Synthesis and molecular structures and oxidation catalysis of mixed alkyl, fluoroalkyl pyrazolylborate metal complexes

First row transition metal complexes of partly fluorinated tris- and bispyrazolylborate complexes are synthesized and structurally characterized. Both the red cobalt complex, [{η3-HB(3-CF3-5-CH3pz)3}Co(η2-NO3)(NCCH3)] (1a) and the colorless manganese analogue, [{η3-HB(3-CF3-5-CH3pz)3}Mn(η2-NO3)(NCCH3)] (1b), exhibit a N4O2 donor set which defines a distorted octahedral geometry. For the blue–purple complex Cu[η2-H2B(3-CF3-5-CH3pz)2]2 (2), the N4 donor set defines a symmetry-imposed tetragonal geometry. The ligand(s) in 1 and 2 define relatively open and closed fluorine-lined cavities around their metal centers, respectively. The cavity of 1a and 1b allows additional facial coordination by small ions and neutral molecules such as NO3 − and MeCN. In contrast, the metal in 2 is in a more saturated, quasi-octahedral environment, defined by two non-bonding axial Cu⋯H contacts and the N4 donor set. Catalytic oxidation of cyclohexane using 1a and cumene hydroperoxide as oxygen donor yields a 1:1 mixture of cyclohexanol and cyclohexanone, and occurs 50% faster compared with the non-fluorinated analogous complex.