A study of Noyori's reagent

The reaction of LiAlH4 with ROH (R = Pr-i, Bu-t) and binaphthol (binapH(2)) in a 1:1:1 ratio in ether-THF yields a dominant Al-27-NMR signal which is attributed to LiAlH(OR)(binap) (1). However, within a short time more signals emerge, and, depending on concentration, temperature and time the following compounds were isolated and characterized by X-ray structure analysis: LiAlH2(binap).2THF (2.2THF), Li3Al(binap)(3).6THF (3.6THF), Li2Al2(binap)(4).4THF (4.4THF), LiAl(OR)(2)binap.2THF (5.2THF), LiAl(OR)(2)binap.PMDTA (SPMDTA) and Li,ALH(binap)(2).4THF (6.4THF). Moreover, the alane derivative AlH(binap)THF (6), which is dimeric in the solid state, has been prepared and its structure determined. Thus, ligand redistribution is a typical feature for the Noyori reagent in consonance with other lithium alkoxyaluminates. The active species of Noyori's reagent still needs to be discovered. (C) 2001 Elsevier Science B.V. All rights reserved.