The constant increase in chemical production and associated increase in energy consumption and waste generation obstruct the achievement of protection of our environment. Water is cheap and non toxic solvent, making it attractive in terms of economy and safety. The overall purpose of this project is to bring together top European laboratories who collectively possess all the required skills to develop and implement the use of catalytic processes compatible with aqueous media, providing a unique training ground for early-stage and experienced researchers. The main project objectives will be:
The design, synthesis and characterization of new hydrosoluble ligands (cyclopentadienyls, phosphines, porphirins, azacrowns, bipyridyls etc.) and macroligands (dendrimers), and the study of their co-ordination chemistry with metals of catalytic relevance.
The design, synthesis and characterization of organometallic compounds with aqua, hydroxo, and oxo ligands.
Studies of substrate activation and stoichiometric reactivity. Activation of inorganic substrates such as water, dioxygen, dihydrogen, carbon and sulphur oxides, bicarbonate and carbonate, phosphorus, organic substrates (alkynes, alkenes, alcohols, thiols, nitriles,) etc. Activation of C-F, C-C and C-Heteroelement bonds.
Physico-chemical studies of complex-solvent interactions including spectroscopic, thermodynamic, kinetic and mechanistic investigations of the interaction between transition metal complexes and solvent molecules. Process to be studied entail: water coordination and exchange; proton transfer to and from a metal centre and ligands as a function of pH; hydrogen bonding interactions between water (as a proton donor) and transition metals or ligands (as a proton acceptor). Study of the effect of solvent composition on pKa, rate constants, reaction enthalpies, etc.
The development or improvement of analytical instrumentation for in situ and on–line analysis of reaction intermediates, by-products and products of stoichiometric or catalytic reactions (ESI-MS, spectroelectrochemistry, photochemistry, NMR spectroscopy, etc).
Theoretical studies, by ab initio and/or density functional methods, in parallel with the experimental studies. Targets of this activity will be the modelling of catalytic cycles and hydrogen bonded interactions. The analysis of solvent effects with different solvent/solute interaction models.
Catalytic studies in aqueous or biphasic media at different pH: CO2 hydrogenation, oxidation of various substrates, hydrodehalogenation of fluorinated and chlorinated hydrocarbons, functionalization of alkanes, metathesis of alkenes, hydroxylation of white phosphorus, detoxication of poisonous nitriles, etc., including comparison of the catalytic activity and selectivity of the water-soluble metalladendrimers with that of the corresponding water-soluble monomers.
Electrocatalytic studies in aqueous/biphasic media.
Photochemistry and photocatalysis in aqueous/biphasic media including solar-induced reactions.
1. New hydrosoluble ligands and their coordination chemistry
design, synthesis and characterization of new hydrosoluble ligands
will be accomplished using an "appropriate modification of
established ligand" approach. General classes of ligands will
include: (a) modified
monodentate and bidentate phosphines bearing hydrophilic substituents
such as aminoacids, (oligo)peptides, nucleosides, sulphonates, and
carbohydrates; (b) functionalised mono- and polysubstituted
cyclopentadienes with hydrophilic substituents as above; (c) modified
water-soluble porphyrin, azacrown, and bipyridyl; (d) functionalised
dendrimers bearing a variety of different donor groups (phosphines,
phosphonites, phosphinites, phosphites, amines, imines, etc) to be
placed either on the surface or within the cavities of the
2. Aqueous organometallic chemistry with aqua, hydroxo, and oxo ligands
This will include: investigations of known high-valent organometallic compounds [e.g. CpReO3, (CH3)ReO3, (CH3)3ReO2, (CH3)4OsO, Cp2M2O5 (M = Mo, W)] and new related derivatives in water. A reductive approach to new middle-valent organometallics containing hydroxo and/or aqua ligands will be examined. Specific aqueous characterization methodologies will be applied such as (a) speciation studies as a function of pH by using a variety of analytical tools (ESI-MS, EPR, NMR spectrometry) and kinetics analyses, (b) studies of the redox behaviour and associated chemical transformations by classical electrochemical techniques and by in-situ techniques, such as coupled ESI-MS electrochemistry and spectroelectrochemical methods.
