Pyrazolium- and 1,2-Cyclopentadiene-Based Ligands as σ-Donors: a Theoretical Study of Electronic Structure and Bonding
Peuronen, A., Hänninen, M. M., & Tuononen, H. (2012). Pyrazolium- and 1,2-Cyclopentadiene-Based Ligands as σ-Donors: a Theoretical Study of Electronic Structure and Bonding. Inorganic Chemistry, 51 (4), 2577-2587. doi:10.1021/ic202546a
Published inInorganic Chemistry
DisciplineEpäorgaaninen ja analyyttinen kemia
© 2012 American Chemical Society. This is a final draft version of an article whose final and definitive form has been published by ACS. Published in this repository with the kind permission of the publisher.
A high-level theoretical investigation of 1,2-cyclopentadiene (4) was performed using density functional theory and wave function methods. The results reveal that, in contrast to earlier assumptions, the ground state of this ephemeral “allene” is carbene-like with a small diradical component. Furthermore, the electronic structure and chemistry of 4 are found to parallel that of 1,2,4,6-cycloheptatetraene: both molecules possess a low-lying excited singlet state with a closed-shell carbenic structure, enabling rich coordination chemistry. Energy decomposition analyses conducted for currently unknown metal complexes of 4 as well as those involving stable carbenes based on the pyrazolium framework (aka “bent allenes” or remote N-heterocyclic carbenes) indicate that all investigated ligands form particularly strong metal–carbon bonds. Most notably, without exocyclic π-type substituents, 4 and pyrazolin-4-ylidenes are the strongest donor ligands examined, in large part because of the energy and shape of their highest occupied molecular orbital. As a whole, the current work opens a new chapter in the chemistry of 1,2-cyclopentadiene, which is hoped to spark renewed interest among experimentalists. In addition, results from the conducted bonding analyses underline that more emphasis should be placed on purely carbocyclic carbenes as unprecedented σ-donor strengths can be realized through this route. ...