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Synthesis of gold and palladium thiolato complexes and their applications as sulfur dioxide sensors

- Dyan, Busiswa

  • Authors: Dyan, Busiswa
  • Date: 2010-03-10T06:26:59Z
  • Subjects: Gold compounds synthesis , Palladium compounds synthesis , Thiols , Ligands , Sulfur dioxide
  • Type: Thesis
  • Identifier: uj:6666 , http://hdl.handle.net/10210/3071
  • Description: M.Sc. , [AuCl(PPh3)] was reacted with mixed thiols in the presence of silver(I) oxide, resulting in complexes of the type [Au(SC6H4X)(PPh3)] X= Cl, NH2,CH2, forming silver chloride as a by-product. In addition to the above series [Au(SCH2(C6H4)3(2-C6H5(C6H4N)] was prepared via a different route, where [AuCl3(2-C6H5(C6H4N)] was reacted with benzyl mercaptan under reflux in the presence of silver(I) oxide for 3 h, forming silver chloride as a by-product. Palladium complex [PdCl2(2-C6H5(C6H4N)] was prepared by reacting [PdCl2(MeCN)] with 2-phenylpyridine at room temperature for 2 h. All complexes were characterized by 1H, 13C, 31P{H} NMR, IR, mass spectrometry and elemental analysis. Characterization of the starting materials [AuCl3(2-C6H5(C6H4N)] and [PdCl2(2- C6H5(6H4N)] by single crystal X-ray diffraction confirmed their chemical formula. All complexes were reacted with sulfur dioxide (SO2) and the reactions were monitored by electrochemistry and UV-vis spectroscopy. The electrochemical study of the complexes, using cyclic voltammetry (CV) and Osteryoung square wave voltammetry (OSWV), showed one anodic peak, which is due to gold(I/III) and an unresolved peak due to thiolate ligand. Upon bubbling of SO2 to the complexes, there was an immediate change of colour from clear to yellow, the CV results showing an increase in current of the gold(I/III) peak. UV-vis spectroscopy studies showed a shift of peak form 250-286 nm, upon bubbling of SO2 to complexes.
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(Acetylacetonato-k2O,O0)carbonyl- {dicyclohexyl[4-(dimethylamino)phenyl]- phosphane-kP}rhodium(I)

- Davis, Wade L., Meijboom, Reinout

Di-μ-iodido-bis{[dicyclohexyl(phenyl)-phosphine-κP](pyridine-κN)silver(I)}

- Omondi, Bernard, Meijboom, Reinout

Rhodium(I) Vaska-type phosphite complexes as model homogeneous catalysts.

- Kirsten, Leo

(Pyrazolylpyridine)- iron, cobalt and nickel complexes as carbon-carbon bond formation catalysts

- Benade, Letitia Lynne

  • Authors: Benade, Letitia Lynne
  • Date: 2011-05-16T08:09:39Z
  • Subjects: Organometallic compounds synthesis , Iron catalysts , Cobalt catalysts , Nickel catalysts , Ligands , Pyridine , Pyrazoles
  • Type: Thesis
  • Identifier: uj:7080 , http://hdl.handle.net/10210/3642
  • Description: M.Sc. , 2-(Pyrazol-1-ylmethyl)pyridine ligands were synthesised by phase transfer alkylation of 2-picolyl hydrochloride with the appropriate pyrazole. These ligands were subsequently reacted with NiCl2, NiBr2, FeCl2 or CoCl2 to form the respective complexes. The substituents on the pyrazole included phenyl and tert-butyl groups as well as electron withdrawing CF3 groups. The substituents played an important role in the steric and electrophilic nature of the metals. A second ligand design is 2,6-bis(pyrazol-1-ylmethyl)pyridine and were prepared by phase transfer alkylation of 2,6-bis(chloromethyl)pyridine with two mole equivalents of the appropriate pyrazole. These ligands were reacted with NiCl2, NiBr2, FeCl2 or CoCl2 to form the respective complexes. A third ligand design is 2-(chloromethyl)- or 2-(bromomethyl)-6-(pyrazol-1-ylmethyl)pyridine and were prepared by the selective alkylation of 2,6-bis(chloromethyl)pyridine with one mole equivalent of the appropriate pyrazole. These ligands were also reacted with NiCl2, NiBr2, FeCl2 or CoCl2 to form the respective complexes. Characterisation of all compounds was done by a range of spectroscopic techniques as well as X-ray crystallography and elemental analysis. The data showed good fit to the proposed structures and in a few cases were confirmed by X-Ray crystallography. All complexes were tested as catalysts for ethylene and higher olefin oligomerisation and showed good activity. The production of alkenes were confirmed in toluene and hexane, however, due to the use of EtAlCl2 and toluene the oligomers were alkylated to form the Friedel-Crafts alkylation products. Similar alkylation was observed for the higher olefin reactions. In comparison, the same reactions in hexane resulted in only C4, C6 and C8 oligomers. When higher olefin reactions were also conducted in hexane, polymeric solids were observed.
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trans-Dichloridobis[tris(2-methoxyphenyl) phosphine]palladium(II)

