New Chiral C₃-Symmetric Triols as Ligands for Vanadium and Titanium Complexes

Abstract

Several new chiral triols 1a − c with C 3 symmetry have been prepared in enantiopure form via a route involving the iterative catalytic asymmetric alkylation of aldehydes by organozinc reagents followed by diastereoselective hydroboration. Reactions of these chiral triols with titanates Ti(OR)4 and vanadates V(O)(OR)3 are reported. The structure of the binuclear vanadium triolato(3−) complex [V(O){(OCH-Et)3CH}]2 (12a) has been determined by X-ray analysis. A series of model reactions was conducted to assess the catalytic properties of the chirally modified titanium and vanadium secondary alkoxides. The reactions chosen were the addition of diethylzinc and of trimethylsilyl cyanide to benzaldehyde and the oxidation of geraniol and of ethyl phenyl sulfide with tert-butyl hydroperoxide. Only a moderate asymmetric induction was found in some model reactions catalyzed by titanium complexes 11a,b. On the other hand, a very efficient chemoselective oxidation of sulfides to sulfoxides with tert-butyl hydroperoxide was possible in the presence of vanadium complex 12a.

Sulfoxidation inside a C3-Vanadium(V) Bowl-Shaped Catalyst

“…Moreover, opposite to the previous catalysts that were unable to induce enantioselectivity for this reaction, ee values of 10% and 17% were achieved using SSS-RRR- 1 with CHP and TBHP as oxidants, respectively. Although good enantioselectivities were reported with Schiff base vanadium complexes, ,, other vanadium-containing systems generally gave low or no ee. ,, In particular, several attempts have been undertaken to obtain enantiomerically enriched sulfoxides with chiral vanatrane catalysts, but enantioselectivity has never been observed, , probably because of the C 3 symmetry of the ligand . These remarkable changes in the catalytic behavior, including both activity and enantioselectivity improvements, indicate that the structure and conformation of the SSS-RRR- 1 complex should strongly differ from those of our previous systems.…”

Synthesis and Structure of Titanatranes Containing Tetradentate Trianionic Donor Ligands of the Type [(O-2,4-R2C6H2-6-CH2)2(OCH2CH2)]N3- and Their Use in Catalysis for Ethylene Polymerization

“…Considerable attention has been paid to the chemistry of metal complexes containing tripodal trianionic ligands such as triamido, tris(amido)amine, tris(alkoxo)amine, and tris(aryloxo)amine. − Especially complexes with triamido or tris(amido)amine ligands displayed unique characteristics . These trianionic, chelating amido and/or alkoxo ligands are capable of providing a range of stable steric and electronic environments for catalytically active metal centers and have thus been the subject of considerable attention .…”

Synthesis of Homochiral Tris(2-alkyl-2-aminoethyl)amine Derivatives from Chiral α-Amino Aldehydes and Their Application in the Synthesis of Water Soluble Chelators

“…For a variety of reasons, the synthesis of chiral, C 3 -symmetric ligands has recently been an area of active investigation. , Ligands exhibiting many of the common donor groups have been synthesized, including phosphorus donors, tris(pyrazolyl)hydro-borates, − alkoxides, , tri- and tetraamines , triamides, , and tripyridines . Additionally, chiral tripodal ligands which do not contain 3-fold symmetry have been prepared, including tris(2-aminoethyl)amine (TREN) derivatives with a single chiral substituent, , or with three different tripodal “arms.”…”