| Abstract
| - The enantioselectivities arising from a Pd-catalyzed Heck reaction(>98% ee) and an allylic alkylation(>90% ee) using a 3,5-di-tert-butyl-MeO−BIPHEP chiralauxiliary (1) are reported. Higher ee's are observedwiththe 3,5-dialkyl substituents than with the unsubstituted parentMeO−BIPHEP. It is proposed that the observeddialkyl “meta-effect”, on enantioselectivity, is the combinedresult of a more rigid and slightly larger chiral pocketand that this effect will have some generality in homogeneouscatalysis. Detailed NMR studies on the allyl complex[Pd(PhCHCHCHPh)(1)]PF6(5), and the model hydrogenation catalyst[RuH(cymene)(1)]BF4(6), reveal restrictedrotation about several of the P−C(ipso) bonds of the phosphorussubstituents containing the 3,5-di-tert-butylgroups.The X-ray structure of 6 reveals that the cymene ligandis not symmetrically bound to the Ru atom. Thisobservationis interpreted as an expression of the chiral pocket of 1.MM3* calculations on 6 support the NMR findingsandreproduce the X-ray results.
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