Pyrazolium- and 1,2-Cyclopentadiene-Based Ligands as 蟽-Donors: a Theoretical Study of Electronic Structure and Bonding

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• 作者：Anssi Peuronen ; Mikko M. H盲nninen ; Heikki M. Tuononen
• 刊名：Inorganic Chemistry
• 出版年：2012
• 出版时间：February 20, 2012
• 年：2012
• 卷：51
• 期：4
• 页码：2577-2587
• 全文大小：539K
• 年卷期：v.51,no.4(February 20, 2012)
• ISSN：1520-510X

文摘

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 鈥渁llene鈥?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 鈥渂ent allenes鈥?or remote N-heterocyclic carbenes) indicate that all investigated ligands form particularly strong metal鈥揷arbon bonds. Most notably, without exocyclic 蟺-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 蟽-donor strengths can be realized through this route.