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Synthesis and structural elucidation of solvent-free and solvated lithium dimethyl (HMDS) zincates

Lookup NU author(s): Emeritus Professor Bill Clegg, Dr Luca Russo

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Abstract

Using a co-complexation methodology the unsolvated lithium zincate [LiZn(HMDS)Me2] (4, HMDS = 1,1,1,3,3,3-hexamethyldisilazide) was prepared by reaction of an equimolar amount of LiHMDS with Me2Zn in a non-polar toluene-hexane solvent mixture. X-Ray crystallographic studies reveal that the asymmetric unit of 4 has a dinuclear arrangement, based on a planar LiNZnC four-membered ring. As a result of intermolecular interactions between the lithium centre of one asymmetric unit and a terminal methyl group of another, 4 presents a polymeric chain array in the solid state. DFT calculations revealed that the formation of the polymer is the driving force for the success of co-complexation of LiHMDS and Me2Zn to yield the unsolvated zincate 4. The reaction of 4 with PMDETA (N,N,N′,N″,N″- pentamethyldiethylenetriamine) afforded the new solvated zincate [(PMDETA)Li(μ-Me)Zn(HMDS)Me] (5). X-Ray crystallographic studies show that the asymmetric unit of 5 consists of an open, dinuclear LiCZnC arrangement rather than a closed cyclic one, in which the HMDS ligand unusually occupies a terminal position on Zn. DFT computational studies showed that the structure found for 5 was energetically preferred to the expected HMDS-bridging isomer due to the steric hindrance imposed by the tridentate PMDETA ligand. The reaction of 4 with the neutral nitrogen donors 4-tert-butylpyridine and tert-butylcyanide afforded the homometallic compounds [(tBu-pyr)Li(HMDS)] (6) and [(tBuCN)Li(HMDS)] (7) respectively as a result of disproportionation reactions. Compounds 6 and 7 were characterized by NMR (1H, 13C and 7Li) spectroscopy. © The Royal Society of Chemistry.


Publication metadata

Author(s): Armstrong DR, Herd E, Graham DV, Hevia E, Kennedy AR, Clegg W, Russo L

Publication type: Article

Publication status: Published

Journal: Dalton Transactions

Year: 2008

Issue: 10

Pages: 1323-1330

Print publication date: 01/01/2008

Date deposited: 05/07/2010

ISSN (print): 1477-9226

ISSN (electronic): 1477-9234

Publisher: Royal Society of Chemistry

URL: http://dx.doi.org/10.1039/b716494g

DOI: 10.1039/b716494g


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