1. [Type here] Research Summary Chi Chen
Z-Selective alkene isomerizationandanti-Markovnikovalkene hydrosilylation withLow CoordinatedCobalt
Complexes
Efficientcatalyticreactionsare akeycomponentof sustainable chemistry,andthe mostdesirable
catalyticreactionsuse sustainablecatalysts. Base metalssuchasFe,Co,and Ni are more sustainable than
precious-metal catalystsbecauseof cost,geopolitical,health,andenergyissues. The lastdecade hasseenthe
discoveryof selective base-metal catalystsinhydrocarbontransformationsandstrongbondactivations.
Alkene Isomerization
C=C double bondsare keyfunctional groupsinmanynatural andindustrial products,and E (trans) isomer
istypicallymore thermodynamicallystableover Z(cis) isomer.Thismakesitdifficulttospecificallyprepare the Z
isomer,though Zalkenesare of greatuse insynthesisandoftenfoundinnatural products.Currentmethods
require eitherspecial directinggroups (the Still-Gennari modificationtothe Horner-Wadsworth-Emmons
olefination),strongbase (WittigandHWEolefination) orexpensive palladiumcatalysts (cross-couplingand
reductionof alkyne overLindlarcatalyst).Thoughalkene isomerization isanatom-economictransformation,it
has notreachedits potential due topoorselectivity.We found thatcobalt(II) catalystssupportedbybulky β-
diketiminate ligandshave the appropriatekineticselectivitytocatalyze the isomerizationof some simple 1-
alkenesspecificallytothe 2-alkeneasthe lessstable Zisomer.The catalysisproceedsviaan"alkyl"mechanism,
witha three-coordinatecobalt(II) alkyl complex asthe restingstate.The catalystshowsmoderate functional group
tolerance. Isolationof cobalt(I) orcobalt(II)productsfromreactionswithpoorsubstratessuggeststhatthe key
catalystdecompositionpathwaysare bimolecular,andloweringthe catalystconcentrationoftenimprovesthe
selectivity.Inadditiontoa potentiallyuseful,selective transformation,thesestudiesprovide amechanistic
understandingforcatalyticalkeneisomerizationbyhigh-spincobaltcomplexes,anddemonstratethe
effectivenessof stericbulkincontrollingthe stereoselectivityof alkene formation.
Alkene Hydrosilylation:
Alkene Hydrosilylationisone of the largesthomogeneouscatalysisinindustry.Itisusedto convert
alkenesintosilanesandsiliconesthatare usedina wide range of applicationsincludinglubricants,rubbers,glues,
high-temperature plastics,andstationaryphasesforchromatography.Currently, alkene hydrosilylationis
performedpredominantlywithPtcatalysts,butinexpensivebase-metalcatalystswouldbe preferred asinmany
large-scale applications(e.g.polymercross-linking),the Ptcatalystremainsinthe product,andevena lowloading
adds upto a large amountof lostPt. Considerationsof sustainabilityandcostmotivate the developmentof
cheapercatalysts. We found an inexpensiveCocatalystsystemthatcan be usedwithoutaddedsolventatlow
temperatureswithlowloadings,and showexcellentfunctional grouptolerance.The cobaltcatalyst canbe
generatedinsitufromanair-stable precursorthatissimple tosynthesizefromlow-cost,commerciallyavailable
materials.Inaddition,amixture of Cocatalystsperformsatandemcatalyticisomerization/hydrosilylation
reactionthat convertsmultiple isomersof hexene tothe same terminal product,whichispromisingforthe use of
alkene mixturestoforma single silane.