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Stabilization of a high-spin three-coordinate Fe(III) imidyl complex by radical delocalization
Chemical Science ( IF 7.6 ) Pub Date : 2022-07-21 , DOI: 10.1039/d2sc02699f
Po-Chun Yang , Kuan-Po Yu , Chi-Tien Hsieh , Junjie Zou , Chia-Te Fang , Hsin-Kuan Liu , Chih-Wen Pao , Mu-Jeng Cheng , Chun-Yi Lin
Chemical Science ( IF 7.6 ) Pub Date : 2022-07-21 , DOI: 10.1039/d2sc02699f
Po-Chun Yang , Kuan-Po Yu , Chi-Tien Hsieh , Junjie Zou , Chia-Te Fang , Hsin-Kuan Liu , Chih-Wen Pao , Mu-Jeng Cheng , Chun-Yi Lin
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High-spin, late transition metal imido complexes have attracted significant interest due to their group transfer reactivity and catalytic C–H activation of organic substrates. Reaction of a new two-coordinate iron complex, Fe{N(tBu)Dipp}2 (1, Dipp = 2,6-diisopropylphenyl), with mesitylazide (MesN3) afforded a three-coordinate Fe–imidyl complex, Fe{N(tBu)Dipp}2(![[double bond, length as m-dash]](https://www.rsc.org/images/entities/char_e001.gif)
NMes) (2). X-ray crystallographic characterization of single crystals of 2 showed a long Fe–N distance of 1.761(1) Å. Combined magnetic and spectroscopic (Mössbauer and X-ray absorption near edge structure spectroscopy, XANES) characterization of 2 suggests that it has an S = 2 ground state comprising an S = 5/2 Fe(III) center antiferromagnetically coupled to an S = 1/2 imidyl ligand. Reaction of 1 and 1-azidoadamantane (AdN3) generated a putative, transient Fe{N(tBu)Dipp}2(NAd) (3′) complex that yielded an intramolecular C–H amination product, Fe{N(tBu)Dipp}{κ2-N,N′-![[- with combining low line]](https://www.rsc.org/images/entities/char_002d_0332.gif)
N(CMe2CH2NHAd)Dipp} (3). Quantum mechanical calculations further confirmed the spectroscopic assignment of 2 and 3′, as well as the differences in their stability and reactivity. Importantly, imidyl radical delocalization onto the mesityl ring significantly increased the stability of 2 and reduced its reactivity toward potential hydrogen atom transfer (HAT) reagents. In contrast, quantum mechanical calculations of 3′ revealed that the radical was solely localized on the imidyl N, leading to a high reactivity toward the proximal C–H bond of the N(tBu)Dipp− ligand.
中文翻译：
自由基离域稳定高自旋三配位 Fe(III) 亚胺配合物
高自旋、后过渡金属亚胺配合物由于其基团转移反应性和有机底物的催化 C-H 活化而引起了人们的极大兴趣。新的二配位铁配合物 Fe{N( t Bu)Dipp} 2 ( 1 , Dipp = 2,6-二异丙基苯基) 与均氮杂叠氮化物 (MesN 3 ) 反应得到三配位 Fe-亚胺配合物 Fe{ N( t Bu)Dipp} 2 (NMes) ( 2 )。2单晶的 X 射线晶体学表征表明，Fe-N 距离很长，为 1.761(1) Å。结合磁性和光谱（穆斯堡尔和 X 射线吸收近边缘结构光谱，XANES）表征2表明它具有S = 2 基态，包括S = 5/2 Fe( III ) 中心反铁磁耦合到S = 1/2 酰亚胺基配体。1和 1-叠氮基金刚烷 (AdN 3 )反应生成假定的瞬时 Fe{N( t Bu)Dipp} 2 ( NAd) ( 3' ) 络合物，产生分子内 C-H 胺化产物 Fe{N( t Bu )Dipp}{κ 2 - N , N ′- N(CMe 2 CH 2 NHAd)Dipp} ( 3）。量子力学计算进一步证实了2和3'的光谱归属，以及它们在稳定性和反应性方面的差异。重要的是，亚甲基自由基离域在异丙叉基环上显着提高了2的稳定性并降低了其对潜在氢原子转移 (HAT) 试剂的反应性。相比之下，3' 的量子力学计算表明自由基仅位于亚氨基 N 上，导致对 N( t Bu)Dipp -配体的近端 C-H 键具有高反应性。
更新日期：2022-07-21
NMes) (2). X-ray crystallographic characterization of single crystals of 2 showed a long Fe–N distance of 1.761(1) Å. Combined magnetic and spectroscopic (Mössbauer and X-ray absorption near edge structure spectroscopy, XANES) characterization of 2 suggests that it has an S = 2 ground state comprising an S = 5/2 Fe(III) center antiferromagnetically coupled to an S = 1/2 imidyl ligand. Reaction of 1 and 1-azidoadamantane (AdN3) generated a putative, transient Fe{N(tBu)Dipp}2(NAd) (3′) complex that yielded an intramolecular C–H amination product, Fe{N(tBu)Dipp}{κ2-N,N′-N(CMe2CH2NHAd)Dipp} (3). Quantum mechanical calculations further confirmed the spectroscopic assignment of 2 and 3′, as well as the differences in their stability and reactivity. Importantly, imidyl radical delocalization onto the mesityl ring significantly increased the stability of 2 and reduced its reactivity toward potential hydrogen atom transfer (HAT) reagents. In contrast, quantum mechanical calculations of 3′ revealed that the radical was solely localized on the imidyl N, leading to a high reactivity toward the proximal C–H bond of the N(tBu)Dipp− ligand.
中文翻译：
自由基离域稳定高自旋三配位 Fe(III) 亚胺配合物
高自旋、后过渡金属亚胺配合物由于其基团转移反应性和有机底物的催化 C-H 活化而引起了人们的极大兴趣。新的二配位铁配合物 Fe{N( t Bu)Dipp} 2 ( 1 , Dipp = 2,6-二异丙基苯基) 与均氮杂叠氮化物 (MesN 3 ) 反应得到三配位 Fe-亚胺配合物 Fe{ N( t Bu)Dipp} 2 (
NMes) ( 2 )。2单晶的 X 射线晶体学表征表明，Fe-N 距离很长，为 1.761(1) Å。结合磁性和光谱（穆斯堡尔和 X 射线吸收近边缘结构光谱，XANES）表征2表明它具有S = 2 基态，包括S = 5/2 Fe( III ) 中心反铁磁耦合到S = 1/2 酰亚胺基配体。1和 1-叠氮基金刚烷 (AdN 3 )反应生成假定的瞬时 Fe{N( t Bu)Dipp} 2 ( NAd) ( 3' ) 络合物，产生分子内 C-H 胺化产物 Fe{N( t Bu )Dipp}{κ 2 - N , N ′- N(CMe 2 CH 2 NHAd)Dipp} ( 3）。量子力学计算进一步证实了2和3'的光谱归属，以及它们在稳定性和反应性方面的差异。重要的是，亚甲基自由基离域在异丙叉基环上显着提高了2的稳定性并降低了其对潜在氢原子转移 (HAT) 试剂的反应性。相比之下，3' 的量子力学计算表明自由基仅位于亚氨基 N 上，导致对 N( t Bu)Dipp -配体的近端 C-H 键具有高反应性。
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