Andrianarison, Mbolatiana M, Avent, Anthony G, Ellerby, Miles C, Gorrell, Ian B, Hitchcock, Peter B, Smith, J David and Stanley, David R (1998) Complexes of lithium tetrahydroaluminate with NNN'N'-tetra-methylethane-12-diamine(tmen). Crystal structures of [\{Li(tmen)-(AlH4)\}2] and [Li(tmen)2][AlH4] and the use of the 6Li-\{1H\} nuclear Overhauser effect to study LiAlH4 and LiBH4 in donor sol. Journal of the Chemical Society, Dalton Transactions. 249 - 253. ISSN 1472-7773

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Abstract

Two crystalline complexes (1∶1 and 1∶2) of LiAlH4 with N,N,N′,N′-tetramethylethane-1,2-diamine (tmen) have been isolated. A crystal structure determination of the 1∶1 complex showed that it formed centrosymmetrical dimers in which [AlH4]– anions and [Li(tmen)]+ cations are linked by µ-hydrogen bridges. Bond lengths and angles within the non-planar eight-membered rings are Al–H 1.55(3), Li–H 1.99(3) Å, H–Li–H 131(1) and H–Al–H 112(1)° and the exocyclic Al–H distance was 1.53(4) Å. Cryoscopic data indicated that the dimeric structure with Li–H–Al bridges was preserved in benzene solution and measurements of the 6Li-{1H} nuclear Overhauser effect (NOE) showed the presence oH–Al interactions. The 1∶2 adduct [Li(tmen)2][AlH4] 2, which crystallised with an ionic NaCl structure, was converted into 1 by heating under vacuum at 120 °C. The NOE measurements on solutions of 2 in benzene showed the presence oH–Al interactions even when a large excess of tmen was present. Aluminium-bound hydrogen was shown to be near to lithium in solutions of LiAlH4 in diethyl ether, tetrahydrofuran, mono- and di-glyme [MeO(CH2)2O(CH2CH2O)nMe, n = 0 or 1]. The NOE measurements on solutions of LiBH4 in Et2O and NMR spectra of partially deuteriated species suggested the formation of contact ion pairs, witH4B interactions which were fluxional on the NMR time-scale.

Item Type:	Article
Schools and Departments:	School of Life Sciences > Chemistry
Depositing User:	David Smith
Date Deposited:	06 Feb 2012 20:11
Last Modified:	11 Jun 2013 14:15
URI:	http://sro.sussex.ac.uk/id/eprint/24564

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