Department of Chemistry, Princeton University, Princeton, New Jersey 08544, USA.
J Am Chem Soc. 2013 Jul 31;135(30):11373-83. doi: 10.1021/ja405477m. Epub 2013 Jul 18.
The synthesis and characterization of a metastable, base-free isocyanato dihafnocene μ-nitrido complex from CO-induced dinitrogen cleavage is described. The open coordination site at hafnium suggested the possibility of functionalization of the nitrogen atom by cycloaddition and insertion chemistry. Addition of the strained, activated alkyne, cyclooctyne, resulted in N-C bond formation by cycloaddition. The alkyne product is kinetically unstable engaging the terminal hafnocene isocyanate and promoting deoxygenation and additional N-C bond formation resulting in a substituted cyanamide ligand. Group transfer between hafnium centers was observed upon treatment with Me3SiCl resulting in bridging carbodiimidyl ligands. Amidinato-type ligands, NC(R)N were prepared by addition of either cyclohexyl or isobutyronitrile to the base free dihafnocene μ-nitrido complex, which also engages in additional N-C bond formation with the terminal isocyanate to form bridging ureate-type ligands. Heterocummulenes also proved reactive as exposure of the nitride complex to CO2 resulted in deoxygenation and N-C bond formation to form isocyanate ligands. With substituted isocyanates, cycloaddition to the dihafnocene μ-nitrido was observed forming ureate ligands, which upon thermolysis isomerize to bridging carbodiimides. Taken together, these results establish the base free dihafnocene μ-nitrido as a versatile platform to synthesize organic molecules from N2 and carbon monoxide.
描述了一种亚稳的、无碱的异氰酸二氫化铪μ-亚硝基配合物的合成与表征，该配合物是通过 CO 诱导的氮气裂解得到的。铪的开放配位位点表明氮原子通过环加成和插入化学进行功能化的可能性。应变活化炔烃，环辛炔的添加导致通过环加成形成 N-C 键。炔烃产物是动力学不稳定的，与末端二氫化铪异氰酸酯结合，并促进脱氧和额外的 N-C 键形成，导致取代的氰酰胺配体。用 Me3SiCl 处理观察到铪中心之间的基团转移，导致桥接碳二亚胺配体。通过将环己基或异丁腈添加到无碱二氫化铪μ-亚硝基配合物中，制备了氨甲酰基型配体NC(R)N，该配合物还与末端异氰酸酯发生额外的 N-C 键形成，形成桥接脲型配体。杂cumulenes 也表现出反应性，因为将氮化物配合物暴露于 CO2 导致脱氧和 N-C 键形成，形成异氰酸酯配体。用取代的异氰酸酯，观察到二氫化铪μ-亚硝基的环加成形成脲配体，其在热解时异构化为桥接碳二亚胺。总之，这些结果确立了无碱二氫化铪μ-亚硝基作为一种从 N2 和一氧化碳合成有机分子的多功能平台。
