The present Ph. D. Thesis deals with the synthesis and characterization of Pdsupporting
materials and their use as catalysts in C-C cross-coupling reactions. The aim
of the work is to obtain recoverable and reusable catalysts that should simplify product
isolation and process design as well as reduce the environmental impact of the system
by avoiding metal wastes.
The materials used as supports cover a wide range including: amorphous and
mesoporous silica, zeolites, polymers, periodic mesoporous organosilicates and single
wall nanotubes (SWNT). The methodology to incorporate the palladium species on the
support depends on the material and includes: i) adsorption of a palladium salt or a
complex onto zeolites and AlMCM-41, ii) adsorption of palladium salts onto zeolites by
incipient wetness methodology, iii) covalent anchoring of a palladium complex on
previously functionalized silicas, iv) covalent anchoring of a palladium complex on
polymers via radical polimerization, v) insertion of the palladium complex
functionalized with two therminal alcoxysilane groups via hydrothermal cocondensation
with TEOS in the framework of a mesoporous silica and vi) palladium (0)
nanoparticles deposition on SWNT.
We have shown that the hardness/softness of Pd2+ Lewis acid sites hosted onto
zeolites are modulated by the framework of the zeolite. This effect influences on the
catalytic activity for the cycloisomerization reaction of 1,6-heptadienes of the Pd2+
Lewis acid supported onto different zeolites.
Palladium salts supported on basic zeolites, acting as catalysts for the Heck and
Suzuki cross-coupling reactions, show the activity of a bifunctional catalyst (metalbase).
They were reusable after the regeneration of the basic sites.
The anchoring on amorphous silica of a highly active palladium complex for the
Suzuki coupling leads to the formation of a reusable catalyst without needing
reactivation of the solid material. The covalent anchoring of the same complex on
mesoporous silica structures, either by tethering it on the wall or by insertion into the
framework, leads to a catalytically active material for the Suzuki reaction, but the
mesoporous structure collapses upon reuse, producing a progressive decrease on the
activity of the catalyst.
The incorporation of the complex on polymers also produces a catalytically active
material for the Suzuki reaction. The comparison between silica and polymeric catalysts
in water, dioxane and water:dioxane mixtures as solvents suggests that the solventsupport
affinity directly influences on the catalytic activity of the supported complex.
The study of the complex stability incorporated on the different supports shows the
progressive degradation of the palladium complex to palladium (0) particles, that are
catalytically active for the coupling reaction. The deposition of palladium (0) as
nanoparticles on SWNT produces a material that is catalytically more active than
commercial Pd/C for the Heck coupling.