Forging Ru-Csp2 Bonds in Paddlewheel Complexes Using the Lithium-Halogen Exchange Reaction

Reported herein are the first examples of the formation of Ru-C-sp(2) bonds in paddlewheel diruthenium species. A series of six Ru-2(ap)(4)(C6H4-4-X) type compounds (ap = 2-anilinopyridinate; X = NMe2 (1), N,N-(C6H4-4-OMe)(2) (2), Bu-t (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 Ru-2(5+) oxidation state, with a ground-state electronic configuration of alpha(2)pi(4)delta(2)(pi*delta*)(3). Crystal structures of 1-6 confirm this, indicating a Ru-Ru bond order of 2.5. Electrochemical data suggest that the sigma-aryls are stronger donors than the sigma-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.