Expanding the Reactivity of Masked Divalent Lanthanide-Isocarbonyl Complexes

Masked divalent reactivity is a potentially powerful strategy for accessing the reducing chemistry of lanthanides without the need to isolate unstable divalent lanthanide compounds. Here, we report the synthesis and characterization of the isocarbonyl-bridged complexes [(Cp*)₂Gd-(THF)-(μ-Fp)]_∞ (1 _Gd ) and [(Cp*)₂Lu-(μ-Fp)]₂ (1 _Lu ) (Fp = CpFe-(CO)₂), aiming to extend the masked divalent approach to gadolinium and lutetium, metals with very limited divalent chemistry. Structural studies show that 1 _Gd forms as a coordination polymer with nine-coordinate gadolinium centers, whereas 1 _Lu is a dimer with eight-coordinate lutetium, reflecting the influence of the lanthanide contraction. FTIR spectroscopy confirms strong isocarbonyl back-bonding in both compounds. Complexes 1 _M (M = Gd, Dy, Lu) react with phenazine to afford dimetallic phenazine-bridged products [{(Cp*)₂M}₂(μ-phnz)] (2 _M ), demonstrating two-electron reduction of an N-heterocyclic substrate by the isocarbonyl-bridged complexes. Magnetic measurements reveal extremely weak antiferromagnetic exchange in 1 _Gd and 2 _Gd , while the dysprosium analogue exhibits slow magnetic relaxation governed by Raman and quantum tunnelling processes. These results establish isocarbonyl-bridged lanthanide metallocenes as platforms for ligand-based reduction chemistry involving metals with very limited divalent chemistry.