The gas chromatographic separation properties of azulene and the synthesis and characterization of bulky bis-pyrazolylpyridine metal-ligand complexes.
The separation of complex mixtures of molecules is vital to the conduct and understanding of modern chemical research. In this work, new materials for gas chromatographic separations are developed, evaluated, and discussed. Also discussed are the synthesis and characterization of bulky tridentate ligand-metal complexes. Azulene is an aromatic molecule with interesting properties, most notably a permanent dipole moment of 1.08 D. This degree of polarity in the absence of heteroatoms is quite rare and offers potential for use in unique gas chromatographic stationary phases. Here, we report the first examples of azulene-derivatized stationary phases for gas chromatographic separations. Poly(dimethyl/azulenylmethyl) siloxane polymers containing 15% and 35% of an azulene derivative were synthesized, coated onto capillary columns, and evaluated. To compare the effects of increased polarity vs the effects of polarizability, isomeric naphthalene analogues were also prepared, coated, and evaluated. The coated phases displayed efficiencies up to 2700 plates/m. For both azulene and naphthalene columns, retention increased as substitution level increased. The more polarizable naphthalene columns tended to retain analytes more strongly. Columns were also evaluated for the separation of several different mixtures of isomers against a commercial HP-5 column. All azulene and naphthalene columns exhibited separations comparable to the commercial column. The solvation thermodynamic parameters phases were measured, showing an excellent linear relationship and no change in the mechanism of interaction over the temperature range measured. Crystal structures of transition metal complexes of a recently-available bis-pyrazolylpyridine (bpp) ligand, 2,6-bis(3',5'-diphenylpyrazolyl)pyridine (bdppp), prepared by reaction with transition metal chlorides, are reported. The ligand forms two types of structures: a 2:1 complex with Fe (II) chloride, and 1:1 complexes with Mn(II), Ni(II), Co(II), Zn(II), Ru(III), Pd(II), and Rh(III) chlorides, resulting in two different geometries. In all cases the ligand is tridentate, but in contrast to reported bpp structures, the plane of the pyridine ring coordinating with the metal is significantly distorted from the plane of the pyrazoles and metal. The Ru, Cu, and Fe complexes show quasi-reversible redox couples.