,ataddition, at theat atthe the completionthethe completionthe completion the completionthehydrogenation hydrogenation hydrogenationhydrogenation of of substrateof ofsubstrate substrate substrate selectivity selectivity selectivityselectivity consumption consumption consumption consumption for for forthefor the the theterminal(100% terminal(100% terminal(100% terminal(100% for forC=C for 1 forC=C 1at C=C C=C 1 at 1bond 3at atbond3h bond 3 bondhvs.3 h vs.ofh vs. 72%ofvs. the of72%of the72% 72% the the bondallenealleneallenealleneallene of group thegroup group group group allene waswas was was was muchmuch group much much much lowerlower waslower lower lower at muchat at the theat at the the thecompletioncompletion lower completion completion completion at the ofof of substratesubstrate completionof of substrate substrate substrate consumptionconsumption consumption consumption consumption of substrate (100%(100% (100% (100% consumption(100% forfor for for 1for1 at1at 1 at 1 3 3at at at at h3h 3 3hvs.33vs. (100%h hhvs.h vs. vs.72%72%vs.vs. 72% 72% 72%72%72% for 1 at (Zallene(Zallene +(Zalleneallene(Z +E) + E)group+ forE) groupE) forgroup group for 21for 21 wasat21 21 wasat 4wasatwas at4muchh). 4 h).much4 muchh). Significantmuchh). Significant lowerSignificant Significant lower lowerlower at at hydrogenation the atathydrogenation the hydrogenation thehydrogenationthecompletion completion completioncompletion of of of ofthe of substrate oftheof substratethe internal substratethesubstrate internal internal internal consumption C=Cconsumption consumptionC=Cconsumption C=C C=C bond bond bond bond of (100%of alleneof(100% ofallene (100%(100% allene allene for 21 for 21 for 1 fortook21 21 at1took 1attook 1 3took at atplaceh3 3placeh3vs. place h placehvs. vs.72%vs.due 72%due 72%due 72%due 3 h(Z(Z vs.(Z +(Z+(Z(Z(Z E)+E)72% + +E)+ + forfor E) E)E)E) for for (Zfor 21for21for 21 +at21 at 21 atE) 4 4at at at at h).4h). for 4 4h).44 h).Significant h).Significanth).h). 21Significant Significant SignificantSignificantSignificantat 4 h). hydrogenationhydrogenation Significanthydrogenation hydrogenation hydrogenationhydrogenationhydrogenation hydrogenation ofof of the the of ofof ofthe the the theinternaltheinternal internal internal internalinternalinternal C=CC=C of C=C theC=C C=CC=CC=C bondbond bond internal bond bondbondbond ofof of allene allene of ofof ofallene C=Callene allenealleneallene 2121 21bond took21 took 21 took took tooktooktook placeplace of place place alleneplaceplaceplace duedue due due duedue due 21 took to(Zto(Z the+to(Z(Z to theE)+ the +absencetheE)+ for E)absenceE) forabsence absence for21for 21 at 21 21of at 4of at atconjugatedofh). 4of conjugated 4h).4 conjugated h).Significantconjugatedh). Significant SignificantSignificant ester ester ester hydrogenationester hydrogenationthat hydrogenationhydrogenationthat that that stabilizes stabilizes stabilizes stabilizes of the of the of of the theinternalthe the theinternal internal internalinternal internalinternal C=C C=C C=C C=CC=C C=Cbond.C=C bondbond. bond. bondbond. bondbond With of With ofWith alleneWith ofof allenete alleneallenete enhancedte te enhanced21 enhanced enhanced21 took 2121 took tooktook placereactivity placereactivity placereactivity placereactivity due due duedue placetototo thethetototo toduethe the the theabsencetheabsence absence to absence absenceabsenceabsence the ofofabsence of conjugated conjugated of ofof ofconjugated conjugated conjugatedconjugatedconjugated of conjugated esterester ester ester esteresterester thatthat that that thatthatthat stabilizesstabilizes stabilizes ester stabilizes stabilizesstabilizesstabilizes that thethe the stabilizesthe the theinternaltheinternal internal internal internalinternalinternal C=CC=C theC=C C=C C=CC=CC=C bond.bond.internal bond. bond. bond.bond.bond. WithWith With With WithWithWith C=C tete te enhanced enhanced te te tete bond.enhanced enhanced enhancedenhancedenhanced With reactivityreactivity reactivity reactivity reactivityreactivityreactivity te enhanced oftoofto theoftoto ofthe the theabsenceinternal absenceinternal absenceinternalabsenceinternal ofC=C ofC=C conjugated ofC=C of C=Cconjugated bond, conjugated conjugatedbond, bond, bond, the the esterthe thecatalytic ester catalytic ester estercatalytic catalyticthat that thatthat stabilizesreaction stabilizesreaction stabilizesreaction stabilizesreaction of the of the1-cyclohexylpropa-1,2-dieneof theof the1-cyclohexylpropa-1,2-dieneinternal 1-cyclohexylpropa-1,2-diene internal1-cyclohexylpropa-1,2-diene internalinternal C=C C=C C=CC=C bond. bond. bond.bond. With With WithWith te te 21 enhanced te21te enhancedproduced 21 enhanced21 enhancedproduced produced produced reactivity reactivity 28% reactivity reactivity28% 28% 28% of of of of reactivityofofof thetheofof the the theinternalinternal internal of internalinternal the C=CC=C internal C=C C=CC=C bond,bond, bond, bond,bond, C=C thethe the the the bond,catalyticcatalytic catalytic catalyticcatalytic the reactionreaction reaction catalytic reactionreactionreactionreaction ofof of 1-cyclohexylpropa-1,2-diene reaction1-cyclohexylpropa-1,2-dieneof ofof of1-cyclohexylpropa-1,2-diene 1-cyclohexylpropa-1,2-diene 1-cyclohexylpropa-1,2-diene1-cyclohexylpropa-1,2-diene1-cyclohexylpropa-1,2-diene of 1-cyclohexylpropa-1,2-diene 2121 21 produced 21 produced21 produced produced producedproducedproduced 28%28% 2128% 28% 28%28%28% ofproducedof of of ofof of theoftheof thetheof ofthe terminalthe theterminal theinternal terminal terminalinternal internalinternal alkene C=Calkene alkeneC=C alkene C=CC=C bond, 24bond, 24bond, bond, 24after24 after the after theafter thethe4catalytic 4 catalytich 4 catalytic catalytic4h of h hof reaction.of of reactionreaction. reaction.reactionreaction. reactionreaction As ofAs of As 1-cyclohexylpropa-1,2-diene seenAsofof 1-cyclohexylpropa-1,2-dieneseen 1-cyclohexylpropa-1,2-dieneseen1-cyclohexylpropa-1,2-dieneseen from from fromfrom the the the thereactions reactions reactionsreactions of of allof21 of all21 all produced21ester21all producedester producedesterproducedester conjugated conjugated conjugated conjugated28% 28% 28%28% of of ofof thethethethe the thetheterminalterminal terminal terminalterminalterminalterminal alkenealkene alkene alkenealkenealkenealkene 2424 24 24afterafter24 after afterafter 44 4 hh 4 4 h ofof h hof reaction.ofreaction.of reaction. reaction.reaction. AsAs As AsAsseenseen seen seenseen fromfrom from fromfrom thethe the the thereactionsreactions reactions reactionsreactions ofof of allofallof all allesterallester ester esterester conjugatedconjugated conjugated conjugatedconjugated 28%cumulenes,thecumulenes,the ofcumulenes,the thecumulenes,terminal theterminal terminalterminal terminal the alkenethe the alkene cisthe alkene alkenecis cis alkenecis alkene alkene24 alkene alkene24 24after24 22after after2422after was 2222 4wasafter 4was h was 4the 4h of theh h of4the majorthereaction.ofof hmajorreaction. major ofreaction.majorreaction. reaction.product product product Asproduct As AsAsseen atseen Asatseen seen theat atfromthe seenthe from earlythe from fromearly early earlythe from thestage thestagethereactions stage stagereactions the reactionsofreactions of theof reactions ofthe the hydrogenationtheof hydrogenationof hydrogenation allofhydrogenationof all allesterall ofester ester allester conjugated esterconjugated reactionconjugatedconjugated reaction reaction reaction conjugated cumulenes,cumulenes,cumulenes,cumulenes,cumulenes, thethe the the theciscis cis cisalkenealkenecis alkene alkenealkene 2222 22 was22 was22 was was waswaswas thethe the the the themajorthemajor major major majormajormajor productproduct product product productproductproduct atat at the the at atat atthe the the theearlytheearly early early earlyearlyearly stagestage stage stage stagestagestage ofof of the the of ofof ofthe the the thehydrogenationthehydrogenation hydrogenation hydrogenation hydrogenationhydrogenationhydrogenation reactionreaction reaction reaction reactionreactionreaction cumulenes,forcumulenes,forcumulenes, forcumulenes,1-cyclohexylpropa-1,2-dienecumulenes,for 1-cyclohexylpropa-1,2-diene 1-cyclohexylpropa-1,2-diene 1-cyclohexylpropa-1,2-diene the the the cisthe thecis cis alkene cisalkenecis alkene alkenealkene 2222 22 was 22was22 was was21was the21the. the21 With 21. the themajorWith. .majorWith major With major majorthe theproduct the increasedtheproduct product productincreasedproduct increased increased at at the atreactionat the reaction the thetheearlyreaction reaction early earlyearly stagetime, stagetime, stagetime, stagetime, stage ofthe ofthe the ofthe of cisthethe of cisthe the hydrogenation cis internal cis thehydrogenation internal hydrogenation hydrogenationinternal internal hydrogenation alkene alkene alkene alkene reaction 22 reaction 22 reaction reactionwas22 22 was was reactionwas forforfor for for1-cyclohexylpropa-1,2-dienefor1-cyclohexylpropa-1,2-dienefor 1-cyclohexylpropa-1,2-diene 1-cyclohexylpropa-1,2-diene 1-cyclohexylpropa-1,2-diene1-cyclohexylpropa-1,2-diene1-cyclohexylpropa-1,2-diene 2121 21. . 21 With21With. .With. . . With WithWithWith thethe the the the theincreasedtheincreased increased increased increasedincreasedincreased reactionreaction reaction reaction reactionreactionreaction time,time, time, time, time,time,time, thethe the the the thecisthecis cis cis cisinternalinternalciscis internal internal internalinternalinternal alkenealkene alkene alkene alkenealkenealkene 2222 22 was 22 was222222 was was waswaswas forisomerizedfor 1-cyclohexylpropa-1,2-dieneisomerizedfor isomerizedfor1-cyclohexylpropa-1,2-dieneforisomerized 1-cyclohexylpropa-1,2-diene 1-cyclohexylpropa-1,2-diene1-cyclohexylpropa-1,2-diene to to theto tothe the transthe trans trans trans internal internal internal internal alkene21 alkene 21 21. alkene 21alkeneWith21.. With. . 23WithWith 23 . the 23 The 23.the the The. the .theTheincreased The terminalincreased increased increasedterminalincreased terminal terminal reactionalkene reactionalkene reactionalkene reaction alkene 24 time,24 was24time, 24 time,wastime, was time, was thealso thealso the also thecisalso converted thecis converted cisinternal cisconverted convertedinternal cis internalinternal internal toalkene toalkene the toalkene alkene tothe the internalthe alkene22 internal 22internal internal was2222 was waswas 22 was isomerizedisomerizedisomerizedisomerizedisomerizedisomerizedisomerized toto to the the to toto tothe the the thetransthetrans trans trans transtranstrans internalinternal internal internal internalinternalinternal alkenealkene alkene alkene alkenealkenealkene 2323 23. . 23 The23The. The.. . . The TheThe The terminalterminal terminal terminal terminalterminalterminal alkenealkene alkene alkene alkenealkenealkene 2424 24 was24 was 24 was was waswaswas alsoalso also also alsoalsoalso convertedconverted converted converted convertedconvertedconverted toto to the the to toto tothe the the theinternaltheinternal internal internal internalinternalinternal isomerizedalkeneisomerizedalkeneisomerizedalkeneisomerizedisomerizedalkene by by isomerization,by toby isomerization,to isomerization, theto isomerization, the toto the thetrans thetrans trans transtrans internal which internal which internal internalwhich which was alkene alkenewas alkene was alkenewas alkeneaccompanied accompanied accompanied 23accompanied 23. 23The23. The. The . TheThe terminal terminal by terminal terminalterminal by theby by the the alkeneformationthe alkeneformation alkeneformationalkene formation 24 24 was 24of24 24 wasof thewasofwas ofalsowasthe the alsofullthe also alsofull converted fullalso fullhydrogenationconverted convertedhydrogenationconverted hydrogenation hydrogenation converted to to the toto the the producttheinternal to productinternal product internal theproductinternal internal alkenealkenealkenealkenealkene byby by isomerization,by isomerization,by isomerization, isomerization, isomerization, whichwhich which which which waswas was was was accompaniedaccompanied accompanied accompanied accompanied byby by theby theby the the formationtheformation formation formation formation ofof of the theof of the the fullthefull full full fullhydrogenationhydrogenation hydrogenation hydrogenation hydrogenation productproduct product product product alkene25alkenealkenealkene25 as asbya byminora isomerization,by byminor isomerization, isomerization, isomerization, product. product. which which which which was was was was accompanied accompanied accompanied accompanied by by theby by the the theformation formation formation formation of of the of of the the thefull full full fullhydrogenation hydrogenation hydrogenation hydrogenation product product product product alkene252525 asas25as25 as by a aaas as as as minorminoraminor a isomerization,a minoraa minor minor minorminor product.product.product. product. product. product. product.product. which was accompanied by the formation of the full hydrogenation product 2525 as2525 asas aas as minoraa a minorminora minor minor product. product.product. product. product. 25 as a minor product.

