The effect of Mo(CO)₆ as a catalyst in the carbonylation of methanol to methyl formate catalyzed by potassium methoxide under CO, syngas and H₂ atmospheres.

Ph. D. University of KwaZulu-Natal, Westville 2010In patents describing the low temperature production of methanol from syngas catalysed by the Ni(CO)₄/KOCH₃ system, Mo(CO)₆ was claimed to enhance the catalytic activity of the system. However, there has been no clarity on the effect of Mo(CO)₆ and KOCH₃ in the activation of the catalyst. Work reported in this thesis showed that most of the methyl formate is produced via a normal KOCH₃ catalyzed process under a CO atm. When the KOCH₃ system is compared with the Mo(CO)₆/KOCH₃ catalyzed system, it is noted that the amount of methyl formate increases very slightly due to the addition of molybdenum hexacarbonyl. The experiments were also performed under H₂ and synags (1:1) atm in different solvents. In all cases dimethyl ether was produced with methyl formate. Preliminary carbonylation studies performed at a syngas ratio of 1:2 showed an increase in the amount of methanol produced. Increasing the amount of Mo(CO)₆ in the Mo(CO)₆/KOCH₃ reaction under syngas (1:1) increases the production of methyl formate. High Pressure infrared (HPIR) studies for Mo(CO)₆/KOCH₃ were carried out under H₂, CO, syngas (1:1) and N₂ atmospheres. The alkoxycarbonyl complex (Mo(CO)₅(COOCH₃)⁻) was observed as an intermediate in all reactions involving Mo(CO)₆ and KOCH₃. Under a hydrogen atmosphere, the metalloester (Mo(CO)₅(COOCH₃)⁻) intermediate diminished to form a bridged molybdenum hydride (µ-HMo₂(CO)₁₀⁻) species as a stable intermediate. In contrast, under syngas atmosphere, the metallloester diminished in concentration to form the bridged hydride (µ-HMo₂(CO)₁₀⁻), which also disappeared to form the molybdenum alkoxide complex (Mo(CO)₅OCH₃⁻). The role of methanol in the formation of methyl formate is also discussed. Based on the HPIR studies, different types of metalloesters (alkoxycarbonyl complexes) were synthesized by nucleophilic reactions of alkoxides with Mo(CO)₆. Reactions of potassium alkoxides (KOR, R = -CH₃, -C(CH₃)₃, -C(CH₃)₂CH₂CH₃) with Mo(CO)₆ in THF produced water soluble alkoxycarbonyl complexes (K[Mo(CO)₅(COOR)]). The reaction of KOCPh₃ with Mo(CO)₆ yielded what is believed to be the metalloester as an insoluble compound. Attempts to improve the solubility of the formed alkoxycarbonyl complexes, K[Mo(CO)₅(COOR)], by metathesis with bulkier counter ions (PPNCl, Et₄NCl and n-Bu₄NI) was not successful. The reaction of K[Mo(CO)₅(COOCH₃)] with 18-crown-6 ether produced [K(18-crown-6)][Mo(CO)₅(COOCH₃)] which was more soluble in organic solvents. The reactions of [PPN][OCH₃] and [n-Bu₄N][OCH₃] with Mo(CO)₆ produced [PPN][Mo(CO)₅(COOCH₃)] and [n-Bu₄N][Mo(CO)₅(COOCH₃)], respectively. The reactions of [K(18-crown-6)][OCH₃] and [K(15-crown-5)₂][OCH₃] with Mo(CO)₆ under reflux gave the [K(18-crown-6)][Mo(CO)₅(COOCH₃)] and [K(15-crown- 5)₂][Mo(CO)₅(COOCH₃)] complexes. Reactions of Ph₃PMo(CO)₅ with KOCH₃ and [PPN][OCH₃] yielded K[Ph₃PMo(CO)₄(COOCH₃)] and [PPN][Ph₃PMo(CO)₄(COOCH₃)]. Other alkoxycarbonyl complexes were synthesized by an alternative approach using alcohols as solvent. For example, [PPN][Mo(CO)₅(COOCH₂CH₃)] was synthesized by refluxing [PPN][OEt] with Mo(CO)₆ in ethanol. The isopropyl derivative [PPN][Mo(CO)₅(COOCH(CH₃)₂)] was synthesized by refluxing [PPN][OCH(CH₃)₂] with Mo(CO)₆ in isopropanol. Two methyl derivatives were also synthesized in methanol as Et₄N and PPN derivatives. A crystal structure of the [PPN]₂[Mo₆O₁₉] oxo cluster, obtained from the decomposition of [PPN][Mo(CO)₅(COOCH(CH₃)₂)] in acetonitrile was solved. The crystal crystallized in the monoclinic form with a space group of P-1. Another oxo cluster, [Et₄N]₂[Mo₄O₁₃], formed from the decomposition of the [Et₄N][Mo(CO)₅(COOCH₃)] derivative. The structure was solved in the monoclinic form with a space group of P 2₁/n. The alkoxycarbonyl complex, [PPN][Mo(CO)₅(COOCH₃)], was tested for catalytic behaviour under hydrogen and syngas to determine its role in the production of methyl formate. No methyl formate was produced under hydrogen, but methyl formate was produced under syngas (1:1). HPIR studies of [PPN][Mo(CO)₅(COOCH₃)] under syngas (1:1) showed that methyl formate is formed via the decomposition of [PPN][Mo(CO)₅(COOCH₃)] to Mo(CO)₆. Interesting results for the reaction of Mo(CO)₆ with KOCH₃ under syngas (1:1) were obtained in triglyme. Here longer carbon chain alcohols were produced and identified by GC and GC-MS. These alcohols include ethanol, 2-propanol, 2-butanol, 3-methyl-2-butanol, 3-pentanol, 2-methyl- 3-pentanol and 2,4-dimethyl-3-pentanol

