G.S. Forman, R.P. Tooze / Journal of Organometallic Chemistry 690 (2005) 5863–5866
5865
with added p-cresol (500 equiv.), whereas only 58% con-
version was obtained in the absence of p-cresol (Entry
3). A similar effect was observed for the CM of methyl
acrylate with styrene (Entries 6–8). Additionally, the
efficiency of CM reactions between methyl oleate and
methyl acrylate was also increased with p-cresol addition
(Entry 9). In certain instances the combination of cata-
lyst 2 and phenols also appear to produce greater selec-
tivity towards the desired product. For example, for the
CM reaction between methyl oleate and methyl acrylate
(Entry 9), in the absence of added p-cresol, 45% conver-
sion was obtained with 87% selectivity towards end
products, while with added p-cresol, 82% conversion
was obtained with 95% selectivity towards products.
In most instances the E/Z ratio in reactions with
added p-cresol is often significantly higher than for reac-
tions with only catalyst 2. For example, with 0.025
mol.% of catalyst 2, the CM of methyl acrylate with 1-
decene produced an E/Z ratio of 26:1 after only 2 h with
added p-cresol (500 equiv.), whereas an E/Z ratio of
only 13:1 was obtained in the absence of p-cresol (Entry
3). In this context, these results can be rationalized in
terms of faster decomposition of catalyst 2 in the ab-
sence of p-cresol, preventing conversion of the sterically
more accessible cis-isomer to the trans-product [8].
Addition of p-cresol appears to impart greater catalyst
lifetime, which allows for continued reprocessing of
the cis-product to the trans-product.
In summary, this report has shown that the activity
and lifetime of CM reactions between acrylate esters
and terminal olefins catalyzed by 2 can be enhanced
by the simple addition of phenols such as p-cresol. This
system gives rise to higher conversions and greater E/Z
selectivity compared to reactions where only 2 is used,
and a natural consequence of the greater catalyst effi-
ciency described above is lower catalyst loadings and
more economical metathesis processes. Studies aimed
at further increasing the efficiency of Ru–carbene
metathesis catalysts and applying them to industrially
relevant applications are ongoing.
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1
[Ru] = CH(CO)R by H NMR in the presence and ab-
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