title: Solvation and structure of LiAlH(4) in ethereal solvents.
abstract: The nature of the solute species present in ethereal solutions of LiAlH(4) is of crucial importance for understanding the mechanisms for the reduction of ketones and other functional groups by LiAlH(4). We have employed a combination of theoretical and experimental techniques to investigate the structure of LiAlH(4) in ethereal solutions. Using complexation agents, we measured the IR spectra of LiAlH(4) and AlH(4)(-) in tetrahydrofuran (THF). Hybrid quantum-classical (QM-MM) simulations have also been carried out to compute the IR spectra of associated and dissociated LiAlH(4) species and the free-energy profile for the dissociation process in solution. Our experimental estimate of the dissociation constant in THF is 0.021 +/- 0.002, while the predicted computational value corresponding to a model dimethyl ether solvent is 0.001. The free-energy profile shows only one minimum corresponding to a contact ion pair at a Li-Al separation distance of 3.0 A. These results are consistent with the fact that LiAlH(4) is essentially associated in ethereal solutions forming contact ion pairs.
authors: Departamento de Química Inorgánica, Analítica y Química Física, INQUIMAE-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Ciudad Universitaria, Pabellón 2, C1428EHA, Buenos Aires, Argentina.
authors: Damián E
authors: DE
authors: Bikiel
authors: Florencia
authors: F
authors: Di Salvo
authors: Mariano C
authors: MC
authors: González Lebrero
authors: Fabio
authors: F
authors: Doctorovich
authors: Darío A
authors: DA
authors: Estrin
mesh_terms: D017607:Aluminum Compounds / Q000737:chemistry*; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D005663:Furans / Q000737:chemistry*; D018020:Lithium Compounds / Q000737:chemistry*; D008738:Methyl Ethers / Q000737:chemistry; D008956:Models, Chemical; D008958:Models, Molecular; D012995:Solubility; D012997:Solvents / Q000737:chemistry
chemical_list: D017607:Aluminum Compounds; D005663:Furans; D018020:Lithium Compounds; D008738:Methyl Ethers; D012997:Solvents; C018674:tetrahydrofuran; C042073:lithium aluminum hydride; C033413:dimethyl ether