Base metal complexes featuring a new pyrazole-derived PCP pincer ligand.

A new pyrazole-derived PCP pincer ligand featuring a 1-methylpyrazole backbone tethered to two di(isopropyl)phosphine moieties phenylene spacers (P(CH)P-iPr) was prepared. When reacting the ligand with group six carbonyl complexes [M(CO)] (M = Cr, Mo, W) at 130 °C, complexes of the type [M(κ-PCP-iPr)(CO)] were obtained featuring a κ,-bound ligand with a pendant phosphine arm. Upon an increase of the reaction temperature to 150 °C, in the case of molybdenum, the formation of the complex [Mo(κ-PCP-iPr)(CO)] was observed featuring a weak Mo-C bond. DFT calculations reveal that there is no agostic η-C-H interaction. Treatment of [Mn(CO)], [Fe(CO)], [Co(CO)] and [Ni(COD)] afforded complexes [Mn(κ-PCP-iPr)(CO)], [Fe(κ-PCP-iPr)(H)(CO)], [Co(κ-PCP-iPr)(CO)] and [Ni(κ-PCP-iPr)(H)], respectively, where the PCP ligand is coordinated in the typical meridional κ-fashion. Postfunctionalization of the anionic PCP pincer ligand was possible -methylation of the second nitrogen atom of the pyrazole unit with the oxonium salt [MeO]BF. Treatment of [Mn(κ-PCP-iPr)(CO)] and [Fe(κ-PCP-iPr)(H)(CO)] with [MeO]BF resulted in the formation of the cationic complexes [Mn(κ-PCP-iPr)(CO)] and [Fe(κ-PCP-iPr)(Cl)(CO)]. In the case of the latter, the chloride ligand seems to originate from the solvent CHCl undergoing a hydride chloride exchange. All complexes were characterized by means of H, C{H}, and P{H} NMR spectroscopy, IR spectroscopy and HR-MS. In addition, the structures of representative complexes were determined by X-ray crystallography.