3. Substrate activation and stoichiometric reactivity
of the interaction between the two above classes of compounds and
different substrates will be accomplished though the isolation or in
situ studies of the substrate-complex adducts. Specific examples
will include the
activation of: (a) water,
of relevance to the photo-induced water splitting process. In model
compounds, O-H activation may lead to hydrido-hydroxo species or oxo
species and dihydrogen; (b) dioxygen
and hydrogen peroxide of relevance to the oxidation and hydroxylation
of organic compounds based on enzymatic processes; (c) C-F bonds for
the purpose of synthesis of fluoro-organic molecules that are
otherwise inaccessible; (d) nitriles, for a variety of nucleophilic
addition processes and 1,3-dipolar
cycloadditions; (e) carbon dioxide, bicarbonate and carbonate in
stoichiometric reactions with pre-formed transition metal hydrides;
(f) other substrates (alkynes,
alkenes, alcohols, thiols, H2, CO, CO2, SO2,
The systematic study of the influence of pH and metal oxidation state
(if redox active) will be performed.
4. Physico-chemical studies of complex-solvent interactions
studies will be carried out based on spectroscopic, thermodynamic
(equilibrium), kinetic and mechanistic investigations of the
interaction between transition metal complexes and solvent molecules.
These will include: (a) water coordination and exchange; (b) proton
transfer to and from a metal centre (lone pair/hydride ligand
equilibrium) and ligands (e.g. oxo/hydroxo, hydroxo/aqua,
sulphide/hydrosulphide, amide/amine, alkylidene/alkyl, alkyl/alkane,
hydride/dihydrogen, etc.) as a function of pH; (c) hydrogen
bonding interactions between water as a proton donor and transition
metals (lone pairs) or ligands (oxo, hydroxo, nitrido, sulphide,
hydride, alkylidene, alkyls, etc.) as proton acceptors.
The studies will be carried out in pure water (whenever possible) and
in water-containing media (e.g. water-alcohol,
water-acetonitrile, etc.). In addition, study of the effect of
solvent composition on pKa,
rate constants, reaction enthalpies, and. spectroelectrochemical
study of the effect of oxidation state on solvent-ligand and -metal
interactions (e.g. hydrogen bonds) will be performed.
5. In-situ analytical techniques.
development or improvement of analytical instrumentation for on–line
analysis of reaction pathways will be pursued as follows: (a)
Evolution of on-line flow-through electrochemical
reactors and ESI-MS in order to: (i) widen the
detection range, (ii) identify short-life intermediates, (iii)
increase the sensitivity (e.g., by introduction of derivatisation
agents), (iv) develop appropriate mathematical models. (b)
Development of an electrochemical flow cell coupled on–line with
ESI-MS detection and capable of performing intermediate
electrophoresis or chromatographic separations. This will allow
increased selectivity and will provide a way to distinguish
speciation induced by the electrospray interface. (c) Expansion of
the scope of on-line, flow through ESI-MS investigations to
photocatalytic processes. The photocatalyst will be either coated on
the inside surface of a quartz capillary or continuously fed in the
form of a colloidal suspension. (d) Development of new
spectroelectrochemical cells for work under cryostatic
conditions in order to study the effect of the oxidation state on
solvent-ligand and -metal interactions. (e) Development of a probe
for low temperature laser photolysis within the NMR probe.
6. Theoretical studies
studies, by ab initio and/or density functional methods, in
parallel with the experimental studies will be done as follows: (a)
Modelling of catalytic cycles by fully quantum mechanical or QM/MM
methods, including the geometry optimisation of reaction
intermediates and transition states and the comparison with available
experimental results (geometries from structural studies, energetics
from thermodynamics and kinetics data). (b) Analysis of the hydrogen
bonded interactions. The polarity of these interactions may be
modified or even reversed upon changing the metal oxidation state.
(c) Modelling of solvent effects by both continuum models (solute
inside a cavity with a polarisable dielectric), and by discrete
solvent models (several solvent molecules are included in the quantum
mechanical calculations). This will be necessary in particular when
the solvent participates in hydrogen-bonding interactions.
