Organolanthanide Complexes Containing Ln-CH 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-CH bond. The complexes are formed by decarboxylating anionic lanthanide acetates to form trivalent [Ln(CH)(CHCO)] (Ln = La, Ce, Pr, Nd, Sm, Tb, Tm, Yb, Lu), divalent [Eu(CH)(CHCO)], and the first examples of tetravalent organocerium complexes featuring Ce-C σ-bonds: [Ce(O)(CH)(CHCO)] and [Ce(O)(CH)(NO)]. Attempts to isolate Pr-CH and Tb-CH were unsuccessful; however, fragmentation patterns reveal that the oxidation of Ln to a Ln-oxo-acetate complex is more favorable for Ln = Pr than for Ln = Tb. The rate of Ln-CH hydrolysis is a measure of bond stability, and it decreases from La-CH to Lu-CH, with increasing steric crowding for smaller Ln stabilizing the harder Ln-CH bond against hydrolysis. [Eu(CH)(CHCO)] engages in a much faster hydrolysis versus Ln-CH. The surprising observation of similar hydrolysis rates for Ce-CH and Ce-CH is discussed with respect to sterics, the oxo ligand, and bond covalency in σ-bonded organolanthanides.