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

The reaction of four equivalents of the monomeric trimethoxysilyl(T)-functionalized ether-phosphine ligand CyP(CH2CH2OCH3)(CH2)(3)SiR3 (R = OMe [1a(T-0)], Me [1b]) with [{mu-ClRh(COE)(2)}(2)] yielded the monomeric pseudo 14 electron rhodium(I) complexes [CIRh(PO)(P similar to O)] (2a(T-0)(2), 2b). For the sol-gel process the complex 2 a(TO), was protected by introduction of the volatile, reversibly binding ligand pyridine. Thus, the monomeric compound 2a(TO), was co-condensed with two and eight equivalents of the co-condensation agent MeSi(OMe)(2)(CH2)(6)(MeO)(2)SiMe (D-0-C-6- D-0) to give the polysiloxane-bound congeners 2(T-n)(2)(D-i-C-6-D-i)(y) (y = 2 and 8, respectively; i = 0 - 2; n = 0 - 3). The polysiloxane-bound complex 2(T-n)(2)-(D-i-C-6-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-C-6-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-C-6-D-i)(2) oxidatively added hydrogen to give the octahedrally configurated complex [ClRhH2(Py)(P similar to O)(2)] [6(T-n)(2)(D-i-C-6-D-i)(2)]. Treatment of dry 2(T-n)(2)(D-i-C-6-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-C-6-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 D-0-C-6-D-0 and on the polarity of the solvent. The polysiloxane-bound complexes 2(T-n)(2)(D-i-C-6-D-i)(y) are more active than their monomeric congener 2a(T-0)(2).