Catalysts 2018, 8, 428 6 of 10 CatalystsCatalysts 2018 2018, 8,, x8 ,FOR x FOR PEER PEER REVIEW REVIEW 6 of6 of10 10 CatalystsCatalystsCatalystsCatalysts 2018 2018 2018, ,8 8 ,2018 , x,x 8FOR FOR, x, 8FOR, PEER xPEER FOR PEER REVIEW REVIEWPEER REVIEW REVIEW 66 of of6 10 10of 610 of 10

a a a a a TableTableTableTableTable Table3.3.Table Kinetic Kinetic3. 3. 3.Kinetic Kinetic3. 3.Kinetic Kinetic Kineticstudystudy study study study ofstudyof study thetheof of of the catalyticof thecatalytic ofthe thecatalytic the catalytic catalytic catalytic catalytic reactionreaction reaction reaction reaction reaction reaction ofof 1-cyclohexylpropa-1,2-diene1-cyclohexylpropa-1,2-dieneof of of1-cyclohexylpropa-1,2-diene 1-cyclohexylpropa-1,2-dieneof of1-cyclohexylpropa-1,2-diene 1-cyclohexylpropa-1,2-diene 1-cyclohexylpropa-1,2-diene 2121 a21. 21. 21 21a. .21 . . .

SubstrateSubstrateSubstrateSubstrateSubstrateSubstrate

ProductProductProductProductProductProduct CompositionComposition Composition Composition Composition Composition Composition

