Sequential Double Dearomatization of the Pyrazolate-Based “Two-in-One” Pincer Ligand in a Dinuclear Rhodium(I) Complex

Abstract

A binucleating pyrazolate-based ligand providing two tridentate PNN compartments is shown to form a dinuclear rhodium(I) complex [L{Rh(CO)}2](PF6) (1) that can be deprotonated at both side arm methylene groups between pyridine and phosphino donors to give K[L**{Rh(CO)}2] (3). Sequential twofold deprotonation has been monitored by NMR and UV/Vis spectroscopy and proceeds via the neutral intermediate L*{Rh(CO)}2 (2). X-ray crystallographic characterization of 1 and the K[2,2,2]+ salt 3′ ([2,2,2] is a cryptand) evidences pyridine dearomatization upon deprotonation, and all spectroscopic and structural signatures are in good agreement with those of related mononuclear rhodium complexes based on a common PNN pincer ligand, which corroborates that pyrazolate-bridged L– is best described as a scaffold with two pincer-type subunits.