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 via phenylene spacers (P(CH)P-iPr) was prepared. When reacting the ligand with group six carbonyl complexes [M(CO)(6)] (M = Cr, Mo, W) at 130 & DEG;C, complexes of the type [M(& kappa;(PN)-P-2-PCP-iPr)(CO)(4)] were obtained featuring a & kappa;P-2,N-bound ligand with a pendant phosphine arm. Upon an increase of the reaction temperature to 150 & DEG;C, in the case of molybdenum, the formation of the complex [Mo(& kappa;(PCP)-P-3-PCP-iPr)(CO)(3)] was observed featuring a weak Mo-C bond. DFT calculations reveal that there is no agostic & eta;(2)-C-H interaction. Treatment of [Mn-2(CO)(10)], [Fe-2(CO)(9)], [Co-2(CO)(8)] and [Ni(COD)(2)] afforded complexes [Mn(& kappa;(PCP)-P-3-PCP-iPr)(CO)(3)], [Fe(& kappa;(PCP)-P-3-PCP-iPr)(H)(CO)(2)], [Co(& kappa;(PCP)-P-3-PCP-iPr)(CO)(2)] and [Ni(& kappa;(PCP)-P-3-PCP-iPr)(H)], respectively, where the PCP ligand is coordinated in the typical meridional & kappa;(3)-fashion. Postfunctionalization of the anionic PCP pincer ligand was possible via N-methylation of the second nitrogen atom of the pyrazole unit with the oxonium salt [Me3O]BF4. Treatment of [Mn(& kappa;(PCP)-P-3-PCP-iPr)(CO)(3)] and [Fe(& kappa;(PCP)-P-3-PCP-iPr)(H)(CO)(2)] with [Me3O]BF4 resulted in the formation of the cationic complexes [Mn(& kappa;(PCP)-P-3-PCPMe-iPr)(CO)(3)](+) and [Fe(& kappa;(PCP)-P-3-PCPMe-iPr)(Cl)(CO)(2)](+). In the case of the latter, the chloride ligand seems to originate from the solvent CH2Cl2 undergoing a hydride chloride exchange. All complexes were characterized by means of H-1, C-13{H-1}, and P-31{H-1} NMR spectroscopy, IR spectroscopy and HR-MS. In addition, the structures of representative complexes were determined by X-ray crystallography.

Automated summary

A new pyrazole-derived PCP pincer ligand was synthesized and reacted with group six carbonyl complexes to obtain [M(& kappa;(PN)-P-2-PCP-iPr)(CO)(4)] complexes. Upon increasing the reaction temperature, the complex [Mo(& kappa;(PCP)-P-3-PCP-iPr)(CO)(3)] featuring a weak Mo-C bond was observed.