Diazomethane Insertion into Lanthanide− and Yttrium−C(allyl) Bonds To Form the η²-Hydrazonato Complexes (C₅Me₅)₂Ln[η²(<i>N</i>,<i>N</i>′)-RNNCHSiMe₃] (R = C₃H₅)

(Trimethylsilyl)diazomethane, Me3SiCHN2, is not metalated by the metallocene allyl complexes (C5Me5)2Ln(C3H5) but instead inserts to form the lanthanide hydrazonato complexes (C5Me5)2Ln[η2(N,N′)-RNNCHSiMe3] (R = CH2CHCH2; Ln = Sm, La, Y). Although the La, Y, and Sm complexes are isomorphous, the double bond in the allyl substituent is oriented toward La and away from Y and Sm.