2121 2121 2121

ReactionReactionReactionReactionReactionReaction TimeTime Time Time Time Time

21 22 23 24 25 2121 2121 2121 2222 2222 2222 2323 2323 2323 24 24 24 24 24 24 25 25 25 25 25 25 22 hh2 h22 h2 h h 42% 42% 42% 42% 42% 42% 42% 36% 36% 36% 36% 36% 36% 7% 7% 7% 7% 7% 7% 17% 17% 17% 17% 17% 17% 17% 0% 0% 0% 0% 0% 0% 4 h 0% 63% 9% 28% 0% 44 hh4 h44 h4 h h 0% 0% 0% 0% 0% 0% 63% 63% 63% 63% 63% 63% 9% 9% 9% 9% 9% 9% 28% 28% 28% 28% 28% 28% 0% 0% 0% 0% 0% 0% 24 h24h 24 h2424 h h h 0% 0% 0% 0% 0% 37% 37% 37% 37% 37% 52% 52% 52% 52% 52% 52% 0% 0% 0% 0% 0% 0% 11% 11% 11% 11% 11% 11% 24a h 0% 37% 52% 0% 11% a a a a a Reaction condition, 0.5 mmol cumulene, 5 mol % Pd catalyst (0.025 mmol Pd), 2.5 mL CDCl3, 1 atm H2. a Reaction Reaction Reaction Reaction condition, condition, condition, condition, 0.5 0.5 mmol0.5 0.5 mmol mmol mmol cumulene, cumulene, cumulene, cumulene, 5 mol 5 5mol 5mol %mol %Pd % %Pd catalystPd Pd catalyst catalyst catalyst (0.025 (0.025 (0.025 (0.025 mmol mmol mmol mmol Pd), Pd), Pd), 2.5Pd), 2.5 mL2.5 2.5 mL mLCDCl mL CDCl 3CDCl CDCl3, 13 ,atm3 1, 3 1,atm 1atm2 Hatm 2H. H 2H.2 . 2. ReactionReaction condition,condition, 0.50.5 mmolmmol cumulene,cumulene, 55 molmol %% PdPd catalystcatalyst (0.025(0.025 mmolmmol Pd),Pd), 2.52.5 mLmL CDClCDCl3, , 11 atmatm HH2.. Considering the interesting catalytic property of C8 PdNP for ester conjugated cumulenes, ConsideringConsideringConsideringConsideringConsidering the the interestingthe the interestingthe interesting interesting interesting catalytic catalytic catalytic catalytic catalytic property property property property property of ofC8 of C8of PdNP ofC8 C8 PdNPC8 PdNP PdNP PdNPfor for ester for for esterfor ester esterconjugated ester conjugated conjugated conjugated conjugated cumulenes, cumulenes, cumulenes, cumulenes, cumulenes, the the the the the theConsidering catalytic hydrogenation the interesting of catalytic some other property unsaturated of C8 substratesPdNP for thatester would conjugated generate cumulenes, same conjugated the catalyticcatalyticcatalyticcatalyticcatalytic hydrogenation hydrogenation hydrogenation hydrogenation hydrogenation of ofsome of someof ofsome some otsome herot herot ot unsaturatedherother unsaturatedher unsaturated unsaturated unsaturated substrates substrates substrates substrates substrates that that thatwould that thatwould would would would generate generate generate generate generate same same same same conjugatedsame conjugated conjugated conjugated conjugated catalyticester hydrogenation as the major product of some wasother compared. unsaturated In substrates addition, that dual-substrates would generate catalytic same reactionsconjugated were esteresterester esterasester asthe as theas as majorthe the majorthe major major majorproduct product product product product was was was compared.was wascompared. compared. compared. compared. In Inadditi In additiIn In additi additi on,addition, dual-substrateson,on, dual-substrateson, dual-substrates dual-substrates dual-substrates catalytic catalytic catalytic catalytic catalytic reactions reactions reactions reactions reactions were were were werealso were also also also also esteralso as the attempted major product (Table4 wasand compared. Figures S11–S14). In additi Foron, dual-substrates the catalytic reaction catalytic of reactions ethyl but-3-enoate were also 26, attemptedattemptedattemptedattemptedattempted (Table (Table (Table (Table (Table4 and4 and4 4 and4 Figuresand andFigures Figures Figures Figures S11–S14). S11–S14). S11–S14). S11–S14). S11–S14). For For theFor For Forthe catalyticthe the catalyticthe catalytic catalytic catalytic reaction reaction reaction reaction reaction of ofethyl of ethylof ofethyl ethyl but-3-enoateethyl but-3-enoate but-3-enoate but-3-enoate but-3-enoate 26 ,26 ethyl26 , 26 ethyl26, ,ethyl , ethyl ethyl attemptedethyl trans (Table-but-2-enoate 4 and Figures3, the S11–S14). trans conjugated For the catalytic ester, was reaction obtained of ethyl as the but-3-enoate major product 26, ethyl after the transtranstrans-but-2-enoatetranstrans-but-2-enoate-but-2-enoate-but-2-enoate-but-2-enoate 3, 3the , 3 the3, 3, thetrans, the thetrans trans transconjugatedtrans conjugated conjugated conjugatedconjugated ester, ester, ester, ester,ester,was was was obtawas wasobta inedobta obtaobtainedined inedasined as the as astheas themajor the themajor major major majorproduct product product productproduct after after after aftertheafter the the the the transisomerization-but-2-enoate of3, thethe terminal trans conjugated C=C bond ester, to the was internal obta C=Cined bond.as the Themajor greater product selectivity after the for the isomerizationisomerizationisomerizationisomerizationisomerization of ofthe of theof ofterminalthe the theterminal terminal terminal terminal C=C C=C C=CbondC=C C=C bond bond bond tobond tothe totheto tointernalthe the theinternal internal internal internal C=C C=C C=Cbond.C=C C=C bond. bond. bond. bond.The The The greaterThe Thegreater greater greater greater selectivity selectivity selectivity selectivity selectivity for for thefor for thefor the the the isomerizationisomerization of the over terminal the hydrogenation C=C bond indicatedto the internal that the C=C reaction bond. mostly The greater involves selectivity the mono- forσ bondedthe isomerizationisomerizationisomerizationisomerizationisomerization over over over theover over the hydrogenation the the hydrogenationthe hydrogenation hydrogenation hydrogenation indicated indicated indicated indicated indicated that that thatthe that thatthe reaction the the reactionthe reaction reaction reaction mostly mostly mostly mostly mostly involves involves involves involves involves the the mono- the the mono-the mono- mono- mono-σ bondedσ bondedσσ bondedσ bonded bonded isomerizationbranched Pdover alkyl the intermediate.hydrogenation In indicated comparison, that the reaction reaction mostly of 1 that involves produced the themono- cis isomerσ bonded as the branchedbranchedbranchedbranchedbranched Pd Pd alkyl Pd Pdalkyl Pd alkyl alkylintermediate. alkyl intermediate. intermediate. intermediate. intermediate. In Incomparison, In comparison,In In comparison, comparison, comparison, the the reaction the the reactionthe reaction reaction reaction of of1 thatof 1of ofthat1 1 thatproduced1 that thatproduced produced produced produced the the cis the the cis theisomer cis cisisomer cis isomer isomer isomer as asthe as theas as the the the branchedinitial Pd major alkyl product intermediate. would take In comparison, place via the the di- reactionσ bonded of Pd 1 that alkyl produced intermediate. the cis The isomer hydrogenation as the initialinitialinitialinitial majorinitial major major major productmajor product product product product would would would would would take take takeplace take take place place placevia place via the via via thevia di- the the di-theσ di-bonded σdi- di- bondedσσ bondedσ bonded bonded Pd Pd alkyl Pd Pdalkyl Pd alkyl alkylintermediate. alkyl intermediate. intermediate. intermediate. intermediate. The The hydrogenationThe The Thehydrogenation hydrogenation hydrogenation hydrogenation initialof themajor substrate, product26 would, via the take di- placeσ bonded via the Pd di- alkylσ bonded intermediate Pd alkyl was intermediate. only limited The to hydrogenation ~17%, which was of oftheof theof substrate, ofthe the substrate,the substrate, substrate, substrate, 26 ,26 via 26, 26 via26 ,the ,via ,via thevia di- the the di-theσ di- bondedσdi- di- bondedσσ bondedσ bonded bonded Pd Pd alkyl Pd Pdalkyl Pd alkyl alkylintermediate alkyl intermediate intermediate intermediate intermediate was was wasonly was wasonly only limitedonly only limited limited limited limited to to~17%, to ~17%,to to~17%, ~17%, ~17%,which which which which whichwas was was was was of theresulted substrate, from 26 the, via impediment the di-σ bonded of ethyl Pd but-3-enoate alkyl intermediate26 in establishing was only limited the strong to ~17%,π bond which coordination was resultedresultedresultedresultedresulted from from from fromthe from the impediment the the impedimentthe impediment impediment impediment of ofethyl of ethyl of ofethyl ethylbut-3-enoate ethyl but-3-enoate but-3-enoate but-3-enoate but-3-enoate 26 26in 26 inestablishing26 26 in establishing in inestablishing establishing establishing the the strong the the strongthe strong strong strong π bondπ πbond π bondπ bondcoordination bond coordination coordination coordination coordination resultedon to from the poisonedthe impediment Pd surface. of ethyl On but-3-enoate the other hand, 26 in establishing the catalytic the reaction strong ofπ bond ethyl coordination but-2-ynoate 27 onon toon on totheon totheto topoisonedthe the poisonedthe poisoned poisoned poisoned Pd Pd surface.Pd Pd surface.Pd surface. surface. surface. On On theOn On theOn otherthe the otherthe other other haother hand, ha nd,ha hathend,nd, nd,the catalyticthe the catalyticthe catalytic catalytic catalytic reaction reaction reaction reaction reaction of ofethyl of ethylof ofethyl ethyl but-2-ynoateethyl but-2-ynoate but-2-ynoate but-2-ynoate but-2-ynoate 27 27 27 27 27 on tomostly the poisoned produced Pd the surface. mono-hydrogenation On the other products,hand, the with catalytic ethyl cisreaction-but-2-enoate of ethyl2 asbut-2-ynoate the major product, 27 mostlymostlymostlymostlymostly produced produced produced producedproduced the the mono-hydro the thethemono-hydro mono-hydro mono-hydromono-hydrogenationgenationgenationgenationgenation products, products, products, products,products, with with with withethylwith ethyl ethyl ethylcisethyl cis-but-2-enoate cis-but-2-enoate ciscis-but-2-enoate-but-2-enoate-but-2-enoate 2 as2 2as 2the 2 as asthe as major the the themajor major major major mostlyafter produced 24 h. It showedthe mono-hydro that the hydrogenationgenation products, reaction with via ethyl the cis di--but-2-enoateσ bonded Pd-alkyl 2 as the intermediate major product,product,product,product,product, after after after after24after 24 h. 24 24h.24It h. h.Itshowed h. Itshowed It It showed showedshowed that that thatthe that thatthe thehydrogenation the thehydrogenation hydrogenation hydrogenationhydrogenation reaction reaction reaction reactionreaction via via thevia via viathe thedi- the thedi-σ di- σdi-bondeddi- σbondedσ σ bonded bondedbonded Pd-alkyl Pd-alkyl Pd-alkyl Pd-alkylPd-alkyl product,was theafter major 24 routeh. It showed producing that the the cis-product. hydrogenation The smallreaction amount via the of remainingdi-σ bonded substrate Pd-alkyl after a intermediateintermediateintermediateintermediateintermediate was was wasthe was wasthe majorthe the themajor major major majorroute route route routerouteproducing producing producing producingproducing the the cis-product.the the thecis-product. cis-product. cis-product.cis-product. The The Thesmall The Thesmall small small smallamount amount amount amountamount of of remaining of ofremaining of remaining remainingremaining intermediate24 h reaction was indicated the major that route thishydrogenation producing the of cis-product. ethyl but-2-ynoate The small27 is kineticallyamount of slower remaining than the substratesubstratesubstratesubstratesubstrate after after after aafter after24 a 24ah a 24reaction ah24 24 reactionh h reactionh reaction reaction indicated indicated indicated indicated indicated that that thatthis that thatthis hydrogenationthis this thishydrogenation hydrogenation hydrogenation hydrogenation of ofethyl of ethylof ofethyl ethylbut-2-ynoate ethyl but-2-ynoate but-2-ynoate but-2-ynoate but-2-ynoate 27 27is 27 kineticallyis27 27 iskinetically is iskinetically kinetically kinetically substratereactions after of a 124and h reaction26. When indicated the reaction that this was hydrogenation continued beyond of ethyl 24 but-2-ynoate h, the subsequent 27 is kinetically isomerization slowerslowerslowerslowerslower than than than thethan than the reactions the the reactionsthe reactions reactions reactions of of1 andof 1of ofand1 1 and261 and and.26 When 26. 26When 26. .When .When Whenthe the reaction the the reactionthe reaction reaction reaction was was wascontinued was wascontinued continued continued continued beyond beyond beyond beyond beyond 24 24h, 24 h,the24 24 h, theh, subsequent h,the the subsequentthe subsequent subsequent subsequent slowerofthe than cis the conjugated reactions of ester 1 and2 to 26 the. When trans the conjugated reaction was ester continued3 took place beyond as indicated24 h, the subsequent by the results isomerizationisomerizationisomerizationisomerizationisomerization of ofthe of theof ofcisthe the cisthe conjugated cis cisconjugated cis conjugated conjugated conjugated ester ester ester ester2 ester to2 to2the 2 to2 theto totransthe the transthe trans transconjugated trans conjugated conjugated conjugated conjugated ester ester ester ester3 ester took3 took3 3 took 3 placetook took place place place asplace asindicated as indicatedas as indicated indicated indicated by by by by by isomerizationanalyzed after of the48 cis h of conjugated reaction. The ester presence 2 to the of trans the unreacted conjugated alkyne ester substrate, 3 took place27, seems as indicated to slow by down thethe resultsthethe resultsthe results results results analyzed analyzed analyzed analyzed analyzed after after after 48after after 48h 48 ofh48 48 ofhreaction. h of h reaction.of ofreaction. reaction. reaction. Th The Thpresence eTh Thpresenceee presencee presence presence of ofthe of theof unreacted ofthe the unreactedthe unreacted unreacted unreacted alkyne alkyne alkyne alkyne alkyne substrate, substrate, substrate, substrate, substrate, 27, 27, seems 27, 27,seems 27, seems seems seems the resultsthe isomerization analyzed after of the 48 h cis of conjugated reaction. Th estere presence2 to the of trans the unreacted conjugated alkyne ester substrate,3. The dual-substrates 27, seems to toslow toslowto toslow downslow slow down down down thedown the isomerization the the isomerizationthe isomerization isomerization isomerization of ofthe of theof cis ofthe the cis theconjugated cis cisconjugated cis conjugated conjugated conjugated ester ester ester 2ester ester to 2 tothe2 2 to2 theto trans tothe the transthe trans transconjugated trans conjugated conjugated conjugated conjugated ester ester ester 3ester ester. The3. 3The 3. 3.dual-The .The Thedual- dual- dual- dual- to slowcatalytic down reactions the isomerization comparing of the the combinations cis conjugated of ester1 and 2 26to thevs. 1transand conjugated27 provided ester additional 3. The dual- evidence substratessubstratessubstratessubstratessubstrates catalytic catalytic catalytic catalyticcatalytic reactions reactions reactions reactionsreactions comparing comparing comparing comparingcomparing the the combinationsthe the thecombinations combinations combinationscombinations of of1 of ofand1 of 1and 1 1 and26 and and 26 vs. 26 26vs. 26 1 vs. vs.and1vs. 1and 1 1 and27 and and 27 provided 27 27provided27 provided providedprovided substratessupporting catalytic the slow reactions hydrogenation comparing activity the ofcombinations ethyl but-2-ynoate of 1 and27. The26 vs. presence 1 and of 27 alkyne provided substrate additionaladditionaladditionaladditionaladditional evidence evidence evidence evidenceevidence supporting supporting supporting supportingsupporting the the slowthe the theslow slow slowhyslow hydrogenation hydrogenation hyhydrogenationdrogenationdrogenation activity activity activity activityactivity of of ethyl of ofethyl of ethyl ethylbut-2-ynoateethyl but-2-ynoate but-2-ynoate but-2-ynoatebut-2-ynoate 27 .27 The 27. 2727The. . The. The The additionalalso inhibited evidence or supporting slowed the the subsequent slow hy isomerizationdrogenation activity of the cisof conjugatedethyl but-2-ynoate ester 2 to27. the The trans presencepresencepresencepresencepresence of ofalkyne of ofalkyne of alkyne alkynealkyne substrate substrate substrate substratesubstrate also also alsoinhibited also alsoinhibited inhibited inhibitedinhibited or or slowed or orslowedor slowed slowedslowed the the subsequentthe the thesubsequent subsequent subsequentsubsequent isomerization isomerization isomerization isomerizationisomerization of ofthe of ofthe of cisthe the thecis cis ciscis presenceconjugated of alkyne ester substrate3. All these also results inhibited indicated or slowed that C8 the PdNP subsequent has a highly isomerization predictable of selectivity the cis to conjugatedconjugatedconjugatedconjugatedconjugated ester ester ester ester 2ester to2 to2 the2 to2 theto totransthe the transthe trans trans conjugatedtrans conjugated conjugated conjugated conjugated ester ester ester ester 3ester. 3All. 3 All3. 3these.All .All theseAll these these resultsthese results results results results indicated indicated indicated indicated indicated that that that C8that thatC8 PdNPC8 C8 PdNPC8 PdNP PdNP PdNPhas has ahas has hasa a a a conjugatedform different ester 2 isomersto the trans based conjugated on the structure ester 3. of All substrates these results and theindicated formation that ofC8 different PdNP has reaction a highlyhighlyhighlyhighlyhighly predictable predictable predictable predictable predictable selectivity selectivity selectivity selectivity selectivity to toform to formto toform formdifferent form different different different different isomers is omersis is omersisomers omersbased based based based basedon on the on onthe on structurethe the structurethe structure structure structure of ofsubstrates of substratesof ofsubstrates substrates substrates and and andthe and andthe the the the highlyintermediates predictable as selectivity the results to of form both different surface crowdingisomers based and partial on the poisoningstructure effectsof substrates [26–28 ].and the formationformationformationformationformationformation ofof ofdifferentdifferent of differentof ofdifferent different different reactionreaction reaction reaction reaction reaction intermediatesintermediates intermediates intermediates intermediates intermediates asas asthethe as asthe as resultsresultsthe the theresults results results results ofof ofbothboth of bothof of both surfacebothsurface both surface surface surface surface crowdingcrowding crowding crowding crowding crowding andand and partialand partialand andpartial partial partial partial poisoningpoisoningpoisoningpoisoningpoisoningpoisoning effectseffects effects effects effects effects[26–28].[26–28]. [26–28]. [26–28]. [26–28]. [26–28].

