Synthesis, characterization and catalytic studies of bis(chloro)dioxomolybdenum(VI)-chiral diimine complexes

• Type: Article in International Scientific Journal
• Date: 2005

Authors

Gago, S (Author) Other; Rodriguez Borges, JE (Author) FCUP; Teixeira, C (Author) Other; Santos, AM (Author) Other; Zhao, J (Author) Other; Pillinger, M (Author) Other; Nunes, CD (Author) Other; Petrovski, Z (Author) Other; Santos, TM (Author) Other; Kuhn, FE (Author) Other; Romao, CC (Author) Other; Goncalves, IS (Author) Other

Journal

Title: Journal of Molecular Catalysis A: Chemical

Vol. 236

Pages: 1-6

ISSN: 1381-1169

Publisher: Elsevier B.V.

Indexing

ISI Web of Knowledge - 47 Citations

Scopus - 49 Citations

Scientific classification

FOS: Natural sciences > Chemical sciences

Other information

Authenticus ID: P-000-2BE

DOI: 10.1016/j.molcata.2005.03.032

Abstract (EN): Chiral 1,4-diazabutadienes (DAB) of the type R*-N=CPh-CPh=N-R* were prepared in quantitative yields by condensation of benzil with two equivalents of R-(+)-alpha-methylbenzylamine or S-(-)-alpha-methylbenzylamine, using ZnCl(2) as catalyst. The chiral diimine (1R,2R)-N,N'-dibenzylidenecyclohexane-1,2-diamine was also prepared by condensation of (1R,2R)-cyclohexane-1,2-diamine with two equivalents of benzaldehyde using a Dean-Stark adapter for the removal of water. Six-coordinate dioxomolybdenum(VI) complexes of the type [MoO(2)Cl(2)L] containing the bidentate chiral ligands were prepared and characterized by FT-IR, FT Raman and NMR spectroscopy. The complexes were evaluated as catalysts for the asymmetric epoxidation of cis- and trans-beta-methylstyrene by tert-butylhydroperoxide at either room temperature or 55 degrees C. The reactions proceeded with high retention of olefin configuration and high selectivity to the epoxide, but only for cis-beta-methyl styrene were significant enantiomeric excesses (e.e.) obtained. With this substrate and the complex containing (1R,2R)-N,N'-dibenzylidenecyclohexane-1,2-diamine, (1S,2R)-cis-beta-methylstyrene oxide was obtained in 77% e.e. at room temperature (24% conversion). Increasing the reaction temperature increased the epoxide yields but good enantiomeric excesses (>= 65%) could only be achieved at low conversions (<= 12%). The two complexes containing the chiral DAB ligands generally exhibited higher catalytic activity than the third complex but lower optical yields.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 6