7. Catalytic studies in aqueous or biphasic media.
new water-soluble metal complexes will be used as catalyst precursors
for a variety of catalytic processes under biphasic conditions at
controlled pH. Typical spectroscopic, kinetic and analytical
techniques will be employed (vide infra). Illustrative examples are:
(a) CO2 hydrogenation aimed at exploiting this
feedstock as a C1 building
block. This may
become a model sink for CO2 and for chemical removal of
this greenhouse gas. (b) Oxidations of various substrates (e.g.
alcohols, sulfides, aromatic hydrocarbons) with dioxygen or H2O2
or the powerful “green” oxidants hydroxyl and hydroperoxyl
radicals (electrogenerated during high potential catalytic splitting
of water), thereby circumventing halogenations. (c)
Hydrodehalogenation of fluorinated and chlorinated hydrocarbons. (d)
Extension of the processes catalysed by natural vanadium catalysts
(Amavadine) [e.g. peroxidative hydroxylation,
oxygenation, carboxylation and halogenation of alkanes] to a wider
variety of substrates and catalysts (e.g. oxo-or hydroxo-3d-metal
systems). (e) Alkene metathesis in water (RCM, ROM and ROMP),
opening the way to biologically active compounds such as
aminoacids, azasugars, and peptidomimetics that are otherwise
difficult to prepare. (f) Catalytic aqueous detoxication of poisonous
nitriles, especially those from industrial waste waters. (g)
Hydroxylation of white phosphorus in water to phosphorus acids, as an
alternative to the currently adopted chlorination of P4
followed by substrate phosphorylation.
catalytic activity of the water-soluble metalladendrimers will be
compared with that of the corresponding water-soluble monomers. The
catalytic activity and selectivity (chemo-, regio-, stereo-, and
enantioselectivities) for all processes will be compared with those
of similar systems operating in non aqueous media. The feedback from
these comparisons will lead to the development of second generation
of ligands and complexes.
8. Electrocatalytic studies in aqueous/biphasic media
electrocatalytic processes of two main different types will be
developed: (1) Electron transfer chain (ETC) catalysed
processes (overall non redox processes, catalytic in electrons,
occurring in the presence of a redox active complex), e.g.
ligand exchange, isomerizations, disproportionation, migratory
insertions and extrusions, etc.
Redox processes using a
stoichiometric amount of electrons and the catalytic action of an
electron-transfer mediator which may be either free in solution or
anchored on the electrode surface. These processes could be related
to regular catalytic processes detailed in the previous section: (a)
reduction processes using proton
and a cathode in place of H2
(e.g. hydrodehalogenation, hydrodesulfurisation, etc.); (b)
oxidation processes using water and an anode in place of an oxygen
atom donor (e.g. alcohols to aldehydes, sulfide to sulfoxides,
of these processes with on-line plug
flow electrochemical cells coupled with on-line diode array
spectrometric or mass spectrometry analyses will allow the study of
both product distribution and catalyst transformation in the
9. Photochemistry and photocatalysis in aqueous/biphasic media.
The development of new photocatalysts in water and biphasic media will be pursued by extending the principles of known photochemical and photocatalytic processes. For instance, YoK will investigate the photochemistry of the [Cp*RuH2(PTA)2]+ system, recently reported to be an excellent catalyst in aqueous media by CNR. The photochemical activity of known systems in organic solvents will be compared with that of water soluble analogues [e.g. Cp*Rh(PMe3)H2 and Cp*Rh(PTA)H2]. Whenever necessary, these studies will also be carried out by using on-line plug flow photoreactors coupled on-line to a mass spectrometer. In this latter device the photocatalyst could either be introduced in the liquid phase along with the reactants or immobilized on sol-gel silicates or organically modified silicate films (Ormosil) spread onto the walls of a fused silica capillary photoreactor. Study of solar-induced reactions catalysed by water soluble metal complexes in aqueous and biphasic conditions will be pursued, first by using a home-built micromolar photoreactor for parameters optimisation (radiation density, temperature, reaction time, etc.), then scaled up to the molar level by using the solar flow reactor (SOLFIN) available at the “Plataforma Solar de Almería”. The influence of the direct solar radiation on the efficiency and product distribution will be evaluated. The solar approach will be focused to the synthesis of added-value molecules (drug precursors or fine materials for industrial applications) or will be targeted to selectively eliminate waste molecules from industrial process.
