PALLADIUM-CATALYZED INSERTION OF ISOCYANIDES INTO THE SILICON-SILICON LINKAGES OF OLIGOSILANES

Full details of a study on the reactions of oligosilanes with isocyanides promoted by a palladium catalyst are described. Heating a mixture of oligosilanes and excess 2,6-disubstituted aryl isocyanide in the presence of palladium(II) acetate led to the complete insertion of isocyanide into all silicon-silicon linkages, giving oligo(silylimine) derivatives. The oligo(silylimine)s have been isolated and characterized so far in the complete insertion reaction with oligosilanes up to a hexasilane. Use of the limiting amount of isocyanide permitted insertion of isocyanide into predominantly the terminal silicon-silicon linkages. The mode of the insertion reaction depends on the substituent at the silicon, e.g., tetrasilanes with phenyl groups on the internal silicon atoms favorably underwent the insertion reaction at the terminal silicon-silicon linkages, resulting in the partial insertion. The bulkiness of the ortho substituents on the aromatic isocyanide was also found to have much influence on the insertion; hence, 2,6-diisopropylphenyl isocyanide favored the partial insertion. New skeletal rearrangement of oligosilanes took place in a palladium-catalyzed reaction of substituted aryl isocyanide with tetra- and hexasilanes, forming 3,3-bis(silyl)-l-aza-2, 4-disilacyclobutane derivatives. The rearrangement, which is unique and intriguing in that the product is properly reconstituted from four fragments of the tetrasilane and two fragments of the isocyanide, was promoted in the copresence of a tert-alkyl isocyanide.