In this thesis, the synthesis and reactivity of metal complexes containing phosphido (PR2−) and phosphenium (PR2+) ligands for the hydrophosphination of alkenes were investigated. The mechanisms of hydrophosphination mediated by these M-PR2 fragments were explored. Based on previous work in the Rosenberg group, Ru(η5-indenyl) complexes were explored and developed as catalysts for hydrophosphination. It was determined that Ru-phosphido complexes are key intermediates in the hydrophosphination of electron-deficient alkenes. A detailed study on the mechanisms of hydrophosphination catalyzed by the phosphido complexes Ru(η5-indenyl)(PPh2)(L)(PPh3) (4a, L = NCPh; b, L = PPh2H; c, L = CO) was performed. Evidence for product inhibition was found for this catalyst system using Reaction Progress Kinetic Analysis. Product inhibition is consistent with the observed catalyst resting state of a complex containing product phosphines and the determination that substitution of the product phosphine from Ru is rate-limiting. The ancillary ligands (L) of 4 were found to influence catalytic activity by enabling catalyst deactivation (L = NCPh) or off-cycle processes including alkene telomerization (L = CO). Proposed mechanisms for catalysis were devised based on these findings. These results are important mechanistic insights that will be useful for designing new catalysts for hydrophosphination. The unprecedented viability of metal phosphenium complexes as intermediates in hydrophosphination was also explored. Three Mo phosphenium complexes were synthesized via P-H bond hydride abstraction from coordinated secondary phosphines, PR2H. These complexes were found to mediate the stoichiometric hydrophosphination of alkenes and ketones. In particular, trans-[Mo(CO)3(PPh2H)2(PPh2)]+ (13) mediates the hydrophosphination of a wide scope of alkenes that includes ethylene, propene and 1-hexene, which are challenging substrates for metal-catalyzed hydrophosphination. Preliminary attempts were conducted to render this synthetic phosphenium-mediated hydrophosphination catalytic. These results provide evidence for the putative steps of a hydrophosphination cycle utilizing metal phosphenium complexes as intermediates. The phosphenium complexes trans-[Mo(CO)4(PR2H)(PR2)] (12a R = Tolp2, b R = Ph) were also investigated as Lewis acid catalysts for hydrosilylation. A tentatively-assigned η1-HSiEt3 adduct of 12a, [Mo(CO)4(PTolp2H)(PTolp2{HSiEt3})] (20a), was observed by low temperature 31P{1H} NMR and was studied computationally. Complex 12b is proposed to behave as a Lewis acid catalyst for hydrosilylation. An off-cycle equilibrium is proposed that results in the formation of EtSi+. This work is a unique example of P(III) Lewis acid catalysis, of which there are few examples in the literature. / Graduate / 2020-07-29

The fundamental knowledge of Cr(III) chemistry has been enhanced via detailed structural and spectroscopic studies of largely novel compounds that may potentially be active tri- and tetramerisation precursors. The compounds are based on various monodentate and bidentate nitrogen and phosphorus ligands which have been coordinated to [CrCl3 (thf) 3]. The few compounds that have been synthesised previously have in this study been made via novel synthetic routes and incorporate a combination of new and more detailed analysis than was carried out previously. The eight structures determined, in addition to offering novel crystallographic data, also provided insights into the synthetic pathways leading to compound formation. The isolation of monomeric structures suggests direct ligand substitution, while the cationic-anionic structures suggest the presence of dimeric intermediates which have been cleaved asymmetrically. Infrared and Raman spectra of these structures were able to add weight to these pathway proposals and, by means of vibrational comparisons, assisted in the general band assignments of the compounds' spectra where structures were not available. Vibrational shifts relative to the free ligands, as well as metal–ligand vibrations in the far infrared region, were also of significant value in terms of ligand coordination and geometry. Closely associated with the infrared and Raman spectra analysis was the generation of theoretical spectra using Density Functional Theory calculations. The excellent agreement between the calculated and experimental spectra confirmed the vibrational assignments. Also generated by computational means were the highest occupied and lowest unoccupied molecular orbitals (HOMO and LUMO) of the compounds which indicated the sites of potential nucleophilic and electrophilic attack. 1H NMR spectroscopy is a technique normally avoided when studying paramagnetic materials. However, by employing a largely novel approach, information pertaining to both ligand coordination and reaction times was obtained. FAB-MS assisted in the confirmation that the single crystal determinations did indeed reflect the composition of the bulk precipitated samples. It also provided additional structural information through the identification of fragmentation patterns which could not be gained by techniques such as elemental analysis. / Thesis (PhD)--University of Pretoria, 2010. / Chemistry / unrestricted

