INVESTIGATION OF THE ELECTRONIC AND GEOMETRIC EFFECTS OF TRIFLUOROMETHYL SUBSTITUENTS ON TRIS(PYRAZOLYL)BORATE LIGANDS USING MANGANESE(I) AND COPPER(I) COMPLEXES

Manganese tricarbonyl complexes of fluorinated tris(pyrazolyl)borate l igands [HB(3,5-(CF3)(2)Pz)(3)](-) and [HB(3-(CF3)Pz)(3)](-) (where Pz = pyrazolyl) were synthesized by treating BrMn(CO)(5) with [HB(3,5-(CF 3)(2)Pz)(3)]Ag(THF) or [HB(3-(CF3)Pz)(3)]Na(THF). The reaction of [HB( 3-(CF3)Pz)(3)]Na(THF) with copper(I) trifluoromethanesulfonate under C O afforded [HB(3-(CF3)Pz)(3)]CuCO. Compounds [HB(3,5-(CF3)(2)Pz)(3)]Mn (CO)(3) (5), [HB(3-(CF3)Pz)(3)]Mn(CO)(3) (6), and [HB(3-(CF3)Pz)(3)]Cu CO (7) were characterized by H-1 NMR, F-19 NMR, and IR spectroscopy an d by X-ray crystallography. They have relatively high C-O stretching f requencies. However, the v(CO) values are much lower than that in free CO and the relative lowering is higher for manganese adducts. The CF3 substitution on the 5-position has a significant effect on the metal center. This is readily apparent from the infrared spectroscopic data. Theoretical calculations of the geometries of [tris(pyrazolyl)borato] manganese(I) and -copper(I) carbonyls are in excellent agreement with the experimental results, increasing the degree of fluorination length ens the metal-C and metal-N bonds and shortens the C-O distance. The m etal-Pz bonding is essentially a pure sigma-interaction. Cyclic voltam metry data for the copper complexes show high oxidation potentials for the fluorinated analogs. IR spectroscopic data of the [tris(pyrazolyl )borato]manganese and -copper carbonyls have also been compared to tho se of cyclopentadienyl analogs.