3,3‘-Bis(trisarylsilyl)-Substituted Binaphtholate Rare Earth Metal Catalysts for Asymmetric Hydroamination

Chiral 3,3‘-bis(trisarylsilyl)-substituted binaphtholate rare earth metal complexes (R)-[Ln{Binol-SiAr3}(o-C6H4CH2NMe2)(Me2NCH2Ph)] (Ln = Sc, Lu, Y; Binol-SiAr3 = 3,3‘-bis(trisarylsilyl)-2,2‘-dihydroxy-1,1‘-binaphthyl; Ar = Ph (2-Ln), 3,5-xylyl (3-Ln)) and (R)-[La{Binol-Si(3,5-xylyl)3}{E(SiMe3)2}(THF)2] (E =
CH (4a), N (4b)) are accessible via facile arene, alkane, and amine elimination. They are efficient catalysts
for the asymmetric hydroamination/cyclization of aminoalkenes, giving TOF of up to 840 h-1 at 25 °C for
2,2-diphenyl-pent-4-enylamine (5c) using (R)-2-Y. Enantioselectivities of up to 95% ee were achieved in
the cyclization of 5c with (R)-2-Sc. The reactions show apparently zero-order rate dependence on substrate
concentration and first-order rate dependence on catalyst concentration, but rates depend on total amine
concentrations. Activation parameters for the cyclization of pent-4-enylamine using (R)-2-Y (ΔH(S)⧧ = 57.4(0.8) kJ mol-1 and ΔS(S)⧧ = −102(3) J K-1 mol-1; ΔH(R)⧧ = 61.5(0.7) kJ mol-1 and ΔS(R)⧧ = −103(3) J
K-1 mol-1) indicate a highly organized transition state. The binaphtholate catalysts were also applied to
the kinetic resolution of chiral α-substituted aminoalkenes with resolution factors f of up to 19. The 2,5-disubstituted aminopentenes were formed in 7:1 to ≥50:1 trans diastereoselectivity, depending on the size
of the α-substituent of the aminoalkene. Rate studies with (S)-1-phenyl-pent-4-enylamine ((S)-15e) gave
the activation parameters for the matching (ΔH⧧ = 52.2(2.8) kJ mol-1, ΔS⧧ = −127(8) J K-1 mol-1 using
(S)-2-Y) and mismatching (ΔH⧧ = 57.7(1.3) kJ mol-1, ΔS⧧ = −126(4) J K-1 mol-1 using (R)-2-Y) substrate/catalyst combination. The absolute configuration of the Mosher amide of (2S)-2-methyl-4,4-diphenyl-pyrrolidine and (2R)-methyl-(5S)-phenyl-pyrrolidinium chloride, prepared from (S)-15e, were determined
by crystallographic analysis. Catalyst (R)-4a showed activity in the anti-Markovnikov addition of n-propylamine to styrene.