Forging Ru–C_sp² Bonds in Paddlewheel Complexes Using the Lithium–Halogen Exchange Reaction

Abstract

Reported herein are the first examples of the formation of Ru–Csp2 bonds in paddlewheel diruthenium species. A series of six Ru2(ap)4(C6H4-4-X) type compounds (ap = 2-anilinopyridinate; X = NMe2 (1), N,N-(C6H4-4-OMe)2 (2), tBu (3), H (4), Br (5), CF3 (6)) was synthesized by employing the lithium–halogen exchange reaction with a variety of para-substituted aryl halides. These compounds have been characterized via electronic absorption spectroscopy, cyclic voltammetry, mass spectrometry, and magnetism studies, and their molecular structures have been established by single-crystal X-ray diffraction studies. All compounds are in the Ru25+ oxidation state, with a ground-state electronic configuration of σ2π4δ2(π*δ*)3. Crystal structures of 1–6 confirm this, indicating a Ru–Ru bond order of 2.5. Electrochemical data suggest that the σ-aryls are stronger donors than the σ-alkynyls. A range of electronically different substituents allows for a closer inspection of the extent of electronic conjugation across the diruthenium paddlewheel core and the axial aryl ligand.