氮杂环卡宾配位的单核型一价铁硫酚基配合物

A Mononuclear Iron Thiolate Complex with N-Heterocyclic Carbene Ligation

含硫配体的低价铁物种被认为是固氮酶配位活化氮气时的活性金属物种,但与之相关的含硫配体的单核型低价铁配合物的合成非常具有挑战性,报道很少.我们发现通过含氮杂环卡宾配体的三配位一价铁配合物(IMes)2FeBr(IMes=1,3-bis(mesityl)imidazole-2-ylidene)与大位阻硫醇钾KSAr^(*)(Ar^(*)=2,6-(2',4',6'-Pri_(3)C_(6)H_(2))_(2)C_(6)H_(3))的反应可以合成得到单核型一价铁硫酚基配合物[(IMes)Fe(SAr^(*))](1).配合物1为顺磁性配合物.单晶X-射线衍射表征显示该一价铁配合物的铁中心除与一个氮杂环卡宾配位外还与大位阻硫酚配体的硫原子和2-位芳环以σ:η^(6)-的方式配位.^(57)Fe-穆斯堡尔谱、电子顺磁共振谱和理论计算共同表明配合物1的基态自旋量子数S=1/2.配合物1可催化N_(2)与KC_(8)和Me_(3)SiCl反应,生成N(SiMe_(3))_(3),转换数(TON)可达87.

The relevance of low-valent iron complexes bearing sulfur-containing ligands with the reactive iron intermediates in enzymatic dinitrogen fixation has stimulated great synthetic efforts toward them.Low-valent iron thiolate complexes have been mostly known for the thiolate-bridged diiron(I)carbonyl compounds.In contrast,isolable mononuclear iron(I)thiolate complexes are exceedingly rare.Herein,we report the synthesis and characterization of a mononuclear iron(I)complex[(IMes)Fe(SAr^(*))](1,IMes=1,3-bis(mesityl)imidazole-2-ylidene,Ar^(*)=2,6-(2',4',6'-Pri_(3)C_(6)H_(2))_(2)C_(6)H_(3))as well as its catalytic performance in dinitrogen silylation reaction.Complex 1 was synthesized from the reaction of(IMes)2FeBr with KSAr^(*)in Et_(2)O in 81%isolated yield.Single-crystal X-ray diffraction studies revealed that the thiolate ligand in 1 is coordinating to the iron center in anσ:η6-fashion via the sulfur atom and one of the flanking Pri 3C6H2 ring with the Fe—S distance of 0.2228(1)nm and the Fe—C(Trip)distances ranging from 0.2076(2)to 0.2205(2)nm.Zero-field 57Fe Mössbauer spectrum at 80 K(δ=0.56 mm·s^(−1);ΔEQ=0.98 mm·s^(−1))and X-band electron paramagnetic resonance data(g=[2.20,2.03,1.99])at 103 K of 1 point to its low-spin iron(I)nature(S=1/2).These data are comparable with those of Holland’s iron(I)thiolate complex K[(2-S-1,3-(6-F-3-(2,4,6-Pri 3C6H2)C6H2)2C6H4)Fe](Nature 2015,526,96).Density functional theory studies support the S=1/2 ground spin-state for 1 and reveal that the interaction between the iron atom and the sulfur atom is essentiallyσ-bonding in character.In addition,π-andδ-type interactions between the iron atom and theη6-Pri 3C6H2 ring in 1 also exist.Complex 1 can catalyze the reaction of N2 with KC8 and Me3SiCl in Et_(2)O at room temperature,affording N(SiMe3)3 with a turn-over number up to 73 in 24 h and 87 in 48 h.The reaction employing(IMes)2FeBr as catalyst has a turn-over number up to 73 in 24 h and elongating the reaction time to 48 h does not lead to further increase of the turn-over number.The fine catalytic performance with 1 over(IMes)2FeBr implies that the thiolate ligand in 1 might render the catalytically active intermediate a relatively long lifetime.