Electron-Deficient η1‑Indenyl,η3‑allylpalladium(II) Complexes Stabilized by Fluxional Non-covalent Interactions

Highly fluxional, solution-persistent, and formally electron-deficient (32e–) binuclear Pd­(II)-C(0) complexes of 2-methyl-1H-indene were synthesized and structurally characterized by X-ray diffraction analysis. DFT investigations combined with a number of theoretical analyses of the bond framework suggest that the polar intermetallic interaction possesses no major covalent character. Instead of bearing a static metal-metal bond as suggested by structural X-ray diffraction analysis, the complexes display in solution significant fluxionality through haptotropy, i.e., a formal “oscillation” of the Pd­(η3-allyl) moiety between two limiting η1-indenyl configurations.