Stoichiometric and catalytic reactions of the polysiloxane-bound (ether-phosphine)rhodium(I) complex [ClRh(PO)(P ~ O)] in interphases

Article abstract of DOI:10.1002/chem.19970031116

The reaction of four equivalents of the monomeric trimethoxysilyl(T)-functionalized ether-phosphine ligand CyP(CH₂CH₂OCH₃)(CH₂)₃SiR₃ (R = OMe [1a(T⁰)], Me [1b]) with [{μ-C1Rh(COE)₂}₂] yielded the monomeric pseudo 14 electron rhodium(I) complexes [C1Rh(PO)(P ~ O)] (2a(T⁰)₂, 2b). For the sol-gel process the complex 2a(T⁰)₂ was protected by introduction of the volatile, reversibly binding ligand pyridine. Thus, the monomeric compound 2a(T⁰)₂ was co-condensed with two and eight equivalents of the co-condensation agent MeSi(OMe)₂(CH₂)₆(MeO)₂SiMe (D⁰-C₆-D₀) to give the polysiloxane-bound congeners 2(T(n))₂(D₁-C₆-D₁)(y) (y = 2 and 8, respectively; i = 0-2; n = 0-3). The polysiloxane-bound complex 2(T(n))₂ (D(i)-C₆-D(i))₂ was treated with a variety of small molecules in the gas/solid and liquid/solid interphases. It was shown that a facile cleavage of the Rh-O bond in the ether-phosphine chelate occurred even in the solid state. The reaction of 2(T(n))₂-(D(i)C₆-D(i))₂ with carbon monoxide, carbon disulfide, and diphenylacetylene resulted in the irreversible coordination of the molecule to the metal. In the presence of pyridine, the polysiloxane-bound complex 2(T(n))₂(D(i)-C₆-D(i))₂ oxidatively added hydrogen to give the octahedrally configurated complex [ClRhH₂(Py)(P ~ O)₂] [6(T(n))₂(D(i)-C₆-D(i))₂]. Treatment of dry 2(T(n))₂(D(i)-C₆-D(i))₂ with ethene led to the reversible formation of the corresponding complex. Although the materials display low surface areas, at least 75% of the rhodium centers within the matrix are accessible to the rather bulky tolan molecules. The complexes 2(T(n))₂(D(i)-C₆-D(i))(y) (y = 2, 8) show high activities and selectivities in the hydrogenation of tolan. The conversion was found to depend markedly on the amount of co-condensate D⁰-C₆-D⁰ and on the polarity of the solvent. The polysiloxane-bound complexes 2(T(n))₂(D(i)-C₆D(i))(y) are more active than their monomeric congener 2a(T⁰)₂.