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M. Camats et al.
field that exploits the non-innocent physicochemical properties of polyols as reducing, stabilizing, and dispersing agents in the quest for tailor-made nanocatalysts
and nanocomposites with enhanced properties as compared to classical ones. In the
framework of the development of greener and more sustainable processes, Cu, Ni,
Co, and Fe nanocatalysts in polyol media represent key alternatives to overcome the
dependence on the scarcity of noble metals in use currently for both academic and
industrial purposes.
The Lewis acidity properties of 3d-transition metals confer them suitable properties as (co)catalysts to achieve new transformations by means of (i) Lewis acid
base-adduct formation, thereby accelerating slow elementary steps, (ii) pKa of the
reaction modulation (e.g., release of a Brønsted acid, proton transfer processes), or
(iii) activating the catalyst precursors or off-cycle catalyst species by tuning its coordination sphere by anion abstraction. This chapter describes the reports on Ni, Cu,
and Fe Lewis acid mediated transformations in polyol medium, but contributions
from other abundant metals will surely appear in the literature in the years to come.
On the other hand, the abundance and redox properties of 3d-metal-oxide-based
materials confer them large applicability as supports for catalysts. In particular, the
magnetic properties of Fe 2 O 3 and Fe 3 O 4 as supports enable the recovery of the prepared composite materials. For instance, the use of such supports for the preparation
of heterogenized Pd catalysts for C–C cross-coupling reactions and hydrogenations
in polyol medium has been widely reported (for selected articles, see: [39, 54, 55,
82, 126, 136]). Other supports based on 3d-transition metals such as TiO 2 [95], CuO
[26], and ZnO [114] have also been used for the same purpose. This heterogenization
strategy efficiently enables the recoverability of the catalytic materials by magnetic
separation, and also in some cases, the enhancement of TON is observed due to the
synergy between catalyst and support. Furthermore, polymetallic systems merit further studies to exploit the cooperative effects between active metal centers in polyol
medium [34]. The intrinsic properties of polyols in terms of favoring 3D organization
via supramolecular interactions, their suitable oxidation potentials for the reduction
of transition metal salts and organometallic complexes, as well as their dispersing
abilities via solvation interactions, which often trigger an activity increase, confer
them unique properties in nanocatalysis.
From a structural point of view, 3d -metals based-species present several oxidation
states, often leading to paramagnetic intermediates of challenging elucidation. Given
the specificity developed by nature in biocatalyzed transformations involving 3dtransition metals and the demonstrated efficiency of nanocatalysts discussed herein
(e.g., Cu NPs for Sonogashira and C–heteroatom couplings, Ni NPs for Suzuki, Co
NPs for Heck–Mizoroki, Fe NPs for Kumada-like couplings …), the fundamental and
applied research in this field foresees new reactivities and deep mechanistic insights
taking advantage of the cutting-edge in operando techniques available nowadays.
M. Camats et al.
field that exploits the non-innocent physicochemical properties of polyols as reducing, stabilizing, and dispersing agents in the quest for tailor-made nanocatalysts
and nanocomposites with enhanced properties as compared to classical ones. In the
framework of the development of greener and more sustainable processes, Cu, Ni,
Co, and Fe nanocatalysts in polyol media represent key alternatives to overcome the
dependence on the scarcity of noble metals in use currently for both academic and
industrial purposes.
The Lewis acidity properties of 3d-transition metals confer them suitable properties as (co)catalysts to achieve new transformations by means of (i) Lewis acid
base-adduct formation, thereby accelerating slow elementary steps, (ii) pKa of the
reaction modulation (e.g., release of a Brønsted acid, proton transfer processes), or
(iii) activating the catalyst precursors or off-cycle catalyst species by tuning its coordination sphere by anion abstraction. This chapter describes the reports on Ni, Cu,
and Fe Lewis acid mediated transformations in polyol medium, but contributions
from other abundant metals will surely appear in the literature in the years to come.
On the other hand, the abundance and redox properties of 3d-metal-oxide-based
materials confer them large applicability as supports for catalysts. In particular, the
magnetic properties of Fe 2 O 3 and Fe 3 O 4 as supports enable the recovery of the prepared composite materials. For instance, the use of such supports for the preparation
of heterogenized Pd catalysts for C–C cross-coupling reactions and hydrogenations
in polyol medium has been widely reported (for selected articles, see: [39, 54, 55,
82, 126, 136]). Other supports based on 3d-transition metals such as TiO 2 [95], CuO
[26], and ZnO [114] have also been used for the same purpose. This heterogenization
strategy efficiently enables the recoverability of the catalytic materials by magnetic
separation, and also in some cases, the enhancement of TON is observed due to the
synergy between catalyst and support. Furthermore, polymetallic systems merit further studies to exploit the cooperative effects between active metal centers in polyol
medium [34]. The intrinsic properties of polyols in terms of favoring 3D organization
via supramolecular interactions, their suitable oxidation potentials for the reduction
of transition metal salts and organometallic complexes, as well as their dispersing
abilities via solvation interactions, which often trigger an activity increase, confer
them unique properties in nanocatalysis.
From a structural point of view, 3d -metals based-species present several oxidation
states, often leading to paramagnetic intermediates of challenging elucidation. Given
the specificity developed by nature in biocatalyzed transformations involving 3dtransition metals and the demonstrated efficiency of nanocatalysts discussed herein
(e.g., Cu NPs for Sonogashira and C–heteroatom couplings, Ni NPs for Suzuki, Co
NPs for Heck–Mizoroki, Fe NPs for Kumada-like couplings …), the fundamental and
applied research in this field foresees new reactivities and deep mechanistic insights
taking advantage of the cutting-edge in operando techniques available nowadays.