alkane was found to be predominant compared to higher alkanes. This was in sharp
contrast to the narrow distribution observed in the case of propane metathesis (C n
+1 > C n À 1) . Further experiments for metathesis of n-hexane to n-nonane also showed
similar product distribution. The distribution of product was found to be independent
of the alkane carbon number. However, such a product distribution was closer to that
reported with fully heterogeneous tandem system (Fig. 4). We assume that we have
an ISOMET-PARAFFIN process by opposition to ISOMET-OLEFIN [6, 75].
The drastic improvement in the catalytic activity was observed when 27 is
replaced by [SiO 2 –Al 2 O 3-500 –WMe 5 ] (28) catalyst precursor [49]. It gave
350 TON as compared to 153 TON using 27 as a catalyst precursor. This clearly
shows the effect of the support as a ligand on the activity of catalyst. It should be
noted that the product distribution was similar for the catalyst precursors 27 and 28.
Further investigation on the metathesis of 1-decene (an expected olefin during
the alkane metathesis of n-decane) and the hydrogenation of the products formed
clearly demonstrated that the distribution resulting from alkane and olefin metathesis completely differs with the same catalyst. If there is no double-bond migration, 9-octadecene and ethylene are expected to be the major primary products.
Indeed, these primary products are observed, as the temperature reaches 150
C.
However, after just 15 min, C 7 to C 12 and C 13 to C 20 olefins are also observed,
clearly indicating that some isomerization of double bond occurs leading to
several competitive metatheses (Fig. 5).
In the proposed mechanism, for the olefin metathesis, the W-bis-carbene is
generated via hydrogen transfer from the methyl to the W-methylidyne in the
presence of an olefin. This further undergoes [2+2] cycloaddition with external
olefin followed by cycloreversion to give ethylene and W-alkylidene, which reacts
Fig. 4 Product distribution of n-decane metathesis for the catalysts [(SiO)WMe 5 ] Si-Al-500
New Concept of C–H and C–C Bond Activation via Surface Organometallic. . .
175
contrast to the narrow distribution observed in the case of propane metathesis (C n
+1 > C n À 1) . Further experiments for metathesis of n-hexane to n-nonane also showed
similar product distribution. The distribution of product was found to be independent
of the alkane carbon number. However, such a product distribution was closer to that
reported with fully heterogeneous tandem system (Fig. 4). We assume that we have
an ISOMET-PARAFFIN process by opposition to ISOMET-OLEFIN [6, 75].
The drastic improvement in the catalytic activity was observed when 27 is
replaced by [SiO 2 –Al 2 O 3-500 –WMe 5 ] (28) catalyst precursor [49]. It gave
350 TON as compared to 153 TON using 27 as a catalyst precursor. This clearly
shows the effect of the support as a ligand on the activity of catalyst. It should be
noted that the product distribution was similar for the catalyst precursors 27 and 28.
Further investigation on the metathesis of 1-decene (an expected olefin during
the alkane metathesis of n-decane) and the hydrogenation of the products formed
clearly demonstrated that the distribution resulting from alkane and olefin metathesis completely differs with the same catalyst. If there is no double-bond migration, 9-octadecene and ethylene are expected to be the major primary products.
Indeed, these primary products are observed, as the temperature reaches 150
C.
However, after just 15 min, C 7 to C 12 and C 13 to C 20 olefins are also observed,
clearly indicating that some isomerization of double bond occurs leading to
several competitive metatheses (Fig. 5).
In the proposed mechanism, for the olefin metathesis, the W-bis-carbene is
generated via hydrogen transfer from the methyl to the W-methylidyne in the
presence of an olefin. This further undergoes [2+2] cycloaddition with external
olefin followed by cycloreversion to give ethylene and W-alkylidene, which reacts
Fig. 4 Product distribution of n-decane metathesis for the catalysts [(SiO)WMe 5 ] Si-Al-500
New Concept of C–H and C–C Bond Activation via Surface Organometallic. . .
175