Synthetic and theoretical studies of lanthanide imide and alkene complexes

This thesis describes the synthetic and theoretical investigations of lanthanide imide complexes stabilised by the N,N\\(^1\\)-deprotonated meso-octaethyl-transdioxaporphyrinogen ligand, of relevance to lanthanide mediated dinitrogen fixation. Also described are the synthesis of dibenzotropylidene based ligands and subsequent Group 1 metal complexes as pre-cursors for lanthanide complexes bearing alkene interactions, of relevance to lanthanide based catalytic alkene polymerisation. Chapter 1 introduces nitrogen fixation in both biological and synthetic systems and includes a review of strategic ligand design in organolanthanide chemistry. The synthesis, characterisation and reactivity of macrocyclic lanthanide complexes bearing auxiliary halide, azo and amide ligands as intermediates in the synthesis of macrocyclic lanthanide imides are described in Chapters 2-4. The Kl incorporating macrocyclic samarium(II) complex, [{(C\\(_6\\)H\\(_5\\)Me)K(Et\\(_8\\)N\\(_2\\)O\\(_2\\))Sm(˜í¬¿-I)}\\(_2\\)] and the macrocyclic samarium(III) bromide, [{(Et\\(_8\\)N\\(_2\\)O\\(_2\\))Sm(˜í¬¿-Br)}\\(_2\\)] were prepared from metathetical exchange reactions, whilst the macrocyclic samarium(III) iodide, [{(Et\\(_8\\)N\\(_2\\)O\\(_2\\))Sm(˜í¬¿-I)}\\(_2\\)] was prepared via oxidation of [{(C\\(_6\\)H\\(_5\\)Me)K(Et\\(_8\\)N\\(_2\\)O\\(_2\\))Sm(˜í¬¿-I)}\\(_2]\\). The macrocyclic azo complexes [Et\\(_8\\)N\\(_2\\)O\\(_2\\)Sm{˜í‚àë\\(^2\\)-N\\(_2\\)(Mes)\\(_2\\)}] and [(Et\\(_8\\)N\\(_2\\)O\\(_2\\))Sm(˜í‚àë\\(^2\\)-N\\(_2\\)Ph\\(_2\\))] were prepared via redox processes from [{(C\\(_6\\)H\\(_5\\)Me)K(Et\\(_8\\)N\\(_2\\)O\\(_2\\))Sm(˜í¬¿-I)}\\(_2\\)] and characterised from X-ray diffraction and NMR spectroscopic studies. The macrocyclic amides [(THF)\\(_2\\)K(Et\\(_8\\)N\\(_2\\)O\\(_2\\))Sm(N(H)Mes)\\(_2\\)], [{-˜í¬¿-˜í‚àë\\(^1\\):˜í‚àë\\(^3\\)-(N(H)Mes)K(Et\\(_8\\)N\\(_2\\)O\\(_2\\))SmN(H)Mes}\\(_n\\)], [(Et\\(_8\\)N\\(_2\\)O\\(_2\\))Sm{N(H)(C\\(_6\\)H\\(_2\\)-2,4,6-t-Bu)}] and [{(Et\\(_8\\)N\\(_2\\)O\\(_2\\))SmN(H)Mes] were synthesised from [{(Et\\(_8\\)N\\(_2\\)O\\(_2\\)Sm(˜í¬¿-I)}\\(_2]\\) via metathetical exchange reactions and their subsequent reactivity with a number of Group 1 metal bases was investigated. The desired ˜í¬±-deprotonation of the amides to yield an imide complex was not observed. A comprehensive analysis of the bonding within the model macrocyclic imide [K(H\\(_8\\)N\\(_2\\)O\\(_2\\))SmN(CH\\(_3\\)] and pre-cursor amide [(H\\(_8\\)N\\(_2\\)O\\(_2\\))SmN(H)CH\\(_3\\)] is presented in Chapter 5, along with a thermodynamic analysis of synthetic methods for imide formation from high-level density functional theory calculations. The samarium-based d orbitals were found to be important in stabilising the imide moiety, and were also found to exhibit strong interactions with the macrocyclic ligand. Synthetic studies of various dibenzotropylidene (trop) functionalised ligands are presented in Chapter 6. The synthesis and characterisation of the novel dibenzotropylidene ligands derived from deprotonation of tropN(H)-t-Bu, tropacacH, tropNsalOH and tropNsal\\(^‚ÄövѬ8\\)OH are described. Subsequent metallation of tropN(H)-tBu and tropNsal\\(^‚ÄövѬ8\\)OH gave the lithium complexes [(tropN(t-Bu)Li)\\(_2\\)OEt\\(_2\\)], [(tropNsal\\(^‚ÄövѬ8\\)OLi)\\(_2\\)] and [{tropN(H)C(n-Bu)sal\\(^‚ÄövѬ8\\)OLi}\\(_2\\)]. Further reactivity studies of these complexes in various reactions, including metathetical exchangea aimed at preparing lanthanide complexes, revealed instability in the tropylidene-heteroatom bond, which restricted the use of the tropylidene framework in organolanthanide studies.