Halide or alkoxide free yttrium-salen complexes are excellent catalysts for the ring opening of epoxides mediated by TMSCN and TMSN3. Substrate to catalyst ratios up to 10000 have been realized in these potentially useful reactions, which can be run under solvent-free conditions. Even though the enantioselectivities for the TMSCN-mediated reaction remains modest (best 77% ee), these studies with a highly tunable ligand system may provide further impetus for work in this important area of catalysis. Even though attempts to isolate a Y-cyanide complex, which was detected by in situ IR spectroscopy, failed, a related dimeric hydroxide complex was isolated. A kinetic study using in situ IR spectroscopy did not provide conclusive data to assign an order with respect to Y in this reaction.
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http://dx.doi.org/10.1021/jo071076h | DOI Listing |
J Org Chem
April 2010
Department of Chemistry, 100 West 18th Avenue, Ohio State University, Columbus, Ohio 43210, USA.
Density functional theory calculations were performed to evaluate the proposed mechanism of a yttrium-salen complex-catalyzed acylation of secondary alcohols using an enol acetate as the acyl-transfer agent. A key step in the proposed mechanism is an intramolecular nucleophilic reaction between the coordinated alcohol and enol ester, brought into close proximity by the yttrium catalyst. The use of the BP86 pure density functional for reproduction of the geometry of the yttrium complex was validated by comparison with the experimental crystal structure.
View Article and Find Full Text PDFJ Org Chem
November 2007
Department of Chemistry, The Ohio State University, Columbus, OH 43210, USA.
Halide or alkoxide free yttrium-salen complexes are excellent catalysts for the ring opening of epoxides mediated by TMSCN and TMSN3. Substrate to catalyst ratios up to 10000 have been realized in these potentially useful reactions, which can be run under solvent-free conditions. Even though the enantioselectivities for the TMSCN-mediated reaction remains modest (best 77% ee), these studies with a highly tunable ligand system may provide further impetus for work in this important area of catalysis.
View Article and Find Full Text PDFOrg Lett
May 2002
Department of Chemistry, The Ohio State University, Columbus, Ohio 43210, USA.
[reaction: see text]. Yttrium-salen complexes effect transacylation between enolesters and chiral secondary alcohols, resulting in varying degrees of kinetic resolution. Even though the enantioselectivity remains modest (k(fast)/k(slow) up to 4.
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