• coordination chemistry;
  • homogeneous catalysis;
  • ligand design;
  • phosphorus;
  • silsesquioxanes


Silsesquioxanes are employed as ligand backbones for the synthesis of novel phosphite compounds with 3,3′-5,5′-tetrakis(tert-butyl)-2,2′-dioxa-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 1 and the monophosphite 2 are prepared from the thallium silsesquioxide derived from a completely condensed silsesquioxane framework (c-C5H9)7Si7O12SiOTl. The diphosphite 3 is synthesized starting with the incompletely condensed monosilylated disilanol (c-C5H9)7Si7O9(OSiMePh2)(OH)2. For monophosphite 2, the corresponding trans-[PtCl2(2)] complex 4 is characterized by NMR spectroscopy as well as by X-ray 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(μ-Cl)(CO)}22-3)] (7) have been determined. In the rhodium-catalyzed hydroformylation of 1-octene high activities, with turnover frequencies of up to 6800 h−1, are obtained with these new nanosized phosphorus ligands.