Organometallics
Communication
Scheme 7
AUTHOR INFORMATION
Corresponding Author
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Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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We acknowledge North Carolina State University and the
National Science Foundation via the CAREER Award (CHE-
0955636) for funding.
REFERENCES
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complex 8. (2) Complex 8 subsequently reduces benzaldehyde
to yield 9. The observed electronic dependence on the
benzaldehyde substrate (electron-withdrawing groups acceler-
ate the rate) is consistent with the reduction of the CO bond
with the Re−H.6 (3) The reaction of 9 with Me2PhSiH results
in the formation of the benzyloxydimethyl(phenyl)silane
product and the regeneration of the active Re−H complex 8.
The observed KIE (1.4) is consistent with Si−H cleavage
occurring in the product-forming step.1f,6 (4) Finally, in the
absence of benzaldehyde, two Re−H complexes 8 couple to
yield 6. Complex 6, however, is not catalytically relevant, as
catalysis with 6 is significantly slower than catalysis with 1.
To summarize, we have demonstrated that the Re(III)
complex 1 is an efficient catalyst for the hydrosilylation of
aldehydes. Catalysis with 1 was performed without solvent and
with low catalyst loadings. Importantly, 1 is significantly more
active as a catalyst than the oxorhenium(V) complexes 2 and 3
and exhibits reactivity comparable to that of the best
oxorhenium(V) complexes reported thus far. Stoichiometric
reactions between 1, 2, and 3 and the dimethylphenylsilane
result in the dirhenium(II) complexes 6 and 7. While 6 and 7
are not catalytically relevant, their facile generation from 2 and
3 and the observed high reactivity of the Re(III) complex 1
suggests that when oxorhenium complexes are employed as
catalysts, the active species are not high-valent rhenium oxos,
but species that are generated upon deoxygenation with
Me2PhSiH. This work suggests that low-valent Re species
that are generated by the reduction of high-valent metal oxos
may be catalytically relevant and, consequently, their activity
should be systematically investigated.
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ASSOCIATED CONTENT
* Supporting Information
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S
Text, figures, tables, and CIF files giving experimental
procedures, crystallographic data for 6 and 7, and spectroscopic
data for organic products. This material is available free of
5997
dx.doi.org/10.1021/om300654q | Organometallics 2012, 31, 5994−5997