Date of Award
Doctor of Philosophy
Lee Keith Woo
The work presented in this report focuses on the synthesis and characterization of new iridium(III) porphyrin complexes, the iridium porphyrin-catalyzed insertion of diazo esters into the S-H bond of thiols (S-H insertion), and the efficient nanogold-catalyzed oxidation of amines into lactams, in the presence of atmospheric oxygen. Preliminary results of the nanogold-catalyzed synthesis of N,N'-disubstituted ureas from the room temperature reaction between primary amines, carbon monoxide and oxygen, are presented as well.
Upon treatment of (carbonyl)chloro(meso-tetra-p-tolylporphyrinato)iridium(III), (TTP)Ir(CO)Cl, with excess primary amines (amine = RNH2 = benzylamine, n-butylamine, isopropylamine, and tert-butylamine), at 23 ºC, in the presence of Na2CO3, trans-amine-coordinated iridium carbamoyl complexes, (TTP)Ir(NH2R)[C(O)NHR], were isolated in yields up to 94%. The lability of the amine ligands was established by variable-temperature NMR studies, ligand replacement reactions, and equilibrium binding studies. Consequently, hexacoordinate complexes of the type (TTP)Ir(L)[C(O)NHR] were synthesized, where L included quinuclidine, 1-methylimidazole, triethylphosphite, and dimethylphosphine. A series of ligand binding studies showed that both electronic and steric factors influenced ligand binding to the metal center. Furthermore, the nature of the trans ligand determined the reactivity of the carbamoyl ligand with the electrophile HBF4. On the other hand, the carbamoyl ligand reacted with CH3I in a similar fashion, whether the trans ligand contained a nitrogen or phosphorus donor.
This work also reports that the pentacoordinated Ir(TTP)CH3 efficiently catalyzed the insertion of the carbene moieties from methyl diazoacetate (MDA), ethyl diazoacetate (EDA), methyl phenyldiazoacetate (MPDA) and methyl (p-tolyl)diazoacetate (MTDA) into the S-H bond of different aromatic and aliphatic thiols. Product yields ranged from 70 – 97%. UV-visible titration showed that electron-rich thiols bind more strongly to iridium than their electron-poor counterparts. Substrate competition and trapping experiments also suggested that the insertion reactions proceed via an ylide intermediate. Furthermore, kinetic experiments showed that the observed reaction rates were a consequence of the competitive binding of thiol to the metal center of the catalyst and the nucleophilic attack of the thiol on the metal carbene intermediate.
The oxidation of cyclic amines into lactams was efficiently catalyzed by CeO2-supported gold nanoparticles (Au/CeO2) in the presence of 1 atmosphere of O2. The complete conversion of pyrrolidine was achieved in 6.5 hours at 160 oC, affording a 97% yield of the lactam product 2-pyrrolidone (γ-butyrolactam), while 2-piperidone (δ-valerolactam) was synthesized from piperidine (83% yield) in of 2.5 hours. Caprolactam, the precursor to nylon-6, was obtained from hexamethyleneimine in 37% yield in 3 hours. The intermediacy of 5-(pyrrolidin-1-yl)-3,4-dihydro-2H-pyrrole (amidine-5) and 4-amino-1-(pyrrolidin-1-yl)butan-1-one) in the oxidation of pyrrolidine was established by their independent syntheses and catalytic conversions into 2-pyrrolidone. In addition, Au/CeO2 efficiently catalyzed the oxidation of N-methyl cyclic tertiary amines to the corresponding lactams at 80 oC and 100 oC.
Finally, CeO2-supported gold nanoparticles (Au/CeO2) was found to catalyze the synthesis of N,N'-disubstituted ureas from the reactions of primary amines with 1 atmosphere each of CO and O2. These reactions were found to proceed at 23 oC. The isolated yield of N,N'-di-n-butylurea was 75%, while N,N'-dicyclohexylurea and N,N'-diisopropylurea were isolated in 40% yield and 37% yield, respectively.
Taiwo Olawale Dairo
Dairo, Taiwo Olawale, "Iridium porphyrin synthesis, reactivity and catalysis, and the nanogold-catalyzed synthesis of lactams" (2016). Graduate Theses and Dissertations. 15146.