Chiral distortion in a Mn(IV)(salen)(N3)2 derived from Jacobsen's catalyst as a possible conformation model for its enantioselective reactions.
The Mn (IV)(salen)(N 3) 2 complex ( 3) from Jacobsen's catalyst is synthesized, and the X-ray crystal structures of 3 as well as the starting Mn (III)(salen)(N 3)(CH 3OH) complex ( 2) are determined in order to investigate the conformation of the high-valent Mn (IV)(salen) molecule in comparison with that of Mn (III)(salen). The asymmetric unit of the crystal of 3 contains four complexes, all of which adopt a nonplanar stepped conformation effectively distorted by the chirality of the diimine bridge. The asymmetric unit of 2 also contains four complexes. Two of them show a stepped conformation of a lesser degree, but the other two adopt a bowl-shaped conformation. Comparison of the structural parameters shows that the Mn center in 3 is coordinated from both sides by two external axial N 3 ligands with significantly shorter bond lengths, which could induce greater preference for the stepped conformation in 3. The CH 3CN solution of 3 shows circular dichroism with a significantly strong band at 275 nm as compared to 2, suggesting that 3 may adopt a more chirally distorted conformation also in solution. The circular dichroism spectrum of 3 is slightly altered with isodichroic points from 298 to 253 K and shows no further change at temperatures lower than 253 K, suggesting that the solution of 3 contains an equilibrium between two conformers, where a low-energy conformer with more chiral distortion is predominantly favored even at room temperature. Complexes 2 and 3 are thoroughly characterized using various techniques including cyclic voltammetry, magnetic susceptibility, UV-vis, electron paramagnetic resonance, (1)H NMR, infrared spectroscopy, and electrospray ionization mass spectrometry.
Kurahashi
Takuya
T
Institute for Molecular Science & Okazaki Institute for Integrative Bioscience, National Institutes of Natural Sciences, Myodaiji, Okazaki, Aichi 444-8787, Japan.
Fujii
Hiroshi
H
D002384:Catalysis; D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D009682:Magnetic Resonance Spectroscopy; D008280:Magnetics; D008345:Manganese / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D021241:Spectrometry, Mass, Electrospray Ionization; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism; D013379:Substrate Specificity
D009942:Organometallic Compounds; D008345:Manganese