Linear Phenylsilanes with PSi4P, PSi5P, and Si-7 Backbones

Linear alpha,omega-diphosphaoligosilanes were prepared starting from 1,5-dilithiodecaphenyl-n-pentasilane, Li(SiPh2)(5)Li, and chlorodiorganophosphanes. The compounds 1,5-bis(diphenylphosphanyl)decaphenyl-n-pentasilane, (Ph2P)Si5Ph10(PPh2), 1,5-bis(di-iso-propylphosphanyl)decaphenyl-n-pentasilane, (iPr(2)P)Si5Ph10(PiPr(2)), and 1,4-bis(di-iso-propylphosphanyl)octaphenyl-n-tetrasilane, (iPr(2)P)Si4Ph8(PiPr(2)), were obtained in moderate to good yields and characterized with IR-, Raman-, UV-, P-31-, Si-29-, and H-1-NMR spectroscopy. Single crystal structure analyses of these three silanes show all-transoid conformations of the atoms along the phosphorus-silicon backbone of the molecules in the solid state. The silicon-silicon and the silicon-phosphorus-bonds are elongated. This is caused by the complete substitution of these molecules by sterically demanding phenyl- and i-propyl-substituents and effective sigma-conjugation along the main chains. Hexadecaphenyl-n-heptasilane, Si7Ph16, was prepared for comparison with the other three compounds. The latter one shows a long wavelength UV-absorption in the same region as 1,5-bis(diphenylphosphanyl)decaphenyl-n-pentasilane.