M.C. White, Chem 153 Overview -286- Week of november 11. 2002 Regioselectivity of hydrometallation Aliphatic terminal olefins: For aliphatic terminal olef re is both a strong thermodynamic preference to form the sterically less hindered M-C bond. Structure& Bonding, pg. 32: As seen for C-H o bonding, there is a general trend towards weaker M-C a bonds with increased substitution LIi- DIr-c: 58 kcal/mol Dr-c: 52 kcal/mol DIr-C: 48 kcal/mol If an equilibration mechanism exists, M-alkyls will isomerize to the least sterically hindered 1o product. For more examples of this see: Hydroformylation, pg 205 and 206 drosilylation,Pg. 183 i olefin isomerization to terminal olefin leads to 1 metal alkyl that undergo h(SirUM Ln(Sir3)R R3Sr-RhLn 少 RhCI(PPhi)z RaSi-H CAHe R3SI CAHl Conjugated terminal olefins: For conjugated olefins, hydride insertion results in formation of the 20 M-C which can be stabilised as a delocalised r -intermediate Hydroform on, pg H2CO(1:1) Rh(Co)L i branched: linear(11: 0) Ligand Effects? Hayashi's observed hydrosilylation regioselectivities with aliphatic terminal olefins cannot be rationalized using our models(Hydrosilylation, pg. 189) 0.1 mol% C!H MOP (0.002 mol%) CHHg OMe iCl regioselectivity(87: 13) MOPM.C. White, Chem 153 Overview -286- Week of November 11, 2002 Regioselectivity of hydrometallation Aliphatic terminal olefins: For aliphatic terminal olefins, there is both a strong thermodynamic preference to form the sterically less hindered M-C bond. LnIr(III) C4H13 LnIr(III) LnIr(III) Structure & Bonding, pg. 32: As seen for C-H σ bonding, there is a general trend towards weaker M-C σ bonds with increased substitution. DIr-C: 58 kcal/mol DIr-C: 52 kcal/mol DIr-C: 48 kcal/mol Ln(SiR3)Rh H Rh(SiR3)Ln H Ln(SiR3)Rh H C4H9 R3Si RhLn R3Si C4H13 If an equilibration mechanism exists, M-alkyls will isomerize to the least sterically hindered 1o product. For more examples of this see: Hydroformylation, pg.205 and 206. RhCl(PPh3)3 R3Si-H olefin isomerization to terminal olefin leads to 1o Hydrosilylation, pg. 183 metal alkyl that undergoes RE to product. Conjugated terminal olefins: For conjugated olefins, hydride insertion results in formation of the 2o M-C which can be stabilized as a delocalized η3-intermediate. RhH(CO)(PPh3) H2:CO (1:1) Rh(CO)Ln Rh(CO)Ln O H branched: linear (11:0) Hydroformylation, pg. 192, 194, 195; Hydrocyanation, pg. 232. Ligand Effects? Hayashi's observed hydrosilylation regioselectivities with aliphatic terminal olefins cannot be rationalized using our models (Hydrosilylation, pg. 189). C4H9 OMe PPh2 Pd Cl Pd Cl HSiCl3 (1.2 eq) 0.1 mol% + MOP (0.002 mol%) C4H9 SiCl3 regioselectivity (87:13) MOP