Polysilane fragmentation

The photolysis of cyclic polysilanes results in ring contraction with concomitant extrusion of a silylene fragment. Although the formation of two reactive intermediates potentially complicates mechanisms for product formation, it has provided a useful method for the synthesis of both unstable and stable disilenes... 

The key intermediates in the process are the silylenes and the radical fragments, both of which should be amenable to trapping experiments. With this in mind, two representative, polysilane derivatives 6 and 9, were irradiated (254 nm) in the presence of excess triethylsilane, and the results of this experiment are shown in Figure 6. Since the polysilane 9 was not soluble in the trapping reagent, it was dissolved in cyclohexane which contained a 100 fold molar excess of triethylsilane. In each case, the major isolable volatile products... 

Fragmentation of pentacoordinate di- or polysilanes, assisted by intramolecular coordination by chelating nitrogen atoms, can occur at very modest temperatures (see Section VIII.D). 

When irradiated with ultraviolet light, most polysilanes undergo chain scission into smaller fragments. When polysilanes (RR Si), are photolyzed with UV light X = 254 nm)... 

The interaction of polysilanes with X-ray photoelectrons (XPS) has been used for theoretical studies" and for analytical purposes.19 Seven polymers with silane, carbosilane, and siloxane fragments—(-Si(CH3)2-)n (PDMS),... 

Table 2 Relative Conformational Energies (in kcal/mol) Polysilane and Polydimethylsilane (PDMS) Fragments...

Their excited states bear considerable similarities to those of polyenes, but also exhibit significant differences (Balaji and Michl, 1991). Upon irradiation, oligosilanes (Ishikawa and Kumada, 1986) and particularly polysilanes (Trefonas et al., 1985), readily fragment to lower-molecular-weight species, and polysilanes show promise as photoresists. 

In the last years transition metal-silyl complexes have received special attention for several reasons [1, 2], On the one hand, they are assumed to be important intermediates in catalytic processes [2] (transition metal-catalyzed hydrosilylation reaction, dehydrogenative coupling of silanes to polysilanes, etc.), on the other metal-substituted silanes show special properties, which can be tuned systematically by judicious choice of the metal and its ligands [3] Furthermore, silylenes (silanediyls) are stabilized by unsaturated transition metal fragments leading to metal-silicon double-bonds [4]. In the light of a possible application in MOCVD processes some of these complexes are of interest as potential single-source precursors for the manufacture of thin silicide films [5]. 

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