Synthesis and Reactivity of Dialkyl Lutetium Complexes Supported by a Novel Bis(phosphinimine)carbazole Pincer Ligand

Abstract

The synthesis of a novel bis(phosphinimine) ancillary ligand based on a carbazole framework is described (HLPh, 4a; HLPipp, 4b; Ph = phenyl, Pipp = para-isopropylphenyl). Protonolysis with Lu(CH2SiMe3)3(THF)2 afforded the corresponding lutetium dialkyl complexes (LuLPh(CH2SiMe3)2, 5a; LuLPipp(CH2SiMe3)2, 5b), which were thermally sensitive and rapidly underwent intramolecular metalative alkane elimination to generate LuLPh*(CH2SiMe3)(THF), 6a, and LuLPipp*(CH2SiMe3)(THF), 6b, as highly reactive intermediates. Complexes 6a and 6b further decomposed, cleanly generating doubly metalated complexes LuLPh**(THF), 7a, and LuLPipp**(THF), 7b, respectively, as the thermodynamic products. Kinetic analysis of the decomposition of 5a revealed a first-order mechanism with activation parameters ΔH⧧ = 19.2(1) kcal·mol−1 and ΔS⧧ = −8.2(2) cal·K−1·mol−1. Compounds 4a, 4b, 6b, and 7b were characterized by single-crystal X-ray diffraction studies.