Abstract

A novel porphyrin-salen compound and corresponding zinc(II) porphyrin-salen compound (ZnPSC₁₀) covalently linked by a flexible alkoxy chain (–O(CH)₁₀O–) have been synthesized and characterized. Molecular recognition of three N-heterocyclic guests, pyridine, 1,4-diazobycyclo[2,2,2]octane (DABCO) and pyrazine, with the host ZnPSC₁₀ was investigated. Binding constants were determined by means of UV-vis titration method. The binding mode of ZnPSC₁₀ with DABCO has been discussed in detail by using ¹H NMR. It was found that the conformations of the recognition system changed from closed to open with the adding of DABCO.

The novel μ-oxo diiron(III) Schiff base complexes, {[Fe(tbusalphn)]₂(μ-O)} (1) [tbusalphn = N,N′-o-pheny-lenebis(3,5-di-tert-butylsalicylideneiminato)] and {[Fe(R,R-salchxn)]₂(μ-O)}(2) [R,R-salchxn = N,N′-R,R-cyclo-hexanebis(salicylideneiminato)] have been synthesized and characterized by elemental analyses, spectroscopy, magnetic susceptibility, electrochemical measurements and X-ray diffraction techniques. X-ray analyses revealed that the complex 1·CH₃OH has nearly linear Fe-O-Fe angle of 176.5(2)° due to their steric crowding of ligands owing bulky substitute group, while fairly bent Fe-O-Fe angle was allowed by the reduced steric crowding of the ligands in 2·C₄H₆N₂·0.5C₂H₅OH [149.6(1)°]. FT-IR, UV-Vis, CD spectra, magnetic susceptibility and cyclic voltammogram (CV) of complexes 1 and 2 have been further investigated.

One kind of novel chiral porphyrin and its zinc complex were synthesized and characterized. The molecular recognition of chiral zinc porphyrin towards amino acid esters in CHCl₃ was investigated by UV-vis spectral titration method. The associative constants of the molecular recognition reactions were all K_D>K_L and followed the order of K(PheOMe)>K(LeuOMe)>K(ValOMe)>K(AlaOMe) in host (Zn(L-BocTyr)TAPP). Circular dichroism spectra were used to explain chiral molecular recognition. The minimal energy conformation of host-guest molecular system was sought by molecular dynamics method. The molecular recognition process of this host-guest system was calculated by quantum chemistry and the results were explained by the experiments

The molecular recognition behavior of the chiral salen-metal complexes towards guest molecules, such as imidazole derivatives and amino-acid ester, was systematically investigated by means of circular dichroism (CD) spectra. The coordination numbers of the host-guest complexes as well as the recognition capability of the salen-metal complexes were explained by character and intensity analyses of the CD spectra.

Dimethyl (2-chloromethyl-2-propenyl)phosphonate (3b) and (tert-butyl)[2-(chloromethyl)-2-propenyl](phenyl)phosphane oxide (3d) were prepared and their reactions with α,β-unsaturated esters 5a−c and ketone 5d, acting as phosphorylated trimethylenemethane equivalents by a [3+2] strategy, were investigated. With the use of LDA in the presence of DMPU, the Michael addition proceeded with high stereoselectivity and regioselectivity to afford methylenecyclopentyl-substituted dimethyl phosphonate or (tert-butyl)(phenyl)phosphane oxide derivatives 6a−d and 14(S_P). Compound 3d reacted with 5a−b and 5d to give phosphorous diastereomers 10(R_P) and 11(S_P), 12(R_P) and 13(S_P), and 16(R_P) and 17(S_P), with complete stereoselectivity at the three stereogenic centers of the 5-methylenecyclopentanes, all possessing 1,2-trans and 2,3-trans stereochemistry. Formation of open-chain syn adduct 15 and of a 2,3-cis-disubstituted cyclopentane compound 18(S_P) could also be achieved. The stereochemical features of all the products were ascertained by 1D and 2D NMR spectra.