Extremely bulky amide ligands in main group chemistry

Abstract

The search for extremely sterically demanding monodentate amide ligands to access main group complexes in low-coordination numbers and highly reactive bonding modes is an area of intense research interest. The recent development of three classes of sterically demanding, monodentate amide ligands - the m-terphenyl anilides [N(R){C6H3Ar2-2,6}](-) (Ar = aryl, R = H, methyl, silyl), substituted carbazol-9-yl and the extremely bulky amides [N(R)(Ar')](-) (Ar' = 2,6-{C(H)Ph2}-4-R'-C6H2, R = silyl, aryl, silyloxy, R' = alkyl) is facilitating the isolation of stable species with new coordination modes for the main group elements. These compounds are of fundamental importance not only from the investigation of their structure and bonding, but also the investigation of their reactivity highlights the potential for small molecule activation chemistry under mild conditions and applications in catalysis. This review reports on the recent developments for these compounds with emphasis on their synthesis, structure and reactivity.

Structural Characterization of Lithium and Sodium Bulky Bis(silyl)amide Complexes

“…Alkali metal amides, {MNR 2 } (M = Li-Cs), are ubiquitous reagents in synthetic chemistry and their steric and electronic properties are readily tuned by R-group substitution [1,2,3]. Their popularity with synthetic chemists can be attributed to a combination of their strong basicity, low nucleophilicity, hydrocarbon solvent solubility and facile preparation from commercially available starting materials [4].…”

“…Their popularity with synthetic chemists can be attributed to a combination of their strong basicity, low nucleophilicity, hydrocarbon solvent solubility and facile preparation from commercially available starting materials [4]. Lithium amides are more frequently utilized than the heavier group 1 congeners as they can be synthesized directly from the parent amine and n BuLi and used in situ; the heavy alkali metal amides tend to be less soluble in hydrocarbons and additionally suffer from decomposition pathways in non-coordinating solvents [1,2,3,4]. …”

Low-coordinate first-row transition metal complexes in catalysis and small molecule activation

“…This ligand has been complexed to numerous metals, and such species have been shown to catalyse a wide variety of transformations including polymerisation, 16,17 catalytic hydrodefluorination, 18,19 Z-selective alkene isomerisation, 20 nitrene transfer reactions, 21,22 the dehydrocoupling of phosphines, 23 phosphine-boranes and amine-boranes, 24 and the hydrophosphination 25 and hydroboration 26 of alkenes and alkynes. One example of such a catalyst is shown in Scheme 1, with the three-coordinate iron(II) catalyst (1), and the proposed mechanism by which it catalyses the dehydrocoupling of dimethylamine-borane. 24 The development of β-diketiminate 3d complexes as catalysts was covered in a recent Perspective article by Ruth Webster, and we recommend consulting this article for a more in-depth look at such species.…”

A Bulky m‐Terphenyl Cyclopentadienyl Ligand and Its Alkali‐Metal Complexes

“…These monoanionic ligands are powerful at stabilizing a variety of unique molecular arrangements, including a digallene, [( m ‐terphenyl‐Cr) 2 ] with fivefold Cr−Cr bonding, and recently a base‐stabilized phosphinidine sulfide . Traditional functional groups outfitted with bulky m ‐terphenyl ligands have been developed, such as amides, isonitriles, and carboxylic acids . Despite many examples of the synthetic utility of both bulky cyclopentadienyl ligands and m ‐terphenyl ligands, only one reported study has brought together these two concepts; namely, with a m ‐terphenyl cyclopentadiene and its zirconium complex I…”