This study investigates the coordination modes of potential multidentate N,O-donor Schiff base ligands to the [ReVO]3+ and fac-[ReI(CO)3]+ cores. The project is aimed at the synthesis of tridentate, tetradentate and pentadentate Schiff bases ligands derived from the condensation reactions of benzaldehyde with different primary amines. The structures of these Schiff bases and their complexes were confirmed by using physical characterization methods, namely melting points, UV-Visible, UV-emission, 1H NMR and IR spectroscopy, X-ray diffractometry and elemental analysis. To further understand the coordination chemistry of rhenium, the prepared diiminediphenol N2O2-donor Schiff base ligand N N′-o-phenylene-bis(salicylaldimine) (H2salphen) was reacted with trans-[ReOCl3(PPh3)2] to yield cis-[ReCl2(ophsal)(PPh3)], whereas its reaction with trans-[ReOBr3(PPh3)2] resulted in the formation of the cis-[ReBr2(aphsal)(PPh3)].2CH3CN complex. In the above complexes the H2salphen ligand was cleaved leading to the coordinated tridentate ophsal NO2- and aphsal N2O-donor ligands. The reaction of H3aphsal with trans-[ReOBr3(PPh3)2] in toluene led to an unexpected compound, trans- [{[ReBr(aphsal)(PPh3)2]Br}{[ReBr(aphsal)(PPh3)2](ReO4)}] with an imido [ReNR]3+core. The ligand aphsal was coordinated tridentately with the doubly deprotonated amino nitrogen leading to Re(V)-imido complexes. The reaction of 2-((Z)-(2-aminoethylimino)methyl)phenol (H3amphol) with [Re(CO)5Cl] led to the rhenium(I) product fac-[Re(CO)3(H3amphol)] with H3amphol coordinated as a monoanionic tridentate chelate through its phenolate oxygen and amino nitrogen atoms. The X-ray crystal structures showed that all complexes display a distorted octahedral geometry around the central rhenium atom. The reaction of 2,6-bis(2-hydroxyphenylimino)pyridine (H2hpp) with cis-[ReO2I(PPh3)2] resulted in the reduced Re(III) product trans-[Re(hpp)(PPh3)2]I, while trans-[Re(hpp)(PPh3)2](ReO4) was isolated from its reaction with trans-[ReOCl3(PPh3)2]. The H2hpp ligand acts as a pentadentate N3O2-donor ligand where the two phenolic protons undergo deprotonation and its three nitrogens act as neutral donor atoms. Both compounds resulted from a disproportionation reaction characterized by the produced perrhenate counter-ion. The complex fac-[Re(CO)3(H2hpp)Cl] was prepared from [Re(CO)5Cl] and H2hpp in toluene. The H2hpp ligand acted as a neutral bidentate N,N-donor chelate. The metal is coordinated to three carbonyl donors in a facial orientation, two neutral nitrogen atoms and a chloride ligand. The reactions of the potentially tetradentate ligand N,N'-ethylenebis(salicylideneimine) (H2salen) with different rhenium(V) precursors resulted in the formation of two dimeric oxorhenium (V) compounds. In the reaction of H2salen with trans-[ReOCl3(PPh3)2] in ethanol, the highly unusual distorted dimeric complex (μ-salen)[ReOCl2(PPh3)]2 was isolated, in which salen2- is coordinated as a tetradentate to two oxorhenium(V) centres, and salen2- is present as a bidentate monoanionic ligand on each rhenium center. The reaction of cis- [ReO2I(PPh3)2] with H2salen led to the formation of the neutral dimeric oxorhenium(V) complex (μ-O)[ReO(salen)]2 in which the tetradentate chelate salen acts as a tetradentate dianionic ligand through its phenolate oxygens and nitrogen atoms of the azomethine groups. In its reaction with H2hmp the compound (μ-O)[ReO(hmp)]2 was isolated. In this product the pentadentate ligand H2hmp coordinated as tetradentate via its phenolic oxygen and nitrogen atoms. The reaction of the potentially tetradentate N1,N2-bis(aminobenzylidene)-1,2-ethylenediamine (H2amben) with trans-[ReOCl3(PPh3)2] led to the formation of the monocationic square-pyramidal complex salt [ReO(amben)](ReO4.

