Dihydroxyoligosilanes as novel ligands in coordination chemistry—first synthesis of 2,5-dioxa-3,4-disilatitanacyclopentanes

The reaction of two equivalents of (Me3Si)2RSiK×3THF (1 R=SiMe3, 2 R=Ph) with Cl2MeSiSiMeCl2, followed by hydrolysis in the presence of NH4(NH2COO) leads to the formation of the dihydroxyoligosilanes MeR(HO)SiSi(OH)RMe [4 R=Si(SiMe3)3, 6 R=Si(SiMe3)2Ph] as diastereomeric mixtures. Addition of two equivalents of n-BuLi to the diastereomerically pure ligands (meso)-4/6 and (rac)-4/6, respectively, and subsequent treatment with Cp2TiCl2 yields the (Z) and (E) arranged five-membered rings (MeRSiO)2TiCp2 [7 R=Si(SiMe3)3, 8 R=Si(SiMe3)2Ph], respectively. The crystal structures of the ligand (rac)-6 as well as of the titanacycles (E)-8 and (Z)-7 are reported.