- Van Blerk, Charmaine, Holzapfel, Cedric W.

trans-Dichloridobis[tris(4-methoxyphenyl) phosphine]palladium(II) benzene monosolvate

- Van Blerk, Charmaine, Holzapfel, Cedric W.

A structural study of palladium complexes containing hemilabile ligands

- Thompson, Catharine

  • Authors: Thompson, Catharine
  • Date: 2012-09-06
  • Subjects: Palladium compounds , Chemical reactions , Ligands , Catalysis , Catalysts
  • Type: Thesis
  • Identifier: uj:9678 , http://hdl.handle.net/10210/7092
  • Description: D.Phil. , Palladium chemistry has advanced dramatically in the last few years, with a huge number of wide-ranging studies, particularly with respect to the application of palladium complexes as catalysts, having been performed. The discovery of the phenomenon of hemilability (the ability of a ligand to be bidentately coordinated but with one donor atom more weakly bound and thus able to decoordinate in the presence of a catalytic substrate) has further assisted the growth, since it has allowed a greater understanding of the mechanisms of catalytic-reactions. However, the focus of much of this work has been on ligands containing phosphorus and oxygen as potential donor atoms, with little attention being turned to ligands with other donor atoms. The current study concentrates on a series of palladium complexes containing potentially hemilabile thioether, selenoether and telluroether carboxylate ligands with the oxygen as the strongly coordinating atom. Each complex was completed by the palladium coordinating to a phenyl ligand trans to the oxygen of the hemilabile ligand and either one or two triphenylphosphine ligands, depending on whether or not the -hemilabile ligand was monodentately or bidentately coordinated. These complexes are of interest as possible catalysts for the oligomerisation of ethene, and had been previously synthesised and characterised by NMR spectroscopy, mass spectrometry and catalytic studies. In the current work the crystal and molecular structures of the various complexes were determined. Since a number of pairs of complexes containing the monodentate and bidentate forms of the ligands were identified the hemilability of the ligands was confirmed.
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Pentacarbonyl-2ĸ⁵C-chlorido-1ĸCl-bis[1(ɳ⁵)-cyclopentadienyl](µ-1-oxidoethylene-1:2ĸ²O:C)chromium(0)-zirconium(IV)

- Esterhuysen, Catharine, Retief, Lizette, Kruger, Gert J., Cronje, Stephanie, Raubenheimer, Helgard G.

Die sintese van groep-VI-oorgangselementkomplekse met nuwe S-, P- en N- bevattende ligande

- Viljoen, Hendrik Willem

Cymene ruthenium N^N and N^N^N cationic species as potential anti-malaria and anti-cancer agents