Synthesis and incorporation of a Trishomocubane Amino Acid into short Peptides

Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2006.Cage compounds have attracted pharmaceutical and biological interest amongst others as anti-Parkinson agents. The serendipitous observation of the activity of 1-aminoadamantane 1 in Parkinsonian patients against selected viruses i.e. Herpes simplex Type I & II and Influenza A2-Asian viruses/Taiwan has increased the interest in cage compounds. This study involves the synthesis of the cage amino acid 14. Due to the insolubility of pentacyclo-[6.3.0.02,6.03,10.05,9]-undecane (trishomocubane) amino acid 14 in both polar and nonpolar solvents, including DMSO (d6), the synthesis of Fmoc-tris amino acid 50 was required for analysis. The Fmoc derivative of trishomocubane amino acid was also useful for controlled* coupling of the cage amino acid 14 to short peptides. The synthesis of the Fmoc-tris amino acid fluoride derivative is described as well as that of the tri-peptide (Ala-Ala-Ala). The incorporation of the Fmoc-tris amino acid fluoride in a tetra-peptide Ala-Ala-Ala-tris and in a hepta-peptide Ala-Ala-Ala-tris-Ala-Ala-Ala will also be presented. A computational chemistry project was undertaken using density functional theory (B3LYP) at the 6-31+G(d) level of theory, so as to enhance the understanding of the mechanism of esterification. Methanol, acetyl chloride and acetic acid were used in the model for simplicity. Four membered ring transition states were obtained with both acetyl chloride and acetic acid. A six membered ring transition state is facilitated by the selective use of one methanol molecule from the solvent. Both a concerted and step-wise mechanism are presented

Dicarbon­yl(η5-cyclo­penta­dien­yl)bis­(trimethyl­phosphine)molybdenum(II) trifluoro­methane­sulfonate

In the title compound, [Mo(C5H5)(CO)2(C3H9P)2]CF3SO3, the cationic complex displays a classical four-legged piano-stool square-pyramidal geometry with a trans configuration of the basal ligands around the Mo atom. The cyclo­penta­dienyl (Cp) ligand occupies the apical position of the piano-stool configuration. The average Mo—P bond length of the two trans PMe3 ligands is 2.474 (5) Å and the Mo—Cp centroid distance is 2.003 (2) Å