Electronic insights into aminoquinoline-based PNHN ligands: protonation state dictates geometry while coordination environment dictates N–H acidity and bond strength,Dalton Transactions

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Electronic insights into aminoquinoline-based PNHN ligands: protonation state dictates geometry while coordination environment dictates N–H acidity and bond strength
Dalton Transactions ( IF 3.5 ) Pub Date : 2022-06-13 , DOI: 10.1039/d2dt01556k
Matthew V Gradiski ₁ , Benjamin E Rennie ₁ , Alan J Lough ₁ , Robert H Morris ₁

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A variety of transition metal complexes bearing aminoquinoline PN^HH′-R ligands R = Ph (L1^H), Cy (L2^H) and their amido analogues are reported for rhodium(I) ([Rh(L1^H)(PPh₃)]⁺ 1 and Rh(L1)(PPh₃) 2), cobalt(II) (Co(L2)(Cl) 3), and iron(II) ([Fe(L1^H)₂]²⁺ 5, Fe(L1)₂ 6, and [Fe(C₅Me₅)(L1^H)]PF₆ 7). The acid–base and redox properties of the amido complexes 2, 6, and their protio parent complexes 1, and 5 permit the determination of the pK_a and bond dissociation free energy (BDFE) of their N–H bonds while the ligand scaffold is coordinated to metal centres of square planar and octahedral geometry, respectively. From relative concentrations obtained by the use of ³¹P{¹H} NMR spectroscopy, a pK_a^THF value of 14 is calculated for rhodium complex 1, 6.4 for iron complex 5, and 24 for iron complex 7. These data, when combined with elecrochemical potentials obtained via cyclic voltammetry, allow the calculations of BDFE values for the N–H bond of 69 kcal mol⁻¹ for 1, and of 55 kcal mol⁻¹ for 5.

中文翻译：

对氨基喹啉基 PNHN 配体的电子洞察：质子化状态决定几何形状，而配位环境决定 N-H 酸度和键强度

各种带有氨基喹啉 PN ^H H'-R 配体 R = Ph ( L1 ^H )、Cy ( L2 ^H ) 的过渡金属配合物及其酰胺基类似物被报道用于铑 ( I ) ([Rh( L1 ^H )(PPh ₃ ) ] ⁺ 1和Rh( L1 )(PPh ₃ ) 2 )、钴( II ) (Co( L2 )(Cl) 3 ) 和铁( II ) ([Fe( L1 ^H ) ₂ ] ²⁺ 5 , Fe( L1 ) ₂ 6, 和 [Fe(C ₅ Me ₅ )( L1 ^H )]PF ₆ 7 )。酰胺配合物2、6及其质子母体配合物1和5的酸碱和氧化还原特性允许测定其 N-H 键的 p _Ka和键解离自由能 (BDFE)，而配体支架分别与方形平面和八面体几何形状的金属中心相协调。从通过使用³¹ P{ ¹ H} NMR 光谱获得的相对浓度，ap K _a^THF铑络合物1的值计算为 14 ，铁络合物5的值为6.4，铁络合物7的值为24 。这些数据与通过循环伏安法获得的电化学势相结合时，可以计算出1为69 kcal mol ^-1和5为 55 kcal mol ^-1的N-H 键的 BDFE 值。

更新日期：2022-06-13

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