- Khumalo, Nozipho Magava

Functionalised porphyrazines and their use in catalysis

- Tshivhase, Mmboneni Gifty

  • Authors: Tshivhase, Mmboneni Gifty
  • Date: 2012-08-16
  • Subjects: Catalysis , Porphyrins , Phthalocyanines , Palladium compounds , Heck reaction , Imidazoles , Ligands
  • Type: Thesis
  • Identifier: http://ujcontent.uj.ac.za8080/10210/367536 , uj:2573 , http://hdl.handle.net/10210/6024
  • Description: D.Phil. , Porphyrazines like porphyrins and phthalocyanines have unique physical, chemical and spectral properties. This allows them to have many impressive applications. They are less studied than phthalocyanines because of the absence of convenient methods for their synthesis. However, recent studies, including this one, have made these compounds more accessible. The palladium-imidazolium salt systems have proved to be one of the most successful catalysts for the Heck and Suzuki coupling reactions. Substituents on nitrogen atoms of imidazolium significantly influence the catalytic activities of the corresponding palladiumimidazolium salt systems in the Heck and Suzuki coupling. The synthesis of the imidazolium salts is discussed in this study. The synthesis of the imidazoles started from diamines. A new route for the synthesis of 4,5-diaminophthalonitrile is discussed here and so far it is the most convenient and less tedious route with higher yields. The catalytic activities on different substrates have also been extensively investigated and gave impressive results, on the Heck and Suzuki reaction. The catalysis study was first performed using the dicyanoimidazolium salts and then with the imidazolium salts of the porphyrazines. The results indicate that both these systems are active ligands for Suzuki and Heck reactions. Two complexes, [1’,1’’-dibutyl-3’,3’’-(4,5-(1,2-dicyanobenzene))diimidazolium dibromide] and [2,3-benzo(2’,3’-(3’’,3’’’-dibutyldiimidazolium-2’,2’’-diylidene)palladium(II)- dibromide)-7,8,12,13,17,18-hexapropyl,porphyrazine] were synthesised successfully in good yields and used for Suzuki and Heck catalysis reactions. Catalyst recovery in homogeneous catalysis is always a major problem; this led this study to make use of porphyrazines in biphasic catalysis because of their high extinction coefficient which comes from their very intense colour. The reactions were performed in a combination of water with toluene and also water with ionic liquid. Both this systems gave results which proved that it is possible to separate the catalyst and the products once the reaction is complete. Two aminoporphyrazines and phthalonitriles were also synthesised in multistep synthesis. The synthesis involved a lot of protection and deprotection steps. These compounds are starting materials to aminophosphine ligands which have a wide variety of catalysis applications.
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Carbonyl(triphenylarsine)(tropolonato)rhodium(I)

- Steyl, Gideon, Roodt, Andreas

DoM chemistry and phosphines: synthesis and catalystic aspects

- Mokhadinyana, Molise Stephen

  • Authors: Mokhadinyana, Molise Stephen
  • Date: 2008-06-11T06:31:34Z
  • Subjects: Phosphine , Ligands , Catalysis , Organometallic compounds' synthesis
  • Type: Thesis
  • Identifier: uj:2601 , http://hdl.handle.net/10210/604
  • Description: The main objective of the research described in this dissertation was the preparation of a range of bulky and electron-rich phosphine ligands using the DoM methodology developed in our labs for this purpose. These ligands would be employed in the Suzuki cross-coupling reaction of deactivated aryl bromides and aryl chlorides. Initially, a range of phosphinic amides was synthesised and tested for DoM reactivity. TMSCl, MeI and O2 were successfully used as electrophiles, incorporating TMS, Me and OH groups in the ortho-position of these phosphinic amide systems. This development was encouraging and provided a route to incorporate a phosphine on the ortho-position of these phosphinic amide systems by using Ph2PCl and Cy2PCl as electrophiles to incorporate Ph2P and Cy2P, respectively. The route was versatile and a range of electrophiles was used to prepare phosphine ligands with varying electronic and steric properties. These electrophiles (of the R2PCl variety) were often specifically prepared from PCl3 and the corresponding Grignard reagent. Phosphine ligands synthesised in this research project using our DoM (directed ortho metallation) methodology were tested in Suzuki cross-coupling reactions of deactivated aryl bromides and some aryl chlorides and showed excellent reactivity, with the advantage that the ligands of this study are oxidatively and hydrolytically stable. Efforts were also made to modifying the phosphinic amide-functionalised phosphine ligands to generate their water-soluble derivatives. One way of achieving this was by the hydrolysis of the phosphinic amide moiety to the phosphinic acid analogue. Salts of these phosphinic acid derivatives have promising activities as water-soluble substrates. This route was successful only iii with less electron-rich systems providing an opening for more research in this regard. In an alternative synthetic route to polar water-soluble phosphines it was envisioned that phosphonate-derivatised phosphines would offer access to water-soluble phosphine ligands by using milder hydrolysis conditions. These phosphonate systems were also tested for DoM reactivity and showed promising reactivity. Phosphonates have not previously being employed as DoM groups, and this alone expands the application and potential scope of P-based DoM groups. , Prof. D.B.G. Williams
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The influence of ligands and co-catalysts on selected catalytic transformations

