Carbon monoxide and ethylene complexes of copper and silver supported by a highly fluorinated tris(triazolyl)borate.

Copper and silver carbonyl and ethylene adducts supported by the highly fluorinated hydridotris(triazolyl)borate ligand [HB(3,5-(CF3)2Tz)3]- have been synthesized and characterized, and compared to the analogous complexes based on the hydridotris(pyrazolyl)borate ligand [HB(3,5-(CF3)2Pz)3]-. 1H and 13C NMR signals of the ethylene moiety of [HB(3,5-(CF3)2Tz)3]Cu(C2H4) and [HB(3,5-(CF3)2Tz)3]Ag(C2H4) appear at a relatively downfield position from the corresponding signals of the [HB(3,5-(CF3)2Pz)3]Cu(C2H4) and [HB(3,5-(CF3)2Pz)3]Ag(C2H4) complexes. This indicates the presence of relatively acidic metal sites in the [HB(3,5-(CF3)2Tz)3]- supported molecules. [HB(3,5-(CF3)2Tz)3]- is also a relatively weaker donor compared to the tris(pyrazolyl)borate version [HB(3,5-(CF3)2Pz)3]-. However, the CO stretching frequency values of [HB(3,5-(CF3)2Tz)3]CuCO (2138 cm(-1)) and [HB(3,5-(CF3)2Pz)3]CuCO (2137 cm(-1)) are essentially identical, and did not reflect the differences in the acidity of the metal sites. The analogous silver carbonyl adducts [HB(3,5-(CF3)2Tz)3]AgCO and [HB(3,5-(CF3)2Pz)3]AgCO also show similar nuCO values (2178 cm(-1)). These results illustrate the limitation of using the nu(CO) value of metal carbonyls as a sole indicator of the electronic structure of metal sites in some metal complexes, especially when the metal-->CO pi-back bonding is less important, and the nuCO values of two adducts are unexpectedly similar and appear at a region closer to that of the free CO (2143 cm(-1)).