Catalysts 2018, 8, 428 7 of 10

CatalystsCatalystsCatalystsCatalysts 20182018 2018Catalysts,, 88,,, x82018x , FOR FORx 2018FOR, 8 PEER,PEER ,x PEER8 FOR, x REVIEWFORREVIEW PEERREVIEW PEER REVIEW REVIEW 77 ofof7 of 1010 10 7 of7 10 of 10 CatalystsCatalystsCatalysts 2018 2018Catalysts, 8,, x20188 ,FOR x 2018FOR, 8 PEER, x, PEER8FOR, x REVIEWFOR PEER REVIEW PEER REVIEW REVIEW 7 of7 of10 107 of 710 of 10 CatalystsCatalystsCatalysts 2018 2018Catalysts, 8,, 2018 8x, FORx 2018 FOR, 8, PEERx, 8PEERFOR, x FORREVIEW PEER REVIEW PEER REVIEW REVIEW 7 of7 of 10 10 7 of7 10 of 10 CatalystsTableCatalystsCatalysts 4.2018 CatalystsThe2018, 8 Catalysts2018, ,x 8 single-substrateFOR, ,x 20188 FOR, xPEER 2018 FOR, 8PEER, x, REVIEW8PEERFOR, x REVIEW FOR PEER REVIEW PEER andREVIEW REVIEW dual-substrates catalytic reaction of various unsaturated7 of 7 10 of7 10 of esters. 107 of7 10 of 10 CatalystsCatalystsCatalysts 2018TableCatalysts Table2018, Table8 2018,Catalysts x, 8FOR 4.,4. ,Tablex 201884. TheThe,FOR x TablePEERThe 2018FOR, single-substrate8 single-substratePEER4., xsingle-substrate , REVIEWThe PEER8FOR4., x TheREVIEW FORsingle-substrate PEER REVIEW single-substrate PEER REVIEW and andREVIEW and dual-substratesdual-substrates dual-substrates and and dual-substrates dual-substrates catalycataly catalytictic catalytic reactionreaction cataly reactiontic reactiontic ofof reaction of variousvarious various of various of unsaturatedunsaturated unsaturatedvarious unsaturated unsaturated esters.esters. esters.7 of 7esters.10 of 7esters. 10of 10 7 of 710 of 10 TableTable 4.Table 4.The TableThe single-substrate4. single-substrate The 4. The single-substrate single-substrate and and dual-substrates dual-substratesand and dual-substrates dual-substrates cataly catalytic catalytic reaction cataly reactiontic reactiontic of reaction ofvarious various of various ofunsaturated unsaturatedvarious unsaturated unsaturated esters. esters. esters. esters. Table 4.Table The 4.single-substrate The single-substrate and dual-substrates and dual-substrates catalytic cataly reactiontic reaction of various of various unsaturated unsaturated esters. esters. Table 4.Table The single-substrate 4. The single-substrate and dual-substrates and dual-substrates catalytic cataly reactiontic reactionof various of variousunsaturated unsaturated esters. esters. Table TableTable 4. The 4. Table The4. single-substrateTable The Reactantsingle-substrate 4.Reactant Reactant single-substrateThe 4.Reactant The single-substrateReactant single-substrate Reactant and and dual-substrates and dual-substrates dual-substratesand and dual-substrates dual-substrates cataly cataly catalytic ticreaction cataly ticreaction cataly reactiontic of reaction tic variousof reaction variousof various Product Product ofunsaturated Product various unsaturatedof Product variousunsaturatedProduct Product unsaturated esters. unsaturated esters. esters. esters. esters. Table TableTable 4. The 4. Table The4. single-substrate TableThe single-substrate 4.Reactant single-substrate The Reactant4. The single-substrateReactant single-substrate Reactant and and dual-substrates and dual-substrates dual-substratesand and dual-substrates dual-substrates cataly cataly catalytic reactiontic cataly ticreaction catalyreactiontic of reactionvarioustic of reactionofvarious various Product unsaturatedof Product various unsaturatedof Productunsaturatedvarious Product unsaturated esters. unsaturated esters. esters. esters. esters. ReactantReactantReactant Reactant Product Product Product Product ReactantReactantReactant Reactant Reactant Product Product Product Product Product Trial ReactantReactantReactant Reactant Reactant ++ + Product Product+ Product Product Product++ + + TrialTrial TrialTrial + + + + Trial 1TrialTrial TrialTrial + + + + + + + + 1 aa + + + + Trial1Trial 1 Trial1 Trial 1 1 a a a 2 + +3 + +4 TrialTrial 1 1 Trial1 1 11 1 1 a 1 2 2 + 2 + 2+ + +3 3 3+3 +3 + + 4+ 4 4 4 1Trial 1 Trial 1 a 1 a 1 a 1 a 2 2 2 + 2 3 3 3 +3 4 4 4 4 TrialTrial Trial1 Trial Trial 1 0% a a a 27% + + + 69%+ + + + 4%+ 1 1 1 1 0%1 0%1 a 1 0% 0%1 27% 2 27% 2 27%2 27% 2 69%3 69% 3 69%3 69% 3 4%4 4% 4 4%4 4% 4 1 1 a 0%1 0% a 0% a 0%1 a 0%a 2 27%2 27% 27%2 27% 3 69%3 69% 69%69%3 69% 4 4%4 4% 4%4 4% 1 1 1 1 1 a 1 1 2 2 3 3 4 4 1 a 1 0% 0%1 a 0%1 a 0%1 a 2 27%2 27%2 27%2 27% 2 3 69%3 69%3 69%3 69% 3 4 4%4 4%4 4%4 4%4 0% 0% 0% 0% 0% 27% 27% 27% 27% 27% 69% 69% 69% 69% 69% 4% 4% 4% 4% 4% Trial 0% 0% 0% 0% 0% 27% 27% 27% 27% + 27%+ + 69% 69% + 69% 69% 69% + + + 4% 4%+ 4% 4% 4% TrialTrial TrialTrial + + TrialTrial TrialTrial + + + + + + + + + + 2 a + + + + Trial 2 Trial2Trial 2 Trial2 Trial 2 26 a a a 2 + +3 + +4 TrialTrial 2 2 Trial2 2 26 26a 26 a26 2 2 + 2 + 2+ + +3 3 +3 +3 + + 4+ 4 4 4 2Trial 2 Trial 2626 26a a 26 a 26 a 2 2 2 + 2 3 3 3 3 +3 4 4 4 4 TrialTrial Trial2 Trial Trial 2 0% a a a 7% + + + 76%+ + + + 17%+ 2 2 2 2 0%26 26 0% a 26 0% 26 0% 7%2 7% 2 7%2 7% 2 76%3 76% 3 76%3 76% 3 17%4 17% 4 17%4 17% 4 2 26 a26 0% a 0% a 26 0% a 0%a 2 7%2 7% 7%2 7% 3 76%3 76% 76%3 76% 4 17%4 17% 17%4 17% 2 2 2 2 2 a26 26 2 2 3 3 4 4 26 a 260% 0% 26 0% a 26 0% a 0%26 a 2 7%2 7%2 7%2 7% 2 3 76%3 76%3 76%76%3 76% 3 4 17%4 17%4 17%4 17% 4 0% 0% 0% 0% 0% 7% 7% 7% 7% 7% 76% 76% 76% 76% 76% 17% 17% 17% 17%17% 0% 0% 0% 0% 0% 7% 7% 7% 7% 7% 76% 76% 76% 76% 76% 17% 17% 17% 17%17% ++ + + + ++ + + + Trial + + + + + + + + TrialTrial TrialTrial TrialTrial TrialTrial + + + + + + + + + + 3 aa a a Trial3Trial 3 Trial3 Trial 3 2727 27 27 a27 22 2 + 2 + 2+ + +33 3 +3 +3 + + 4+4 4 4 4 TrialTrial 3 3 Trial3 Trial 3 27 a a 27 a a 2 + 2 + + + 3+ + 3 + + + 4+ 4 Trial 3 Trial 27aa a 27 2 2 3 3 4 4 TrialTrial 3Trial 3 Trial3 Trial 3 27 3%27 3% 27 3% a 27 3% 27 3% a 86% 86%2 86% 2 86%2 86% 2 10%10%3 10% 3 10% 3 10% 3 1%1%4 1% 4 1%4 1%4 4 3 3 a a a a a 3 3 3 27 27 3% 27 3% b 27 3% 27 3% 2 86%2 86%2 b 86%2 86% 2 3 10%3 10%3 b 10%3 10% 3 4 1%4 1% b4 1%4 1%4 3 3 3 3 3 27 a 0%270% 3% 0%a27 3% b ab 0%27 3% a 0%b 3%27 ab 2 23%23% 86%223% 86% 2b b 23% 86%2 23% 86% b 2 b 3 73% 73%10%3 73% 10% 3b b 73%10%3 73%10% b 3 b 4 4% 4%1%4 4%1% b4 b 4%1%4 4%b1% 4 b 3% 0% 3% 0% 3%b b 0% 3% b0% 3% b 86% 23% 86% 23% 86% 86% b b 23% 86% 23% 86% b b 10% 73%10% 73% 10% b b 73%10%10% 73% 10%b b 1% 4%1% 4% 1%b b 4%1% b 4%1% b 3% 3%0% 0% 3%b b b 0% 3% b0% 3% b 86% 86%23% 23% 86% b b 23% 86% 23% b 86% b 10% 10% 73% 73% 10% b b 73%10% 73% b10% b 1% 1% 4% 4% 1% b b 4%1% b 4% 1% bb 0% 0%b 0%b b 0% b0% b 23% 23% b 23%23% b b23% 23% b b 73% 73% b 73% b 73%b 73% 73% b b 4% 4%b 4%b b 4% b 4% b + b0% 0% b b 0% b b 23%b 23% b b 23% b+ b 73%b 73% b b 73% b + b b 4% 4% b b 4% b b TrialTrialTrial TrialTrial + + 0%+ + 0% 23% 23%+ + 73%+ + 73%+ + 4%+ + 4% TrialTrial TrialTrial + + + + + + + + + + + + 4 + + + + + + Trial4Trial 4 Trial4 Trial 4 1 c c c c + 26+ cc c c 2 + +3 + + 4 TrialTrial 4 4 Trial4 4 1 1 +1 c +1 + + 26+ 26 26 c26 2 2 + 2 + 2+ + +3 3 +3 +3 + + 4+ 4 4 4 4Trial 4 Trial1 c 1 c 1 c+ 1+ c 26 26c c 26 c 26 c 2 2 2 + 2 + 3 3 3 +3 + 4 4 4 4 TrialTrial 4Trial Trial4 TrialTrial 4 0% c + c c + + 0%+ c c c 22% + + + 67%+ + + + 11%+ 4 4 4 c 40% 10%1 c 0%1 0%1 0%26 26c0% c 260% 26 0% 22% 2 22% 2 22%2 22% 2 67%3 67% 3 67%3 67% 3 11% 4 11% 4 11% 4 11% 4 4 11 c 10% c 0% c 0%1 c 0% c 26 c26 0% c0% c 260% c 0%c 2 22%2 22%2 22%2 22% 3 67%3 67% 67% 33 67% 4 11% 4 11% 11% 4 11% 4 4 4 4 4 4 c 1 1 c26 26 2 2 3 3 4 4 1 c 10% 0%1 c 0%1 c 0%1 c 26 c 260% 260% c 260% c 0%26 c 2 22%2 22%2 22%2 22% 2 3 67%3 67%3 67%3 67% 3 4 11% 4 11% 4 11% 4 11% 4 0% 0% 0% 0% 0% 0% 0% 0% 0% 0% 22% 22% 22% 22% 22% 67% 67% 67% 67% 67% 11% 11% 11% 11%11% 0% 0%0% 0% 0% 0% 0% 0% 0% 0% 22% 22% 22% 22% 22% 22% 67% 67% 67% 67%67% 67% 11% 11% 11% 11% 11%11% TrialTrialTrial Trial ++ + + + ++ + + + ++ + + + Trial + + + + + + + + + + + + Trial5Trial TrialTrial Trial5Trial 5 Trial5 Trial 5 + + + + + + + + + + + + cc c c cc c c TrialTrial 5Trial 5 Trial5 Trial 5 11 1 +1 c +1 + + 2727+ 27 27 c27 22 2 + 2 + 2+ + +33 3 +3 +3 + + 4+4 4 4 4 Trial5Trial 5 Trial5 5 1 c c 1+ c + c + + 27+ c c 27 c c 2 + 2 + + + 3+ + 3 + + + 4+ 4 Trial Trial c1 c+ 1 27 c c 27 2 2 + 3 3 + 4 4 Trial5 5 5 5 5 50% 0%1 0%1 c 10% 0%1 c 0%270% 270% c 270% 270% c 66% 66%2 66% 2 66%2 66% 2 32%32%3 32% 3 32%3 32% 3 2%2%4 2% 4 2%4 2%4 5 5 5 51 c 510% c 0%1 c 0%1 c 0%1 c 27 c27 0% c270% c 270% c 270% c 2 66%2 66%2 66%2 66% 2 3 32%3 32%3 32%3 32% 3 4 2%4 2% 4 2%4 2%4 aa a c 10% ca c 0%c c c 270% c c 0%c c 66%2 66% 3 32%3 232% 2%4bb b 2% b 0.50.5 0.5 mmolmmol11 mmola 0.5 0% substrate, 1 substrate,0.5mmol substrate, mmol1 substrate,0%1 5substrate,5 molmol5 mol27 % % 5 27 % PdPdmol 270%5Pd catalystmolcatalyst %catalyst27 Pd % 0% 27Pdcatalyst (0.025(0.025 (0.025catalyst mmolmmol (0.025 mmol (0.025 2 Pd), Pd), mmol Pd), mmol 66% 2.52.52 2.5 Pd), mLmL mLPd),2 CDCl2.5 66%CDCl 2CDCl 2.5mL 3 ,mL, 3 CDCl131 , atmatm1 CDCl atm32% 3 H,H 1 2H 3,atm, , 24 2 32413, 24atm 32% h hH 3 reaction;hreaction; 2 , H reaction;242, h244 reaction; h reaction;482% 484 48 b4 482% 44 48 a a 0%a 0%a 0% 0% 0% 0% 0% 0% 0% 0% 66% 66% 66% 66% 66% 332% 32% 32% 3 2 32% 32% 2 2% 2%b 2%b 2%b 2%b a 0.5 0.5 mmol mmola 0.5 substrate, 0.5mmol substrate, mmolc substrate, 5substrate, mol 5 mol % 5 %Pdmol 5Pd catalystmol % catalyst Pd % catalystPd (0.025 (0.025catalyst mmol (0.025 mmol (0.025 Pd), mmol Pd), mmol 2.5 2.5Pd), mL mLPd), 2.5CDCl CDCl 2.5mL ,mL CDCl13, atm 1 CDCl atm ,H 1 H ,3atm ,24 21, 24 atmh H reaction;h, Hreaction;242, h24 reaction; h b reaction;48 48 b 48 48 h 0.5areaction mmol0% 0.50%a time;0% substrate,mmol 0% c Eachsubstrate,c 0% 5 individualmolc 0%c %5 0% molPd 0% catalyst % substrate 0%Pd catalyst0% (0.025 is 0.25 mmol(0.025 mmol, 66% Pd),mmol 66% 66%5 2.5 mol Pd), mL 66% % 2.5 CDCl 66% Pd mL catalyst32%3 ,CDCl 1 32% atm 32% 3(0.0125 , H1 32atm,32% 24 32%mmol), Hh reaction;2, 242 2%h 2.5 reaction; 2% mL 2% 48b 2% 48 2%b a ah reactionh 0.5 reaction0% mmolah reaction ahtime; 0.5 reaction time;substrate, mmol Each time; Each time;substrate, individual5 Eachmolindividual Each 0%% individual 5Pd molindividual substrate catalyst substrate % Pd substrate catalyst (0.025 issubstrate is0.25 0.25 mmol mmol, is(0.025 mmol,0.25 is Pd),0.25 mmol5 66%mmol, mol5 2.5 mmol,mol %mLPd), 5 % Pdmol CDCl 5 Pd2.5 molcatalyst % catalystmL 3 Pd,% 1 CDCl Pdatmcatalyst (0.0125 catalyst(0.0125 H 32%, 21, atm24 (0.0125mmol), mmol),h(0.0125 Hreaction;, mmol),24b2.5 2.5hmmol),b mL reaction; mL 48 2.5 b2.5mL 2% bmL 48 0.5a mmol 0.5 substrate, mmolc substrate,c 5 molc c% 5 Pd mol catalyst % Pd catalyst (0.025 mmol (0.025 Pd), mmol 2.5 Pd),mL CDCl2.53 mL3, 1CDCl3 atm2 3H, 12, 3 atm242 h H reaction;2, 242 h reaction; 48b 48 0.5ah mmol reactionha 0.5reaction mmol hasubstrate, reaction htime; 0.5 reaction time;substrate, mmol c Eachtime;5 molEach time;substrate, individual c 5% Eachindividualmol Pd Each %catalystindividual 5Pd molindividual substrate catalyst substrate %(0.025 Pd substrate catalyst(0.025 is mmolsubstrate is0.25 0.25 mmol Pd),mmol,is (0.025 mmol,0.25 is 2.5 Pd),0.25 5mmol,mmol mL mol5 2.5 mmol,mol CDCl % mLPd),5 %Pdmol 5CDCl Pd,2.5 1catalystmol % atm catalystmL Pd %, 1 HCDCl Pdcatalystatm (0.0125, 24 catalyst(0.0125 H h, 1 ,reaction; atm(0.012524mmol), mmol),h(0.0125 Hreaction;, mmol),242.5 48 2.5hmmol), b mL reaction; bmL 482.5 2.5bmL mL 48 a 0.5 CDClh0.5mmol reaction 0.5 mmol3 ,mmol h substrate,1 0.5reaction atm asubstrate,time; mmol0.5 substrate, H mmol2 , time;5 24Eachsubstrate,c mol h5 substrate, reaction.mol individual5% Each mol Pdc % 5 catalystPd %individualmol 5Pd catalyst mol %substrate catalyst Pd (0.025% catalyst Pd(0.025substrate (0.025catalyst mmolis 0.25 mmol (0.025 mmol Pd), ismmol, (0.025 0.25 Pd), mmol2.5 Pd), mmol, mmol52.5mL mol 2.5 Pd),mL CDCl mL%Pd),5 CDCl2.5 molPd 3CDCl, mL2.51 catalyst %3atm, mL 1CDClPd3 ,atm 1H CDCl catalystatm2 , 3(0.0125 H,24 12 H ,atm3h 24, 2 1reaction;, (0.012524hatm mmol),H reaction; h2, reaction;H242 , mmol),h b 24 2.5 48reaction; h mL 48reaction; 482.5 mL 48 b 48 a CDClhCDCl reaction3, CDCl13, atm1hCDCl atm reactiontime;c3 H, 1 2Hc 3,atm, 242 1,c 24atm Eachh time;H reaction.h2 c, H reaction. 