Organolanthanide Complexes Containing Ln-CH3 σ-bonds: Unexpectedly Similar Hydrolysis Rates for Trivalent and Tetravalent Organocerium

We report the gas-phase preparation, isolation, and reactivity of a series of organolanthanides featuring the Ln-CH3 bond. The complexes are formed by decarboxylating anionic lanthanide acetates to form trivalent [Ln(III)(CH3)(CH3CO2)(3)](-) (Ln = La, Ce, Pr, Nd, Sm, Tb, Tm, Yb, Lu), divalent [Eu-II(CH3)(CH3CO2)(2)](-), and the first examples of tetravalent organocerium complexes featuring Ce-IV-C-alkyl sigma-bonds: [Ce-IV(O)(CH3)(CH3CO2)(2)](-) and [Ce-IV(O)(CH3)(NO3)(2)](-). Attempts to isolate Pr-IV-CH3 and Tb-IV-CH3 were unsuccessful; however, fragmentation patterns reveal that the oxidation of Ln(III) to a Ln(IV)-oxo-acetate complex is more favorable for Ln = Pr than for Ln = Tb. The rate of Ln-CH3 hydrolysis is a measure of bond stability, and it decreases from La-III-CH3 to Lu-III-CH3, with increasing steric crowding for smaller Ln stabilizing the harder Ln-CH3 bond against hydrolysis. [Eu-II(CH3)(CH3CO2)(2)](-) engages in a much faster hydrolysis versus Ln(III)-CH3. The surprising observation of similar hydrolysis rates for Ce-IV-CH3 and Ce-III-CH3 is discussed with respect to sterics, the oxo ligand, and bond covalency in sigma-bonded organolanthanides.

Automated summary

In this study, gas-phase preparation, isolation, and reactivity of a series of organolanthanides with the Ln-CH3 bond were reported. These complexes were formed by decarboxylating anionic lanthanide acetates. The hydrolysis rate of Ln-CH3 bonds decreases from La-III-CH3 to Lu-III-CH3, with smaller Ln and increased steric crowding stabilizing the harder Ln-CH3 bond against hydrolysis.