- Bredenkamp, Tyler

  • Authors: Bredenkamp, Tyler
  • Date: 2011-11-21
  • Subjects: Ligands , Catalysis , Phosphine , Organometallic compounds
  • Type: Thesis
  • Identifier: uj:1718 , http://hdl.handle.net/10210/4060
  • Description: M.Sc. , There were two main objectives of the research presented m this dissertation. Firstly, the synthesis of bulky electron withdrawing phosphine-alkene ligands for classic ligand testing in the Suzuki cross-coupling reaction was performed. Previously, a range of electron deficient phosphine-alkenes was prepared from 2- ( diphenylphosphino )benzaldehyde, using both Wittig and Knoevenagel chemistry. These were tested for catalysis and gave high yields for the Suzuki reaction. In the present instance, 2-( di-otolylphosphino) benzaldehyde was synthesised making use of Grignard technology from acetyl protected 2-bromobenzaldehyde and chloro(di-o-tolyl)phosphine (itself prepared from PCh. And the appropriate o-tolyl Grignard reagent. This material served as a building block for the generation of P-alkene ligands which were synthesised making use of Wittig, Knoevenagel and transesterification chemistry. These o-tolyl analogues of the P-alkene ligands prepared in the previous study were used in ligand testing experiments in the Pd-catalysed Suzuki cross-coupling reaction. The results of the catalysis showed an enhanced activity with these ligands over the previous cases The second part of this dissertation involved determining the role (influence on activity) of the non coordinating counterion in the catalyst system in the methoxycarbonylation reaction. To this end discrete Pd complexes were synthesised and used directly in the methoxycarbonylation reaction. There have been a few reports on the role of the non-coordinating counterions of the catalyst systems in the methoxycarbonylation reaction. The catalyst is typically a palladium compound in the presence of a Bmnsted acid co-catalyst. Changes to the Bmnsted co-catalyst cause two variables to change, namely the acidity of the acid and the nature of the counterion that the acid provides. The work presented in this dissertation shows the results of only one variable being changed (that of the counterion) and as such allowed the specific role of the counterion in the outcome of the reaction to be determined. Previous work done in our laboratories made use of the Lewis acid Al(OTf)3 to co-catalyse the methoxycarbonylation reaction with rates and high yields being observed. In the present instance discrete Pd complexes were synthesised from Pd(OAc)2 using p-TsOH, MsOH and TfOH as the acids containing the weakly coordinating counterions. These Bnmsted acids have the ability to displace the OAc- anion from the Pd and as such formed the discrete L2PdX2complexes (L = PPh3; X = Mso-, p-Tso-, TfO} Synthesis of these discrete complexes was impeded by a lack of knowledge of the specific conditions under which to prepare the complexes and many avenues were pursued before successful isolation of these complexes was achieved. These discrete catalysts were used in the methoxycarbonylation reaction co-catalysed by Al(OT£)3. Here, the Al(OTt)3 forms the basis of a constant acid cocatalyst allowing only the counterion to be changed with the view to determining its role in these reactions. It was found that the counterion appears to play no role at all (Aco-, p-Tso-, Mso-, TfO-) in the outcomes of these reactions under the conditions employed. A comparative study is also detailed herewithin of the effects of both ex situ and in situ catalyst generation on the activity in the methoxycarbonylation reaction, which provides some insightful results.
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Bifunctional phosphines : synthesis and evaluation in catalysis

