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 °C, complexes of the type [M(κ 2 PN -PCP-iPr)(CO) 4 ] were obtained featuring a κ 2 P , N -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 3 PCP -PCP-iPr)(CO) 3 ] was observed featuring a weak Mo-C bond. DFT calculations reveal that there is no agostic η 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(κ 3 PCP -PCP-iPr)(CO) 3 ], [Fe(κ 3 PCP -PCP-iPr)(H)(CO) 2 ], [Co(κ 3 PCP -PCP-iPr)(CO) 2 ] and [Ni(κ 3 PCP -PCP-iPr)(H)], respectively, where the PCP ligand is coordinated in the typical meridional κ 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 [Me 3 O]BF 4 . Treatment of [Mn(κ 3 PCP -PCP-iPr)(CO) 3 ] and [Fe(κ 3 PCP -PCP-iPr)(H)(CO) 2 ] with [Me 3 O]BF 4 resulted in the formation of the cationic complexes [Mn(κ 3 PCP -PCP Me -iPr)(CO) 3 ] + and [Fe(κ 3 PCP -PCP Me -iPr)(Cl)(CO) 2 ] + . In the case of the latter, the chloride ligand seems to originate from the solvent CH 2 Cl 2 undergoing a hydride chloride exchange. All complexes were characterized by means of 1 H, 13 C{ 1 H}, and 31 P{ 1 H} NMR spectroscopy, IR spectroscopy and HR-MS. In addition, the structures of representative complexes were determined by X-ray crystallography.