Kothe Thomas, Diefenbach Martin, Tagliavini Valeria, Dechert Sebastian, Krewald Vera, Meyer Franc
University of Göttingen, Institute of Inorganic Chemistry, Tammannstrasse 4, D-37077 Göttingen, Germany.
Fachbereich Chemie, Quantenchemie, Technische Universität Darmstadt, Peter-Grünberg-Straße 4, D-64287 Darmstadt, Germany.
Inorg Chem. 2025 Jan 27;64(3):1219-1227. doi: 10.1021/acs.inorgchem.4c04255. Epub 2025 Jan 14.
Alkyl nickel intermediates relevant to catalytic processes often feature agostic stabilization, but relatively little is known about the situation in oligonickel systems. The dinickel(I) complex K[LNi], which is based on a compartmental pyrazolato-bridged ligand L with two β-diketiminato chelate arms, or its masked version, the dihydride complex [KL(Ni-H)] that readily releases H, oxidatively add methyl tosylate to give diamagnetic [LNi(CH)] () with (Ni···Ni) ≈ 3.7 Å. Structural characterization shows that the methyl group in is bound to one Ni and exhibits an intramolecular agostic interaction with the more distant Ni. This is supported spectroscopically (viz., a ν(C-H) stretch at 2658 cm and lowered of 114 Hz) and by DFT calculations, including topological analysis of the computed electron density for . NMR spectroscopy reveals very fast hopping of the CH group between the two Ni ions, which according to DFT has a minute barrier of 4 kcal mol and proceeds via a planar CH moiety in the transition state (Walden-like inversion). The alkylidene group in K[LNi(μ-CHSi(Me))], obtained from the reaction of [KL(Ni-H)] with NCHSiMe, is symmetrically bridging. This work provides new insight into the stabilization and dynamics of alkyl ligands at dinickel sites with a constrained metal···metal distance.
与催化过程相关的烷基镍中间体通常具有 agostic 稳定作用，但对于低聚镍体系中的情况了解相对较少。基于具有两个 β-二酮亚胺基螯合臂的间隔吡唑啉酮桥连配体 L 的二镍(I)配合物 K[LNi]，或其掩蔽形式、易于释放 H 的二氢化物配合物 [KL(Ni-H)]，将对甲苯磺酸甲酯进行氧化加成，得到反磁性的 [LNi(CH)] ()，其中 (Ni···Ni) ≈ 3.7 Å。结构表征表明， 中的甲基与一个 Ni 结合，并与较远的 Ni 表现出分子内 agostic 相互作用。这通过光谱学（即 2658 cm 处的 ν(C-H) 伸缩振动和 114 Hz 的降低）以及 DFT 计算得到支持，包括对 计算电子密度的拓扑分析。NMR 光谱显示 CH 基团在两个 Ni 离子之间非常快速地跳跃，根据 DFT，其势垒极小，为 4 kcal mol，并且在过渡态通过平面 CH 部分进行（类似瓦尔登反转）。由 [KL(Ni-H)] 与 NCHSiMe 反应得到的 K[LNi(μ-CHSi(Me))] 中的亚烷基是对称桥连的。这项工作为在具有受限金属···金属距离的二镍位点上烷基配体的稳定作用和动力学提供了新的见解。
