Lanthanide versus Actinide Reactivity in the Formation of Sterically Crowded [(C5Me5)(3)MLn] Nitrile and Isocyanide Complexes

The limits of steric crowding in organometallic metallocene complexes have been examined by studying the synthesis of [C5Me5)(3)MLn] complexe, as a function of metal in which L = Me3CCN, Me3CNC, and Me3SiCN. The bis(tert-butyl nitrile) complexes [(C5Me5)(3)Ln(NCCMe3)(2)] (Ln = La, 1; Ce, 2; Pr, 3) can be isolated with the largest lanthanide metal ions, La3+, Ce3+, and Pr3+. The Pr3+ ion also forms an isolable mono-nitrile complex, [(C5Me5)(3)Pr(NCCMe3)] (4), whereas for Nd3+ only the mono-adduct [(C5Me5)(3)Nd(NCCMe3)] (5) was observed. With smaller metal ions, Sm3+ and Y3+, insertion of Me3CCN into the M-C(C5Me5) bond was observed to form the cyclopentadiene-substituted ketimide complexes [(C5Me5)(2)Ln{NC(C5Me5)(CMe3)}-(NCCMe3)] (Ln = Sm, 6; Y, 7). With tert-butyl isocyanide ligands, a bis-isocyanide product can be isolated with lanthanum, [(C5Me5)(3)La(CNCMe3)(2)] (8), and a mono-isocyanide product with neodymium, [(C5Me5)(3)Nd(CNCMe3)] (9). Silicon-carbon bond cleavage was observed in reactions between [(C5Me5)(3)Ln] complexes and trimethylsilyl cyanide, Me3SiCN, to produce the trimeric cyanide complexes [{(C5Me5)(2)Ln(mu-CN)(NCSiMe3)}(3)] (Ln = La, 10; Pr, 11). With uranium, a mono-nitrile reaction product, [(C5Me5)(3)U(NCCMe3)] (12), which is analogous to 5, was obtained from the reaction between [(C5Me5)(3)U] and Me3CCN, but [(C5Me5)(3)U] reacts with Me3CNC through C-N bond cleavage to form a trimeric cyanide complex, [{(C5Me5)(2)U(mu-CN)(CNCMe3)}(3)] (13).