I am using the said reagent (0.5 eq) to cleave off the allyl Pg on resin, in presence of phenylsilane (25 eq) in DCM.
After repeating the protocol 6 times for 20 min, the resin changed color, becoming dark orange. Would this be indicative of some kind of contamination, and if so, could this hamper any following synthetic step?
Thank you
Thank you dott. Shaban but i do not have access to this papers....any clue about the reason why my resin turns dark ?(ps the HPLC of my product after alloc cleavage is completely fine and clean...I am just a bit concerned about this intense color change of the resin...)
A colour change in the resin would suggest the formation of a charge transfer complex in the resin polymer; This is likely to only be an extremely minor occurrence, as the molar extinction coefficients for charge transfer complexes tend to be very high.
If it is a charge transfer complex then it is unlikely to significantly interfere with any further chemistry.
I don't know what the reagents you use and the treatment youn want to do. The color of Pd(PPh3) turn to deep brown usually indicate oxidation of Pd(0) to Pd(II) was occurred. Pd(PPh3) is easy oxidized even by PhX(x=-Cl, Br). I hope it is helpful for your reference.
thanks to everybody.....since the hplc did not show any significant impurity beside the expected peak, I guess that this is the case of a charge transfer complex in the polymer as Enric suggested....probably the event could have been promoted by the catalyst used...another chance could be that the oxidized Pd(II) somehow is bound to the resin as consequence of what Keh suggests....still thank you
If the Palladium is bound to the resin causing the colour change then you could try washing the resin with aqueous Na2EDTA. Although that might only be worth doing if you would expect the presence of Pd(II) to interfere with further chemistry.
The best washing is 5% sodium diethyldithiocarmate in DMF twice 5 in. Your resin will become clean of Pd
I always wash throughly with DCM and DMF and then with 0.5% sodium diethyldithiocarmate in DMF, 10 mL/g resin, 3 times, 5 min each washing.
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