sonogashira party!
I'll start by admitting how much I love the Sonogashira coupling. It's a fun reaction, and it LOVES my substrates. Plus, it gives me an excuse to make Pd(Ph3P)4. Making tetrakis is one of those things you can do on a particularly bad lab day that is guaranteed to make you feel better. It's very hard to screw up, and you get shiny yellow crystals.[1] Anyway, I set three of these up the other day:
If you were wondering, yes, there appears to be a shortage of tiny little clamps in my lab. We just don't do much with 14/20 glassware (this is an exception of sorts). Maybe they're in the stockroom, but by the time I need one I'm always in the middle of setting something up, so I haven't checked. Yes, my oil bath is nasty looking. It was like that when I inherited it from the hood's previous occupant. The color reminds me of motor oil, which is a quick way to ick me out a little.[2] 
It looked exactly like metallic copper, which it doesn't quite in the picture, but close enough. Does anyone know what it could be? I've seen palladium plate out of a reaction, but copper?[3] That just seems weird. It worked, though, so I'm not complaining.
I took all three of those through silica plugs, which was more time-consuming than I would have liked.[4] I know this is pretty routine, and barely worth reading about, but since some chemists seem to be complaining about the lack of pretty colors in their lives, I had to show mine off. (You have permission to be jealous now.) Here is one of the fractions I collected:
I know blue isn't too much to be excited about in the way of fluorescence (yeah, yeah, emission probability goes as ν3, I know, red is cooler) but it's still surprising to look at a TLC plate and be distracted by an unexpected glow from elsewhere on the bench.
[1] And then you wash them with ether. Mmm. Keeps getting better and better, doesn't it?
19 comments:
The red stuff is most likely Cu2O from decomposed Cu(I) salt.
If you are working with Ar-Br (but not with Ar-I) I can recommend the PdCl2(Dppf) (3mol%) + CuI (1 mol%,) system in THF with NEt3 (1.5 eq), it is a total sweetness and one does not have to deoxygenate too much, sloppy exeecution does not hurt as long as you don't overload the reaction with copper and add the Cu salt as the last component before capping the vial.
(Adding too much Cu(I) does not make the reacion go faster, it only craps up the acetylene because of Cu promotes acetylene dimerisation)
You would also probably like Beth's latest piece too then: http://pubs.acs.org/cen/science/85/8520sci2.html
Mitch
Milkshake- what do you recommend for aryl iodides then?
Mitch- I saw those. They are stunning.
I have to admit (to my shame) that my exposure was only to aryl bromides, for which the above procedure worked best (RT to 60C) among many that I tried for my difficult heterocycles (and I kept using it ever after). Also, in attempt to make the reaction go faster I re-synthsized my substrates once with iodine and it made the the initial rate faster but reaction refused to go to completion under these conditions.
Milkshake: Thanks! According to the pic on wikipedia, that could well be it. Curiosity satisfied, I guess. I'm using aryl iodides, though, so your other recommedation won't help.
Glass TLC plates? Get a diamond or Kennametal scribe from Wale Apparatus,
http://www.waleapparatus.com/
Better still is a boron carbide flake. Lightly stroke it to glass, flex and pull, and it's effortlessly like Moses and the Red Sea. A German grad student demonstrated his, then returned it to a body cavity for safekeeping. (What, metaphor is not OK?)
I've found that the amount of unintentional breakage of TLC plates is related to the surface on which I'm cutting them. Give me a good piece of cardstock and I'm set. That one, however, was cut in a hurry on my notebook.
"Ever wonder how many YEARS of your life you've wasted staring at a rotavap?"
Oh noooooooo! i'm still trying to forget about that evil machine >_<
Warning: never ever ever play with guanindine
It's your compound on the filter and you're left with glowing Cu(II) blue solution. :)
Because copper salts will make it through a plug of silica?
I think someone's been sniffing the ether too much... ;)
Mmmmm, ether.
I heart Sonagashira reactions. And paladium catalysts. Woo hoo.
I find that repeating "I love chemistry" while watching the hypnotic spin of the 'vap keeps me going. That, and rocking back and forth in a corner.
I've changed out the oil on two vacuum pumps this week...not only is it a little weird texture-wise, it's a bitch to clean!
Something about vacuum grease also bugs me.
Also, feel free to come up and take pictures in the laser lab; we always have something pretty going (look for some blues and greens in the near future).
Vacuum grease doesn't really bother me, but automotive grease does. Plus, it's so hard to get it off your hands! Still beats getting overcharged by a mechanic, I guess.
Lasers are definitely colorful, but it's SO hard to get a good shot. You can't use a flash at all, and it's almost impossible to keep the camera still enough for a decent long exposure unless you use a tripod. I may go bother you and the supremely cool people you work with, though.
in my previous life, while doing a laser diffraction experiment, we sprayed prickly heat powder/chalk powder on the path of the diffracted light and quickly clicked away. They made it into our record notebooks. It worked fine for he-ne (is that right?) laser, we couldn't make it to the nd-yag though.
You've just discovered intelligent copper(II). Not only it glows, but leaks through silica: ionic T-1000!
Your colors are pretty....
Your oil bath is nasty...
I am suffering an amazing lack of words today!
I don't do a lot of Cu chemistry, so unsure about the copper plating out, but it certainly seems reasonable.
I inherited our Dept Head's oil baths and they resemble yours quite well. I feel the compulsion to not only change gloves, but wash hands after using them. And the rinsing of the RBFs after pulling them from said baths... EW!
Speaking of said Dept Head, Coffee break over! Time to column my amidations and electrophilic aromatic substitutions! Yay!
*also chants "I Love Chemistry" when watching either the rotovap turn or waiting for fractions to elute.
*I have found chanting not necessary when the iPod is in use.
*Can't think of any other reason for an asterisk, other than they ought to be used in numbers greater then 3, no?
Guanidine has been rocking my socks off lately, despina. Don't go knocking it.
Wow. This is what being productive in the lab will do to a person: he gets woefully behind on blog reading!
I'm going to second Milkshake's recommendation of PdCl2(DPPF). Not only is it really nice for Sonogashira reactions, but it also works really nicely in Buchwalds, especially if there's something with lone pairs around that might want to associate with the palladium.
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