24individual2 ,c h24Each reaction. h reaction. individual substrate substrate is 0.25 mmol, is 0.25 5 mmol, mol % 5 Pd mol catalyst % Pd catalyst(0.0125 mmol),(0.0125b 2.5mmol), mL 2.5 mL h reactionh reaction3 htime;3 reaction time;h reaction3 Each 23 Each 2time; individual time; individual2 Each2 Each individualsubstrate individualsubstrate is substrate 0.25 is substrate 0.25 mmol, mmol, is 0.25 is5 mol0.25 5mmol, mol %mmol, Pd% 5 Pdcatalystmol 5 catalystmol % Pd %(0.0125 Pd catalyst(0.0125 catalyst mmol), (0.0125mmol), (0.0125 2.5 mmol), 2.5mL mmol),mL 2.5 2.5mL mL 0.5 mmolCDCl substrate,CDClh reaction, CDCl1, atm1CDCl atm 5ctime; ,Hmol 1 Hc,atm ,24 1 , %c 24 atmEachh H Pd reaction.h, c Hreaction.24 catalystindividual, c h24 reaction. h reaction. (0.025 substrate mmol is Pd), 0.25 2.5 mmol, mL CDCl5 mol 3%, 1Pd atm catalyst H2, 24 (0.0125 h reaction; mmol), 482.5 h mL reaction time; c h reactionhCDCl reactionCDClh reaction3 ,CDCltime;h 31, reaction1atm CDCltime;h atm 3reactiontime; , EachH1 H32atm, , Each2124time; , atmindividual24Each Hh time; h2reaction.individual , H reaction.24 Eachindividual2, h24 Each reaction. individualhsubstrate reaction. individualsubstrate substrate is substrate 0.25 is substrate 0.25is mmol, 0.25 mmol, is mmol,0.25 5is mol 0.25 5mmol, mol 5% mmol,mol Pd % 5 %Pdcatalystmol 5Pd catalystmol % catalyst Pd (0.0125% catalystPd (0.0125 (0.0125catalyst mmol), (0.0125mmol), mmol), (0.0125 2.5 mmol),2.5mL 2.5 mmol),mL mL 2.5 mL2.5 mL Each individualCDClCDCl3CDCl, 13 atm, 1CDCl3 substrate,atm 1HCDCl atm2 3,H ,24 12 , H3 atm,h24 21 ,reaction. is atm24h H 0.25reaction. h2, Hreaction.242mmol,, h24 reaction. h reaction. 5 mol % Pd catalyst (0.0125 mmol), 2.5 mL CDCl3, 1 atm H2, 24 h reaction. 3.3.CDCl 3. MaterialsMaterials MaterialsCDCl3CDCl, 1 3.3atm, 1CDClMaterials3 ,andatmand 1H CDCl andatm2, 3 H ,24Methods Methods12 MethodsH, 3atm h,24 2 1reaction., and 24atmh H reaction. h2, MethodsHreaction. 24 2 , h 24 reaction. h reaction. 3. 3.Materials Materials3.3. MaterialsMaterials3. Materials and and Methods andMethodsand and MethodsMethods Methods 3.3. Materials Materials3. Materials3. Materials and and Methods andMethods and Methods Methods 3. Materials3. Materials3. Materials3. Materials 3.and Materials and Methods and Methods andMethods and Methods Methods 3. Materials3. Materials3.3.1.3.1. 3.1.Materials3. MaterialsMaterials and Materials3. Materials 3.1.and3. Methods Materialsand MaterialsMethods and Methods andMethods and Methods Methods 3.1.3.1. Materials Materials3.1.3.1.3.1. MaterialsMaterials Materials 3.1.3.1. Materials Materials3.1.3.1. Materials Materials 3.1.3.1. Materials3.1. MaterialsAllAll Materials3.1.All reagentsreagents3.1. Materialsreagents MaterialsAll werereagentswere were purchasedpurchased purchased were purchased fromfrom from thethe the followingfromfollowing following the following supplierssuppliers suppliers suppliers andand and usedused used and asas as receivedreceived used received as withoutreceivedwithout without further furtherwithout further further 3.1.3.1. Materials3.1. MaterialsAll Materials3.1.All reagents 3.1. reagentsMaterialsAll MaterialsAll reagents werereagents were purchased were purchased were purchased purchased from from the from the followingfrom following the the following following suppliers suppliers supplierssuppliers suppliersand and used usedandand andas usedused as received used received asas receivedreceivedas withoutreceived without withoutwithout further without further furtherfurther further 3.1. Materials All reagentsAll reagents were purchasedwere purchased8 from17 thefrom following the following suppliers suppliers and used and asused received as received2 without3 2 without2 further further purification.purification.purification.purification.Allpurification. reagents 1-BromooctaneAll 1-Bromooctane1-Bromooctane reagents were1-Bromooctane 1-Bromooctane purchased were (C (C purchased(C8HH8 17H fromBr),(CBr),17 Br),8(CH thesodium178 sodiumHfromBr),sodium 17followingBr), thesodium thiosulfsodium thiosulffollowingthiosulf suppliers thiosulfate atethiosulfate supplierspentahydrate pentahydrate andpentahydrateateate usedpentahydrate andpentahydrate as used received(Na (Na(Na as2OO 2received3O(NaSS without23·5HS·5H(Na22·5HO23O),2O),SO2 2O),without·5H3 Sfurther 2and and·5H2andO), 2 O), furtherand and purification.Allpurification.All reagentspurification.All reagentspurification. reagentsAll 1-BromooctaneAll werereagents1-Bromooctane were reagents werepurchased1-Bromooctane purchased 1-Bromooctanewere purchased were purchased (Cfrom purchased(C8 fromH8 17H fromtheBr),(C17 Br),the8 following(CHfrom the17sodium 8 followingHfromBr),sodium 17following theBr), sodiumthe following suppliersthiosulfsodium followingsuppliersthiosulf suppliers thiosulfate suppliersandthiosulfate suppliersandpentahydrate used andatepentahydrate used ate andusedaspentahydrate asreceivedandpentahydrate used asreceived used received(Na as(Na without receivedas2O without 23received(NaOS 2without3·5HS(Na2·5HO further 2without3O),2S Ofurther22 O),·5Hwithout3 Sfurther2and ·5H 2O),and further 2O), furtherand and All reagentsAll reagents were purchased were purchased 8from17 the8 from17 following the following suppliers suppliers and used and as used received as received2 without3 2 2 without32 further2 2 further substratessubstratespurification.Allpurification.substrates reagentspurification.substratesAllpurification.substrates reagents(ethyl(ethyl (ethyl were 1-BromooctaneAll1-Bromooctane reagents(ethyl buta-2,3-dienoat buta-2,3-dienoat werepurchased1-Bromooctanebuta-2,3-dienoat(ethyl 1-Bromooctane purchasedbuta-2,3-dienoat werebuta-2,3-dienoat from (C purchased(CH8e, e,Hfromthe (Ce, Br),17 benzylbenzyl Br), (CfollowingHbenzyl thee,8 sodiumH Br), fromsodiume, 17benzyl following Br), buta-2,3-dienoate,buta-2,3-dienoate, benzylbuta-2,3-dienoate,sodium the suppliers sodium thiosulf followingbuta-2,3-dienoate,thiosulf suppliersbuta-2,3-dienoate, thiosulf ateandthiosulfate suppliers pentahydrateused andatepentahydrateetet hyl-2-methylethyl-2-methylate usedhyl-2-methylaspentahydrate receivedetpentahydrateand hyl-2-methyl aset hyl-2-methylused received (Na(Na without buta-2,3-dienoate,buta-2,3-dienoate,as Obuta-2,3-dienoate,2 (NaOreceivedS without3 S(Na·5H2buta-2,3-dienoate,·5H Ofurther buta-2,3-dienoate,2SO),O2O),·5H 3without Sfurther 2·5Hand O),and2 O), andfurther and Allpurification.purification.substrates reagentssubstratespurification.substratespurification. purification.substrates 1-Bromooctane(ethyl were(ethyl1-Bromooctane 1-Bromooctane (ethylbuta-2,3-dienoat purchased1-Bromooctanebuta-2,3-dienoat(ethyl 1-Bromooctane buta-2,3-dienoat (Cbuta-2,3-dienoat 8(CH 178(CHBr), from8e,17 HBr), (Ce, 17benzyl Br),sodium8(C Hbenzyle,sodium17 the8 H Br),sodiume,benzyl17 Br),buta-2,3-dienoate, followingbenzylthiosulfbuta-2,3-dienoate,sodium thiosulf sodium buta-2,3-dienoate,thiosulf buta-2,3-dienoate,ate thiosulfate pentahydratethiosulf suppliersate pentahydrate atepentahydrateet hyl-2-methyletate hyl-2-methylpentahydrate etpentahydrate hyl-2-methyl andet(Na hyl-2-methyl(Na 2O used(Na32buta-2,3-dienoate,SO 2buta-2,3-dienoate,·5H32(NaSO2 3·5H S2 as(Nabuta-2,3-dienoate,O),2·5HO 2O),3buta-2,3-dienoate, 2receivedSO2andO),·5H3 Sand2·5H 2O),and 2O), and withoutand purification.purification.diethyldiethylsubstratessubstratesdiethylpurification.substratespurification. buta-1,2-dieno-3,4-dicarbobuta-1,2-dieno-3,4-dicarbo substratesdiethylpurification.buta-1,2-dieno-3,4-dicarbo 1-Bromooctane(ethyl (ethyl1-Bromooctane 1-Bromooctane buta-1,2-dieno-3,4-dicarbo (ethyl buta-2,3-dienoat1-Bromooctanebuta-2,3-dienoat(ethyl 1-Bromooctane buta-2,3-dienoat (Cbuta-2,3-dienoat 8(CH 17(C8HBr),xylate,8xylate,17 e,Hxylate,Br),e,(C 17 benzylsodiumBr),8Hbenzyl(C e, sodium17ethyl 8ethyl HBr),xylate,sodiume,ethylbenzyl17 Br), buta-2,3-dienoate,benzyl thiosulfbuta-2,3-dienoate,sodiumpenta-2,3-dienoate,penta-2,3-dienoate, penta-2,3-dienoate,thiosulf sodium ethylbuta-2,3-dienoate,thiosulf buta-2,3-dienoate,ate thiosulfpenta-2,3-dienoate, ate pentahydratethiosulfate pentahydrate atepentahydrate etet hyl-2-methyl ateandandhyl-2-methyl pentahydrate and et pentahydrate hyl-2-methylethylethyl et(Naethyl hyl-2-methyl (Naand 2 Obut-2-ynoate)(Nabut-2-ynoate) 32S but-2-ynoate)buta-2,3-dienoate,O2 ethylbuta-2,3-dienoate,·5H23(NaOS2 3 ·5HS2(NaO),buta-2,3-dienoate, 2·5HObut-2-ynoate) 2buta-2,3-dienoate,3O), S2O2and2O),·5H 3Swerewere and2 ·5Hwere2O),and 2 O), and wereand substratessubstratesdiethyldiethylsubstratesdiethylsubstrates buta-1,2-dieno-3,4-dicarbo(ethyl substratesdiethyl buta-1,2-dieno-3,4-dicarbo(ethyl (ethyl buta-1,2-dieno-3,4-dicarbobuta-2,3-dienoat buta-1,2-dieno-3,4-dicarbo(ethylbuta-2,3-dienoat (ethylbuta-2,3-dienoat buta-2,3-dienoat buta-2,3-dienoate, xylate,e,benzyl xylate,e,benzyl benzylxylate, xylate,e, ethyl buta-2,3-dienoate,xylate,e,ethyl benzylbuta-2,3-dienoate, benzyl buta-2,3-dienoate,penta-2,3-dienoate,ethylethyl penta-2,3-dienoate, ethylbuta-2,3-dienoate, penta-2,3-dienoate,penta-2,3-dienoate,buta-2,3-dienoate, penta-2,3-dienoate, et hyl-2-methylet hyl-2-methyl etandhyl-2-methyl andet hyl-2-methylethyl etandandethylhyl-2-methyl andbuta-2,3-dienoate, but-2-ynoate)ethylethyl buta-2,3-dienoate, but-2-ynoate) ethylbuta-2,3-dienoate, but-2-ynoate) but-2-ynoate)buta-2,3-dienoate, but-2-ynoate) buta-2,3-dienoate, were were werewere were furthersubstrates purification.substratesobtainedobtaineddiethyldiethylobtainedsubstratesdiethylsubstrates (ethylbuta-1,2-dieno-3,4-dicarbo diethyl obtainedsubstrates frombuta-1,2-dieno-3,4-dicarbofrom (ethylfrom (ethyl buta-1,2-dieno-3,4-dicarbo 1-Bromooctanebuta-2,3-dienoatSigma-AldrichSigma-Aldrich buta-1,2-dieno-3,4-dicarboSigma-Aldrich(ethyl buta-2,3-dienoatfrom buta-2,3-dienoat(ethyl buta-2,3-dienoatSigma-Aldrich buta-2,3-dienoat (St.e,(St. (St.e,benzyl xylate, (CLouis, xylate,Louis, e,benzylLouis,8 H benzylxylate,(St.e, 17 ethylbuta-2,3-dienoate, MO,xylate,MO,Br), ethyl benzyle,MO,Louis,buta-2,3-dienoate, benzyl buta-2,3-dienoate,ethylUSA).penta-2,3-dienoate, USA).sodium penta-2,3-dienoate,USA). ethyl buta-2,3-dienoate,MO, penta-2,3-dienoate, buta-2,3-dienoate,Tetra-Tetra- penta-2,3-dienoate,Tetra-USA). thiosulfate netn-octylammonium-octylammonium nhyl-2-methyl -octylammoniumetTetra- hyl-2-methylet andhyl-2-methyl andnet-octylammonium hyl-2-methyl pentahydrateethyl andetethyl hyl-2-methylandbuta-2,3-dienoate, ethylbut-2-ynoate) buta-2,3-dienoate,bromide but-2-ynoate)bromide ethylbromidebuta-2,3-dienoate, but-2-ynoate) buta-2,3-dienoate,but-2-ynoate) bromidebuta-2,3-dienoate,(TOAB),(TOAB),(Na (TOAB), were were2O 3(TOAB),wereS 2were·5H 2 O), diethyldiethylobtainedobtaineddiethyl buta-1,2-dieno-3,4-dicarboobtaineddiethylobtained buta-1,2-dieno-3,4-dicarbo diethylobtainedfrombuta-1,2-dieno-3,4-dicarbo from buta-1,2-dieno-3,4-dicarbo Sigma-Aldrichfrom from buta-1,2-dieno-3,4-dicarboSigma-Aldrich from Sigma-AldrichSigma-Aldrich Sigma-Aldrich xylate,(St. (St.xylate, Louis,xylate, Louis, (St.