The complex trans-[Re(dab)Cl3(PPh3)2] (H2dab=1,2-diaminobenzene) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2dab in ethanol. The ligand dab is coordinated to the rhenium(V) centre through a dianionic imido nitrogen only, in a distorted octahedral coordination geometry around the metal ion. The complex trans-[Re(ada)Cl3(PPh3)2] (H2ada=2-aminodiphenylamine) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2ada in acetonitrile. The ligand ada is coordinated to the rhenium(V) centre through a dianionic imido nitrogen only, in a distorted octahedral coordination geometry around the metal ion. Surprisingly, the Re-Cl bond length trans to the Re=N bond is shorter than the two equatorial Re-Cl bond lengths. The reaction of equimolar quantities of cis-[ReO2I(PPh3)2] with 5,6-diamino-1,3- dimethyluracil (H2ddd) in acetonitrile led to the formation of [Re(ddd)(Hddd)I(PPh3)2](ReO4). The X-ray crystal structure shows that the ligand ddd is coordinated monodentately through the doubly deprotonated amino nitrogen and is therefore present as an imide. The chelate Hddd is coordinated bidentately via the neutral amino nitrogen, which is coordinated trans to the imido nitrogen, and the singly deprotonated amido nitrogen, trans to the iodide. The reaction of equimolar quantities of [NH4(ReO4)] with H2ddd in methanol under reflux conditions led to the isolation of [C12H12N6O4] as only product. The [ReO4]- ion is therefore instrumental in the formation of [C12H12N6O4], and since the product contains no rhenium in any oxidation state, the conclusion is that [ReO4]- catalyses the oxidative deamination of H2ddd. The X-ray crystal structure consists of two centrosymmetric, tricyclic rings, comprising a central pyrazine ring and two terminal pyrimidine rings. The reaction of a twofold molar excess of H2apb (H2apb=2-(2-aminophenyl)-1Hbenzimidazole) with trans-[ReO2(py)4]Cl in ethanol gave the green product of the formulation [ReO(Hapb)(apb)] in good yield. The rhenium atom lies in a distorted trigonal-bipyramidal environment. The two imidazole N(2) atoms lie in the apical positions trans to each other, with the oxo-oxygen and two amido N(1) atoms in the trigonal plane. The complex has C2-symmetry. The two amino groups are singly deprotonated and provide a negative charge each, so that they are coordinated as amides. The oxo group provides two negative charges. In order to obtain electroneutrality for the rhenium(V) complex, the two coordinated imidazole nitrogens provide one negative charge. The complex salt trans-[Re(mps)Cl(PPh3)2](ReO4) (H3mps=N-(2-amino-3- methylphenyl)salicylideneimine) was prepared by the reaction of trans- [ReOCl3(PPh3)2] with a twofold molar excess of H3mps. The X-ray crystal structure shows that the trianionic ligand mps acts as a tridentate chelate via the doubly deprotonated amino nitrogen (which is present in trans- [Re(mps)Cl(PPh3)2](ReO4) as an imide), the neutral imino nitrogen and the deprotonated phenolic oxygen. The [ReO4]- anion has approximately regular tetrahedral geometry. Two significant hydrogen bonds are formed between two of the perrhenyl oxygens and the water of crystallization. The six-coordinated complex cis-[Re(mps)Cl2(PPh3)2] was prepared by the reaction of trans-[ReOCl3(PPh3)2] with a twofold molar excess of H3mps in benzene. The Xray crystal structure shows that the mps ligand coordinates as a tridentate chelate via the doubly deprotonated 2-amino nitrogen, the neutral imino nitrogen and the phenolate oxygen. The imide and phenolate oxygen coordinate trans to each other in a distorted octahedral geometry around the rhenium(V) centre, with the two chlorides in cis positions.

