Silver and copper ethylene adducts and the silver carbonyl complex of the tris(pyrazolyl)borate [HB(3,4,5-(CF3)(3)Pz)(3)](-) (which is based on one of the most acidic pyrazoles known) have been synthesized. C-13 NMR resonance signals of metal-bound ethylene carbon atoms of [HB(3,4,5-(CF3)(3)Pz)(3)]Ag(C2H4) and [HB(3,4,5-(CF3)(3)Pz)(3)]Cu(C2H4) appear at delta 111.6 and 94.9, respectively. The CO stretching frequency of the silver adduct [HB(3,4,5-(CF3)(3)Pz)(3)]Ag(CO) is significantly higher than that of free CO, but it appears at a region less sensitive to the ligand electronic effects of tris(azolyl)borate silver adducts.