(St.ethyl xylate,(St. ethyl Louis,Louis, MO,xylate, ethylMO,Louis,penta-2,3-dienoate, penta-2,3-dienoate, ethyl USA). MO, MO, penta-2,3-dienoate,USA). ethylMO, penta-2,3-dienoate,USA).USA).Tetra- penta-2,3-dienoate,Tetra-USA). nTetra-Tetra--octylammoniumn -octylammoniumTetra-and andnn -octylammonium-octylammoniumethylandn -octylammoniumethyl and ethyl but-2-ynoate)and but-2-ynoate)ethyl bromide but-2-ynoate) ethylbromide but-2-ynoate) bromide bromidebut-2-ynoate) bromide(TOAB),were (TOAB),were were (TOAB),(TOAB), (TOAB),were were diethyldiethylobtaineddiethyl buta-1,2-dieno-3,4-dicarboobtaineddiethyl buta-1,2-dieno-3,4-dicarbo diethylbuta-1,2-dieno-3,4-dicarbofrom buta-1,2-dieno-3,4-dicarbo fromSigma-Aldrich buta-1,2-dieno-3,4-dicarbo Sigma-Aldrich4 xylate,(St.xylate, Louis,xylate, (St.ethyl xylate, ethylLouis, MO, xylate,ethylpenta-2,3-dienoate, penta-2,3-dienoate,ethyl USA).MO,penta-2,3-dienoate, ethyl penta-2,3-dienoate,USA). Tetra- penta-2,3-dienoate, Tetra-n-octylammonium and nand -octylammonium ethyland 2 ethyl and ethylbut-2-ynoate) 4and but-2-ynoate)ethyl but-2-ynoate)bromide ethyl but-2-ynoate) bromide but-2-ynoate) were(TOAB), were were(TOAB), were were and substratessodiumsodiumobtainedsodiumsodium (ethyl borohydrideborohydrideobtainedsodium borohydride from borohydride buta-2,3-dienoate, borohydrideSigma-Aldrich from (NaBH(NaBH (NaBH Sigma-Aldrich (NaBH4),), 4 (NaBH and),and and(St. 4 potassium),potassium potassiumand4Louis,), benzyl and(St. potassium potassiumLouis,MO, tetrachloropalladate(II)tetrachloropalladate(II) tetrachloropalladate(II) buta-2,3-dienoate, USA). MO,tetrachloropalladate(II) tetrachloropalladate(II) Tetra-USA).n -octylammoniumTetra- (K(Kn (K ethyl-2-methyl2-octylammoniumPdClPdCl2PdCl (K4 )2)(K PdCl 4werewere) 2werePdCl bromide4 ) obtainedobtained were 4obtained) were bromide buta-2,3-dienoate, obtained(TOAB), obtainedfromfrom from (TOAB), from from obtainedobtainedsodiumsodiumobtained sodiumobtainedfrom borohydride obtainedsodiumfrom borohydride fromSigma-Aldrich borohydride Sigma-Aldrichfrom borohydrideSigma-Aldrich from (NaBHSigma-Aldrich (NaBH Sigma-Aldrich (NaBH4(St.), 4 (NaBHand),(St. andLouis,(St. 4potassium),Louis, potassiumand4(St.Louis,), andMO,(St. potassium Louis,MO, potassium Louis,MO, USA).tetrachloropalladate(II) tetrachloropalladate(II)USA). MO, USA). tetrachloropalladate(II)MO,Tetra- USA).tetrachloropalladate(II)Tetra- Tetra-USA).n-octylammonium nTetra--octylammoniumn -octylammoniumTetra-n -octylammonium(K n(K2-octylammoniumPdCl2PdCl (K 4) bromide2(KPdCl were4 )bromide 2werePdCl bromide4 )obtained were 4obtained)bromide(TOAB), were (TOAB),bromide obtained (TOAB), fromobtained from(TOAB), (TOAB), from from obtainedobtained from Sigma-Aldrichfrom Sigma-Aldrich4 (St.4 Louis, (St. Louis,MO, USA).MO, USA).Tetra- nTetra--octylammoniumn-octylammonium2 42 bromide4 bromide (TOAB), (TOAB), obtainedAcrosAcrossodiumsodiumAcrosobtained sodiumAcrosfrom(Hampton,(Hampton, (Hampton,borohydridesodiumAcros obtainedborohydride from Sigma-Aldrich(Hampton, borohydride (Hampton, borohydride Sigma-Aldrich NH,NH,from NH, (NaBH (NaBHUSA).USA). NH,Sigma-AldrichUSA). (NaBHNH,(St. ), 4USA).(NaBHEthanol, ),Ethanol,and Ethanol, andLouis,USA).(St. ),potassium Ethanol,andpotassium4),Louis, methanol,Ethanol,andmethanol,MO, (St.potassiummethanol, potassium MO, Louis,USA). methanol,tetrachloropalladate(II) tetrachloropalladate(II) methanol, acetacetUSA). tetrachloropalladate(II)acetTetra-MO,one, one,tetrachloropalladate(II) one, acet Tetra-USA). n andacetand-octylammonium one,and one,ntoluene toluene -octylammoniumTetra-tolueneand and (Ktoluene n (K were were-octylammoniumPdCltoluene 2werePdCl (K obtained bromideobtained(Kwere)PdCl 4obtainedwere) 2werePdCl bromide obtained) obtainedwere 4obtained )from(TOAB),from werefrom bromideobtained (TOAB),Fisher Fisher fromobtained fromFisher fromfrom Fisher (TOAB),from Fisher from diethylsodium buta-1,2-dieno-3,4-dicarboxylate,sodiumAcrosAcrossodium borohydride sodiumAcros(Hampton, borohydride (Hampton,sodiumAcros borohydride (Hampton, borohydride (Hampton, borohydride (NaBHNH, NH,(NaBH (NaBHUSA). NH,4USA).), (NaBHandNH,4), USA).4andEthanol,(NaBH), potassium Ethanol,andUSA). 4potassium), Ethanol,andpotassium4), methanol,Ethanol,and methanol,potassium ethyl tetrachloropalladate(II) potassium tetrachloropalladate(II)methanol, tetrachloropalladate(II)methanol, penta-2,3-dienoate,acet acettetrachloropalladate(II)one, tetrachloropalladate(II) one,acet andacet one,and one,toluene andtoluene (K and 2(K PdCltoluene 2(KwerePdCl toluene 2were4PdCl and) (K were 4 )obtained 2were (KPdCl were4obtained) ethyl2 werePdClobtained 4 obtained)obtained were 4obtainedfrom) but-2-ynoate)werefrom fromobtained Fisher from obtainedFisher fromfrom Fisher from Fisher from were sodiumsodiumAcrossodium borohydrideAcros sodium(Hampton, borohydridesodium borohydride (Hampton, borohydride borohydride(NaBH NH, (NaBH (NaBH USA).NH,4), and(NaBH4), USA). 4and(NaBHEthanol,), potassium and 4potassium), Ethanol,potassiumand4), methanol,and potassium tetrachloropalladate(II) potassium tetrachloropalladate(II)methanol, tetrachloropalladate(II) acet tetrachloropalladate(II)one, tetrachloropalladate(II)3 acet andone, toluene and (K2 (KPdCltoluene (K2 PdClwere24PdCl) (Kwere4 )obtainedwere2 PdCl(Kwere4) 2wereobtainedPdCl 4obtained )obtained were obtained4)from were fromobtained Fisherfrom fromobtained from Fisher from from ScientificScientificAcrosScientificScientific (Hampton, AcrosScientific (Hampton,(Hampton, (Hampton, (Hampton,(Hampton, (Hampton, NH, NH,NH, NH, USA). USA). NH,USA). NH,USA). NH, Ethanol,USA). USA).Chloroform-dChloroform-d Chloroform-dUSA). Ethanol, Chloroform-dmethanol, Chloroform-d methanol,(CDCl(CDCl (CDCl acet 3(CDCl)one,) 3was)was(CDCl acetwas and 3 )purchasedpurchased one, waspurchased3 )toluene was andpurchased purchased toluene fromwerefrom from obtainedCambridgeCambridge from wereCambridge from Cambridgeobtained Cambridgefrom IsotopeIsotope Isotope Fisher from Isotope Isotope Fisher AcrosAcrosScientificScientificAcros (Hampton, (Hampton,AcrosScientific (Hampton, AcrosScientific(Hampton, (Hampton, (Hampton, NH, (Hampton,(Hampton, NH, (Hampton, NH,USA). NH, USA).NH, NH,USA). USA). Ethanol,NH, NH, USA).USA).Ethanol, NH, Ethanol, USA). USA).Chloroform-d Chloroform-dUSA).methanol,Ethanol, methanol, Ethanol,Chloroform-d methanol, Chloroform-d methanol, acet methanol,(CDCl acet (CDClone, acetone, 3(CDCl )andone, acet3 was) (CDCl andnacetwas one,tolueneand 3)purchased one,toluene waspurchased3 )andtoluene was andpurchasedwere toluene werepurchased toluene from wereobtained from obtained were Cambridgeobtainedfrom wereCambridge from obtainedfrom Cambridge fromobtained Cambridge fromFisher IsotopeFisher fromIsotope Fisher from Isotope Fisher Isotope Fisher obtainedAcros from (Hampton,Acros Sigma-Aldrich (Hampton, NH, USA). NH, (St. Louis,USA).Ethanol, Ethanol, MO, methanol, USA). methanol, acet Tetra-one,3 acet and-octylammoniumone,3 toluene and toluene were obtained were bromide obtained from Fisher (TOAB),from Fisher sodium AcrosLaboratories,Laboratories,ScientificScientificLaboratories,Acros (Hampton,ScientificLaboratories, (Hampton,ScientificLaboratories, Acros(Hampton, (Hampton, Inc.Inc. NH, Inc.(Hampton, (Tewksbury,(Tewksbury,(Hampton, (Tewksbury,USA).Inc.NH, NH, Inc.NH, (Tewksbury, USA). Ethanol,(Tewksbury,USA).NH, USA). NH, MA, MA, Ethanol, USA).MA,USA). Chloroform-d Chloroform-d USA).methanol,USA)USA) MA,USA) Ethanol, Chloroform-dMA, methanol, WaterWaterUSA)Chloroform-d Water USA) acet methanol,Waterwas(CDClwas (CDClone, was Wateracet purified purified (CDClwaspurifiedandone,) 3) (CDClwas was was acet purifiedtolueneand ) by purchasedbypurified one,was 3purchasedby) tolueneBarnsteadBarnsteadwas Barnstead andpurchasedwereby purchased byBarnstead toluene werefrom obtained Barnsteadfrom NANONANO NANO obtainedfromCambridge wereCambridge fromNANO frompurepure NANOCambridgepure obtained Cambridge from FisherDiamondDiamond pure DiamondIsotope pureIsotope Fisher Diamondfrom Isotope Diamond Isotope Fisher ScientificScientificLaboratories,Laboratories,Scientific ScientificLaboratories,(Hampton, ScientificLaboratories,(Hampton, (Hampton, Inc. Inc.(Hampton, (Tewksbury, NH,(Hampton, (Tewksbury,Inc. NH, Inc. NH,USA).(Tewksbury, USA). (Tewksbury, NH,USA). Chloroform-dNH,MA, MA,USA).Chloroform-d Chloroform-dUSA).USA) MA, USA) Chloroform-dMA, WaterUSA)Chloroform-d Water USA)(CDCl (CDCl Waterwas (CDCl wasWater3) purified was3 (CDCl)waspurified was3 )(CDCl was purchased waspurified 3 purchased) by purified was 3purchasedby) Barnsteadwas Barnstead purchasedby from purchasedbyBarnstead from Barnstead fromNANOCambridge NANO Cambridgefrom Cambridge NANOfrom pure NANOCambridgepure IsotopeCambridge Diamond pure IsotopeDiamond pureIsotope Diamond Isotope Diamond Isotope borohydrideScientificScientificionionLaboratories,Laboratories,ionScientific exchangeexchange (NaBHexchange Laboratories,Scientific(Hampton, Laboratories,ionScientific(Hampton, (Hampton, exchange resinsresinsInc.4 ),resinsInc.(Hampton, and (Tewksbury,NH, (Hampton, (Tewksbury,Inc.purificationpurification NH,purification Inc.resins potassium NH,USA).(Tewksbury, USA).