The problem of colorimetrically determining rhenium in the presence of molybdenum, copper, iron, sulphur, and rare earth elements with the use of dimethylglyoxime as the complexing compound was accomplished by the method reported here-in. The interfering elements were eliminated either as gaseous oxides and sulfides or were precipitated from a highly basic solution by means of a strong alkaline fusion of equal weights of sodium hydroxide and sodium peroxide, and the ore sample containing rhenium. The fusion product was dissolved in water, the solution boiled with a slight excess of sodium peroxide, and the hydroxide of all the interfering ions precipitated. The filtrate was neutralized with sulphuric acid after the precipitate had been removed and thoroughly washed. Aliquot portions of this solution were then diluted to specified concentrations in fifty ml. flasks. Stannous chloride was used for the reduction of rhenium to an oxidation state wherein it forms a colored complex with dimethylglyoxime. The optical density of the rhenium color complex was measured with a Colman Spetrophotometer and compared with the optical density of the same concentration of standard solution. The optical densities of the fusion rhenium solutions were exactly equal to those of the standard solutions of equal rhenium concentration up to about twenty-five parts per million. This method appears to give very accurate results for the determination of rhenium up to this concentration.

The purpose of the investigation was to determine the catalytic activity of rhenium blacks obtained by reduction of rhenium salts in alkali metal-ammonia or amine systems. A review is presented on the chemical, physical and catalytic properties of rhenium, and on the rhenide ion, on the nature of the alkali metal-liquid ammonia system, and the reduction of metallic salts therein. The first reduction system studied was that obtained by dissolving sodium in liquid ammonia. The salts reduced in this system were KReO_4, Re_2O_7 and NH_4ReO_4. The reduction of KReO_4 was unsuccessful, and the heptoxide was difficult to handle. The product obtained by the reduction of NH_4ReO_4 was the best characterized. The lithium-ammonia system was also used to reduce NH_4ReO_4. One amine-alkali metal system was studied extensively. Lithium was used as the reducing agent and ethylamine as the solvent on NH_4ReO_4. A standard method of preparation was developed for each catalytst. It was found that the order of addition of the salt and alkali metal, the reaction ratio employed and the amount of solvent used apparently had no effect on the activity of the catalyst. It was found, however, that unless the alkali metal amide formed during the reduction process was removed completely, the catalysts were almost entirely inactive. For this purpose an acid extraction was employed. A spectrophotometric method, based upon the strong absorption of the hexachlororhenate ion at a wave length of 281 mμ, as well as the well recognized gravimetric method, based upon the insolubility of tetraphenylarsonium chloride, were used for the analysis of the catalysts. The spectrophotometric method was shown to be suitable for obtaining an approximate analysis, but lacked the precision necessary for an ultimate analysis. To determine the exact rhenium content of the material, the gravimetric method was therefore used. The valence state of the rhenium in the catalyst material was determined by oxidizing the catalyst in acidic potassium dichromate and then back titrating the excess oxidant. The analytical data indicated that all the catalysts were identical in composition; apparently a definite compound (ReO•2H_2O). The activities of the sodium-ammonia catalysts were evaluated by 69 reductions of organic substrates. The lithium-ammonia catalyst's activity was demonstrated in 24 hydrogenations, while the lithium-ethylamine catalyst was similarly used in a total of 55 reductions. Several catalysts prepared in miscellaneous systems were also evaluated. In all, a total of 161 hydrogenations were performed. The analysis of the reduction products was performed by means of gas chromatography except in the case of simple substrates used without solvent, for which refractive indices were used. In general the activity of the lithium-ethylamine catalyst was found to be somewhat superior to that of the catalysts prepared in ammonia. This was definitely the case in the reduction of the carbonyl group as contained in such substrates as butanone, acetone, and cyclohexanone. Acetone was reduced by the Li-EtNH_2 catalyst at about 55°C., butanone required 90°C., while cyclohexanone required a temperature of ca. 120°C. In contrast the Na-NH_3 catalyst required a temperature of 78°C. to reduce acetone, 130°C. to reduce butanone, and 160-170°c. to reduce cyclohexanone. In the case of the olefinic bond, except