Projects per year
Abstract
The lithium TMP-aluminate bases "LiTMP·Al(iBu) 3" 1 and "LiTMP·Al(TMP)(iBu) 2" 2, where TMP is 2,2,6,6-tetramethylpiperidide, have recently come under the spotlight as "aluminating" reagents in that they can perform aluminium-hydrogen exchange on a wide variety of aromatic substrates. Previous studies have intimated that 1 existed as a single species in THF solution formulated as [(THF)·Li(μ-TMP)(μ-iBu)Al( iBu)2] 1·THF, having a contacted ion pair structure as evidenced by an X-ray crystallographic study of isolated crystals. But here using anisole as a case substrate it is revealed that pre-crystallised 1·THF cannot deprotonate anisole at all whether in hexane or THF solution contradicting earlier in situ applications of 1 which revealed near quantitative metallation of anisole. NMR spectroscopic studies of 1 made in situ in THF solution ascribe this reactivity distinction from 1·THF to complex equilibria involving five major species in LiTMP·THF, Al( iBu)3·THF, [{Li(THF)4} +{Al(TMP)(iBu)3}-] 1·(THF)4, [(THF)·Li(μ-TMP)(μ-OC4H 7)Al(iBu)2], 4, and (TMP)Al( iBu)2·THF. Reagent 2 in contrast is found to exist as only two separated homometallic species in LiTMP·THF and (TMP)Al( iBu)2·THF in THF solution. The constitutions of 1 and 2 in non-polar hexane solution are also revealed. With the aid of DFT calculations, discussion focuses on the fact that none of the aluminate species present in THF solutions of 1 or 2 can deprotonate/metallate anisole, instead the metallation processes appear to be LiTMP lithiations followed immediately by trapping by an alkylaluminium complex, in a metal exchange which drives the reaction to the product (arylaluminated) side.
Original language | English |
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Pages (from-to) | 3031-3045 |
Number of pages | 15 |
Journal | Chemical Science |
Volume | 5 |
Issue number | 8 |
Early online date | 7 May 2014 |
DOIs | |
Publication status | Published - 1 Aug 2014 |
Keywords
- aluminium–hydrogen exchange
- x-ray crystallography
- lithium-mediated alumination
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Projects
- 2 Finished
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A co-operative bimetallic approach for the transformation of lithiation
Mulvey, R. (Principal Investigator)
EPSRC (Engineering and Physical Sciences Research Council)
1/03/13 → 29/02/16
Project: Research
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MIXED-METAL MOLECULAR SYNERGY (WOLFSON MERIT AWARD)
Mulvey, R. (Principal Investigator)
1/04/09 → 31/03/14
Project: Research