4 Concluding Remarks
This chapter illustrates the progress made during recent years in the field of iridiumcatalyzed reduction of CO 2 with hydrogen and/or silicon hydrides as reductants. It is
difficult to draw general conclusions since not only the characteristics of the ligands
but also the nature of the reducing agent (hydrogen, hydrosilanes, and/or
hydrosiloxanes) strongly influences the reaction conditions and the mechanism. It
has been observed that most of the iridium CO 2 hydrogenation and hydrosilylation
catalysts are based on Ir(III) species. The selectivity is one of the challenges of
homogeneous catalytic CO 2 reduction with hydrogen and silicon hydrides, this is
because mixtures of different reduction products are frequently obtained. In this
regard, it is worth mentioning that iridium(III) half-sandwich-DHBP species and
iridium(III)-PNP pincer complexes have found to be highly efficient and selective
CO 2 hydrogenation catalysts and that Ir(III)-NSiN and Ir(III)-NSi
Me species have
proven to be highly selective CO 2 hydrosilylation catalysts. From the point of view
of the mechanism, it is difficult to establish a general behavior trend. Thus, although
most of the reported homogeneous Ir(III) catalysts follow an outer-sphere CO 2
activation mechanism, when using Ir-NSiN and Ir-NSi
Me trifluoroacetate derivatives
as CO 2 hydrosilation catalysts, an inner-sphere CO 2 activation mechanism is preferred. Therefore, it could be concluded that iridium(III) complexes have great
potential as homogeneous CO 2 reduction catalysts; however, there are still many
mechanistic questions to answer and future applications to unveil.
References
1. Artz J, Müller TE, Thenert K, Kleinekorte J, Meys R, Sternberg A, Bardow A, Leitner W
(2018) Sustainable conversion of carbon dioxide: an integrated review of catalysis and life
cycle assessment. Chem Rev 118:434–504
2. Stahel WR (2016) Circular economy. Nature 531:435–438
Scheme 12 Ir-(POCOP) catalyzed CO 2 reduction to methane with HSiMe 2 Ph
318
F. J. Fernández-Alvarez and L. A. Oro
This chapter illustrates the progress made during recent years in the field of iridiumcatalyzed reduction of CO 2 with hydrogen and/or silicon hydrides as reductants. It is
difficult to draw general conclusions since not only the characteristics of the ligands
but also the nature of the reducing agent (hydrogen, hydrosilanes, and/or
hydrosiloxanes) strongly influences the reaction conditions and the mechanism. It
has been observed that most of the iridium CO 2 hydrogenation and hydrosilylation
catalysts are based on Ir(III) species. The selectivity is one of the challenges of
homogeneous catalytic CO 2 reduction with hydrogen and silicon hydrides, this is
because mixtures of different reduction products are frequently obtained. In this
regard, it is worth mentioning that iridium(III) half-sandwich-DHBP species and
iridium(III)-PNP pincer complexes have found to be highly efficient and selective
CO 2 hydrogenation catalysts and that Ir(III)-NSiN and Ir(III)-NSi
Me species have
proven to be highly selective CO 2 hydrosilylation catalysts. From the point of view
of the mechanism, it is difficult to establish a general behavior trend. Thus, although
most of the reported homogeneous Ir(III) catalysts follow an outer-sphere CO 2
activation mechanism, when using Ir-NSiN and Ir-NSi
Me trifluoroacetate derivatives
as CO 2 hydrosilation catalysts, an inner-sphere CO 2 activation mechanism is preferred. Therefore, it could be concluded that iridium(III) complexes have great
potential as homogeneous CO 2 reduction catalysts; however, there are still many
mechanistic questions to answer and future applications to unveil.
References
1. Artz J, Müller TE, Thenert K, Kleinekorte J, Meys R, Sternberg A, Bardow A, Leitner W
(2018) Sustainable conversion of carbon dioxide: an integrated review of catalysis and life
cycle assessment. Chem Rev 118:434–504
2. Stahel WR (2016) Circular economy. Nature 531:435–438
Scheme 12 Ir-(POCOP) catalyzed CO 2 reduction to methane with HSiMe 2 Ph
318
F. J. Fernández-Alvarez and L. A. Oro