DECAMETHYLSILICOCENE CHEMISTRY - UNPRECEDENTED MULTISTEP REACTIONS OFA 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 R NCS, multistep processes are observed, which in most cases proceed via several highly reactive intermediates. In all reactions, the formal o xidation 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-bon d species of the type (Me(5)C(5))(2)Si = X (X = O, S) are formed, whic h 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 hete rocycle [(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. Di thiasiletane derivates of the type (Me(5)C(5))(2)SiS2C = NR (10, 11) a re the final products from the reaction of 1 with RNCS (R = CH3, C6H5) . Multistep rearrangement processes have to be postulated to explain t he formation of the dithiadisiletane derivate 15 in the surprising rea ction 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 th e literature. The crystal strucutres of 4, 5, 10, and 15 were determin ed by X-ray crystallography and are presented.