Studies On Synthesis, Characterization And Catalytic Propetries Of Metal Complexes Supported By Chiral Tetraaza Chelating Ligands

The high importance of nitrogen-containing compounds, such as amines, enaminesand imines, as part of natural products and biological systems has sparked significantresearch efforts for their efficient synthesis. Their use is especially important inindustrial basic and fine chemicals, where several million tons of amines are producedper year. Hydroamination of unsaturated compounds, which constitutes the formaladdition of a N-H bond across a carbon-carbon multiple bond, is emerging as a superioralternative way to nitrogen-containing molecules. This fundamentally simpletransformation proceeds with100%atom efficincy and without waste formation,offering environmental and economical benefits to chemical industry. Since the firstexample of the asymmetric intramolecular hydroamination was reported by Marksgroup, many chiral catalysts based on lanthanide metals, main group metals, group4metals and late transition metals have been widely studied. However, only a smallnumber of successful catalysts have been reported affording signifcantenantioselectivity (>90%ee), and those highly enantioselective inductions are observedonly for one or two substrates. Thus, alkene hydroamination remains an open area ofresearch, and the development of new catalysts for this transformation is still a desirableand challenging goal.Conclusions were summarized as follows:A number of new chiral tetradentate anilido-imine ligands (1R,2R)-N,N′-bis(ortho-arylamino-benzylidene)-1,2-diaminocyclohexane {(1R,2R)-[(ArHN)C₆H4CH=N]2C₆H10(L^AH₂), Ar=2,6-Me₂C₆H₃(L^A1H₂),2,6-Et2C₆H₃(L^A2H₂),2,6-ⁱPr₂C₆H₃(L^A3H₂)} havebeen synthesized via a nucleophilic displacement of the two fluorine atoms in(ortho-C₆H₄FCH=N)₂C₆H₁₀with the lithium salt of the corresponding aniline derivative.Their rare earth metal complexes1–9were synthesized in good yields via metathesis ofLnCl₃(Ln=Sc, Lu, Y, La) with the lithium salt of the corresponding ligands [L^A1Li₂(THF)₄, L^A2Li₂(THF)₄, and L^A3Li₂(THF)₄], respectively. Five complexes of allthese were determined by X-ray crystallography. After in situ treatment withⁿBuLi,complexes1–9show moderate catalytic activities and good enantioselectivities (up to90%) for intramolecular asymmetric hydroamination reaction of terminal aminoalkenes.To our knowledge, this result is among the best ones obtained so far with chiral rareearth metal catalysts.A series of tetra-azane ligands (1R,2R)-N,N′-bis(ortho-arylamino-benzyl)-1,2-diaminocyclohexane [(1R,2R)-[(ArHN)C₆H₄CHNH]₂C₆H₁₀(L^BH₄), Ar=2,6-Me₂C₆H₃(L^B1H₄),2,6-iPr₂C₆H₃(L^B2H₄),2-MeC₆H₄(L^B3H₄),4-MeC₆H₄(L^B4H₄),2-iPrC₆H₄(L^B5H₄),] were easily prepared by reducting the imino groups in respectivechiral quadridentate amino-imino ligands L^AH₂. The chloride complexes[L^B1H₂ScCl₂Li(THF)₃(10), L^B1H₂YCl₂Li(THF)₃(11), L^B1H₂ScCl₂Li(THF)₃(12)] weresynthesized through a metathetical reaction between the dilithium salts[L^B1H₂Li₂(THF)₄] and LnCl₃(Ln=Sc, Y, Lu) in THF. The chloride complexes werealso used as a precatalysts for intramolecular asymmetric hydroamination reaction,while a number of scadium complexes were easier in situ prepared by reaction betweenthe ligands L^BH₄and the precursor Sc(TMSCH₂)₃(THF)₃.The complexes show highenantioselectivities (up to100%).A new chiral tetraaza ligand (1R,2R)-N,N'-Bis[2-(N-methylanilino) benzylidene]cyclohexane-1,2-diamine (L^C) and its reducted product (1R,2R)-N,N'-Bis[2-(N-methylanilino)benzyl]cyclohexane-1,2-diamine (L^DH₂) were synthesized, whiletheir transition metal complexes were generated in situ and used as catalysts forasymmetric Henry reaction with up to49%ee. The iron complex {(1R,2R)-N,N'-Bis[2-(N-methylanilino) benzylidene]cyclohexane-1,2-diamine-²N,N'} dichloridoiron(II)(L^CFeCl₂) was isolated and characterized by elemental analysis and single crystal X-raydiffraction.