Toward an Understanding of 1,5-Asymmetric Induction during Nucleophilic Addition to (Arene)chromium Tricarbonyl Complexes: Conformational Preference of the Chromium Tricarbonyl Tripod for Transmission of Chirality

Abstract

Asymmetric induction during enolate nucleophile addition to chromium tricarbonyl complexes of 4-alkoxy-1-(trimethylsilyl)benzene derivatives, in which the alkoxy group (R*O) is derived from an optically pure alcohol, is analyzed in terms of the effect of the chiral auxiliary (R*) on the conformation of the tricarbonylchromium tripod. Crystal structure determination on the three complexes 3a (R* ) 2-phenylisobornyl), 3b (R* ) 2-methylisobornyl), and 3c (R* ) 2-(3-[1,3]-dioxalanyl)isobornyl) reveals that the chiral group R* causes a rotation of the Cr(CO) 3 group from the normally preferred orientation, the extent and direction of which are dependent on the auxiliary. NMR studies on seven complexes indicate the presence of a single conformation in solution for each, which is assumed to be the same as that shown in the solid state. There is a correlation between the observed asymmetric induction and the Cr(CO) 3 tripod rotation, which is believed to be a result of the effect of this conformational distortion on the arene-centered FMO coefficients.

1,5-Asymmetric induction during nucleophilic additions to arenetricarbonylchromium complexes: tricarbonyl(η6-1-methyl-4-{spiro[(1R,2S)-1,7,7-trimethylbicyclo[2.2.1]heptane-3,2′-1,3-dioxolan]-2-yloxy}benzene)chromium

“…As part of an effort to determine the extent to which the chiral alkoxy group causes this rotation, and therefore whether it might be a causative factor in asymmetric induction, the crystal structures of several alkoxyarenetricarbonylchromium complexes are being studied. We have already reported some of these results for complexes having a trimethylsilyl substituent [(I), with R 0 = Si(CH 3 ) 3 ] para to the chiral alkoxy group, all of which structures support our hypothesis (Paramahamsan et al, 2008). In order to show that such rotation of the Cr(CO) 3 group is not specific to the nature of the R 0 substituents, we have also more recently determined the structure the title complex, (II), a complex bearing a simple alkyl group.…”

A successful DFT calculation of carbon-13 NMR chemical shifts and carbon–fluorine spin–spin coupling constants in (η6-fluoroarene)tricarbonylchromium complexes

“…[3][4][5][6] Susceptibility of these complexes to the various reactions and rearrangements is tightly connected with the orientation of the tricarbonylchromium tripod with respect to the aromatic ligand. 1,2,7,8 In the solid state this conformation can be established by crystallographic methods. In liquids the problem is more severe, although a detailed interpretation of 1 H NMR, 13 C NMR or 19 F NMR spectra can provide information allowing a preferred conformation to be recognized.…”

Cationic Planar Chiral (η6-Arene)Mn(CO)3+ Complexes: Resolution, NMR Study in Chiral-Oriented Solvents, and Applications to the Enantioselective Synthesis of 4-Substituted Cyclohexenones and (η6-Phosphinoarene)Mn(CO)3+ Complexes

“…We then turned our attention to a more rigid chiral auxiliary, namely, camphor enolate, which comes from a commercially available, enantiopure compound . Addition of camphor enolate to meta -methylanisole−Mn(CO) 3 in THF at low temperature should lead to the formation of four diastereoisomers due to the presence of two types of chirality: (i) the planar chirality of the η 5 complexes; (ii) the new stereogenic center C 9 formed at the carbon α to the carbonyl of the camphyl group with formation of the endo and exo isomers (Scheme ).…”