7/26/2007

Medusa's Silylation Reagent of Choice

First, I apologize for my blogging infrequency- I have been busy, stressed out, dejected, pissed off and making significant progress all at the same time. Seminar season is almost upon me, and you damn well better know you'll be hearing about it. I haven't posted anything recently with the F-word in it, too, so... I need to change that.

I've been working with triethoxysilane recently. It is a useful precursor to alkyltriethoxysilanes. Hydrosilylation of olefins with triethoxysilane requires a catalyst. Typically, chloroplatinic acid, H2PtCl6, is used, but another, far more powerful hydrosilylation catalyst, Karstedt's Catalyst (shown below), is my catalyst of choice. Catalytic hydrosilylation of terminal olefins with platinum proceeds with anti-Markovnikov addition. Karstedt's catalyst has also been used frequently in silicon-based cross-coupling reactions.


But triethoxysilane is a double-edged sword, a monster in disguise. You have to treat her with respect, or, like Medusa's gaze, she will do the following:



As it turns out, triethoxysilane and its cousins trimethoxysilane and tetramethyl orthosilicate (a useful sol-gel precursor) have this awesome tendency to form silica and polysiloxanes upon contact with water. Your eyes, by the way, have water in and on them, so you can imagine the havoc these things can wreak. (Then again, having a real, living glass eye... would be so pirate-chic.) These compounds are also volatile enough that goggles are pretty much a requirement when handling them.

Upon first seeing the label, I thought "oh fuck me, I have to use this shit, don't I?" But I am careful- I wear goggles when this stuff is open, and am pretty careful with it, and the foul beast has yet to blind me with her evil mist. Now every time I see the label, I think, "Bring it on, motherfucker."

Bring. It. ON.

11 comments:

Alcifer said...

Haha - nice pirate-chic joke.

Ψ*Ψ said...

That's a label I'm glad I've not yet come across.

Kyle Finchsigmate said...

The first rule of blogclub is to never apologize for infrequent blogging. Remember: you are the Beethoven here. The artist doesn't decide when the art happens, s/he just makes it happen when it comes.

Excimer said...

If I'm the Beethoven, then ψ*ψ is the, um... Bach. Or something. Anyway, I generally write the apology for her cause I feel bad having her pick up my slack.

Propter Doc said...

Tetramethoxysilane gives the double blindness whammy - methanol and Si-O-Si on contact with water. I always find tetraethoxysilane smells like parsnip. Three years of the stuff and my eyesight is still fine.
The cool thing with Karstedt's and Spieir's Catalysts is they work better with a touch of oxygen in the system. Provided your substrate works fine with that of course.

Excimer said...

tetraethoxysilane is apparently not blindness-causing according to Gelest's MSDS, probably because it's neither very reactive with water nor volatile.

I have yet to see a decent mechanism for Karstedt hydrosilylation (I haven't really looked either), but I wonder why oxygen helps the reaction? Pt(0) need an additional oxidant to get to Pt(II)?

Ψ*Ψ said...

Ah, another case of paranoia on the label? I saw a good one the other day. I'll post it soon...
Oh, and Excimer...you'll be picking up the slack for me here in a week-ish. Heh heh heh...

Propter Doc said...

I have it down that oxygen acts as a promoting agent in the reaction and prevents deactivation of the platinum complexes. Karstedt's catalyst was my weapon of choice for hydrosilation - just seemed to work better. There was some talk that the active catalyst was colloidal platinum but I never really liked the papers that proposed that mechanism. The arguements were never totally convincing.
Strange, we were always told that TEOS also carried a blindness risk, glad to hear it doesn't! Trichlorosilanes often result in loss of nasal hair...HCL...yum

mevans said...

Yay silicon!

Ψ*Ψ said...

Loss of nasal hair?! This means I need to get the man in my life over to the trichlorosilane cabinet ASAP. ;)

Hap said...

There have to be easier ways of removing nasal hair than trichlorosilane - the HCl side product can't be so fun.

On the other hand, that sounds like good news for grad students and postdocs in Prof. Denmark's lab.