To tilt or not to tilt? The dilemma of μ-C₃R₃ ligands in binuclear complexes

Abstract

The symmetrical or tilted positioning of μ-C₃R₃ groups that straddle an otherwise symmetrical metal.metal bond is dictated by the geometric flexibility available to the terminal ligands of the metal. The C₃Cl₃ in [(OC)Ni(μ-C₃Cl₃)Ni(CO)]₂Cl₂ is symmetrical because the Ni(CO)Cl groups are free to pyramidalize around the metal so that both metals can bond simultaneously with the bridging ligand. The additional bridging CR group in L₂W(μ-CR)(μ-C₃R₃)WL₂ prevents substantial pyramidalization at the WL₂ centre. In unsymmetrical metal environments the middle carbon of the C₃R₃ group tilts toward the ML_n fragment that provides the more diffuse frontier orbitals. For example, (η⁵-C₅(C₆R₅)₂)Ni(μ-C₃(C₆H₅)₂)Ni(η⁴- C₄(C₆H₅)₄) has the middle CR group tilted towards (η⁴-C₄(C₆H₅)₄)NI.