| Permethylazacyclopolysilanes MeN(SiMe(,2))(,n) (n = 4,5), and permethylphosphacyclopolysilanes, MeP(SiMe(,2))(,n) (n = 4,5,6), were prepared by the ring closure reactions of (alpha),(omega)-dichloropermethylpolysilanes Cl(SiMe(,2))(,n)Cl (n = 4,5,6) with monomethylamine and dilithium methylphosphide, respectively. The permethylazacyclopolysilane MeN(SiMe(,2))(,6) was prepared by pyrolysis of Me(H)N(SiMe(,2))(,6)N(H)Me which was the initial product from the reaction of 1,6-Cl(SiMe(,2))(,6)Cl with monomethylamine. Ultraviolet spectra were obtained for the nitrogen and phosphorus heterocyclic compounds and the results are compared with the data for linear and cyclic permethylpolysilanes. The observed trend in the uv absorptions for the permethylazacyclopolysilanes is similar to that observed for the linear permethylpolysilanes. However the trend in the uv absorptions for the permethylphosphacyclopolysilanes is similar to the trend for the cyclic polysilanes in that both MeP(SiMe(,2))(,4) and (Me(,2)Si)(,5) have unusually long wavelength absorptions in their uv spectra. The ('1)H, ('13)C, ('31)P and ('29)Si nmr parameters for the permethyl-phosphacyclopolysilanes are reported and discussed in terms of electronic and molecular structure variations with ring size.;The heterocyclic diphosphapolysilanes (PhP)(,2)(SiMe(,2))(,n) (n = 2,3,4) were synthesized by the reactions of 1,2-dilithium-1,2-diphenyldiphosphide with (alpha),(omega)-dichloropermethylpolysilanes Cl(SiMe(,2))(,n)Cl (n = 2,3,4). The stereochemical fluxionality of these compounds was examined by dynamic nuclear magnetic resonance spectroscopy. The results of ('1)H, ('13)C, ('31)P and ('29)Si nmr spectra are reported and discussed in terms of a phosphorus inversion mechanism. The values of the free energy of activation for phosphorus inversion in (PhP)(,2)(SiMe(,2))(,2), (PhP)(,2)(SiMe(,2))(,3) and (PhP)(,2)(SiMe(,2))(,4) were determined to be 15.2, 12.6 and 12.4 kcal/mol, respectively. These results are compared with those for related compounds.;The x-ray crystal structure of (PhP)(,2)(SiMe(,2))(,3) was determined in order to establish its conformation in the solid state. The molecule exists in the dl trans form with the five-membered ring significantly twisted in the crystal. The angle between the phosphorus-phosphorus bond and the plane of the three silicon atoms is 43(DEGREES).;The ('1)H and ('31)P dynamic nuclear magnetic resonance spectra of (PhPSiMe(,2))(,2), an isomer of the previous heterocyclic diphosphadisilane, were also obtained. The results are discussed in terms of a phosphorus inversion mechanism and an approximate value of 13 kcal/mol was determined for this process.;Organosilicon substituted phosphoranyl radicals were generated by the addition of tert-butoxyl radical to the corresponding phosphine and studied by electron spin resonance spectroscopy. The compounds examined were tris(trimethylsilyl)phosphine and the permethylphosphacyclopolysilanes MeP(SiMe(,2))(,n) (n = 4,5,6). Irradiation of a solution of tris-(trimethylsilyl)phosphine and di-tert-butyl-peroxide in cyclopropane at -100(DEGREES)C produced two types of phosphoranyl radicals: the initial adduct, (Me(,3)Si)(,3)POtBu (a(,p) = 452 G) and a second species, (Me(,3)Si)(,2)P(OtBu)(,2) (a(,p) = 574 G). Kinetic measurements of the decay of these phosphoranyl radicals upon shuttering the light are reported and indicate that the di-tert-butoxyphosphoranyl radical (Me(,3)Si)(,2)P(OtBu)(,2) is much more stable than the monoadduct (Me(,3)Si)(,3)POtBu. Irradiation of solutions of the heterocyclic phosphasilanes MeP(SiMe(,2))(,n) (n = 5,6) and di-tert-butylperoxide in cyclopropane at -100(DEGREES)C generated the phosphoranyl radicals Me(tBuO)P(SiMe(,2))(,5) (a(,p) = 407 G) and Me(tBuO)P(SiMe(,2))(,6) (a(,p) = 403 G). However under similar conditions no radical species were detected for MeP(SiMe(,2))(,4) by esr spectroscopy. |