(Tewksbury, NH, USA).purification Chloroform-d NH, MA, unit. unit. MA,USA). Chloroform-dunit. Chloroform-d USA). USA) tetrachloropalladate(II)MA, USA) MA,Chloroform-d unit. USA)WaterChloroform-d Water USA)(CDCl (CDClWater was (CDCl wasWater3) waspurified 3 (CDClwas)purified 3was ) was(CDCl purchased waspurified 3purchased) purifiedby waspurchasedby3) Barnstead (KwasBarnstead purchasedby 2from PdCl bypurchasedBarnstead from Barnstead from CambridgeNANO4 NANO ) Cambridge werefrom Cambridge NANOfrom pure NANO Cambridgepure obtained IsotopeCambridge Diamond pure IsotopeDiamond pureIsotope Diamond Isotope fromDiamond Isotope Acros Laboratories,Laboratories,ionionLaboratories, exchange exchangeionLaboratories,ionLaboratories,ion exchangeexchangeInc. exchangeInc.resins (Tewksbury,resinsInc. (Tewksbury, resinspurificationInc.(Tewksbury,resins purification resinsInc. (Tewksbury, purificationpurification (Tewksbury, MA, purification MA, unit. MA,USA) unit. USA) MA, USA)unit. unit.Water MA, unit. WaterUSA) Water USA) was wasWater purified wasWater purified waspurified was bypurified by Barnsteadpurified by Barnstead Barnstead by byBarnstead NANO Barnstead NANO NANO pure NANO pure NANO pureDiamond Diamond pure Diamond pure Diamond Diamond Laboratories,Laboratories,ionionLaboratories, exchange exchangeionLaboratories,ion Laboratories, exchangeInc. exchange Inc.resins (Tewksbury, resinsInc. (Tewksbury, resins (Tewksbury,Inc.purification purification resinsInc. (Tewksbury, purification (Tewksbury,MA, purification MA, unit.USA)MA, unit. USA) MA, unit.USA) Water MA,unit. WaterUSA) Water USA)was Waterwas purifiedwas Water purified waspurified wasby purified byBarnstead purified by Barnstead Barnstead by byBarnstead NANO Barnstead NANO NANO pure NANO pure NANOpureDiamond Diamond pure Diamond pure Diamond Diamond (Hampton,ionion exchangeion NH,exchange exchangeionion USA). exchangeresins exchangeresins resins purification Ethanol, purificationresins purification resins purification methanol,unit.purification unit. unit. unit. unit. acetone, and toluene were obtained from Fisher Scientific ionion 3.2.3.2.exchange3.2.ion exchange SynthesisSynthesis exchangeSynthesision3.2.3.2.ion exchangeresinsSynthesis Synthesisofexchangeresinsof ofSodiumresinsSodium purification Sodium purificationofresins Sodiumpurification of S-OctylthiosulfateresinsS-Octylthiosulfate SodiumS-Octylthiosulfate purification unit.purificationS-Octylthiosulfate unit.S-Octylthiosulfate unit. unit. unit. (Hampton,3.2.3.2. NH, Synthesis Synthesis3.2. USA).3.2. Synthesis ofSynthesis ofSodium Chloroform-d Sodium of Sodium ofS-Octylthiosulfate SodiumS-Octylthiosulfate S-Octylthiosulfate S-Octylthiosulfate (CDCl 3 ) was purchased from Cambridge Isotope Laboratories, Inc. 3.2.3.2. Synthesis Synthesis3.2.3.2. Synthesis Synthesis of of Sodium Sodium of Sodium of S-Octylthiosulfate SodiumS-Octylthiosulfate S-Octylthiosulfate S-Octylthiosulfate 3.2.3.2. Synthesis3.2. SynthesisSodiumSodium Synthesis3.2.Sodium3.2. ofSynthesis Sodium of SynthesisthiosulfatethiosulfateSodium Sodiumthiosulfateof Sodium ofS-Octylthiosulfate Sodium ofS-Octylthiosulfatethiosulfate pentahydrateSodiumpentahydrateS-Octylthiosulfate pentahydrate S-Octylthiosulfate S-Octylthiosulfate pentahydrate (20(20 (20 mmol)mmol) mmol) (20 andand andmmol) 1-bromooctane1-bromooctane 1-bromooctane and 1-bromooctane (20(20 (20 mmol)mmol) mmol) (20 werewere weremmol) mixedmixed mixed were inin in mixed thethe the in the (Tewksbury,3.2.3.2. Synthesis3.2. SynthesisSodium MA, Synthesis3.2.Sodium 3.2. ofSynthesis USA)SodiumSodium Sodium ofthiosulfateSynthesisSodium Sodiumthiosulfateof Sodium Water thiosulfateofS-Octylthiosulfatethiosulfate Sodium thiosulfateS-Octylthiosulfateof pentahydrateSodiumS-Octylthiosulfate pentahydrate was S-Octylthiosulfate pentahydratepentahydrate purifiedS-Octylthiosulfate pentahydrate (20 (20 mmol) by mmol) (20(20 Barnstead (20 mmol) mmol) and andmmol) 1-bromooctane and1-bromooctaneand and NANO1-bromooctane1-bromooctane 1-bromooctane pure(20 (20 mmol) mmol) (20 Diamond(20 (20 mmol) mmol)were weremmol) mixed werewere mixed ion were mixedmixedin exchange inmixedthe the inin thethein the resins mixturemixturemixtureSodiumSodium ofofmixture of waterSodiumwater water thiosulfateSodium thiosulfate andandof andthiosulfate water ethanol ethanolthiosulfate ethanol pentahydrate andpentahydrate (1/1(1/1 ethanol pentahydrate(1/1 volumepentahydratevolume volume (1/1(20 (20 ratio)ratio) volumemmol) ratio) mmol)(20 so(20so mmol) so lutionlutionand ratio)mmol)lutionand 1-bromooctane and1-bromooctane andso and andlution refluxed1-bromooctanerefluxed refluxed 1-bromooctane and forfor refluxed(20 for(20 33 mmol)h.3h. mmol) h.(20 TheThe forThe(20 mmol) crudecrude were3 mmol)crudewere h. The productmixedwereproduct mixedproduct werecrude mixed in wasinmixed wasproductthe was the in thein wasthe mixtureSodiumSodiummixtureSodium of thiosulfate waterSodium thiosulfateSodium ofthiosulfate andwater thiosulfate ethanolpentahydrate thiosulfate andpentahydrate pentahydrate ethanol (1/1 pentahydrate volumepentahydrate (20(1/1 (20 mmol) volume(20 ratio)mmol) mmol)(20 and so (20 ratio) mmol)andlution 1-bromooctanemmol)and 1-bromooctaneso andlution1-bromooctane and refluxed1-bromooctane and 1-bromooctane (20refluxed for(20 mmol) (20 3mmol) h. mmol)for (20The were (203 mmol) wereh.crude mmol)wereThemixed mixed productwerecrude mixed werein mixed intheproduct wasinmixedthe the in wasthein the purificationmixture unit.Sodiummixturemixture of waterthiosulfate of waterof and water ethanoland pentahydrate and ethanol ethanol (1/1 volume(1/1 (20(1/1 volume1 mmol) volume ratio) ratio) soand ratio)lution so1-bromooctanelution so andlution refluxedand and refluxed refluxed(20 for mmol) 3 for h. forThe3 h.were 3 crudeThe h. Themixed crude product crude inproduct theproduct was was was furthermixtureSodiummixturemixtureSodium recrystallized ofmixture thiosulfateof Sodiumwater water Sodium ofthiosulfate waterofand and thiosulfatewater pentahydrateethanolusing thiosulfateethanoland andpentahydrate ethanolhot (1/1 ethanol pentahydrate(1/1 ethanol. volumepentahydrate volume(20(1/1 (1/1mmol) volume 1(20H ratio)1 volume ratio)NMR mmol)(20 and1 ratio)so (20mmol) so1(400lution ratio) 1-bromooctanelutionandmmol) so MHz, lution and1-bromooctaneandso and lutionand 1-bromooctaneDrefluxed refluxedand2 O):1-bromooctane2 and refluxed(20δ 3.1 refluxed formmol) for ppm(20 3 3h. for mmol)h.(20 The(triplet,were forThe 3 (20 mmol)h. crude3 crude Theweremmol)h.mixed α The-CH crudewereproduct mixedproduct crudeinwere2-S), 2 themixedproduct δ in wasproductmixed 1.7was the in was thein was the mixturemixturefurtherfurther ofmixturefurther recrystallizedwaterof furtherrecrystallized water andrecrystallized of and recrystallizedwater ethanol ethanol using andusing (1/1 ethanolhotusing (1/1 hot volumeusing ethanol. volumeethanol. hot (1/1 hot ethanol.ratio) volume1 Hethanol.ratio) 1 HNMR so NMR 1lutionso Hratio) lution (4001NMRH (400 NMRand soMHz, and(400lutionMHz, refluxed (400 refluxed DMHz, 2Dand O):MHz,O): for δrefluxedD 3.1 δ2for O): 3D3.1 h.2ppm O):3 δ ppmTheh. 3.1 for δThe (triplet, 3.1 crudeppm (triplet,3 crudeh.ppm The(triplet, product α (triplet,-CHproduct αcrude-CH2 -S),α was-CH -S),product α δwas-CH 1.7δ2-S), 1.7 2-S), δwas 1.7 δ 1.7 furtherfurthermixturefurther recrystallized mixturefurtherrecrystallized of water recrystallized recrystallized of and water using ethanolusing and hotusing hot ethanol using(1/1ethanol. ethanol.hot volume hot ethanol. 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H NMR H (400 NMR1 MHz, (4002 DMHz,2O):22 δ D 3.12O): ppm2 δ 3.1 (triplet, ppm (triplet, α-CH2 2 -S),3α2-CH δ 1.732-S), 2 δ 1.7 furthercharacterizationcharacterizationppmppmcharacterizationfurther recrystallized (quintet,ppm characterization(quintet, ppmcharacterizationfurtherrecrystallized (quintet, (quintet,β results-CHβresultsrecrystallized -CHusingresults βCH2-CH CH results usingare βarehot -CH-S),areresults2 -S), CHavailable availableethanol. available2δhot CH are δusing-S),1.3 are 1.3 ethanol.2available-S), ppmδ availableppmininhot1.3 H δin the the NMR 1.3 (broadethanol.ppmthe (broad H previous previousinppm previousNMR the(400in(broad peak,the (broadpreviouspeak, H MHz,(400 previouspublicationpublicationNMR peak,publication-CH -CHMHz, peak,D (400publication-), O):2-CH-), publication and D δ-CHMHz, and [20].[20].O):3.1-), [20].δ 2 -), andppmδ 0.90 D3.1 0.90 [20].and O):δ ppm(triplet,[20].ppm 0.90 ppmδδ 0.903.1 (triplet,(triplet,ppm (triplet, ppmα ppm-CH (triplet, (triplet, α CH-S),(triplet, -CHCH -).δ3 -).-S),CH1.7 αMore -CHMore CH δ-). 1.7 3 -).More-S), More δ 1.7 ppmppmcharacterization characterizationppm(quintet, (quintet,ppmcharacterization (quintet,ppmcharacterization β(quintet,-CH β(quintet,-CH resultsβ2 CH-CHresults2 CHβ2-S), 2-CHresultsCH areβ2-S), -CHareresultsδ22 -S), availableCH 1.3 δavailable 2 areCH 1.32 δ-S),ppm are 1.3 2available-S),ppm δ available inppm(broad1.3 δ in the (broad 1.3 ppmthe (broad previousin ppm peak,previous the in (broadpeak, the previous(broadpeak, -CH previouspublication -CH peak,publication2 -),-CH peak,2 -),publicationand 2-CH -), andpublication -CHδ and[20]. 2 -),0.90 δ[20]. 2 0.90-),and δ ppm 0.90[20].and ppmδ [20]. 0.90 ppm(triplet,δ 0.90 (triplet, ppm (triplet, ppm CH (triplet, CH 3(triplet,-). CH3 -).More3 -).CHMore MoreCH 3-). 3-).More More ppmppmcharacterization characterizationppm(quintet, (quintet,characterizationppm (quintet,characterizationppm β(quintet,-CH β(quintet,-CH βresults2CH -CHresults2 CH2β-S), 2-CHresultsCH are2β-S), areresults-CHδ22 -S),CHavailable1.3 δavailable 2are CH 21.3δ-S),ppm are 1.3available 2ppm-S), δ available ppm(broadin1.3 inδ the (broad 1.3theppm (broad inprevious ppmpeak,previous thein (broadpeak, the previouspeak,(broad -CH previous publication -CHpublicationpeak,2 -),-CH peak, 2 andpublication-), 2-CH -),publicationand δ-CHand 2[20].0.90-), [20].δ 20.90and-),δ ppm 0.90[20].and δppm[20]. 0.90 ppm(triplet,δ 0.90(triplet, ppm (triplet, ppm CH (triplet, CH3 -). (triplet,CH 3More-).3 -).CHMore More CH3-). 3More-). More Sodiumcharacterizationcharacterizationcharacterization thiosulfatecharacterizationcharacterization results results results pentahydrate are resultsare available areresults available available are are availablein theinavailable (20 inthe previous the mmol)previous in previous thein the publicationprevious and publicationprevious publication 1-bromooctane publication [20].publication [20]. [20]. [20]. [20]. (20 mmol) were mixed in the characterizationcharacterizationcharacterizationcharacterizationcharacterization results results results are resultsare available areresults available available are areinavailable the inavailable inthe previous the previousin previous the in the publicationprevious publicationprevious publication publication [20]. publication [20]. [20]. [20]. [20]. mixture of water and ethanol (1/1 volume ratio) solution and refluxed for 3 h. The crude product 1 was further recrystallized using hot ethanol. H NMR (400 MHz, D2O): δ 3.1 ppm (triplet, α-CH2-S), δ 1.7 ppm (quintet, β-CH2CH2-S), δ 1.3 ppm (broad peak, -CH2-), and δ 0.90 ppm (triplet, CH3-).

