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Interest in the catalytic activation of peroxides, together with the requirement of stereoselectivity for the production of enantiopure sulfoxides, has made sulfoxidation the ideal playground for theoretical and experimental physical organic chemists investigating oxidation reactivity. Efforts have been dedicated for elucidating the catalytic pathway regarding these species and for dissecting out the dominant factors influencing the yield and stereochemistry. In this article, Ti(IV) and Hf(IV) aminotriphenolate complexes have been prepared and investigated as catalysts in the presence of peroxides in sulfide oxidation. Experimental results have been combined with theoretical calculations obtaining detailed mechanistic information on oxygen transfer processes. The study revealed that steric issues are mainly responsible for the formation of intermediates in the oxidation pathway. In particular, we could highlight the occurrence of a blended situation where the steric effects of sulfides, ligands, and oxidants influence the formation of different intermediates and reaction pathways.

Reaction of R-styreneoxide with glycine-tert-butylester yielded amino alcohols of the general formula (NRRR3)-R-1-R-2, where R-1 = CH2COO t Bu and R-2 = R-3 = 2-phenyl-2-hydroxyethyl (H(2)LA); R-2 = 2-phenyl-2-hydroxyethyl and R-3 = 1-phenyl-2-hydroxyethyl (H2LB); R-2 = H and R-3 = 2-phenyl-2-hydroxyethyl (HLC); and R-2 = H and R-3 = 1-phenyl-2-hydroxyethyl (HLD). The corresponding reaction with sarcosine-tert-butylester and subsequent hydrolysis provided the zwitterion (CH3){CH2CHPh(OH)}(CH2CO2-), HLE* (asterisk refers to unprotected carboxylate). Reaction of these ligands with VO(OiPr)(3) in CH2Cl2 gave the oxovanadium(V) complexes [VOL(OiPr)(2)] and [VOL2-(OiPr)] (for L-C and L-D) or, when reacted in the presence of MeOH, [VOL'(OMe)], where L' represents the methyl ester of L-A, L-B, and L-E. The crystal and molecular structures of R-HLC, S-HLD, R,S-HLE*center dot H2O, and Lambda[VO(R,S-L-B')OMe] have been determined. The complex [VOLB'(OMe)] contains vanadium in a distorted trigonal-bipyramidal array (tau = 0.72), the oxo group in the equatorial plane, and methoxide and N in the apical positions, and thus, it structurally models the active center of vanadate-dependent haloperoxidases. The structure and the bonding parameters, including a particularly long d(V-N) of 2.562 angstrom, are backed up by DFT calculations. The isolated oxovanadium(V) complexes and the in situ systems L VO(OiPr)(3) catalyze the oxidation, by cumylhydroperoxide HO2R', of prochiral sulfides (MeSPh, MeSp-Tol, PhSBn) to chiral sulfoxides plus some sulfone. The best results with respect to enantioselectivity (enantiomeric excess (ee) = 38%) were obtained with the system VO(OiPr)(3)/L-A, and the best selectivity with respect to sulfoxide (100%) was obtained with [VOLA(OiPr)]. The reaction with the hexacoordinated [VO(OMe)(HOMe)L-D*] was very slow. Oxidation of PhSBn is faster than that of MeSPh and MeSpTol. Turn-over numbers are up to 60 mol of sulfoxide mol(-1) of catalyst h(-1) (-20 degrees

Al-III and Ti-IV complexes of C-3-symmetric tetradentate trisamidoamme ligands with trigonal bipyramidal coordination geometry, containing chlorine or dialkylamido groups, or with a free coordination site in the apical position, have been synthesised by salt metathesis and amine elimination. Products with threefold symmetry were generally obtained for tetravalent titanium, whereas for the aluminium complexes either asymmetric structures with two of the three podand arms taking part in coordination to the metal or symmetric arrangements possessing the full threefold symmetry were formed depending on the steric properties of the ligands., QC 20100525