Ohki Yasuhiro, Hatanaka Tsubasa, Tatsumi Kazuyuki
Department of Chemistry, Graduate School of Science, and Research Center for Meterials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan.
J Am Chem Soc. 2008 Dec 17;130(50):17174-86. doi: 10.1021/ja8063028.
Half-sandwich iron complexes of N-heterocyclic carbenes, CpFe(L(R))Cl (2a; L(Mes) = 1,3-dimesityl-imidazol-2-ylidene, 2b; L(iPr) = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene, Cp = eta(5)-C5Me5), have been synthesized by the reaction of CpFe{N(SiMe3)2} (1) with the corresponding imidazolium salts. Treatment of 2a with either methyllithium or phenyllithium replaces the chloride with either a methyl or a phenyl group, generating CpFe(L(Mes))R (3a; R = Me, 3b; R = Ph). These complexes, in turn, undergo cyclometalation at elevated temperatures, and CpFe{kappa2-(C,C)-L'(Mes)} (4; L'(Mes) = CH2C6H2-3,5-Me2-2-(3-mesityl-imidazol-2-ylidene-1-yl)) was isolated. On the other hand, methylation of 2b at room temperature leads directly to the formation of a cyclometalated complex, CpFe{kappa2-(C,C)-L'(iPr)} (6; L'(iPr) = CH2CH(CH3)(3-isopropyl-4,5-dimethylimidazol-2-ylidene-1-yl)). The Fe(II) center of 6 traps atmospheric dinitrogen reversibly to produce a dinuclear end-on N2 complex [CpFe{kappa2-(C,C)-L'(iPr)}]2(mu-eta(1):eta(1)-N2) (7). Complex 6 also promotes C-H bond activation of thiophene, furan, benzothiophene, and benzofuran at room temperature. In these reactions, C-H bond cleavage occurred exclusively at the 2-position of the rings, generating CpFe(L(iPr))(2-C4H3E) (8; E = S, 9; E = O) and CpFe(L(iPr))(2-C8H5E) (10; E = S, 11; E = O), while C-H cleavage took place mainly at the 4-position in the case of pyridine. Coupling reactions between heteroarenes and catecholborane (HBcat) can be carried out by treatment of 6 with heteroarenes followed by the addition of excess HBcat, giving rise to 2-boryl-heteroarenes and the borohydride complex CpFe(L(iPr))(H2Bcat) (14).
通过CpFe{N(SiMe3)2} (1)与相应的咪唑盐反应，合成了N-杂环卡宾的半夹心铁配合物CpFe(L(R))Cl (2a; L(Mes) = 1,3-二甲基苯并咪唑-2-亚基，2b; L(iPr) = 1,3-二异丙基-4,5-二甲基咪唑-2-亚基，Cp* = η(5)-C5Me5)。用甲基锂或苯基锂处理2a，用甲基或苯基取代氯，生成CpFe(L(Mes))R (3a; R = Me，3b; R = Ph)。这些配合物在高温下会发生环金属化反应，分离得到了CpFe{κ2-(C,C)-L'(Mes)} (4; L'(Mes) = CH2C6H2-3,5-Me2-2-(3-甲基苯并咪唑-2-亚基-1-基))。另一方面，2b在室温下甲基化直接导致形成环金属化配合物CpFe{κ2-(C,C)-L'(iPr)} (6; L'(iPr) = CH2CH(CH3)(3-异丙基-4,5-二甲基咪唑-2-亚基-1-基))。6的Fe(II)中心可逆地捕获大气中的二氮，生成双核端基N2配合物[CpFe{κ2-(C,C)-L'(iPr)}]2(μ-η(1):η(1)-N2) (7)。配合物6在室温下也能促进噻吩、呋喃、苯并噻吩和苯并呋喃的C-H键活化。在这些反应中，C-H键断裂仅发生在环的2-位，生成CpFe(L(iPr))(2-C4H3E) (8; E = S，9; E = O)和CpFe(L(iPr))(2-C8H5E) (10; E = S，11; E = O)，而在吡啶的情况下，C-H键断裂主要发生在4-位。杂芳烃与儿茶酚硼烷(HBcat)之间的偶联反应可以通过用杂芳烃处理6，然后加入过量的HBcat来进行，生成2-硼基杂芳烃和硼氢化物配合物Cp*Fe(L(iPr))(H2Bcat) (14)。
