Carbosilane Dendrons as Solubilizers of Metal Complexes in Supercritical Carbon Dioxide

Abstract

Palladium complexes of general formula [PdCl2(L)2], 3a−c, were synthesized by reaction of [PdCl2(COD)] (COD = 1,5-cyclooctadiene) with the appropriate functionalized phosphine L = [P(C6H5) n ((C6H4CH2CH2Si(CH2CH2CH2SiEtMe2)3)3 - n )] (n = 2, 2a; 1, 2b; 0, 2c, respectively), which integrated carbosilane dendritic wedges attached to the para-carbon atom of the phenyl group. As a result of the inclusion of the carbosilane dendrons, the solubility of the corresponding palladium complexes 3 in supercritical carbon dioxide (scCO2) was increased in comparison with the palladium complex containing a PPh3 ligand, which showed negligible solubility. The employment of these complexes as precatalysts in a selected Heck coupling reaction in scCO2 was investigated. Good activities were found for 3a−c in such a medium due to the acquired solubility, in contrast with the palladium complex containing PPh3, which showed no activity.

Mizoroki–Heck Reactions: Modern Solvent Systems and Reaction Techniques

“…Carbosilane dendrons were prepared for enhancing the solubility of catalysts. In contrast to the catalytically inactive palladium complexes containing PPh 3 , palladium complexes with functionalized phosphines showed good activity due to increased solubility in scCO 2 [124]. Supercritical conditions were also used for the preparation of new materials applicable as catalysts in Mizoroki-Heck chemistry.…”

“…The reaction was conducted at room temperature in the presence of Pd(OAc) 2 (10 mol%) and a variety of phosphine ligands: tpp, P(o-tol) 3 , P(p-tol) 3 , P(2-furyl) 3 Reports about a toluene-ethylene glycol biphasic catalytic system for a Mizoroki-Heck reaction of iodobenzene and butyl acrylate are rare [115,124]. Potassium acetate was used as a base and various catalyst precursors (Pd(OAc) 2 , PdCl 2 , Ni(OAc) 2 , Rh(CO) 2 acac, RhCl 3 , RuCl 3 , Pt(COD)Cl 2 , CoCl 2 , 1.0 mol% each) were applied in the presence of the water-soluble ligand TPPTS.…”

Palladocarbosilane dendrimers as catalysts for the asymmetric hydrovinylation of styrene in supercritical carbon dioxide

“…More recently, trimethylsilyl units have been incorporated to this set [4], because of their generally inexpensive synthesis and the fact that the trimethylsilyl groups do not affect the electronic properties of the metal centers. In this context, in the area of dendrimers, a relevant report by de Jesú s and co-workers [5] showed, for the first time, that a number of palladium dendrimers containing functionalized phosphines with trialkylsilyl groups, were relatively soluble in scCO 2 , in clear contrast with the negligible solubility in the same solvent observed for the palladium complex [PdCl 2 (PPh 3 ) 2 ]. Thus, the enhanced solubility of the dendrimers allowed successfully their employ as precatalysts in a selected Heck coupling reaction in scCO 2 [5].…”

“…In this context, in the area of dendrimers, a relevant report by de Jesú s and co-workers [5] showed, for the first time, that a number of palladium dendrimers containing functionalized phosphines with trialkylsilyl groups, were relatively soluble in scCO 2 , in clear contrast with the negligible solubility in the same solvent observed for the palladium complex [PdCl 2 (PPh 3 ) 2 ]. Thus, the enhanced solubility of the dendrimers allowed successfully their employ as precatalysts in a selected Heck coupling reaction in scCO 2 [5]. These interesting findings reveal the high potential of metallodendrimers with carbosilane scaffold as catalysts in supercritical media.…”

The use of pyridine-functionalised polydimethylsiloxane polymers as a supercritical carbon dioxide solubilising support for copper compounds

“…The aim of the work described here was to confirm experimentally the solubility in scCO 2 of metal complexes supported by functionalised PDMS. Previously, our group has successfully attached trimethylsilyl groups [12] and carbosilane dendrons [13] to ligands, yielding soluble metal complexes that were active catalysts in scCO 2 .…”