The Characterization and Reactivity of Tris(4-methylpyrazolyl)methane and its Tungsten and Molybdenum Metal Complexes

The scorpionate ligand tris(pyrazolyl)borate (Tp) has contributed to the understanding of coordination and organometallic chemistry and has proven to be useful in the synthesis of metalloprotein models. Studies focusing on the similar ligand, tris(pyrazolyl)methane (Tpm), have recently been made possible with improved synthetic techniques. Characterization of the Tpm ligand and its metal derivatives, [TpmW(CO)3L]+ and [TpmMo(CO)3L]+, unveiled unexpected activity in the 1H NMR chemical shift of the methane hydrogen after the coordination of a seventh ligand. The more electronegative the seventh ligand was, the more downfield the chemical shift appeared. Various analogs of Tpm have since been synthesized that substitute methyl groups on different positions of the pyrazolyl rings and the effect of these substitutions on the methane hydrogen was examined. This work successfully synthesized an analog of Tpm(4-methyl) and its metal complexes of Tpm(4-methyl)W(CO)3 and Tpm(4-methyl)Mo(CO)3. The reactivity of Tpm(4-methyl)M(CO)3 (M = W or Mo) was observed and FTIR, 1H NMR, and 13C NMR were used for the characterization of [Tpm(4-methyl)M(CO)3L]+[X]- (L = H, I, or Br; X = counterion). The chemical shift of the methane hydrogen was further examined and determined to follow the same trend seen in the previously reported Tpm metal complexes