Synthesis of Mn[N(SiMe3)(2)][Me3SiNC(Bu-t)NSiMe3] (M = Sn, Ge) from amidinate precursors: Active catalysts for phenyl isocyanate cyclization

Mixed amidinato amido complexes [Me3SiNC(Bu-t)NSiMe3]M[N(SiMe3)(2)] (M = Sn 2, Ge 3) were prepared by the reaction of [Me3SiNC(Bu-t)NSiMe3]Li (la) wit h SnCl2 and GeCl2(dioxane) in ether. The N(SiMe3)(2) ligand in these compou nds is derived from the rearrangement of the [Me3SiNC(Bu-t)NSiMe3](-) anion with extrusion of (BuCN)-Bu-t. The susceptibility of [Me3SiNC(Bu-t)NSiMe3] (-) to rearrangement appears to be dependent on reaction solvent and on the coordinated metal center. Single-crystal X-ray diffraction studies of 2 an d 3 are presented. Replacement of Me for Bu-t in the ligand allowed [Me3SiN C(Me)NSiMe3](2)Sn-II (4) to be isolated, and an X-ray structure of this com pound is reported. The isolation of 4 indicates that steric factors also pl ay a role in the stability of [Me3SiNC(Bu-t)NSiMe3](-). Compounds 2 and 3 a re outstanding catalysts for the cyclotrimerization of phenyl isocyanates t o perhydro-1,3,5-triazine-2,4,6-triones (isocyanurates) at room temperature . In contrast, complex 4 catalytically reacts with phenyl isocyanate to pro duce isocyanate dimer and trimer in a 52:35 ratio.