Department of Chemistry, University of Manchester, Manchester, UK.
Dalton Trans. 2012 Mar 7;41(9):2685-93. doi: 10.1039/c2dt12048h. Epub 2012 Jan 11.
The synthesis and isolation of low coordinate methylenebis-(N-DIPP-imidazole-2-ylidene)iron((II))hydrides, (((DIPP)C)(2)CH(2))FeH(2-y)I(y) ((DIPP = 2,6-di-isopropylphenyl, y = 1 or 0), was complicated by competitive reactions with solvent, rapid reductive elimination of H(2) and/or dissociation of the bis-N-heterocyclic carbene ligand. Addition of KH to (((DIPP)C)(2)CH(2))FeI(2) in THF/haloalkane mixtures enabled a short lived mono-hydride to be trapped by reaction with CH(2)Cl(2) or cyclo-heptylbromide to form (((DIPP)C)(2)CH(2))FeI(X) (X = Cl or Br, respectively). Toluene coordination stabilises iron-mono hydride complexes as (((DIPP)C)(2)CH(2))Fe(II)H{η(6)-(toluene)} species, which can be isolated in low yield from combination of borohydride salts and (((DIPP)C)(2)CH(2))FeI(2) in toluene, including an imidazole C4 deprotonated carbene-borane, methylene(N-DIPP-imidazole-2-ylidene)(N-DIPP-4-triethyl-borane-imidazole-2-ylidene)](hydrido)(η(6)-toluene)iron. In the absence of toluene, or at short reaction times compounds with empirical formula (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI (R = Et or sec-Bu) that function as a masked Fe((II))-dihydride are isolated. Whilst (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI was stable for days in Et(2)O, more polar solvents (MeCN, THF) led to formation of the carbene borane adducts (((DIPP)C)(2)CH(2))(BR(3))(2). The addition of CO or cyclo-heptylbromide to (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI formed (((DIPP)C)(2)CH(2))Fe(CO)(3) and (((DIPP)C)(2)CH(2))FeBr(2), respectively with BR(3) evolved from both reactions as a by-product.
低配位亚甲基双（N-DIPP-咪唑-2-亚基）铁（II）氢化物（((DIPP)C)(2)CH(2))FeH(2-y)I(y)（((DIPP)=2,6-二异丙基苯基，y=1 或 0）的合成和分离受到溶剂的竞争性反应、H(2)的快速还原消除和/或双氮杂环卡宾配体的解离的影响。在 THF/卤代烷混合物中添加 KH 至 (((DIPP)C)(2)CH(2))FeI(2)，可使瞬态单氢化物与 CH(2)Cl(2)或环庚基溴反应，形成 (((DIPP)C)(2)CH(2))FeI(X)（X=Cl 或 Br，分别）。甲苯配位稳定铁单氢化物配合物，如 (((DIPP)C)(2)CH(2))Fe(II)H{η(6)-(甲苯)}物种，可通过硼氢化物盐与 (((DIPP)C)(2)CH(2))FeI(2)在甲苯中的组合以低产率分离，包括咪唑 C4 去质子化卡宾-硼烷、亚甲基（N-DIPP-咪唑-2-亚基）（N-DIPP-4-三乙基-硼烷-咪唑-2-亚基）](氢化物）（η(6)-甲苯)铁。在没有甲苯或反应时间较短的情况下，可分离出具有经验式 (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI（R=Et 或 sec-Bu）的化合物，该化合物作为掩蔽的 Fe((II))-二氢化物起作用。虽然 (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI 在 Et(2)O 中稳定数天，但更极性的溶剂（MeCN、THF）导致形成卡宾硼烷加合物 (((DIPP)C)(2)CH(2))(BR(3))(2)。向 (((DIPP)C)(2)CH(2))Fe(H)(HB(R)(3))·LiI 添加 CO 或环庚基溴，分别形成 (((DIPP)C)(2)CH(2))Fe(CO)(3)和 (((DIPP)C)(2)CH(2))FeBr(2)，这两种反应的副产物都是 BR(3)。
