EARLY TRANSITION-METAL ALKOXIDE COMPLEXES BEARING HOMOCHIRAL TRIALKANOLAMINE LIGANDS

Enantiomerically pure trialkanolamines of the formula N(CH(2)CHROH)(3), where R = methyl (3a), cyclohexyl (3b), tert-butyl (3c), or phenyl (3d), are readily synthesized by the reaction of ammonia with 3 equiv of an enantiopure epoxide. Trialkanolamines 3a-d replace n-propanol in tri-n-propyl vanadate to afford corresponding complexes 4a-d of the formula LV=O, where L is the deprotonated trialkanolamine. Similarly, (S,S,S)-triisopropanolamine 3a reacts with Ti((OPr)-Pr-i)(4) to produce monomeric LTi((OPr)-Pr-i), 7a, which upon treatment with acetyl chloride gives the chloro complex LTiCl, 7b. The later group 5 ethoxides react with 3a to produce LM(OEt)(2) (M = Nb, Ta). Partial hydrolysis of the Nb and Ta derivatives produces tetrameric mu-oxo-bridged structures which retain the trialkanolamine ligands. In all complexes the transition metal resides in a highly asymmetric environment, suggesting that this class of complexes may find use in the field of asymmetric catalysis. The X-ray crystal structures of complexes 4c and 7b are reported.