L-Phenylalanine derived tripodal vanadium complexes as catalysts for the asymmetric reductive coupling of benzaldehyde

Teixeira, Carlos M.; Adão, Pedro; Carvalho, M. Fernanda N.N.; Gomes, Clara S.B.; Pessoa, João Costa

http://hdl.handle.net/10400.8/5100

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Authors

Teixeira, Carlos M.

Adão, Pedro

Carvalho, M. Fernanda N.N.

Gomes, Clara S.B.

Pessoa, João Costa

Abstract(s)

Two tripodal vanadium complexes derived from modified L-phenylalanine were prepared and characterised. Both compounds were tested for their catalytic activity in the reductive coupling of benzaldehyde. Overall, the complexes are capable of catalysing the reductive coupling of benzaldehyde in the presence of metallic zinc as co-reductant and alkylammonium or alkylpyridinium acetate salts in ethanol under mild aerobic conditions. While benzyl alcohol is generally the major product, the yield of hydrobenzoin reaches ca. 38% under these conditions. Enantioselectivities reach 39% and there is a preferential formation of the trans diastereoisomer of hydrobenzoin. Attempts to study some aspects of the underlying mechanism were made. It was found that metallic zinc is capable of reducing the complexes to VIII species, which are likely to be the active catalytic species. The methodology described may set up a basis for the development of catalytic systems for the asymmetric synthesis of hydrobenzoins under mild conditions, not requiring chlorosilanes as electrophilic reagents for the regeneration of the catalyst.

Description

Acknowledgements The authors of Centro de Química Estrutural acknowledge the financial support of Fundação para a Ciência e a Tecnologia (UIDB/ 0100/2020), the IST-UL Centers of the Portuguese NMR and Mass Spectrometry Networks (REM2013, RNNMR), RECI/QEQ-QIN/0189/ 2012, RECI/QEQ-MED/0330/2012, grants SFRH/BPD/79778/2011, BL/CQE-2014-001 and PD/BD/106078/2015. The authors also acknowledge Dr. Maria da Conceição Oliveira and MSc. Ana Dias for the ESI mass spectrometry experiments carried out. Pedro Adão acknowledges the MARE– Marine and Environmental Sciences Centre, Polytechnic of Leiria, which is financed by national funds from FCT/ MCTES (UID/MAR/04292/2019, UIDB/04292/2020) and the project “SmartBioR- Smart Valorization of Endogenous Marine Biological Resources Under a Changing Climate” (Centro-01-0145-FEDER000018) co-funded by Centro 2020, Portugal 2020 and European Regional Development Fund (FEDER). Clara S. B. Gomes acknowledges the Associate Laboratory for Green Chemistry– LAQV and the Applied Molecular Biosciences UnitUCIBIO, which are financed by national funds from Fundação para a Ciência e a Tecnologia (UIDB/50006/2020 and UIDB/04378/2020, respectively).

Keywords

Vanadium Pinacol coupling Modified phenylalanine Benzaldehyde Asymmetric catalysis

URI

http://hdl.handle.net/10400.8/5100

Citation

Teixeira, C., Adão, P., Carvalho, M., Gomes, C., & Pessoa, J. (2020) .L-Phenylalanine derived tripodal vanadium complexes as catalysts for the asymmetric reductive coupling of benzaldehyde. Inorganica Chimica Acta. DOI: 10.1016/j.ica.2020.119727