There is considerable current interest in the design and synthesis of new phosphorus ligands and their transition metal complexes in view of their potential applications in homogeneous catalysis. The present study is concerned with the synthesis of new chiral and achiral “ diphosphazanes”, which constitute a class of versatile short-bite bidentate phosphine ligands, and studying their reactivity towards late transition metals (Ag, Pd and Ru). Symmetrical diphosphazane ligands, MeN{P(OR)2}2 (R = (1R, 2S, 5R)-menthyl) and MeN{P(SR)2}2, (R = C6H5) and unsymmetrical diphosphazane ligands, Ph2PN(Pri)PPhY, (Y =OC6H3Me2-2,6 or NMePh) have been synthesized and structurally characterized. The reactivity of these ligands towards the transition metal precursors viz., [PdCl2(COD)] and [CpRu(PPh3)2Cl] has been investigated. The reaction of [Ru(bipy)2Cl2] with the diphosphazane, PriN(PPh2)2 in the presence of AgOTf to synthesize [Ru(bipy)2{PriN(PPh2)2}2]OTf led to an unexpected entry into the Ag(I) chemistry of this ligand. By optimizing the reaction conditions, several mononuclear, dinuclear and trinuclear complexes such as [Ag(K2-PriN(PPh2)2)2]X, [Ag(µ-PriN(PPh2)2)X]2 and [Ag3(µ-(Cl)2(µ-PriN(PPh2)2)3]X (X = NO3, OTf or PF6) have been synthesized. A polymeric complex, [Ag2(µ-PriN(PPh2)2)( µ-NO3)2]n in which the ligand adopts a unique ‘Cs’ geometry has also beenstructurally characterized. This polymeric complex is used to synthesize a helical polymer,[Ag2{µ-PriN(PPh2)2}(DABCO)(NO3)2]n and π- π stacked supramolecular assemblies such as [Ag2(NO3)2(µ-Ph2PN(Pri)PPh2)(2,2'-bipy)2] and [Ag2{µ-PriN(PPh2)2}(1,10-phen)2](NO3)2]. The reaction of a sterically bulky diphosphazane ligand, EtN{P(OC6H3(Pri)2-2,6)2}2 (L) with[(η3-1-R,R’-C3H3)Pd(µ-Cl)]2 in the presence of NH4PF6 gives the cationic complex, [(η 3-1-R,R’-C3H3)Pd(L)]PF6 (R = H; R’= H or Me) as the sole product. In the absence of NH4PF6, theinitially formed cationic complex, [(η 3-C3H5)Pd(L)]PF6 is transformed into a mixture of chlorobridged complexes over a period of 96 h. An octa-palladium complex [(η3-C3H5)(2-Cl- η3-C3H4)Pd4(µ-Cl)4(µ-L)]2 is formed as a result of nucleophilic substitution by a chloride ligand at the central allyl carbon atom. The reaction of L with [(η3-C3H5)Pd(µ-Cl)]2 in the presence of K2CO3 yields a dinuclear complex, [(η3-C3H5)Pd2(µ-L)Cl] containing a coordinatively unsaturated T-shaped palladium center. This complex exhibits high catalytic activity and large“turn-over numbers” in the catalytic hydrophenylation of norbornene. Reactions of diphosphazanes with cyclometalated palladium complexes of the general formula [Pd( k2-(C,N)-Me2NCHMe(C6H4))(solvent)2]PF6 derived from a chiral amine, (S)-N,N-dimethyl-1-phenethylamine give chelate complexes of the type [Pd{ k2-(C,N)-Me2NCHMe(C6H4)}(LL)] PF6, (L-L = diphosphazane). Chiral racemic diphosphazanes give a mixture of diastereomeric(S,R and S,S) complexes which could not be separated. These cyclometalated complexes show moderate catalytic activity in C−C bond forming reactions (hydrophenylation /Suzuki coupling).

Les alpha oléfines linéaires courtes sont des molécules de base en pétrochimie donc le marché est en constante augmentation notamment pour les oléfines légères (butène-1, hexène-1, octène-1). Ces oléfines, utilisées massivement dans l’industrie des plastiques, sont produites par la réaction catalytique d’oligomerisation de l’éthylène. IFPEN a contribué à développer plusieurs procédés homogènes d’oligomérisation de l’éthylène (AlphaButol, AlphaHexol, AlphaSelect) à base des complexes de titane, chrome ou zirconium. A travers une collaboration avec l’Université d’Amsterdam de nouvelles stratégies de développement de ligands ont été entreprises afin de rendre les catalyseurs à base de nickel sélectifs pour cette transformation. Ainsi, une approche supramoléculaire basée sur des interactions par liaison hydrogène, jusqu’alors décrite pour les métaux nobles, a été développée et appliquée aux complexes de nickel. Des complexes organométalliques originaux ont pu être générés et les interactions supramoléculaires ont été caractérisées par diffraction aux rayons X notamment. Ces complexes se présentent sous forme zwitterionique et sont formés par la combinaison de deux ligands simples donneurs et/ou accepteurs d’hydrogène. Ces complexes se sont avérés très actifs vis-à-vis de l’éthylène et ne nécessite pas l’ajout d’activateur du fait de la présence d’une liaison nickel-carbone réactive. Ils ont permis d’accéder à des sélectivités très importantes en butène-1. Appuyé par des expériences in situ et l’évaluation en catalyse de plusieurs complexes aux propriétés électroniques et stériques variées, cette approche a permis d’identifier l’espèce active et de mesurer l’impact de plusieurs descripteurs permettant de moduler la sélectivité et l’activité de la réaction catalytique en profondeur. / The demand for short linear alpha olefins is constantly increasing and motivates the development of robust and selective catalysts. In this thesis, several libraries of phosphorus ligands with the capacity to form dissymmetric or supramolecular assemblies were synthesized. The variability observed within the aminophosphine libraries, clearly reflected by the various tautomeric equilibrium of the ligand, was also observed in the nickel complexes as a single ligand could generate several complexes with different structures. Sulphonyliminobisphosphine were then introduced as a new class of ligands. These precursors rearrange in the presence of nickel to generate diphosphinamine nickel complexes. Activated by MAO, these complexes are active in the reaction of ethylene oligomerisation and produce short chain olefins. A new approach that forms stable supramolecular nickel complexes was developed by combining two phosphorus ligands with Ni(0). These complexes stabilised by hydrogen bonding are directly active in the reaction of ethylene oligomerisation with some catalysts leading to high selectivity to 1-butene (up to 84%). To understand the origin of that selectivity, the scope of complexes was extended to ligands with different steric and electronic properties. Their evaluation in the reaction of ethylene oligomerisation evidenced a relation between the catalyst structure and the selectivity of the reaction. Mechanistic studies, under an ethylene atmosphere, reveals that cationic complexes rearrange to neutral complexes, which are likely, the active species.