NafionW-supported oxovanadium catalyzed hydrophosphonylation
result suggests that the background reaction catalyzed by
perfluorinated sulfonic acid can be excluded (Table 1, entry 12).
The advantages of this Nafion-Vpowder catalytic system are that
the catalyst can be recovered by simple filtration and reused for
several runs (Table 1, entries 4–7), and that the reaction does
not require the use of any organic solvent. Thus the catalytic
protocol meets the standards of green chemistry from an envi-
ronmental point of view. It is worth noting that a slight decrease
in yield was observed after every three runs (Table 1, compare
entries 5–7), indicating a loss of vanadium metal during the
reaction and catalyst recovery processes. Further investigations
of the leaching of vanadium metal during the recycle reactions
were also carried out. TGA of recovered Nafion-Vpowder catalyst
after the ninth run showed that the V=O metal composition of
the powder Nafion support was 0.0041 mmol mgꢀ1. This result
indicates that approximately 2–3% of vanadium metal leached
out of the support during each reaction cycle.
and aliphatic aldehydes. This new catalytic protocol represents a
mild and practical synthetic approach to achieve potentially
biologically and pharmaceutically useful a-hydroxyphosphonates
under mild conditions without using organic solvents. Further-
more, the solid perfluorinated oxovanadium catalyst can be easy
recovered and recycled and therefore meets the standards of
green chemistry.
Acknowledgements
Financial support was granted by the National Science Council
of the Republic of China (98-2119-M-145-001-MY2). We thank
Professor Chien-Tien Chen for providing chemicals and for
useful discussions and fruitful contributions. We thank the
thermogravimetric analysis laboratory of National Taiwan Univer-
sity and the X-ray photoelectron spectrometry and electron para-
magnetic resonance laboratory of National Chung Hsing University
for TGA, XPS, and EPR measurements.
Hydrophosphonylation with Various Aldehydes
References
In addition to the parent benzaldehyde, various aromatic alde-
hydes with varying electron demands (heterocyclic, a,b-unsaturated,
and propargyl) and aliphatic aldehydes were also tested in the
hydrophosphonylation reaction catalyzed by 5 mol% recoverable
Nafion-Vpowder catalyst under solvent-free conditions (Table 2). In
general, reactions with liquid aromatic aldehydes (entries 5–9 and
12–16) proceeded faster than those with solid aldehydes (entries
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Conclusions
We have developed a highly potent NafionW-supported oxovanadium
catalyst for the hydrophosphonylation of a wide range of aromatic
Appl. Organometal. Chem. (2012)
Copyright © 2012 John Wiley & Sons, Ltd.
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