Heavier Main Group Dimetallene Reactivity: Effects of Frontier Orbital Symmetry

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• 作者：Christine A. Caputo ; Philip P. Power
• 刊名：Organometallics
• 出版年：2013
• 出版时间：April 22, 2013
• 年：2013
• 卷：32
• 期：8
• 页码：2278-2286
• 全文大小：400K
• 年卷期：v.32,no.8(April 22, 2013)
• ISSN：1520-6041

文摘

The major theme of this review concerns the reaction pathways of heavier main group 13 dimetallenes with olefins, cyclic olefins, polyolefins, other unsaturated molecules, and hydrogen. For gallium derivatives, these reactions proceed readily in high yield under ambient conditions. Early investigations showed that the group 13 dimetallenes dissociated to one-coordinate metallanediyl monomers, which suggested that they reacted as monomeric species due to their more open, less hindered structures. However, recent DFT calculations by Tuononen and co-workers show that the reaction of the monomers with olefins or hydrogen involves very large energy barriers and that the dimetallenes react instead as undissociated dimers. In contrast to the corresponding all-carbon systems, where [2 + 2] cycloadditions are forbidden because of 蟺鈥撓€* symmetry mismatch, the dimetallenes react with olefins via two stepwise, symmetry-allowed [2 + 2] cycloadditions to give 1,4-digallacyclohexanes. The addition of the H₂ proceeds by a different mechanism, initially involving a 1,2-dihydride intermediate to ultimately yield two ArGaH₂ molecules, which recombine to give Ar(H)Ga(渭-H)₂Ga(H)Ar. The corresponding dialuminene is more highly reactive and reacts with solvent toluene to give an unusual [2 + 4] cycloaddition product. Calculations reveal that there is an enhanced diradical character in its bonding and that the reaction with propene affords an open-shell transition state involving a dangling CH₃膴HCH₂Al moiety with unpaired spin density also on aluminum.