A Computational Foray into the Formation and Reactivity of Metallabenzenes

Abstract

Various metallabenzene complexes, analogues of benzene where one CH unit has been replaced by an organometallic fragment, have been reported in the literature. A detailed theoretical investigation on the chemistry of these complexes is presented here. This includes an evaluation of their aromaticity, the mechanisms of formation of osmium, iridium, and platinum metallabenzene complexes, and one intriguing aspect of their chemistry, the formation of cyclopentadienyl (Cp) complexes. X-ray photoelectron spectroscopy (XPS) measurements on two osmabenzene examples are also presented. In addition, diffuse functions for use with the SDD and SDB-cc-pVDZ basis set-RECP combinations are presented for the transition metals.

Recent Advances in Metallabenzene Chemistry

“…Consistent with the mechanism calculated by Martin, van der Boom, and co-workers, [33] Elliott and Roper have found that the reaction of diphenylacetylene with [Os(CS)(CO)-(PPh 3 ) 3 ] produces the alkyne-substituted complex 42 and an osmacyclohexadienethione. [49] Unlike in the case calculated for acetylene, a second equivalent of diphenylacetylene does not add to generate the osmabenzene.…”

“…[23,26] Recently, van der Boom, Martin, and co-workers calculated the energies of the various transition states in the formation of 1 by using model 6 as the starting complex to prepare 7 (Scheme 1). [33] Their study revealed that the first step in osmabenzene formation is loss of a phosphine ligand, followed by coordination to an acetylene molecule. The lowest-energy pathway was found to proceed by migratory insertion of the CS ligand into the s bond of the osmacyclopropene (Dewar-Chatt-Duncanson model).…”

“…[33] In addition to higher transition-state energies, it was found that the final step, rearrangement of the 2-osma-3,5-cyclohexadiene-1-one to the osmabenzene, would not take place owing to the strain in the resulting three-membered ring. The larger size of the sulfur atom reduces the ring strain sufficiently to allow formation of 7.…”

“…[33,67,68] One pathway begins by dissociation of the cyclopropene from the metal center and subsequent oxidative addition to generate Dewar benzene 74, which quickly rearranges into 71. Evidence for this pathway lies in the ability of donor solvents to rapidly increase the rate of isomerization.…”

Double Stabilization of Highly Strained Six-Membered Rings by Phosphonium and Transition Metal

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