ISSN:
0947-6539
Keywords:
immobilized catalysts
;
polysiloxanes
;
P ligands
;
rhodium
;
sol-gel processes
;
Chemistry
;
General Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The reaction of four equivalents of the monomeric trimethoxysilyl(T)-functionalized ether-phosphine ligand CyP(CH2CH2OCH3)(CH2)3SiR3 (R = OMe [1 a(T0)], Me [1 b]) with [{μ-ClRh(COE)2}2] yielded the monomeric pseudo 14 electron rhodium(I) complexes [ClRh(PO)(P∼O)] (2a(T0)2, 2 b). For the sol-gel process the complex 2 a(T0)2 was protected by introduction of the volatile, reversibly binding ligand pyridine. Thus, the monomeric compound 2 a(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(Tn)2(Di-C6-Di)y (y = 2 and 8, respectively; i = 0-2; n = 0-3). The polysiloxane-bound complex 2(Tn)2-(Di-C6-Di)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(Tn)2-(Di-C6-Di)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(Tn)2-(Di-C6-Di)2 oxidatively added hydrogen to give the octahedrally configurated complex [ClRhH2(Py)(P ∼ O)2] [6(Tn)2(Di-C6-Di)2]. Treatment of dry 2(Tn)2-(Di-C6-Di)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(Tn)2(Di-C6-Di)y (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(Tn)2(Di-C6-Di)y are more active than their monomeric congener 2 a(T0)2.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/chem.19970031116
Permalink