Were Reactions of Triplet Silylenes Observed?
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- 作者：Monica Kosa ; Miriam Karni ; Yitzhak Apeloig
- 刊名：The Journal of the American Chemical Society
- 出版年：2013
- 出版时间：June 19, 2013
- 年：2013
- 卷：135
- 期：24
- 页码：9032-9040
- 全文大小：406K
- 年卷期：v.135,no.24(June 19, 2013)
- ISSN：1520-5126
文摘
The observation that (iPr3Si)(tBu3Si)Si: (1) yields an intramolecular C鈥揌 bond insertion product at room temperature, together with earlier computational predictions that triplet 1 is slightly more stable (or isoenergetic) than singlet 1 and additional considerations, led previous investigators to conclude that 1 is the first silylene to exhibit triplet electronic state reactivity. In this paper we test, using DFT and ab initio methods, whether the occurrence of intramolecular C鈥揌 bond insertion indeed indicates the presence of a triplet-state silylene. DFT calculations at the B3LYP/6-31+G(d,p)//B3LYP/6-31+G(d,p) level show that singlet (iPr3Si)(tBuMe2Si)Si: (9), a close model of singlet 1, inserts intramolecularly into a C鈥揌 bond of the tBu group with a barrier of 22.7 kcal/mol (22.2 kcal/mol at SCS-MP2/cc-PVTZ). However, for triplet9 the barrier of this insertion reaction is significantly higher, 34.6 kcal/mol (41.9 kcal/mol at SCS-MP2/cc-PVTZ). This implies that at room temperature the intramolecular insertion reaction of the singlet is 109鈥?012 faster than that of the triplet. We conclude, in contrast to previous conclusions, that the observed intramolecular C鈥揌 bond insertion reactions of 1 as well as of (tBu3Si)2Si: (2) occur from the singlet state. Furthermore, the occurrence of an intramolecular C鈥揌 bond insertion cannot serve as evidence for the presence of a triplet silylene, either in cases where the singlet and triplet states are nearly isoenergetic (e.g., 1 and 9) or even for silylenes where the triplet state is the ground state (e.g., 2), because the corresponding singlet silylenes insert intramolecularly much faster. The search for a genuine reaction of a triplet silylene has to continue.