Diversity of Imidazolin-2-iminato Ligands in Group 2 and 4 Metal Coordination Sphere– Syntheses, Structures & Reactivity

Naktode, K (2015) Diversity of Imidazolin-2-iminato Ligands in Group 2 and 4 Metal Coordination Sphere– Syntheses, Structures & Reactivity. PhD thesis, Indian Institute of Technology Hyderabad.

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Abstract

For over 3 decades, transition-metal complexes containing multiply bonded ligands have generated considerable interest and considerable advances have been made in understanding and developing their structures and reactivity. The impressive variety of structural types and, in particular, reactivity properties of such complexes is an evidence to the wide range of ancillary ligand environments available to support these multiply bonded functional groups. In my dissertation thesis we focus on titanium imido chemistry in particular. The Ti=NR linkage has been shown to couple stoichiometrically with a variety of unsaturated substrates including CO2, carbodiimides, isocyanates, isocyanides, acetonitrile, phosphaalkynes, alkynes, alkenes, and allenes. Especially recently, there has been much interest in using titanium imides as catalysts for hydroamination and olefin polymerization. Likewise tremendous research efforts have been devoted to the development of various types of ancillary ligands as alternatives for cyclopentadienyl ligands. Among those cyclopentadienyl alternatives, novel and versatile imidazolin-2-iminato ligand which can be regarded as monodentate analogues to cyclopentadienyls, due to their capability to act as 2σ, 4π-electron donors. We have established a general method for the synthesis of related imidazolin-2-iminato titanium amide complexes. We also explore the reactivity properties of these imidazolin-2-iminato titanium amide complexes. We present a method for the preparation of imidazolin-2-iminato supported titanium imido complexes. With this contribution, we have functionalised imidazolin-2-imine ligand include p-donors such as phosphoraneimides and ureate and thioureate ligands from readily available starting materials chorodiphenylphosphine, phenyl isocyanate and phenyl isothiocyanate. As a development of our work in imidazolin-2-iminato titanium chemistry we have become interested in exploring the apparently related ureate and thioureate ligands employing in group 2 chemistry. Group 2 metal complexes have been received considerable attention as initiators for the Ring-opening polymerization (ROP) of cyclic esters and some of them have demonstrated impressive results. Ring-opening polymerization of cyclic esters promoted by alkaline-earth & rare-earth metal initiators proved to be the most efficient way for preparing polyesters with controlled molecular weight and microstructure and narrow molecular-weight distribution.

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