Design of (phenoxy)imine palladium complexes as homogeneous and immobilized catalysts for methoxycarbonylation of olefins.

Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.Abstract available in pdf

Syntheses of mixed donor homogeneous and immobilized palladium (II) complexes as catalysts for methoxycarbonylation and hydrogenation reactions.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Abstract available in PDF

Syntheses of mixed donor homogeneous and immobilized palladium(II) complexes catalysts for methoxycarbonylation and hydrogenation reactions.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Reactions of ligands (E)-N'-(2,6-diisopropylphenyl)-N-(4-methylpyridin-2-yl)benzimidamide (L1), (E)-N'-(2,6-diisopropylphenyl)-N-(6-methylpyridin-2-yl)benzimidamide (L2), (E)-N'-(2,6-dimethylphenyl)-N-(6-methylpyridin-2-yl)benzimidamide (L3), (E)-N'-(2,6-dimethylphenyl)-N-(4-methylpyridin-2-yl)benzimidamide (L4) and (E)-N-(6-methylpyridin-2-yl)-N'-phenylbenzimidamide (L5) with [Pd(NCMe)2Cl2] furnished the corresponding palladium(II) pre-catalysts (Pd1-Pd5), in good yields. Molecular structures of Pd2 and Pd3 revealed an N^N bidentate coordination mode to afford square planar compounds. Activation of the palladium(II) complexes with para tolyl sulfonic acid (PTSA) afforded active catalysts in the alkenes methoxycarbonylation. The resultant catalytic activities were controlled by both the complex structure and alkene substrate. While aliphatic substrates favoured the formation of linear esters (>70%), styrene substrate resulted in predominantly branched esters of up to 91%. The water-soluble ligands; sodium 4-hydroxy-3-((phenylimino)methyl)benzenesulfonate (L6), sodium 3-(((2,6-dimethylphenyl)imino)methyl)-4-hydroxybenzenesulfonate (L7) and sodium 3-(2,6-diisopropylphenyl)imino)methyl)-4-hydroxybenzenesulfonate (L8) reacted with with Pd(OAc)2 afford their respective palladium(II) complexes [Pd(6)2] (Pd6), [Pd(L7)2] (Pd7) and [Pd(L8)2] (PdL8). In addition, treatment of the non-water-soluble ligands 2-((phenylimino)methyl)phenol (L9), 2-(((2,6-dimethylphenyl)imino)methyl)phenol (L10) and 2-((2,6 diisopropylphenyl)imino)methyl)phenol (L11) with Pd(OAc)2 yielded complexes [Pd(L9)2] (Pd9), [Pd(10)2] (Pd10) and [Pd(L11)2] (Pd11), respectively in good yields. Solid-state structures of compounds Pd6 and Pd9 revealed bis(chelated) square planar neutral compounds. All the complexes formed active catalysts in the methoxycarbonylation of 1- hexene, affording yields of up to 92% within 20 h and regioselectivity of 73% in favour of linear esters. The activities and selectivities of the compounds depended on the steric encumbrance around the coordination centre. The water-soluble complexes displayed comparable catalytic behaviour to the non-water-soluble systems. The complexes could be recycled five times with minimal changes in both the catalytic activities and regio-selectivity. Reactions of (amino)phenyl ligands, (E)-N-((Z)-4-(phenylamino)pent-3-en-2-ylidene)aniline (L12) and N,N'E,N,N'E)-N,N'-(3-(3 (triethoxysilyl)propyl)pentane-2,4-diylidene)dianiline (L13) with [Pd(NCMe)2Cl2] led to the formation of homogeneous complexes Pd13 and Pd14. Besides, supporting of complex Pd14 with either MCM-41, SBA-15, or Fe3O4 magnetic nanoparticles gave immobilized complexes P15-Pd17, respectively. Using varying metal loading in the MCM-41 immobilization of complex Pd14 produced complexes Pd18 and Pd 19. In addition, calcination of complex Pd16 at 150oC and 200oC led to the formation of complexes Pd20 and Pd21, respectively. All the complexes were received in good yields. The catalytic activities and selectivities of the homogeneous complexes were influenced by the coordination sphere, with the complexes predominantly forming linear esters. On the other hand, the catalytic behaviours of the immobilized catalysts depended on the nature of support and calcination temperatures. In addition, the catalytic activities were observed to depend on the reaction temperature, catalyst loading, amounts of PPh3 and acid promoters. The immobilized complexes Pd15, Pd16 and Pd17, were recycled up to five times. The homogeneous and silica immobilized palladium(II) complexes of ligands (2-phenyl-2-((3(triethoxysilyl)propyl)imino)ethanol) (L14), (4-methyl-2-((3(triethoxysilyl)propyl)imino)methyl)phenol ) (L15 ), [L14-MCM-41 (L16), and [L15- MCM-41 (L17)]. The homogeneous complexes [Pd(L14)2] (Pd22), [Pd(L14)2] (Pd23), [Pd(L14)(Cl2)] (Pd24), [Pd(L15)(Cl2)] (Pd25) were obtained from homogenous ligands L14, L15, L16 and L17 respectively. In addition, the silica immobilized compounds [Pd(L14)2]-MCM-41] (Pd26) and [Pd(L15)2)-MCM-4] (Pd27) were obtained through convergence immobilization of complexes Pd22 and Pd23, respectively. Comparatively, immobilized complexes [Pd (L14)(Cl2)-MCM-41] (Pd28) and [Pd(L15)(Cl2)]-MCM-41] (Pd29) were obtained from the complexation of immobilized ligands L16 and L17. Both sets of complexes gave active catalysts in molecular hydrogenation of alkenes, alkynes and functionalized benzenes. The catalytic activities and product distribution in these reactions were largely dictated by the nature of the substrate. The kinetic studies revealed reaction orders dependence on styrene for both the homogeneous and supported catalysts. Significantly, the selectivity of both sets of catalysts was comparable in the hydrogenation of alkynes and multi-functionalized benzenes. The supported catalysts could be recycled up to four times with minimum reduction in catalytic activities and showed the absence of any leaching from hot filtration experiments. Kinetics and poisoning studies established the presence of active homogeneous species for complexes Pd22-Pd5 and Pd(0) nanoparticles for the immobilized complexes Pd26-Pd29, respectively

