Cyclic Polysilanes : XIII. Ring closure reactions of α,ω-dichloropermethylpolysilanes; The preparation of heterocyclic phenylphosphapermethylsilanes (PhP) m(SiMe 2) n

Abstract

The reactions of the dichloropermethylsilanes Cl(SiMe 2) n Cl ( n = 1−6) with dilithium phenylphosphide yield a series of novel heterocyclic phosphasilanes. For n = 4, 5 and 6, the reaction leads to the corresponding 5-, 6- and 7-membered cyclic monophosphapolysilanes PhP(SiMe 2) n , but when n = 3, a polymeric material of probable formula [PhP(SiMe 2) 3] n is formed. For n = 2, ring closure again occurs, to yield the 6-membered P 2Si 4 ring compound [PhP(SiMe 2) 2] 2. With dimethyldichlorosilane, cyclization results in the dimeric phosphasilane (PhPSiMe 2) 2 at −40°C, and the corresponding trimeric derivative (PhPSiMe 2) 3 at +40°C. These two ring sizes exist in an equilibrium (PhPSiMe 2) 2 ⇌ (PhPSiMe 2) 3, the dimer being stable at room temperature, but being converted into the trimer above 150°C. The 1H, 13C, 29Si and 31P NMR parameters are reported for all the compounds, and the chemical shifts and coupling constants interpreted in terms of the molecular and electronic structures of the different ring sizes.