The overall project may be
broken down into six tasks, labelled from T1 to T6. The relationship
between the tasks and expertises, and between the expertises and the
teams, are shown in the flow diagram below.
Further details on each task are as follows:
Task 1: Hydrosoluble ligands and their complexes. Synthesis of new hydrosoluble ligands: (i) new water-soluble complexes with phosphines and carbene-type ligands; (ii) functionalised phosphines and cyclopentadienes bearing highly polar water soluble substituents; (iii) modified porphyrin, azacrown, and bipyridines; (iv) functionalized dendrons, bis dendrons and dendrimers. Co-ordination chemistry of the new ligands on catalytically active metal centres and model studies with heavier congeners of the above metals. Hydrosoluble organometallic complexes containing these ligands. Characterization by MS analysis and IR, UV-vis, NMR, and EPR spectroscopic techniques. Structural studies by single crystal X-ray diffraction. Electrochemical and photochemical investigations of the redox-active complexes. Computational investigations. Task coordinator: YoK. Participants: YoK, CNR-ICCOM, UD, UAL, CNRS-LCC/a, UAB, IST.
Task 2: High oxidation state organometallic aqua ions. Synthesis of new ionic aqua complexes of low-to-intermediate oxidation states transition metals (V, Ru, Rh, Pd) and hydroxo and oxo complexes of middle-to-high oxidation state early transition metals (Nb, Ta, Mo, W, Re). Thermodynamics and kinetics of ligand binding studies. Binding on dendrimers. Spectroscopic studies of hydrogen bonding interactions. Structural studies by single crystal X-ray diffraction. Electrochemical investigations. Computational investigations. Task coordinator: CNRS-LCC/b. Participants: CNRS-LCC/a, CNRS-LCC/b, uab, UEN, INEOS, IST.
Task 3: Solvent-complex interactions. Hydrogen-bonding between solvent molecules and ligands or metal centres. Hydrogen-bonding between solvent molecules and dendrimers and metalladendrimers. Mechanistic studies of water exchange and proton transfer processes to and from ligands or metal centres, detection and characterization of reaction intermediates. Hydrogen bonding to metal fluorides, interactions of pendant groups to metal hydrides, hydrogen bonding of water to metal hydrides. Computational studies by PCM or discrete solvent models. Task coordinator: UAB. Participants: UAB, INEOS, CNRS-LCC/a, YoK, UEN, CNRS-LCC/b.
Task 4: Speciation studies. Investigation of the nature of aqua/hydroxo/oxo ions or other hydrosoluble complexes in water or aqueous solvents at different pH by potentiometry, electrospray ionisation mass spectrometry, high-pressure and stopped-flow. Effect of the oxidation state on ligand binding properties. Flow-through electrochemistry and on-line ESI-MS studies. Task coordinator: HUJI. Participants: HUJI, UD, UEN, CNRS-LCC/b, YoK, IST.
Task 5: Substrate activation and mechanistic studies. Stoichiometric reactivity of transition metal complexes containing hydrosoluble ligands and/or aqua/hydroxo/oxo ligands with inorganic and organic substrates, including: dihydrogen, dioxygen, nitriles, saturated and fluorinated hydrocarbons, terminal alkynes and propargylic alcohols. Mechanistic studies using rapid-mixing techniques, high-pressure techniques including T-jump, flash photolysis, pulse radiolysis, etc., low-temperature spectroscopy, parahydrogen NMR, pH-potentiometry, and electrochemistry. Task coordinator: UEN. Participants: CNR-ICCOM, UD, UAB, YoK, CNRS-LCC/b, IST, UAL, INEOS, UEN.
Task 6: Catalysis, photocatalysis and electrocatalysis in water and biphasic media. Catalytic studies in aqueous and biphasic media at both atmospheric and high pressure. In situ monitoring by high-pressure NMR and IR. Photocatalytic investigations. Solar photocatalytic process mediated by water soluble metal complexes. Electrocatalytic investigations. Focused microwave irradiation studies. Task coordinator: UD. Participants: UD, IST, CNR-ICCOM, YoK, UAL, CNRS-LCC/a, HUJI.