Substituent effects of beta-diketiminate ligands on the structure and physicochemical properties of the copper(II) complexes have been systematically investigated by using 3-iminopropenylamine derivatives R1LR3H, R3-N=CH-C(R1)=CH-NH-R3, where R1 is Me, H, CN, or NO2, and R3 is Ph, Mes (mesityl), Dep (2,6-diethylphenyl), Dipp (2,6-diisopropylphenyl), or Dtbp (3,5-di-tert-butylphenyl). When the ligands with R3=Ph or Dtbp were treated with CuII(OAc)2, bis(beta-diketiminate) copper(II) complexes exhibiting distorted tetrahedral geometries were obtained, the crystal structures of which were nearly the same as each other regardless of the alpha-substituent (R1); dihedral angles between the two beta-diketiminate coordination planes are 62.5 +/- 1.2 degrees, and the Cu-N bond lengths are 1.959 +/- 0.008 A. The distorted tetrahedral structures are maintained in solution, but the spectroscopic features, especially gII values of the ESR spectra and the d-d bands of the absorption spectra, as well as the electrochemical behaviors of the complexes, are significantly affected by the electronic nature of R1. The ligands with R3=Mes and Dep, on the other hand, gave di(mu-hydroxo)dicopper(II) complexes, and their crystal structures as well as spectroscopic and electrochemical features have also been explored. Furthermore, the ligand with the more sterically encumbered aromatic substituent (Dipp) provided a mononuclear four-coordinate square planar copper(II) complex supported by one beta-diketiminate ligand and one didentate acetate ion. Thus, the beta-diketiminate ligands with a variety of substituents (R1 and R3) have been explored to provide coordinatively unsaturated (four-coordinate) mononuclear and dinuclear copper(II) complexes with significantly different coordination geometry and properties.

Copper(I) complexes generated by using a series of β-diketiminate ligands (R1,R2LR3−, [(R3)N–C(R2)–C(R1)–C(R2)–N(R3)]−, see Chart 1; “β-diketiminate” denotes enaminone imine analogs) have been structurally characterized by X-ray crystallographic analysis. In the α-nitro-ligand system (R1 = NO2 and R2 = H), the structure of the resulting products were largely affected by the nitrogen substituent R3, providing bis(β-diketiminato)copper(II) complex 1 [a product of the disproportionation reaction of copper(I)] (R3 = Ph), head-to-tail linear coordination polymer copper(I) complex 2 (R3 = Mes, (mesityl)), and mononuclear copper(I) complex 3 (R3 = Dipp (2,6-diisopropylphenyl)). On the other hand, α-cyano-ligand (R1 = CN and R2 = H or Me) always gave head-to-tail coordination polymer copper(I) complexes (4–8) regardless of the aromatic substituent R3. In both systems, β-diketiminate ligands exhibited a U-shaped closed conformation, forming a six-membered chelate ring with copper(I). Copper(I) complexes with a β-diketiminate ligand with a W-shaped open conformation were also obtained in the case of α-methyl and α-hydrogen derivatives (R1 = Me or H, R2 = H, and R3 = Dipp). In these cases, the dinuclear and tetranuclear copper(I) macrocyclic complexes 9 and 10 were obtained.

Acylation of 2,4,4-trimethyl-2-oxazoline with acid chlorides having no α-proton and triethylamine gave C,N-diacylated products. Hydrolysis of the products with potassium hydroxide gave the enols of 2-acylmethyl-oxazolines, which were selectively C-monoalkylated by alkyl halides.

Crystalline derivatives of the following l-amino acids modified by 3,5-dinitro-4-pyridone have been prepared: glycine, alanine, valine, leucine, isoleucine, phenylalanine, serine, threonine, tyrosine, aspartic acid, asparagine, glutamic acid, glutamine, tryptophan, histidine, arginine, methionine and lysine. The modified l-amino acids (DNPY-l-amino acids) could be purified by recrystallization and were characterized by 1H-NMR, IR and UV spectral data. The molar rotation of the DNPY-l-amino acids varied from 2 to 100 times those of the parent amino acids. The effectiveness of 3,5-dinitro-1-(4-nitrophenyl)-4-pyridone as an amino-protecting reagent of l-amino acids is described.