Organolanthanide Complexes Containing Ln-CH 3 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 3 bond. The complexes are formed by decarboxylating anionic lanthanide acetates to form trivalent [Ln III (CH 3 )(CH 3 CO 2 ) 3 ] - (Ln = La, Ce, Pr, Nd, Sm, Tb, Tm, Yb, Lu), divalent [Eu II (CH 3 )(CH 3 CO 2 ) 2 ] - , and the first examples of tetravalent organocerium complexes featuring Ce IV -C alkyl σ-bonds: [Ce IV (O)(CH 3 )(CH 3 CO 2 ) 2 ] - and [Ce IV (O)(CH 3 )(NO 3 ) 2 ] - . Attempts to isolate Pr IV -CH 3 and Tb IV -CH 3 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-CH 3 hydrolysis is a measure of bond stability, and it decreases from La III -CH 3 to Lu III -CH 3 , with increasing steric crowding for smaller Ln stabilizing the harder Ln-CH 3 bond against hydrolysis. [Eu II (CH 3 )(CH 3 CO 2 ) 2 ] - engages in a much faster hydrolysis versus Ln III -CH 3 . The surprising observation of similar hydrolysis rates for Ce IV -CH 3 and Ce III -CH 3 is discussed with respect to sterics, the oxo ligand, and bond covalency in σ-bonded organolanthanides.