More characterization results are available in the previous publication [20].

3.3. Synthesis of Octanethiolate-Capped Palladium Nanoparticles (C8 PdNP)

K2PdCl4 (0.4 mmol) and sodium S-octylthiosulfate ligand (0.8 mmol) were transferred from aqueous phase to organic phase by a phase transfer agent of TOAB (4 mmol) and then reduced by NaBH4 (8 mmol). Ethanol and methanol were used to wash the excess TOAB after reaction was completed. Nanoparticle size was estimated to be 2.3 ± 1.2 nm. The organic weight fraction of 19% Catalysts 2018, 8, 428 8 of 10 and palladium weight fraction of 81% based on the thermogravimetric analysis. These characterization results are available in the previous publication [20].

3.4. Synthesis of Ethyl but-3-enoate (Compound 26) Ethyl but-3-enolate was synthesized following the published procedure [29]. Briefly, pentane (5 mL) was placed in a 50 mL round bottle flask with ethanol (863 µL) and trimethylamine (1.34 mL) under 0 ◦C. Crotonoyl chloride (916 µL) was dissolved in pentane (5 mL) and the solution was added dropwise into the round bottle flask for 10 min. The solution was then removed from an ice bath and stirred for 3 h at room temperature. Saturated NaHCO3 (1 mL) and water (10 mL) were added in the round bottle flask after the 3 h reaction. Diethyl ether (12 mL) was added and the reaction mixture was extracted using a separatory funnel. The organic solution was further dried by sodium sulfate before the removal of solvent using rotary evaporation. The purity and structure of the obtained product were confirmed according to the characterization data in the literature [29].

3.5. Catalysis Experiments The substrates (0.5 mmol) with 5 mol % of octanethiolate-capped palladium nanoparticle (Pd: 0.025 mmol) were mixed in a 2.5 mL CDCl3 in the 50 mL round bottom flask and purged with H2 for 10 min. For 36 and 48 h experiments, the second 5 min H2 purge would be needed after 24 h of the first purge. The composition of the crude product containing octanethiolate-capped palladium nanoparticle (C8 PdNP) were characterized by Bruker Fourier 400 MHz NMR.

4. Conclusions The catalytic reactions of various unsaturated organic substrates using octanethiolate-capped Pd nanoparticle demonstrated that this catalyst has an excellent potential for the selective hydrogenation of the less hindered C=C bond of cumulated dienes conjugated with an ester group. Initially, the mono-hydrogenation produced the cis (or Z) conjugated esters with a high selectivity. The subsequent isomerization of the cis conjugated esters to the trans conjugated esters took place for the compounds that possess no steric group at C2 carbon of conjugated esters. For the substrates containing a steric group, the Z product would remain as the major product. This interesting activity and selectivity of the catalyst is due to the partial poisoning and surface crowding effects of octanethiolate ligands on the Pd nanoparticle surface. The hydrogenation of the second C=C bond is inhibited without the presence of an additional π coordinating group that enhances the adsorption of the substrate. With a decreased activity for hydrogenation, the alkanethiolate-capped Pd nanoparticle catalyst would isomerize the terminal C=C bond to an internal C=C bond and cis alkene to trans alkene. This study clearly demonstrates the strong influence of alkanethiolate passivation on the electronic and geometric properties of colloidal nanoparticle catalysts.

Supplementary Materials: The following are available online at http://www.mdpi.com/2073-4344/8/10/428/s1, 1H NMR spectra obtained from various catalytic hydrogenation reactions using Pd nanoparticles. Author Contributions: T.-A.C. conducted the experimental work and Y.-S.S. supervised the project. The manuscript was written through contributions of both authors. Both authors have given approval to the final version of the manuscript. Funding: This research was funded by the National Institute of General Medical Science grant number [GM089562] and CSULB. Acknowledgments: We thank the National Institute of General Medical Science for financial support. Conflicts of Interest: The authors declare no conflict of interest. The founding sponsor had no role in the design of the study, in the writing of the manuscript, and in the decision to publish the research results. Catalysts 2018, 8, 428 9 of 10

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