Decamethylsilicocene chemistry: Unprecedented multistep reactions of a silicon(II) compound with the heterocumulenes CO2, COS, CS2, and RNCS (R=methyl, phenyl)

In the reaction of the nucleophilic decamethylsilicocene, ((Me(5)C(5))(2)Si (1), with the electrophilic heterocumulenes CO2, COS, CS2, and RNCS, multistep processes are observed, which in most cases proceed via several highly reactive intermediates. In all reactions, the formal oxidation state of the silicon atom changes from +2 in 1 to +4, and the hapticity of the pentamethylcyclopentadienyl ligands changes from eta(5) to eta(1). In the reaction of 1 with CO2, COS, or RNCS, double-bond species of the type (Me(5)C(5))(2)Si = X (X = O, S) are formed, which are stabilized via different routes. Thus, reaction of 1 with CO2 in toluene as solvent finally leads to the spiro compound [(Me(5)C(5))(2)SiO2]C-2 (4), whereas in pyridine as solvent, the eight-membered heterocycle [(Me(5)C(5))(2)SiO2CO](2) (5) is formed. The dithiadisiletane [(Me(5)C(5))(2)SiS](2) (9) results from the reaction of 1 with COS. Dithiasiletane derivates of the type (Me(5)C(5))(2)SiS2C = NR (10, 11) are the final products from the reaction of 1 with RNCS (R = CH3, C6H5). Multistep rearrangement processes have to be postulated to explain the formation of the dithiadisiletane derivate 15 in the surprising reaction of 1 with CS2; ligands that initially are bonded to the silicon (Me(5)C(5)) and to the carbon atom (S) have to be completely exchanged to build up the final product. The silaheterocycles 4, 5, 10, and 15 and also some of the basic molecular framework have been unknown in the literature. The crystal strucutres of 4, 5, 10, and 15 were determined by X-ray crystallography and are presented.