1,23-Diphospha-3,6,9,12,15,18,21-heptasilatricosane,6,18-bis[2-[[(diphenylphosphino)methyl]dimethylsilyl]ethyl]-12,12-bis[6-[2-[[(diphenylphosphino)methyl]dimethylsilyl]ethyl]-3,3,6,9,9-pentamethyl-11,11-diphenyl-11-phospha-3,6,9-trisilaundec-1-yl]-3,3,6,