- Shaw, Megan Lorraine

  • Authors: Shaw, Megan Lorraine
  • Date: 2012-09-10
  • Subjects: Phosphorus compounds - Synthesis , Catalysis , Ligands , Transition metal catalysts
  • Type: Thesis
  • Identifier: uj:9860 , http://hdl.handle.net/10210/7261
  • Description: M.Sc. , This study focused on the synthesis and evaluation of phosphine ligands with multiple functional ities. Polar ligands suitable for use in homogeneous catalysis in aqueous/organic systems were synthesised, as were ligands incorporating a boron atom in an intramolecular Lewis acid-Lewis base interaction with the phosphorus atom. A malonate moiety was readily incorporated into a phosphorus starting material, and derivatives were obtained by reduction of the ester groups. The polar diol products were reacted with 1,4-butanesultone which made them water soluble and thus ideal for biphasic catalysis. Wittig chemistry was employed to introduce alkenes of varying electronic nature into a phosphorus-containing aldehyde starting material. The catalysed hydroboration reaction making use of diboron reagents was used to introduce a boron functionality into the resulting a, n-unsaturated ester phosphine I igands. All of the ligands produced were tested in transition metal-catalysed reactions, namely the Heck reaction, the Suzuki reaction, the Stille reaction, the carboxymethylation reaction and the hydroformylation reaction. The polar and water soluble ligands all showed comparable or improved yields to the standard benchmark triphenylphosphine ligand in organic, biphasic and ionic liquid media. The electronic nature of the alkene ligands largely dictated the activities observed in the Heck, Suzuki and Stille reactions. The electron rich ligands showed improved activities in the Heck reaction, while the electron poor ligands showed improved activities in the Suzuki reaction. In contrast, the Stille reaction seemed to be more affected by the steric demands of the ligands rather than by electronic considerations. It was also found that the boron containing ligands showed an enhanced activity in comparison to the boron free unsaturated and saturated ester ligands. This enhancement was directly ascribable to the Lewis acidic boron atom. This study allowed the synthesis of a range of functionally varying phosphine ligands which where shown to influence transition metal-catalysed reactions based specifically on the functionality present.
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Trans-Bis[bis(2-methoxyphenyl)phenylphosphine- κP]dichloridopalladium(II)

- Van Blerk, Charmaine, Holzapfel, Cedric W.

Divalent iron, cobalt, nickel and palladium complexes of 1H-pyrazol-1-yl-imine and 1H-pyrazol-1-yl-ethanol ligands: coordination chemistry and evaluation as ethylene oligomerization catalysts

- Ainooson, Michael Kojo

  • Authors: Ainooson, Michael Kojo
  • Date: 2011-05-16T08:07:20Z
  • Subjects: Ligands , Ethylene , Catalysts , Coordination compounds synthesis , Transition metals synthesis
  • Type: Thesis
  • Identifier: uj:7079 , http://hdl.handle.net/10210/3641
  • Description: M.Sc. , This dissertation deals with the syntheses of tridentate (O^N^N) coordination ligands [{2,4-di-tert-butyl-6-[(2-(3,5-RR-pyrazol-1-yl-ethylimino)-methyl] phenol}, R = H (L1), Me(L2), Ph(L3), t-Bu(L4)], which was reacted initially with MX2 (M = Fe, Co, Ni; X = Cl, Br). The ligands L1-L4 were also modified by functionalizing the phenol group in this ligand group to an ethoxy in L5 and L6 (L5 = [(3,5-di-tert-butyl-2-ethoxy-benzylidene)-[2-(3,5-dimethyl-pyrazol-1-yl)-ethyl]-amine, L6 = [(3,5-di-tert-butyl-2-ethoxy-benzylidene)-[2-(3,5-di-tert-butyl-pyrazol-1-yl)-ethyl]-amine)], or into a phenoxy in L7 (L7 = (3,5-di-tert-butyl-2-phenoxy-benzylidene-(2-pyrazol-1-yl-ethyl)-amine)). Another ligand L8 (L8 = [4-(4-tert-butyl-benzylidene)-[2-(3,5-dimethyl-pyrazol-1-yl)-ethyl]-amine], which was devoid of the phenoxy group was also synthesized. These modified ligands were also reacted with MX2 or PdCl(COD)Me to form bidentate (N^N) chelating complexes. Further modification of the ligand L1-L4, to replace the phenoxy pyrazolylimine unit with a source of oxygen donor other than a phenoxy led to the use of already known ligands L9, L10 (L9 = 2-(3,5-dimethyl-pyrazol-1-yl)-ethanol, L10 = 2-(3,5-di-tert-butyl-pyrazol-1yl)-ethanol and L11, where in L11, the alcohol moiety is replaced by an electron withdrawing chloro group, L11 = 1-(2-chloroethyl)-3,5-di-methyl-pyrazole). These ligands were also reacted with MX2 (M = Fe, Co, Ni, Pd; X = Cl, Br) to form complexes. The synthesized complexes were characterized by a combination of IR and NMR spectroscopy, mass spectrometry, microanalysis and in selected cases single crystal X-ray crystallography.
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Ligand synthesis and Pd-catalysed C-C bond-forming reactions

