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The Intramolecular Allenylidene to Indenylidene Rearrangement Demonstration

Kinetic studies of diallyltosylamide RCM reaction monitored by NMR and UV/VIS spectroscopy showed that thermal activation of the catalyst precursors la and Ib (25-80 °C) led to the in situ formation of a new species which could not be identified but appeared to be the active catalytic species [52]. Attempts to identify this thermally generated species were made in parallel by protonation of the catalysts I. Indeed, the protonation of allenylidene-ruthenium complex la by HBF4 revealed a significant increase in catalyst activity in the RCM reaction [31,32]. The influence of the addition of triflic acid to catalyst Ib in the ROMP of cyclooctene at room temperature (Table 8.2, entries 1,3) was even more dramatic. For a cyclooctene/ruthenium ratio of 1000 the TOF of ROMP with Ib was 1 min and with Ib and Sequiv. of TfOH it reached 950min [33]. [Pg.259]

The stoichiometric protonation of complex Ib with TfOH at low temperature was followed by H, NMR spectroscopy [34]. At —40°C, the protonation of the [Pg.259]

Entry Catalyst Ratio Acid (amount(eq)) Time Yield (%) 10 xM PDI TOF (min ) [Pg.260]

This carbyne was shown not to be the RCM active species. At —20 °C it rearranged spontaneously into the indenylidene complex XV with release of TfOH. This intramolecular transformation corresponds to the electrophilic ortho-substitution of one phenyl group by the electrophilic carbyne carbon of XIV. The carbene complex XV was identified as the species thermally formed in situ from the catalyst precursors Ia,b in the range 25-80 °C. [Pg.260]

These observations constituted the first evidence for intramolecular rearrangement of allenylidene into indenylidene ligand, although the first isolation by [Pg.260]


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Allenylidene

Allenylidenes

Demonstration

Demonstrators

Indenylidene

Intramolecular rearrangements

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