MOLECULAR DESIGN OF C-PIVOT TRIPODAL LIGANDS - IMPORTANCE OF THE GLYCEROL STRUCTURE FOR EFFECTIVE COMPLEXATION TOWARD ALKALI-METAL CATIONS

A new series of C-pivot tripodal ligands 1-4 containing a 2-methylglyc erol unit were prepared and their complexation properties toward alkal i metal cations were examined by measuring the extractability, stabili ty constant in THF, characteristic absorption in the UV spectrum, chan ge in the chemical shia in the H-1 NMR, and competitive passive transp ort. This type of compound (1-4) was found to possess excellent comple xing ability and higher selectivity than another type of tripodal Liga nd 5 derived from tris(hydroxymethyl)ethane. This remarkable differenc e in the stability constants was reasonably explained by considering t hat the former takes a three-dimensional coordination toward alkali me tal cations by cooperatively using the three electron-donating arms bu t the latter does not. This finding clearly shows that a proper select ion of the structure of the basic skeleton is important for the molecu lar design of C-pivot tripodal ligands.