| Abstract: | 這個研究計畫主要包含了三個有趣的課題，而這三個課題將分述如下: (1) 不正常的氮雜環碳烯基(N-heterocyclic carbene) 碳烯基(carbene)中有一個二配位的碳，只含了六個電子因而違反了路易士八隅體法則(Lewis’octet rule) ，致使它們反應性過高而無法分離。毫無疑問，在實驗上要檢測它們的性質也是困難的。然而在1991 年，Arduengo 等人應用電子效應以及立體保護合成了第一個在室溫下穩定的碳烯基(1)。1 從那時起，這些氮雜環碳烯基在合成上扮演著重要的角色，尤其是均勻相催化以及當成配位基與過渡金屬形成配位錯合物。2 碳烯基(1)通常以標號為C2 的碳與金屬鍵結形成錯合物(2) 。相反地， Cratree 等人在2001 年發現2-pyridylmethylimidazolium 的鹽類與錯合物IrH5(PPh3)2 時卻以不同配位方式(C5 而不是C2,見於錯合物3)配位。3 繼這個例外(3)之後，也在一些錯合物中發現這種俗稱不正常氮雜環碳烯基。不久之前，Bates 等人發現一個氮雜環碳烯基與磷碳雙鍵之間的不尋常反應(見下面的eq. 1) 。4 所以本計畫擬以密度泛函數理論方法研究正常的與不正常的氮雜環碳烯基之間的差異。 (2) 含有B--Li+的物質在2006 年，Segawa 等人以一個含有硼溴鍵的前驅物合成了第一個含有雙氨基 (diamino)取代且含有B--Li+的物質(4) 。經由X 射線結晶學以及硼-11 核磁共振光譜證明此物質裡的硼原子上帶有一負電荷。5 這些含硼物質可以用來合成新的含硼物質或提供一些不同以往的合成路徑。例如，它們可當成親核劑與親電子劑(H2O, methyltrifluoromethanesulfonate, 1-chlorobutane, and benzaldehyde)反應。5 最近，Segawa 等人用它們來合成了含硼的Grignard 試劑。6 這些物質也可當成親核劑攻擊一些第11 族金屬含氯錯合物。7 所以，本計畫也擬以一些計算方法來探討它們的電子性質。 (3) 硫化氫(H2S)與一氧化氮提供者之間的作用近十年間，由於硫化氫在生物體中可能扮演著傳遞者的角色而受到重視。8-10 然而最近研究發現硫化氫是與一氧化氮的代謝有關，例如硫化氫能幫助一氧化氮的生成。 11-12 在這一年中，也將利用計算方法來探討硫化氫與一氧化氮提供者之間有何作用。
This research project contains three interesting topics and they are listed as below: (1) The abnormal N-heterocyclic carbene Carbenes, which have a divalent and six-electron carbon violate Lewis’ octet rule, render high reactivity. Therefore, carbenes were long considered too reactive for isolation and further studies. In 1991, Arduengo and coworkers combined electronic stabilization and steric protection to synthesize the first free carbenes that are stable at room temperature (1).1 From then on, these N-heterocyclic carbenes (NHC) rapidly became very useful for synthesis, especially in homogeneous catalysis and as ligands for complexing transition metals.2 As expected, NHCs 1 shown below usually bind metals via the carbenic carbon (C2) to give η1 complexes 2. However, in 2001, Crabtree and co-workers found that 2-pyridylmethylimidazolium salts react with IrH5(PPh3)2 to give a different coordination model (C5 not C2, see 3).3 Subsequently, a few other complexes featuring the so-called abnormal NHCs as ligands have been prepared. Very recently, Bates and coworkers reported an unexpected reaction between NHC and a phosphaalkene (see eq. 1).4 Therefore, the electronic properties and reactivities of these abnormal NHCs have received great interest, particularly via theoretical approaches. N1 C5 C4 N3 C2 Mes Mes Mes= mesityphenyl N1 C5 C4 N3 C2 M Ir H L L N H N N R 1 2 3 N C C N C Mes Mes + P Mes C Ph Ph N C C N C Mes Mes P C Mes Ph Ph eq. 1 (2) The boryllithium In 2006, Nozaki, Yamashita and Segawa, firstly utilized a boron-bromide precursor to synthesize a stable diamino-substituted boryllithium 4. X-ray crystallography and 11B NMR spectroscopy of the compound matched with the prediction of a boron anion.5 Boryllithium can be used to synthesize new boron-containing compounds or to