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In this study, we used different ways to synthetize four-coordinate zinc(II) and nickel(II) complexes with optically active Schiff base offering N2S2 coordination, i.e. N,N'-Bis(2-thiobenzylidene)-l,2-(R,R)cycholhexyl- enediaminatozinc(II) (1) and N,N'-Bis(2-thiobenzylidene)-l,2-(R,R)cychol- hexylenediaminatonickel(II) (2). We obtained the crystal structure of 2 and the pyridine adduct of 1, N,N'-Bis(2-thiobenzylidene)-l,2-(R,R)cycholhexylenediaminopyridylzinc(II) (1¡DPy). Coordination geometry around Zn atom in 1¡DPy is a distorted trigonal bipyramid. These structures were compared with the N2O2 stuctural analogues reported in the literature. We hope these chiral complexes can make contribution to the enzyme model studies in the future.

In this study, we took four diamines of different carbon chain lengthes to synthesize several thiosalen derived zinc(II) complexes, i.e. N, N¡¦-Bis- (2-thio-benzylidene)- 1,3-propylenediaminato-zinc(II)(1),N,N¡¦-Bis(2-thio-benzylidene)-2,2-dimethyl- 1,3-propylenediaminato-zinc(II)(2),N,N¡¦-Bis-(2-thio-benzylidene)-1,2-ethylene- diaminato-zinc(II)(3),andN,N¡¦-Bis(2-thio-benzylidene)-1-methyl-1,2-ethylene- diaminato-zinc(II)(4). The crystal structure of 1 was shown to be trimeric. We then used NaBH4 to reduced complexes1, 2, and 4 to get complexes 5, 6, and 7 respectively for reactivity and structure studies. To expand our current study, we also synthesized nickel analogue (8) of complex 1 by transmetallation.

We have successfully used the cadmium ion with (2-thiophenyl)phenylphosphine(PS2) or Bis(3-trimethylsilyl-2-thiophenyl)phenylphosphine(SiPS2) to synthesize [(PS2)Cd(TMEDA)](2) and [(SiPS2)Cd(TMEDA)](4) that were structurally similar to [(PS2)Zn(TMEDA)](1). We also obtained a series of zinc complxes [NEt4][(PS2)Zn(SC6H5)](6), [NEt4][{[(PS2)Zn](SC6H11)[(PS2)Zn]}](7) and [NEt4][(PS2)Zn(SCH2C6H5)](8) with systematically varied thiolates. From studying of the methylation reactions of these complexeswith methyliodine or trimethylphosphate, we found that the metal center(zinc or cadmium), ligand(PS2 or SiPS2) or the net charge (neutral ornegative) can influence the reaction time, selectivity of reaction site ormechanism. The zinc complexes (6), (7), and (8) are capable of completingthe catalytic cycle of mthylation-demethylation and hence a good model for related enzyme system.