Abstract
The nickel-catalyzed addition of Hydrocyanic acid (HCN) to butadiene usually leads to a mixture of the branched 2-methyl-3-butenenitrile (2M3BN) and the linear 3-pentenenitrile (3PN) with a 30:70 ratio by employing mono-dentate phosphites, while a 97% selectivity to 3PN is obtained using a 1,4-bis(diphenyphosphino)butane (dppb) ligand and Ni(COD)2 (1,5-Cyclooctadiene) as catalysts. To explain this phenomenon, a reasonable mechanism of the hydrocyanation, involving the cyano (CN) migration (for 3PN) and the methylallyl rotation (for 2M3BN) pathways, is proposed. The key intermediates and the rate-determining steps in the pathways have been illustrated. The methylallyl rearrangement is the rate-determining step in the formation of 3PN while the reductive elimination governs the reaction to 2M3BN, which is subsequently isomerized to 3PN. Moreover, the opposite changes of the bite angle of the intermediates and transition states explain how the reactions proceed in two different directions.
Highlights
The hydrocyanation of alkenes is one of the most important applications of homogeneous catalysis in industry [1,2,3]
The DuPont process, which forms the basis of an industrial process for the manufacture of adiponitrile (ADN), is an early successful example of homogeneous catalysis application [4]
The toxicity of Hydrocyanic acid (HCN) requires a special experimental setup and the excess HCN causes the deactivation of the NiL4 catalyst (L = phosphite) [5], the excellent atom economy and the inexpensive feedstocks (BD and HCN) are still great advantages of the DuPont process in relation to its practical application
Summary
The hydrocyanation of alkenes is one of the most important applications of homogeneous catalysis in industry [1,2,3]. (ScEhxepmereim3)e.nEtsxptehraimt eunstes dtheautteursaetedeu2tMer3aBteNd g2Mive3BrNisegitvoe 3riPsNe -tdo w3PitNh-dstwatitshticsataltidsteiucatelrdaetiuotneratioCn-2ataCn-d2 aCn-d5 C[2-50][2a0n]danadrearceocnosnisstiesntetnwt witihthththee ddeehhyyddrrooccyyaanation pathway ((SScchheemmee33aa).).HoHwoewveerv,eSra, bSoaEbotieEntnienpnreopporsoepsotsheesretharerarneagrermanegnet mmeencht amniescmhabnaisemd obnastehde on the isolated Ni(η3-1-Me-C3H4)(CN)(dppb) complex, (dppb: 1,4-bis(diphenyphosphino)butane) involving the following steps: (i) the coordination of 2M3BN with a nickel atom via its C=C bond, (ii) C-CN bond breaking and formation of a σ-allyl species (oxidative addition), (iii) isomerization to π-allyl species and σ-allyl formation (rearrangement), (iv) C-CN bond coupling to 3PN coordination (reductive elimination) (Scheme 3b) [21]. Density Functional Theory (DFT) calculations support that the isomerization is initiated with the C-CN bond cleavage (oxidation addition), followed by methylallyl rotation and C-CN bond reformation (reductive elimination) in the isomerization of 2M3BN to 3PN [22,23]. Aislotmhoeurgizhattihoenmofec2hMan3BisNm tfoor 3PthNe [N20iL,241c]ahtaalvyezbeedehnyrdeproocryteadn,atthioenhy[6d]roacnydanthaetiorenaocftibvuetpadatiehnweaeymopflothyeinigsodmpeprbizraetmioaninosfu2nMk3nBoNwnt.o T3hPeNrefo[2re0,,2th1]e fhuanvdeambeeenntalrsetpeoprsteind,thtehenichkyedl-rdopcypabncaattiaolnyzoefd hbuydtardoiceynaenaetmiopnlopyroincgessdnpepebd fruermthaeinrs thuenokrnetoiwcanl .inTvheesrteifgoarteio, nth. eInfutnhdisawmoenrkta, linssteigphstiinnttohethneicrkeealc-tdiopnpbmceacthaalynzisemd hanyddrtohceyacnomatipoanripsoroncoefss dniffeeerdenfturrethaectrivtheepoartehtwicaalysinhvaevsetibgeaetinona.chInievthedisbwyourski,nginDsiFgThtcainlctuolathtieonrse.action mechanism and the comparison of different reactive pathways have been achieved by using DFT calculations
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