COORDINATION-INDUCED KETO-ENOL TAUTOMERIZATION IN THE FORMATION OF NI2-DIOL( AND CU2+ COMPLEXES OF A FLUORINATED KETO)

The fluorinated keto-diol (CF3)2C(OH)CH2C(=O)CH2C(CF3)2OH forms stable , neutral, 1:1 complexes of Ni2+ (6a) and Cu2+ (6b) with tetramethylet hylenediamine (TMED) as coligand. The structure of each complex has be en determined crystallographically; they are isomorphous and isostruct ural, monoclinic with space group Cc (No. 9). Complex 6a, C15H20F12N2N iO3, has a = 11.495(2), b = 15.516(2), c = 12.323(2) angstrom, beta = 99.88(1)degrees, V = 2165.4(6) angstrom3, Z = 4. Complex 6b, C15H20CuF 12N2O3, has a = 11.603(2) b = 15.661(2), c = 12.276(2) angstrom, beta = 99.75(2)degrees, V = 2198.5(6) angstrom3, Z = 4. In each, the metal is in square-planar geometry bonded to two alkoxide groups and two N a toms of TMED. A previous assignment of a zwitterionic structure to the se complexes has been shown to be incorrect. Instead, the ligand is co ordinated as the di-ionized enol tautomer (CF3)2C(-O-)CH2C(-O-)=CHC(CF 3)2OH, the C=C double bond being external to the six-membered chelate ring. The remaining OH group of the ligand forms part of a second six- membered ring held together by hydrogen bonding.