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)]∞ (1Gd) and [(Cp*)2Lu(μ-Fp)]2 (1Lu) (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 1Gd forms as a coordination polymer with nine-coordinate gadolinium centers, whereas 1Lu 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 1M (M = Gd, Dy, Lu) react with phenazine to afford dimetallic phenazine-bridged products [{(Cp*)2M}2(μ-phnz)] (2M), demonstrating two-electron reduction of an N-heterocyclic substrate by the isocarbonyl-bridged complexes. Magnetic measurements reveal extremely weak antiferromagnetic exchange in 1Gd and 2Gd, 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.