Dr. Beaker - 9-11-2007 at 12:40
Hi All,
I've been attempting the last week to make TiBn4:
http://www.syntheticpages.org/browse.php?&action=1&p...
My first attempt was with 2M BnMgCl in THF. I got only traces of the tetrabenzyl.
2nd attempt was with 1M BnMgCl in ether. I got red crystlline material, but NMR showed me it has about 40% mol of dibenzyl. (and that after 2
recrystalizations from hexane...)
any idea to get the pure compound?
JohnWW - 9-11-2007 at 13:08
Attempting to make it with a Grignard reagent like that may not be particularly easy, because of Ti being fairly electropositive and quite high in the
electrochemical series, although Mg (byproduct MgCl2 here) is higher in the series.
vulture - 9-11-2007 at 15:24
The writeup is a bit ambigous, they mention schlenk, but do not explicitly mention inert atmosphere. I'd think tetravalent Ti(0) compounds would be
pretty air sensitive.
Dr. Beaker - 9-11-2007 at 23:44
The procedure in that web page is a modification of the one in the reference (Gianni et all).
This paper is referred to by many papers who used TiBn4 as a reagent.
So, I don't think there's something wrong with the procedure.
I'm doing this on a Schlenck line, and yes, TiBn4 is highly air and water sensitive
vulture - 10-11-2007 at 03:47
I'm not saying the procedure is wrong, it's just somewhat short and not very detailed.
Apart from testing the purity of your Grignard and TiCl4, I can't see what's going wrong here. Maybe something goes wrong in the filtering step? Have
you tried sampling the crude reaction mixture?
Dr. Beaker - 10-11-2007 at 06:27
The grignard is new from aldrich. The TiCl4 is double distilled (from a very old botlle, though...) so it's the only suspect.
I may order a new one and use it, though I managed to make Cp2TiCl2 with it...
But any idea to seperate TiBn4 from Bn2?
vulture - 10-11-2007 at 06:41
Well, nevertheless check the Grignard reagent if you can't figure out what's going wrong. I've had a new bottle of methylmagnesiumchloride that turned
out to be a batch of gunk for some weird reason.
This compound apparently has to be stored below -30C. Is it possible that it just decomposes while you're taking the NMR spectrum?
Dr. Beaker - 10-11-2007 at 10:14
according to the Gianni paper only 1.5% TiBn4 decompose in toluene solution in RT after 8 hrs.
I took the NMR 20 min after making the solution.
I may also try to titrate the grignard just to be sure..
[Edited on 10-11-2007 by Dr. Beaker]