Versatile phosphite ligands based on silsesquioxane backbones

Silsesquioxanes are employed as ligand backbones for the synthesis of novel phosphite compounds with 3,3'-5,5'-tetrakis(tert-butyl)-2,2'-di-oxa-1,1'-biphenyl substituents. Both mono- and bidentate phosphites are prepared in good yields. Two types of silsesquioxanes are employed as starting materials. The monophosphinite I and the monophosphite 2 are prepared from the thallium silsesquioxide derived from a completely condensed silsesquioxane framework (c-C5H9)(7)Si7O12SiOTl. The diphosphite 3 is synthesized starting with the incompletely condensed monosilylated disilanol (cC(5)H(9))(7)Si7O9(OSiMePh2)(OH)(2). For monophosphite 2, the corresponding trans- [PtCl2(2)] complex 4 is characterized by NMR spectroscopy as well as by Xray crystallography, as the first example of a completely condensed oxo-functionalized silsesquioxane framework. The coordination of the bidentate ligand 3 towards Pd, Mo and Rh is studied, both by NMR spectroscopy as well as by X-ray crystallography. Various modes of coordination are shown to be possible. The molecular structures for the complexes trans- [PdCl2(3)] (5), cis-[Mo(CO)(4)(3)] (6) and the dinuclear complex [{Rh( mu-Cl)(CO)}(2)(kappa(2)-3)] (7) have been determined. In the rhodium-catalyzed hydro-formylation of I-octene high activities, with turnover frequencies of up to 6800 h(-1), are obtained with these new nanosized phosphorus ligands.