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Author: Subject: Synthesis of palladium nano-particules and their use in Suzuki coupling
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[*] posted on 18-1-2010 at 13:25
Synthesis of palladium nano-particules and their use in Suzuki coupling

I present the preparation of palladium nanoparticules and their use in Suzuki cross-coupling reaction.

Palladium nanoparticules are efficient heterogeneous catalysts for number of palladium-catalyzed reactions. Unlike precipitated particules, they are active without dissolution or use of ligands.
To favor small particule size, a linear polymer (PolyVinylPyrrolidone, PVP, M: 40 000) is used to ensuregood distribution of the particules and to prevent agglomeration.

Preparation of nano-particules of palladium

5,0mg (0,028 mmoles) of PdCl2, 0,5mL 2M HCl and 14,5mL milli-Q H2O are combined in an erlenmeyer flask. The suspension is stirred until complete dissolution of th solids
The solution is then transfered to a 100mL RBF with 21mL dH2O, 14mL EtOH and 66,7mg PVP (Pd/PVP 1/20). The light orange solution is heated to reflux for 2H, during which the solution turns dark brown/grey. The reaction is followed by UV-Vis, follwing the disaperance of a peak at 235nm ([PdCl4]-). The nano particules are then cooled to room temp and used as is in the coupling reaction

Synthesis of biphenyl via Suzuki coupling

In a 250mL RBF are combined: 183,0mg (1,5mmol) phenylboronic acid, 78,5mg (0,5mmol) bromobenzene and 408,2mg (3mmol) sodium acetate trihydrate. 50mL MeCn and 25mL dH2O are added, followed by the nanoparticules solution. The dark brown solution is heated to reflux for 30min.
The flask is then cooled down and extracted with 3x40mL pet ether. the xtracts are dried and evaporated at the rotavap. The biphenyl is obtained in a yield of 43%.

I'm going to try using PD/C as a catalyst for this wonderfull reaction, as I haven't got any PdCl2 left.. I would like to get some more exotic boronic acids, surely making then by grignard, as I only have a gram of phenylboronic acid left. I could always make it from bromobenzene, of which I have enough.

Any suggestions on new substrates? I'd like to look into chiral products, with susbtitued arylbromide, I worked on a Suzuki coupling with calixarene-phosphine ligands on chiral products, and I am going to work 2 to 4 months on this same reaction using chiral ferrocene-phosphine ligands! Whoho very interesting!

Lets' revive the organometallic and catalysis spirit of SM!

EDIT: forgot the ref:

Size control of palladium nanoparticules and their crystals structures
T. Teranishi and M. Miyake
Chem. Mater.; 10, 594-600 (1998)

[Edited on 18-1-2010 by Klute]

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[*] posted on 18-1-2010 at 15:33

Hm, you have milliQ on tap there? Very nice.

I would think that the Suzuki coupling would be good for larger functionalized molecules, or perhaps a macrocyclization. If you used the Suzuki coupling on smaller molecules as a substitute for a grignard reacting on a relatively plain molecule, it would seem like a bit of a waste.

Also, how do you plan on recovering the catalyst?
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[*] posted on 24-1-2010 at 13:42

Beautiful ligand-free contribution and thanks a lot Klute.

The paper you refer to only gives the instructions to prepare the Pd nanoparticles. Is the application of the so prepared solution in the Suzuki coupling your idea or you found similar examples in the literature?
You should however know, that with 5.6 mol% palladium and a threefold bromobenzene excess, a 43% yield leaves much to be optimized. It is known that on similarly easy ortho-unsubstituted substrates even using the same amount of palladium on carbon (ligand-free) gives good results (biphasic Na2CO3(aq) or K2CO3(aq) with toluene, THF or DME) even without bromoaromate excess. Perhaps the nanoparticles collapsed under the reaction conditions? Have you noticed palladium black formation (the reaction mixture typically turns dark and sometimes a fine black precipitate forms when more Pd catalyst is used)? If so, you might try using only tiny amounts of your palladium nanoparticles solution (<0.1 mol%). This is a now already known trick to prevent ligand-free palladium(0) deactivation in Suzuki, Heck and other couplings (provided of course that you have reactive substrates: ortho-unsubstituted, not electron rich aryl bromide/iodide). I know it is somewhat paradoxical and counterintuitive that the lower the catalyst loading the better the results, but then again, here we talk about phosphineless situations. Check Adv. Synth. Catal., 346[7i], 1812–1817 for one such example.

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[*] posted on 24-1-2010 at 14:28

I want to ask plz can this be used in reduction of aromatic nitro group
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