Top Organomet Chem (2016) 59: 31–58
DOI: 10.1007/3418_2015_145
# Springer International Publishing Switzerland 2015
Published online: 26 August 2015
Binuclear Iridium Complexes in Catalysis
Manuel Iglesias, Eduardo Sola, and Luis A. Oro
Abstract In this chapter, recent progresses in the use of binuclear iridium complexes as catalysts for the preparation of value-added organic molecules and the
catalytic cycles involved in these reactions are presented. The reactivity of these
complexes toward a variety of substrates and the intermetallic cooperation mechanisms that differentiate binuclear entities from their mononuclear counterparts are
reviewed and analyzed in detail. Oxidative addition and reductive elimination
reactions usually occur at one of the iridium centers followed by ligand migration
to the vicinal iridium atom or to bridging positions, although cooperative activation
of various substrates has been proposed in the literature. The close proximity of two
metal centers in binuclear complexes, and their ability to cooperate, brings about
new reactivity patterns that very often differ from those expected for related
monometallic systems. Especially noteworthy is the transmission of ligands trans
effects (or influences) via bridging ligands or intermetallic bonds, together with the
facile migration of hydrides between metals and the interaction between iridium
centers in Ir 2
I,I dimers, which seem to govern the chemistry of diiridium complexes.
In this regard, it is worth noting that single-site activation does not exclude a
cooperative bimetallic cycle. Most of the reported catalytic cycles based on bimetallic iridium complexes follow inner sphere mechanisms, but the presence of outer
sphere pathways cannot be excluded as exemplified by recent reports on ionic or
dimetal–ligand bifunctional mechanisms; therefore, bimetallic iridium catalysis
may show one or more cooperation mechanism.
Keywords Binuclear complexes, Bond activation, Homogeneous catalysis,
Intermetallic cooperation, Iridium, Ligand migration, Trans effect
M. Iglesias (*), E. Sola, and L.A. Oro (*)
Department of Inorganic Chemistry, ISQCH, University of Zaragoza-CSIC, Pedro Cerbuna 12,
50009 Zaragoza, Spain
e-mail: miglesia@unizar.es; oro@unizar.es
DOI: 10.1007/3418_2015_145
# Springer International Publishing Switzerland 2015
Published online: 26 August 2015
Binuclear Iridium Complexes in Catalysis
Manuel Iglesias, Eduardo Sola, and Luis A. Oro
Abstract In this chapter, recent progresses in the use of binuclear iridium complexes as catalysts for the preparation of value-added organic molecules and the
catalytic cycles involved in these reactions are presented. The reactivity of these
complexes toward a variety of substrates and the intermetallic cooperation mechanisms that differentiate binuclear entities from their mononuclear counterparts are
reviewed and analyzed in detail. Oxidative addition and reductive elimination
reactions usually occur at one of the iridium centers followed by ligand migration
to the vicinal iridium atom or to bridging positions, although cooperative activation
of various substrates has been proposed in the literature. The close proximity of two
metal centers in binuclear complexes, and their ability to cooperate, brings about
new reactivity patterns that very often differ from those expected for related
monometallic systems. Especially noteworthy is the transmission of ligands trans
effects (or influences) via bridging ligands or intermetallic bonds, together with the
facile migration of hydrides between metals and the interaction between iridium
centers in Ir 2
I,I dimers, which seem to govern the chemistry of diiridium complexes.
In this regard, it is worth noting that single-site activation does not exclude a
cooperative bimetallic cycle. Most of the reported catalytic cycles based on bimetallic iridium complexes follow inner sphere mechanisms, but the presence of outer
sphere pathways cannot be excluded as exemplified by recent reports on ionic or
dimetal–ligand bifunctional mechanisms; therefore, bimetallic iridium catalysis
may show one or more cooperation mechanism.
Keywords Binuclear complexes, Bond activation, Homogeneous catalysis,
Intermetallic cooperation, Iridium, Ligand migration, Trans effect
M. Iglesias (*), E. Sola, and L.A. Oro (*)
Department of Inorganic Chemistry, ISQCH, University of Zaragoza-CSIC, Pedro Cerbuna 12,
50009 Zaragoza, Spain
e-mail: miglesia@unizar.es; oro@unizar.es