Structural and Spectroscopic Trends in a Series of Half-Sandwich Scorpionate Complexes

Fifteen half-sandwich scorpionate complexes [(L)­M­(NCMe)3]­(BF4)n (L = tris­(3,5-dimethylpyrazol-1-yl)­methane, TpmMe,Me, n = 2, 1M, M = Mn, Fe, Co, Ni; L = tris­(3-phenylpyrazol-1-yl)­methane, TpmPh, n = 2, 2M, M = Mn, Fe, Co, Ni; L = hydrotris­(3,5-dimethylpyrazol-1-yl)­borate, [TpMe,Me]−, n = 1, 3M, M = Fe, Co, Ni; L = hydrotris­(3-phenyl-5-methylpyrazol-1-yl)­borate, [TpPh,Me]−, n = 1, 4M, M = Mn, Fe, Co, Ni) were prepared by addition of the tripodal ligands to solvated [M­(NCMe)x]2+ (M = Mn, x = 4; M = Fe, Co, Ni, x = 6) precursor complexes. The product complexes were characterized by 1H NMR (except M = Mn), UV–vis–NIR, and FTIR spectroscopy. The structures of 2Mn, 2Ni, 3Fe, 3Co, and 4Fe were determined by X-ray crystallography. The data were consistent with complexes of high-spin divalent metal ions in idealized piano-stool geometries in all cases. Consequent lability of the acetonitrile ligands will enable use of these complexes as synthetic precursors and as catalysts. Comparison to previously reported structures of 1Fe, 1Co, 2Fe, and 2Co, the triflate salt analogues of 4Co and 4Ni, as well as related sandwich complexes (e.g., [(TpMe,Me)2M]) and solvated metal dications [M­(NCMe)6]2+ reveals numerous trends in M–N bond lengths. Primary among these are the Irving–Williams series, with significant structural effects also arising from ligand charge and sterics. Systematic trends in spectroscopic data were also observed which further elucidate these issues.

本数据集包含15种半夹心蝎形配合物（half-sandwich scorpionate complexes），通式为[(L)­M­(NCMe)₃]­(BF₄)ₙ，其中配体L分别为：三(3,5-二甲基吡唑-1-基)甲烷（tris(3,5-dimethylpyrazol-1-yl)methane, TpmMe,Me）、三(3-苯基吡唑-1-基)甲烷（tris(3-phenylpyrazol-1-yl)methane, TpmPh）、氢三(3,5-二甲基吡唑-1-基)硼酸根（hydrotris(3,5-dimethylpyrazol-1-yl)borate, [TpMe,Me]⁻）以及氢三(3-苯基-5-甲基吡唑-1-基)硼酸根（hydrotris(3-phenyl-5-methylpyrazol-1-yl)borate, [TpPh,Me]⁻）；对应电荷数n分别为2（对应1M、2M系列）与1（对应3M、4M系列），金属中心M涵盖Mn、Fe、Co、Ni。上述配合物通过将三脚架配体与溶剂化的[M(NCMe)ₓ]²⁺前驱体配合物反应制备得到，其中当M为Mn时x=4，当M为Fe、Co、Ni时x=6。所得产物通过¹H核磁共振波谱（金属中心为Mn时除外）、紫外-可见-近红外光谱以及傅里叶变换红外光谱进行了表征。通过X射线晶体衍射测定了2Mn、2Ni、3Fe、3Co及4Fe的晶体结构。所有实验数据均表明，所有目标配合物中的二价金属离子均处于高自旋状态，且配位几何构型均为理想化的钢琴凳式结构。由于乙腈配体具有良好的配位解离性，该类配合物可作为合成前驱体与催化剂加以应用。通过与已报道的1Fe、1Co、2Fe、2Co的晶体结构，以及4Co、4Ni的三氟甲磺酸盐类似物、相关夹心配合物（如[(TpMe,Me)₂M]）与溶剂化金属二阳离子[M(NCMe)₆]²⁺进行对比，本研究揭示了M-N键长的诸多变化规律。其中最具代表性的规律为欧文-威廉姆斯序列（Irving–Williams series），同时配体电荷与空间位阻效应也会对配合物结构产生显著影响。此外，光谱数据也呈现出系统性的变化趋势，进一步阐明了上述构效关系。