Synthesis of MCM-41 Immobilized (Phenoxy)Imine Palladium(II) Complexes as Recyclable Catalysts in the Methoxycarbonylation of 1-Hexene

The immobilization of 2-phenyl-2-((3(tryethoxysicyl)propyl)imino)ethanol (HL1) and 4-methyl-2-(((3(triethoxysilyl)propyl)imino)methyl)phenol (HL2) on MCM-41 afforded the respective ligands HL1-MCM-41 (HL3) and HL2-MCM-41 (HL4). The treatment of complexes Pd(L1)2 and Pd(L2)2 with MCM-41 afforded the immobilized complexes (Pd(L1)2)-MCM-41 (1) and (Pd(L2)2)-MCM-41 (2) respectively. Separately, the reactions of HL3 and HL4 with Pd(NCMe)2Cl2 produced the immobilized complexes Pd(HL3)Cl2 (3) and Pd(HL4)Cl2 (4) respectively. The immobilized compounds were characterized by FT-IR, Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), energy-dispersive X-ray (EDX), Thermogravimetric Analysis (TGA) and X-ray Powder Diffraction (XRD). All the complexes (1⁻4) formed active catalysts in the methoxycarbonylation of 1-hexene to give linear and branched esters. The catalysts were recycled four times without the loss of catalytic activity. Hot filtration experiments established the absence of leaching, and the heterogeneous nature of the active species was derived from mercury drop experiments

Controlling the Physical Properties of Fe₃O₄-Immobilized Palladium Complexes towards Reusable Catalysts in the Methoxycarbonylation of 1-Hexene

This paper describes the use of immobilized palladium catalysts on Fe3O4 magnetic nanoparticles (MNPs) to afford magnetically separable catalysts in the methoxycarbonylation of 1-hexene. Immobilization of homogeneous complex [Pd(L1)Cl2] (Pd1), where L1 = N,N′E,N,N′E)-N,N′-(3-(3-(triethoxysilyl)propyl)pentane-2,4-diylidene)dianiline, on Fe3O4 MNPs at 100 °C and Pd loading of 10% (based on wt% of Pd1) afforded the corresponding complex [Pd1@Fe3O4] (Pd2) in good yields. The use of calcination temperatures of 150 °C and 200 °C produced compounds Pd3 and Pd4, respectively, while Pd metal loadings (based on wt% of Pd1) of 5% and 15% provided complexes Pd5 and Pd6, respectively. The immobilized compounds were analyzed using FT-IR spectroscopy, SEM-EDX, TEM, ICP-OES, and PXRD techniques. The surface areas and porosity of the materials were determined using nitrogen physisorption measurements and confirmed the formation of mesoporous materials, while SQUID measurements established Ms values in the range of 60.69 to 69.93 emu/g. The immobilized Pd(II) complexes catalyzed the methoxycarbonylation of 1-hexene, yielding mainly linear esters. The immobilized compounds could be recycled up to five times via magnetic separation without significant loss in catalytic activities