Bis(pyrazolyl)carbazole as a Versatile Ligand for Supporting Lutetium Alkyl and Hydride Complexes

Two derivatives of a new bis(pyrazolyl)carbazole pincer ligand H(CzPz(R)), R = Pr-i and Me, and their syntheses are reported. Lutetium dialkyl complexes of the ligand (CzPz(R))Lu(CH2SiMe3)(2), R = Pr-i and Me, have been prepared and found to exhibit high thermal stability in solution. These organolutetium compounds are Lewis base free, and the solid-state structure of (CzPz(iPr))Lu(CH2SiMe3)(2) revealed that the complex is monomeric with a trigonal-bipyramidal geometry. Hydrogenolysis of (CzPz(iPr))Lu(CH2SiMe3)(2) afforded a trimetallic lutetium hydride complex that possesses five bridging hydride ligands. Notably, intramolecular C-H bond activation of the CzPz(iPr) ligand was found to occur during the formation of this latter hydride complex, with metalation of a pyrazole carbon atom.