[Jens]

Hello. I am trying to better understand the reaction mechanism between tert-butyldimethylsilyl chloride and a primary alcohol (i just used butan-1-ol as an example) in pyridine as solvent.

I have searched all over the internet and found that some people mention pentavalent Si intermediates. I have drawn two (I think) possible reaction mechanisms, but are not quite sure if they're correct.
In reaction two I am assuming pyridine will react with tbdms and make a more reactive intermediate?
I am not quite sure about the role of pyridine as a weak base, or if pentavalent intermediates do "appear" or if the reaction is more Sn2 like.
Any help is greatly appreciated
Reaction mechanism 1:

Reaction mechanism 2:

[Babcock_Hall]

I don't know what the mechanism is.  However, the ability of pyridine to act as a nucleophile in some alkylations and acylations is made plausible by the ability of DMAP to act as a very good nucleophilic catalyst in some reactions.

[Jens]

If DMAP was present wouldn't DMAP just react nucleophillic with Si and form a more reactive intermediate?
I am thinking that both DMAP, imidazole and pyridine should be able to do this, DMAP and imidazole just being more reactive?

[Babcock_Hall]

You are probably correct, but I would not rule out the possibility that DMAP can also act as a base (maybe both are occurring--one would have to study this to be certain).  I only raised DMAP to illustrate plausibility in any case.  BTW, I seem to recall seeing some silylation recipes that use imidazole, which (as you point out) could also be a nucleophilic catalyst.

[Jens]

If DMAP reacted like a base, would it deprotonate the alcohol group to form an alkoxide anion, which would be a stronger nucleophile and hence more reactive towards silylation?

Thank you for your replies btw

Best regards

[Babcock_Hall]

Catalysis by a base might also be concerted with bond formation between the oxygen and the Si atom.

[AWK]

http://www.organic-chemistry.org/protectivegroups/hydroxyl/tbdms-ethers.htm