when conjugated to the benzenoid structure, the Li-NH_3 catalyst was the most effective. This castalyst reduced hexene-1 at about 100°C. and cyclohexene at 105°C. Styrene on the other hand was reduced by the Li-EtNH_2 catalyst in one experiment at room temperature while the Li-NH_3 catalyst required 70°C. and the Na-NH_3 catalyst 100°C. The Li-EtNH_2 and Li-NH_3 catalysts were about equally effective in the reduction of nitrobenzene. The temperature required was about 110°C. The Na-NH_3 catalysts in contrast required temperatures of about 175°C. The Na-NH_3 catalyst was used in an evaluation of the ease of reduction of a series of ketones. A very interesting relationship evolved from this study. It was observed that in all but two cases, the ketones containing an even number of carbon atoms in the principal chain reduced under significantly milder conditions than their odd numbered homologs. A number of hydrogenations were attempted on compounds containing a nitro group and another easily reducible group. In all cases, no reduction of the second group occurred until the nitro group was hydrogenated, inspite of the fact that the conditions for the reduction of the nitro group alone were more drastic than for the reduction of any of the other functions. This phenomenon has been observed in previous investigations in which selectivity of reduction, with a rhenium catalyst, involving the nitro group was attempted. A number of compounds containing both the carbonyl group and olefinic bond, i.e., allylacetone, 2-allylcyclohexanone, were hydrogenated in attempt to obtain selective reduction. The results clearly indicated that the rhenium catalysts reduce the olefinic bond preferentially to the carbonyl group. This was also demonstrated to be the case with the "Standard" catalysts. However, in one experiment in which a partial poisoning of the catalyst from pyridine occurred, the product obtained was 5-hexene-2-ol, indicating a reversal of ease of reduction of the two groups in this case. In the case of crotonaldehyde the carbonyl group was apparently more easily reduced than the olefinic bond by both the rhenium and "Standard" catalysts. On one occasion, however, the Li-EtNH_2 catalyst produced crotyl alcohol. The greatest worth of the catalyts of this investigation was undoubtly their ability to catalyze the reduction of carboxylic acids. The catalysts prepared in all three systems seemed to be equally active in this respect. It was observed in this connection that when the reduction was run without solvent, the product was a mixture of both the alcohol and ester. However, if water was used as a solvent, the reduction yielded in most cases only the alcohol. The Li-EtNH_2 catalyst was used in the reduction of a series of carboxylic acids. Included in the series were acetic, propionic, isobutyric, valeric, caproic, caprylic, capric, and lauric. All were reduced in the temperature range of 160-180°C., except acetic which was reduced at 145°C. This catalyst, therefore, is as effective in this reaction as any rhenium catalyst heretofore studied and much superior to any other catalyst reported in the literature.

The epoxide deoxygenation reaction is formally the reverse of the epoxidation reaction. Compared to epoxidation, which has reached its full maturity, epoxide deoxygenation has not been as intensively developed. Among the few deoxygenation reagents, a handful are catalytic in a metal complex, show high stereospecificity and operate under mild conditions. A common feature of all present deoxygenation reagents is that they do not perform asymmetric deoxygenation of racemic epoxides. Rhenium (VII) trioxo complexes are emerging as pliable catalysts for epoxide deoxygenation. Designing a chiral rhenium (VII) trioxo complex was our goal. Guided by the mechanism of rhenium (VII) trioxo catalyzed epoxide deoxygenation and the mechanism of the stereogenic information transfer, we have designed and prepared a chiral rhenium(VII) trioxo complex. This complex is void of stereogenic centers and the source of asymmetry is the restricted rotation around a carbon-carbon bond. Detailed conformational analysis of the new chiral complex was done by extensive NMR measurements and molecular modeling. The rotation barrier for the diolate was experimentally and computationally estimated to be 9.72 kcal/mol and 8.06 kcal/mol, respectively. Unsuccessful attempts were made to prepare a camphor based scorpionate because of the extreme steric congestion. A menthone based scorpionate was successfully prepared. The related rhenium (TII) trioxo complex with this scorpionate revealed contradicting chemical and spectroscopic features. / Graduation date: 2005

Graduation date: 2002

Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (leaves 325-336). Also available via World Wide Web.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy