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A Computational Investigation of the Insertion of Carbon Dioxide into Four‐ and Five‐Coordinate Iridium Hydrides
Author(s) -
Bernskoetter Wesley H.,
Hazari Nilay
Publication year - 2013
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201300170
Subject(s) - iridium , chemistry , pincer movement , catalysis , formic acid , photochemistry , organic chemistry
Recently, it has been demonstrated that the insertion of CO 2 into iridium hydrides is a crucial step in the catalytic conversion of CO 2 and H 2 into formic acid. We and others have elucidated the mechanism by which CO 2 inserts into six‐coordinate iridium(III) trihydrides supported by pincer ligands; these complexes are very active catalysts for CO 2 hydrogenation. However, it has also been demonstrated that five‐coordinate iridium(III) dihydrides can react with CO 2 and catalyze both thermal and electrochemical CO 2 hydrogenation. In this work, we study the mechanism of CO 2 insertion into pincer‐supported five‐coordinate iridium(III) dihydrides and four‐coordinate iridium(I) hydrides using density functional theory. The mechanisms differ slightly between the two cases. Insertion into the five‐coordinate species is a multistep process involving initial CO 2 precoordination, whereas insertion into the four‐coordinate species proceeds via a single step with no prior CO 2 coordination. Both of these mechanisms are different from the pathway that was recently proposed for CO 2 insertion into six‐coordinate iridium(III) trihydrides. In addition, a complete pathway for catalytic CO 2 hydrogenation using a five‐coordinate iridium(III) dihydride has been calculated.