provide a different synthetic route from the traditional ones. For example, boryllithium behaves as an efficient nucleophile when it reacts with the electrophiles such as water, methyltrifluoromethanesulfonate, 1-chlorobutane, and benzaldehyde.5 Recently, Segawa and coworkers synthesized a borylmagnesium that may be served as a boron-containing Grignard reagent.6 In yet another approach, boryllithium may act as a nucleophile and attack on Group 11 metal chloride complexes. On this basis, Segawa and coworkers reported the examples of borylsilver and borylgold complexes.7 Therefore, the intrinsic properties and the substituent effect of this anionic boron species are interesting and of importance. Herein, I propose to investigate the corresponding properties computationally via DFT functionals. N N BLi+ i-Pr i-Pr i-Pr i-Pr 4 (3) The relationship between H2S and nitric oxide (NO) donors In the last decade, hydrogen sulfide (H2S) was attracted much attention due to the fact that it may be a possible gasotransmitter in vivo.8-10 However, nowadays, the attention has been focused on the possible synergy between H2S and nitric oxide (NO); for example, the role of H2S in improving the NO production from NO donors,11 or the action of NO in inducing an increase in the amount of enzymes which are responsible for the H2S production.12 At the first stage of this propose, we will make attempts to investigate the interactions between H2S and three kinds of NO donors (S-nitrosothiols, Se-nitrososelenols and nitrosamines). This goal of the study is to realize the interactions between NO donors and other molecules like H2S here. Based on the results, it may be possible to avoid vascular collapse with inhibiting an excess of nitric oxide in vivo. References: 1. Arduengo III, A. J.; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1991, 113, 361. 2. For example: Hahn, F. E.; Jahnke, M. C. Angew. Chem. Int. Ed. 2008, 47, 3122 3. (a) Gr?ndemann, S.; Kovacevic, A.; Albrecht, M.; Faller, J. W.; Crabtree, R. H. Chem. Commun. 2001, 21, 2274. (b) Sini, G.; Eisenstein, O.; Crabtree, R. H. Inorg. Chem. 2002, 41, 602. 4. Bates, J. I.; Kennepohl, P. and Gates, D. P. Angew. Chem. Int. Ed. 2009, 48, 1. 5. Segawa, Y.; Yamashita, M.; Nozaki, K. Science 2006, 314, 113. 6. Yamashita, M.; Suzuki, Y.; Segawa, Y. and Nozaki, K. J. Am. Chem. Soc. 2007, 129, 9570. 7. Segawa, Y.; Yamashita, M.; Nozaki, K. Angew. Chem. Int. Ed. 2007, 46, 6710. 8. Qu, K.; Chen, C. P. L. H.; Halliwell, B.; Moore, P. K.; Wong, P. T.-H. Stroke 2006, 37, 889. 9. Wang, R. Antioxid. Redox Signal. 2003, 5, 493. 10. Yang, G.;Wu, L.; Jiang, B.; Yang, W.; Qi, J.; Cao, K.; Meng, Q.; Mustafa, A. K.; Mu, W.; Zhang, S.; Snyder, S. H.; Wang, R. Science 2008, 322, 587. 11. Kamoun, P. Amino Acids 2004, 26, 243. 12. Zhao, W.; Zhang, J.; Lu, Y.; Wang, R. EMBO J. 2001, 20, 6008. |
