On the insertion into the lanthanide-carbon bond. Synthesis and structure of [(Cp2Sm)-Sm-*(C6H5CH2NNO)](2) and [K(18-crown-6)(Cp2Yb)-Yb-* (NCS)(2)](infinity)

The compound [Cp-2*Sm(CH2C6H5)(thf)] was investigated, regarding its reacti ons with small molecules. The main subject was to detect an insertion into the Ln-C bond. With N2O an insertion reaction is observed, yielding the dim er [Cp-2*Sm(C6H5CH2NNO)](2) (1). The structural data of 1 was collected by a single crystal X-Ray diffraction analysis. (Space group P (1) over bar, Z = 1, a = 982.8(2) pm, b = 1052.2(2) pm, c = 1383.8(3) pm, alpha = 89.29(3) degrees, beta = 73.64(3)degrees, gamma = 66.41(3)degrees). In the dimer, th e two Samarium ions are linked via an (eta(1): eta(2)) bridge by two benzyl diazotato ligands. A nearly planar six-membered central Sm2N2O2-ring is fo rmend. Two pentamethylcyclopentadienyl ligands complete the coordination sp here of each Samarium ion, which are thus sur-rounded by four ligands each and have a distorted tetrahedral coordination geometry. An insertion of a SCN- fragment in the Ln-C bond could not be observed. The substitution of the benzyl ligand leads to a polymeric chain structure. Th e new compound [K(18-crown-6)Cp-2*Yb(NCS)(2)](infinity) 2 contains a tetrah edrally coordinated Yb(III)-ion. (Space group P2(1)/n}, Z = 4, a = 1640.6(3 ) pm, b = 1482.2(3) pm, c = 1674.5(3) pm, beta = 102.82(1)degrees).