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 (H L Ph, 4a; H L Pipp, 4b; Ph = phenyl, Pipp = para -isopropylphenyl). Protonolysis with Lu(CH 2 SiMe 3 ) 3 (THF) 2 afforded the corresponding lutetium dialkyl complexes (Lu L Ph (CH 2 SiMe 3 ) 2, 5a; Lu L Pipp (CH 2 SiMe 3 ) 2, 5b ), which were thermally sensitive and rapidly underwent intramolecular metalative alkane elimination to generate Lu L Ph* (CH 2 SiMe 3 )(THF), 6a, and Lu L Pipp* (CH 2 SiMe 3 )(THF), 6b, as highly reactive intermediates. Complexes 6a and 6b further decomposed, cleanly generating doubly metalated complexes Lu L Ph** (THF), 7a, and Lu L Pipp** (THF), 7b, respectively, as the thermodynamic products. Kinetic analysis of the decomposition of 5a revealed a first-order mechanism with activation parameters Δ H ⧧ = 19.2(1) kcal·mol −1 and Δ S ⧧ = −8.2(2) cal·K −1 ·mol −1 . Compounds 4a, 4b, 6b, and 7b were characterized by single-crystal X-ray diffraction studies.