Mokhtarzadeh Charles C, Margulieux Grant W, Carpenter Alex E, Weidemann Nils, Moore Curtis E, Rheingold Arnold L, Figueroa Joshua S
Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Drive Mail Code 0358, La Jolla California 92093-0358, United States.
Inorg Chem. 2015 Jun 1;54(11):5579-87. doi: 10.1021/acs.inorgchem.5b00730. Epub 2015 May 12.
Reported here are synthetic studies probing highly reduced iron centers in an encumbering tetraisocyano ligand environment. Treatment of FeCl2 with sodium amalgam in the presence of 2 equiv of the m-terphenyl isocyanide CNAr(Mes2) (Ar(Mes2) = 2,6-(2,4,6-Me3C6H2)2C6H3) produces the disodium tetraisocyanoferrate Na2[Fe(CNAr(Mes2))4]. Structural characterization of Na2[Fe(CNAr(Mes2))4] revealed a tight ion pair, with the Fe center adopting a tetrahedral coordination geometry consistent with a d(10) metal center. Attempts to disrupt the cation-anion contacts in Na2[Fe(CNAr(Mes2))4] with cation-sequestration reagents lead to decomposition, except for the case of 18-crown-6, where a mononuclear complex featuring a dianionic 1-azabenz[b]azulene ligand was isolated in low yield. Formation of this 1-azabenz[b]azulene is rationalized to proceed by an aza-Büchner ring expansion of a CNAr(Mes2) ligand mediated by a coordinatively unsaturated Fe center. Disodium tetraisocyanoferrate Na2[Fe(CNAr(Mes2))4] is readily protonated by trimethylsilanol (HOSiMe3) to produce the monohydride ferrate salt, Na[HFe(CNAr(Mes2))4], the anionic portion of which serves as an isocyano analogue of the hydrido-tetracarbonyl metalate HFe(CO)4. Treatment of Na[HFe(CNAr(Mes2))4] with methyl triflate (MeOTf; OTf = O3SCF3) at low temperature in the presence of dinitrogen yields the five-coordinate Fe(0) complex Fe(N2)(CNAr(Mes2))4. The formation of Fe(N2)(CNAr(Mes2))4 in this reaction is consistent with the intermediacy of the neutral tetraisocyanide Fe(CNAr(Mes2))4. The decomposition of Fe(N2)(CNAr(Mes2))4 to the dimeric complex [Fe(η(6)-(Mes)-μ(2)-C-CNAr(Mes))]2 and a seven-membered cyclic imine derived from a CNAr(Mes2) ligand is presented and provides insight into the ability of CNAr(Mes2) and related m-terphenyl isocyanides to stabilize zerovalent four-coordinate iron complexes in a strongly π-acidic ligand field.
本文报道了在具有阻碍作用的四异氰基配体环境中对高度还原铁中心的合成研究。在2当量的间三联苯异氰化物CNAr(Mes2)（Ar(Mes2)=2,6-(2,4,6-三甲基苯基)2苯）存在下，用钠汞齐处理FeCl2得到四异氰基铁酸钠Na2[Fe(CNAr(Mes2))4]。Na2[Fe(CNAr(Mes2))4]的结构表征显示为紧密离子对，其中Fe中心采用与d(10)金属中心一致的四面体配位几何结构。除了18-冠-6的情况外，用阳离子螯合剂破坏Na2[Fe(CNAr(Mes2))4]中的阳离子-阴离子接触会导致分解，在18-冠-6的情况下，以低产率分离出具有双阴离子1-氮杂苯并[b]薁配体的单核配合物。这种1-氮杂苯并[b]薁的形成被认为是通过由配位不饱和的Fe中心介导的CNAr(Mes2)配体的氮杂-布赫纳环扩展来进行的。四异氰基铁酸钠Na2[Fe(CNAr(Mes2))4]很容易被三甲基硅醇(HOSiMe3)质子化，生成一氢铁酸盐Na[HFe(CNAr(Mes2))4]，其阴离子部分作为氢化物-四羰基金属酸盐HFe(CO)4的异氰基类似物。在低温下，在氮气存在下，用三氟甲磺酸甲酯(MeOTf；OTf = O3SCF3)处理Na[HFe(CNAr(Mes2))4]，得到五配位的Fe(0)配合物Fe(N2)(CNAr(Mes2))4。该反应中Fe(N2)(CNAr(Mes2))4的形成与中性四异氰化物Fe(CNAr(Mes2))4的中间体一致。本文还介绍了Fe(N2)(CNAr(Mes2))4分解为二聚配合物[Fe(η(6)-(Mes)-μ(2)-C-CNAr(Mes))]2和源自CNAr(Mes2)配体的七元环亚胺的过程，这为CNAr(Mes2)和相关的间三联苯异氰化物在强π-酸性配体场中稳定零价四配位铁配合物的能力提供了见解。
