Main group metal hydrides supported by picolyl-based and chemically non-innocent N, N’-bidentate and N, N’, N”-tridentate ligands

Mandal, Chhotan (2025) Main group metal hydrides supported by picolyl-based and chemically non-innocent N, N’-bidentate and N, N’, N”-tridentate ligands. PhD thesis, Indian Institute of Science Education and Research Kolkata.

Text (PhD thesis of Chhotan Mandal (19RS014)) 19RS014.pdf - Submitted Version Restricted to Repository staff only Download (13MB)

Abstract

This PhD thesis, titled "Main-group Metal Hydrides Supported by Picolyl-based and Chemically Non-innocent N, N'-bidentate and N, N', N"-tridentate Ligands," investigates the potential of picolyl-based and chemically non-innocent bidentate and tridentate ligands for the synthesis of main-group metal compounds, with particular emphasis on the hydrides of main-group metals such as aluminium, zinc, and magnesium. The research primarily focuses on the synthesis, characterization, and application of these hydrides in organic transformations and small molecule activation, while also exploring the reactivity of these main-group compounds. The thesis is divided into five chapters. The first chapter, "Introduction," provides an overview of the general synthesis procedures for main-group metal hydrides and discusses previously reported nitrogen donor-stabilized aluminium, zinc, magnesium, and calcium hydrides, emphasizing their formation, stoichiometric reactions with Brønsted acids and small molecules, as well as their catalytic applications. In chapter two, we emphasize that a bidentate 2-anilidomethylpyridine ligand, known for its efficacy as an ancillary support, undergoes 1,4-hydroalumination with AlH₃(NMe₂Et) and mimics the hydride storage capabilities observed in Hantzsch esters, as well as in biological cofactors like NADH or NAD(P)H. In chapter three, we successfully synthesized and characterized a three-coordinated zinc hydride supported by 2-anilidomethylpyridine, demonstrating noteworthy catalytic performance in carbonyl hydroboration. Additionally, we observed that the ligand backbone is susceptible to electrophilic attack. In chapter four, we explore the coordination of a chemically non-innocent 2-anilidomethylpyridine ligand with magnesium, placing particular emphasis on magnesium hydrides. Here, a heteroleptic Mg-nBu precursor leads to the formation of various hydride clusters depending on the hydride sources used. In chapter five introduces a new dearomatized picolyl-based NNN ligand, and investigates its heteroleptic Mg-nBu and Mg-H complexes. The behaviour of Mg-H in relation to electrophiles reveals a competitive interaction between the metal center and the picolyl ligand backbone, with both the picolyl framework and Mg-H exhibiting nucleophilic properties. In Chapter Six, we present [9-{2-(dimethylamino)ethyl}fluorenyl] (L²) as a simple yet effective ancillary ligand for heteroleptic magnesium chemistry. While the corresponding complex [(L²)MgnBu(thf)] catalyzes the hydroamination/cyclization of primary aminoalkenes, attempts to form the desired [(L²)MgH] results in the THF-ring opening by a fluorenyl anion, despite the latter being considered not highly nucleophilic.

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