Phosphine scavengers

NMR and UV-visible kinetics, and mass spectrometry [8], Consistent with a dissociative mechanism, catalytic turnover is inhibited by the addition of free phosphine, and enhanced by the addition of phosphine scavengers [8],... 

T, T -PhC=C=CH2)] (56) is promoted by the phosphine scavenger Fe2(CO)9. This represents the first example of such a transformation. Reacting Pt(PPh3)4 with [Ru(CO)2Cp(CH2C=CPh)] gave high yields of the binuclear /A-Tj, ij -allenyl 55, with the presence of excess phosphine preventing conversion to the form (Jb). 

Finally, in efforts aimed at accomplishing both RCM and cross-metathesis (CM) in protic solvents [225], hydrophilic PEGA-NH2 resin was acylated with 3-(3-iso-propoxy-4-vinylphenyl)propionic acid, and the resulting amide (109) was treated ivith the Grubbs ruthenium alkylidene in the presence of CuCl as a phosphine scavenger (Scheme 25). 

Recently, Grubbs and co-workers reported the use of neutral salicylaldimine nickel complexes (e.g., complex III) for ethylene polymerizations.A phosphine scavenger (e.g., Ni(COD)2) is used as an activa-... 

These results have signihcant implicahons for olehn metathesis reachons involving ruthenium methyhdene versus subshtuted alkylidene complexes. First, the use of phosphine scavengers to increase the overall rate of metathesis results in a concomitant increase in the rate of catalyst decomposition. This effect is manifested in the high reachvity but limited longevity of catalysts in the presence of CuCl and HCl [86,93,94], For instance, the half life of (PCy3)2(Cl)2Ru=CHPh... 

The highly substituted, chelating, vinylcarbene ruthenium complex 22 has been prepared by Fiirstner [40] via the reaction of 6 with ortho-isopropoxyethynylbenzene in dichloromethane at room temperature. Silver chloride (AgCl) was added to this reaction as a phosphine scavenger. Complex 22, which results from a formal insertion of the triple bond into the Ru=C via a [2-1-2] cycloaddition, was not evaluated as a metathesis catalyst in this report. 

It is common to use Bronsted acids as phosphine scavengers in olefin metathesis phosphine bearing catalysts. On the other hand, it is obvious that HCl plays a different role in catalyst 4d, since this complex does not carry a phosphine ligand. To understand more about the activation mechanism, an NMR study was undertaken. 

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