Counterintuitive kinetics in Tsuji-Trost allylation: ion-pair partitioning and implications for asymmetric catalysis.
The kinetics of Pd-catalyzed Tsuji-Trost allylation employing simple phosphine ligands (L = Ar3P, etc.) are consistent with turnover-limiting nucleophilic attack of an electrophilic [L2Pd(allyl)]+ catalytic intermediate. Counter-intuitively, when L is made more electron donating, which renders [L2Pd(allyl)]+ less electrophilic (by up to an order of magnitude), higher rates of turnover are observed. In the presence of catalytic NaBAr'F, large rate differentials arise by attenuation of ion-pair return (via generation of [L2Pd(allyl)]+ [BAr'F]-) a process that also increases the asymmetric induction from 28 to 78% ee in an archetypal asymmetric allylation employing BINAP (L*) as ligand. There is substantial potential for analogous application of [M]n+([BAr'F]-)n cocatalysis in other transition metal catalyzed processes involving an ionic reactant or reagent and an ionogenic catalytic cycle.
Evans
Louise A
LA
University of Bristol, Cantock's Close, Bristol, BS8 1TS, UK.
Fey
Natalie
N
Harvey
Jeremy N
JN
Hose
David
D
Lloyd-Jones
Guy C
GC
Murray
Paul
P
Orpen
A Guy
AG
Osborne
Robert
R
Owen-Smith
Gareth J J
GJ
Purdie
Mark
M
D000498:Allyl Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D002384:Catalysis; D007477:Ions / Q000737:chemistry; D007700:Kinetics; D009281:Naphthalenes / Q000737:chemistry; D010165:Palladium / Q000737:chemistry; D010720:Phosphines / Q000737:chemistry
D000498:Allyl Compounds; C406943:BINAP, 2-naphthol; D007477:Ions; D009281:Naphthalenes; D010720:Phosphines; D010165:Palladium