- Hughes, Tanya

  • Authors: Hughes, Tanya
  • Date: 2012-08-17
  • Subjects: Ligands , Catalysis , Catalysts - Synthesis , Phosphine
  • Type: Thesis
  • Identifier: uj:2667 , http://hdl.handle.net/10210/6110
  • Description: Ph.D. , The focus of this study was placed on developing stable recyclable catalyst systems that are both active and selective in Pd-catalysed reactions such as the Suzuki-Miyaura cross-coupling reaction, and the methoxycarbonylation reaction. The aim was therefore to prepare ligands with improved efficiencies as catalyst precursors, which are stable towards oxidation and/or hydrolysis, that are soluble in aqueous media and that can be recycled a number of times without significant loss in activity. This study initially focused on the preparation of functionalised phosphine ligands to be loaded onto the peripheries of different generations of PAMAM and PPI dendrimers. These functionalised ligands were then to be used in the Pd catalysed Suzuki-Miyaura cross-coupling of phenylboronic acid and aryl halides, as well as the Pd catalysed carbonylation of phenylacetylene. It was thought that loading of these ligands onto the dendrimers would result in a soluble support for subsequent catalyst systems to allow catalyst recycling. This would then potentially bridge the gap between heterogeneous and homogeneous catalysis. There has been a lot of progress made over the last decade or so in the preparation and use of dendritic phosphines and the positive effects seen are summarised in the first chapter. Water-soluble and thus environmentally friendly ligands have also gained widespread interest as these ligands offer economical and environmental advantages for many reactions. One of the aims of this study was therefore to prepare ligands that show greater solubility in aqueous solvents that can be successfully recycled and that show retention of activity upon reuse. Initially covalent loading of the prepared phosphine ligands onto the peripheries of the dendrimers were attempted. However based on all the problems experienced with the covalent bonding, as discussed in Chapter 2 of this document, a simple acid base titration allowed loading of the prepared phosphine ligands onto the peripheries of the dendrimers via electrostatic interactions, to afford a stable phosphine ligand-dendrimer salt. Electrostatic interactions contribute much more to the solubility enhancement of poorly soluble compounds, thus the formation of the non-covalent phosphine-dendrimer salts was expected to result in greater potential for catalysis in biphasic systems as well as catalyst recycling. Only low generation dendrimers were utilised as previous reports indicated that an increase of the dendrimer generation leads to observation of negative dendritic effects due to the increased bulk that inhibits the approach of the catalytic metal centre.
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Steric and electronic effects of phosphine and phosphite ligands in vaska-type complexes of rodium

- Muller, Alfred Johannes

  • Authors: Muller, Alfred Johannes
  • Date: 2008-10-14T11:38:32Z
  • Subjects: Phosphine , Organometallic compounds synthesis , Rhodium , Ligands , Crystallization , Complex compounds
  • Type: Thesis
  • Identifier: uj:12255 , http://hdl.handle.net/10210/1201
  • Description: Ph.D. , In order for any new useful complexes to be developed, whether of catalytic, biological or of other importance, it is very important that sufficient knowledge exists regarding the fundamental principles applying to the chemistry involved. In all chemical processes involving metal complexes, the coordinated ligands govern the reactions to a great extent. It is thus very important that the properties (solubility, reactivity, steric bulk, etc.) of various ligands of these complexes is clearly understood in order to enable intelligent adjustments to be made, inducing the effects of choice. In most catalytic cycles, basic chemical reactions like substitution, addition, oxidative addition and reductive elimination are of importance. Some of the methods used to quantify ligand properties include single crystal X-ray studies as well as investigating various reactions on model square planar complexes. Several problems are normally associated with this type of investigation and are summarized below along with the aims of this study to improve upon this. (i) Very often the Vaska type compounds crystallise on an inversion centre as is shown in a generalized structure in Figure 1.1. This creates several problems ranging from less accurate bond distances/angles to problematic refinement of single crystal data. As the disorder is ruled by symmetry, the occupancies of the disordered atoms are 50%. The example shown in Figure 1.1 is also a fortunate case where the disordered atoms do not have the same positions, making refinement of the data easier, but there are examples27 such as [Pt(Me)Cl(PCy3)2] where the disordered moieties (Me- and Cl-) occupy virtually the same positions. In examples such as these restraints have to be applied, i.e. fixing bond distances to average distances from literature. The important parameter of the ligand trans effect is then meaningless and cannot be reliably compared to data from solution studies. , Prof. A. Roodt
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