Alkylidene proton exchange

The stable ruthenium alkyhdenes, used for catalysis of ring opening metathesis polymerizations, were found to exchange the alkylidene proton for a deuteron in D2O or in CD3OD (Scheme 9.4) [13],... 

The reaction is thought to proceed with the dissociation of Cl" followed by release of the extra charge of the mthenium complex by dissociating a proton from the alkylidene ligand. Such an exchange in itself does not lead to the decomposition of the alkylidene complex. Nevertheless, both the formation of the charged species, both the intermediate existence of the carbyne complex (Scheme 9.5) may open new ways to the deterioration of the ROMP catalysts. 

Only alkyl groups at indole a-positions show any special reactions. Many related observations confirm that in a series of equilibria, / -protonation can lead to 2-alkylidene-indolines, and hence reactivity towards electrophiles at an a-, but not a /3-alkyl group, for example in DCl at 100 °C 2,3-dimethylindole exchanges H for D only at the 2-methyl. 

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