[Dan]

I was wondering if anyone knows of a method to do this:

R-C≡C-TMS    R-C≡C-MgX

Either in one pot or directly in one step.

Normally I make these Grignards by deprotonation of terminal alkynes with iPr-MgCl, but in this case the terminal alkyne I would need is volatile (but I can access the TMS-capped version quite easily).

It seems I could probably access the iodoalkyne (hopefully not too volatile) directly from the TMS-alkyne and then do a metal-halogen exchange, but if anyone knows a way to directly exchange the TMS, I would be interested to know.

[TheUnassuming]

What are you trying to add the alkyne into? 
I've seen some one pot methods that use lewis acids to one pot add TMS-alkynes to acyl-chlorides

[pgk]

R-C≡C-I  +  Mg  →  R-C≡C-MgX
The problem is that electron pairs of Iodine will conjugate with the triple bond and make the magnesium insertion, very difficult. However, vinyl Grignards from vinyl halides (that behave the same way) can directly be prepared by the Normant method.
1). Org. Synth. 1959, vol. 39, p.10, (1959)
http://www.orgsyn.org/demo.aspx?prep=cv4p0258
2). Org. Synth. Coll. Vol. 4, p.258, (1963)
http://www.orgsyn.org/Content/pdfs/procedures/cv4p0258.pdf
So, try to do something similar or modify the conditions. It may work.
PS1: Take care of any exothermic or vigorous reaction.
PS2: Pay attention to an adequate activation by adding a small crystal of iodine or traces of Pr-MgCl
PS3: If you need higher temperature, you can use anhydrous glyme (1,2-dimethoxyethane) with bp = 85 °C. Glyme and higher glymes are water soluble that makes extraction difficult. So, you need to saturate the aqueous phase with NaCl, during extractions.

[discodermolide]

Is it not worth just trying the Si to Mg exchange reaction? Perhaps adding LiCl (Knochel).

[Dan]

R-C≡C-I  +  Mg  →  R-C≡C-MgX
The problem is that electron pairs of Iodine will conjugate with the triple bond and make the magnesium insertion, very difficult. However, vinyl Grignards from vinyl halides (that behave the same way) can directly be prepared by the Normant method.

I am not planning to do a Mg insertion, but rather a metal halogen exchange with iPrMgX. Also, I need an alkynly Grignard, not an alkenenyl Grignard.

What are you trying to add the alkyne into? 

An in-situ generated N-acylquinolinium - it's a Reissert type reaction. It works extremely well with other alkynyl Grignards I have tried already.

Is it not worth just trying the Si to Mg exchange reaction? Perhaps adding LiCl (Knochel).

Since I have to make the TMS-alkyne whatever I do, I will of course test this.

[pgk]

It was proposed for alkynyl Grignard preparation but I do not insist because it might not work.