Synthesis and structural characterization of zirconium complexes containing aminodiolate ligands and their use as Lewis acid catalysts

A series of aminodiols RN(CH2CH2C(OH)R-2')(2) (R, R' = Me, Me 4; Me, Ph 5; tert-butyl, Me 6; tert-Bu, Ph 7; (S)-PhCH(Me), Me 8) were prepared by the M ichael addition of a primary amine to methyl acrylate followed by reaction of the resulting aminodiester with excess methyl or phenyl lithium. Reactio n of two equivalents of the aminodiols 4-8 with tetrabenzylzirconium afford ed the zirconium bis(aminodiolates) 10-14 in excellent yield. Complex 11 (R , R' = Me, Ph) adopts a cis, fac-octahedral geometry in solution and in the solid state. Complexes 10-14 are fluxional in solution by NMR spectroscopy : small substituents at nitrogen and large substituents at the alkoxide car bons slow the rate of exchange. The chiral complex 14 functions as a Lewis acid catalyst in the nitroaldol (Henry) reaction and the oxidation of geran iol by tert-butyl hydroperoxide with modest enantioselectivities (30 and 46 % enantiomeric excess (ee), respectively).