Thermodynamic Enantioface‐Binding Selectivities of Monosubstituted Alkenes to a Highly Discriminating Chiral Transition ‐Metal Lewis Acid; equilibration of diastereoisomeric (cyclopentadienyl)(alkene)(nitrosyl)(triphenylphosphine)rhenium complexes ([Re(η5–C5H5)(CH2 = CHR)(NO) (PPh3)]+BF 4−) Academic Article uri icon

abstract

  • Reactions of monosubstituted alkenes RCH = CH2 and [Re(η5–C5H5)(CH2Cl2) (NO)(PPh3)]+BF 4− give complexes ([Re(η5–C5H5))(CH2CHR)(NO) (PPh3)]+BF 4− (1a–g) in 63–99% yields as mixtures of (RS,SR)‐ and (RR,SS)‐diastereoisomers (1a (R = Me), 66:34; 1b (R = Pr), 63:37; 1c (R = PhCH2), 70:30; 1d (R = Ph), 75:25; 1e (R = i‐Pr), 64:36; 1f (R = t‐Bu), 84:16; 1g (R = Me3Si), 69:31; Scheme 2). These differ in the CC enantioface bound to the chiral Re fragment. In most cases, the analogous reactions of RCHCH2 and [Re(η5–C5H5) (C6H5Cl)(NO)(PPh3)]+ BF 4+ give comparable results. When 1a–e, g are heated in PhCl at 95–100°, equilibration to 96:4, 97:3, 97:3, 90:10, > 99:< 1, and > 99:< 1 (RS,SR)/(RR,SS) mixtures occurs (79–99% recoveries; Tables 1 and 2). Thus, thermodynamic enantioface‐binding selectivities are much higher than kinetic binding selectivities. This phenomenon is analyzed in detail. A crystal structure of (RS,SR)‐1e (monoclinic, P21/c, a = 10.256(1) Å. b = 17.191(1) Å, c = 16.191(1) Å, β = 101.04(1)°, Z = 4) shows that the Re–C(1)–C(2) plane (see Fig.2) is nearly coincident with the Re–P bond (angle 15°), and that the i‐Pr group is ‘syn’ to the nitrosyl ligand. Copyright © 1992 Verlag GmbH & Co. KGaA, Weinheim

author list (cited authors)

  • Peng, T., Arif, A. M., & Gladysz, J. A.

citation count

  • 11

publication date

  • March 1992

publisher