Thumbnail Image

An Investigation of the Multifunctional Alkylation Chemistry of [Pt₂(μ-S)₂(PPh₃)₄]

This thesis presents the studies on the multifunctional alkylation of the metalloligand [Pt₂ (μ-S)₂(PPh₃)₄] 1.1. Multifunctional organic groups which include semicarbazone and thiosemicarbazone, urea, isocyanate, guanidine, ketones and amides react with 1.1 to generate the corresponding functionalised derivatives containing thiolate ligands produced by alkylation of one or both sulfide centres. Polymers with suitable electrophilic branches also react to immobilise 1.1. By using Electrospray Ionisation Mass Spectrometry (ESI-MS) as the monitoring technique, [Pt₂ (μ-S)₂(PPh₃)₄] was employed as a productive template for structurally and chemically diverse thiolate-platinum complexes. Before this study, 1.1 was known to be one of the best building blocks for multimetallic molecules through the exceptional ligating ability of the two sulfide centres to virtually any transition and main group metal fragment. However, extension of the synthetic versatility of 1.1 to multifunctional non-metallic positive centres has only been explored to a lesser extent and thus far less developed. This thesis is organised into five chapters. Chapter one is the review of literature on [Pt₂ (μ-S)₂(PPh₃)₄] and the development of its chemistry from an efficacious metalloligand for multimetallic assembly to a powerful nucleophile for organic electrophiles. The main geometry and electronic features of 1.1 and analogous complexes were highlighted especially as it affects the dihedral angle (θ) between the two Pt₂S₂ planes in [Pt₂ (μ-S)₂(PPh₃)₄]. The variable reaction modes of 1.1 with different electrophiles were discussed especially as it may affect the less studied multifunctional alkylation. The effectiveness of the ESI-MS as a monitoring tool in the study of 1.1 chemistry is also discussed. Chapter two details the study of the multifunctional monoalkylation reactions of the aforementioned array of multifunctional organic groups with [Pt₂ (μ-S)₂(PPh₃)₄]. Alkylation reaction of 1.1 with organo-halide of the type R–CH₂-X and R–CH₂CH₂-X (R= organic group and X = Cl or Br) formed thiolate-bridged platinum complexes. The main discovery in this study is that any suitable organic functionality can be incorporated into an electrophile for 1.1. By using the ESI-MS monitoring technique, they successfully reacted with 1.1 to give novel monoalkylated platinum complexes with μ-thiolate ligands of the type [Pt₂(μ-S){μ-SR}(PPh₃)₄](PF₆) which included [Pt₂(μ-S){μ-SCH₂C(=NNHC(O)NH₂)R} (PPh₃)₄](PF₆) in 2.1b•PF₆ (R = Ph) and 2.2b•PF₆ (R = CH₃) and [Pt₂(μ-S){μ-SR}(PPh₃)₄](PF₆) (R = -CH₂C(=NOH)Ph 2.3b•PF₆, -CH₂C(=NNHC(NH₂)NH₂) Ph 2.4b•(PF₆)₂, -CH₂C(=NNHC(S)NH₂)CH₂ 2.5b•PF₆, -CH₂CH₂NHC(O)NHPy 2.6b•PF₆ (Py = o-C₅H₄N), -CH₂CH₂NHC(O)N(CH₂CH₂)₂S 2.7b•PF₆ and -CH₂ C(O)NHC(O)NHCH₂CH₃ 2.8b•PF₆. -CH₂C(═NNHTs)Ph 2.9b•PF₆, -CH₂C(═N NHTs)CH₃ 2.10b•PF₆ (Ts = -SO₂C₆H₄CH₃), -CH₂C(=NHNC(O) Py)Ph (Py = o-C₅H₄N) 2.11b•PF₆ and -CH₂C(=NNHC(O)NH₂)C₆H₄C₆H₅ 2.12b•PF₆. Geome- trical isomers formed with BrCH₂C(NNHAr)C₆H₄Ph 2.13a (Ar = 2,4-dinitrophenyl) was studied and characterised with 2D NMR techniques. The X-ray crystal structures of 2.1b•PF₆, 2.4b•(PF₆)₂, 2.7b•PF₆ and 2.8b•PF₆ are also reported. Chapter three reports an investigation of conditions that encourage the formation of homo- and heterodialkylated thiolate complexes of the type [Pt₂(μ-SR)₂(PPh₃)4]² + and [Pt₂(μ-SR){μ-SR'}(PPh₃)₄]²+ since these are currently not well understood. The factors were employed in the selective choice of alkylating agents used in the sequential syntheses of homodialkylated derivatives [Pt₂(μ-SCH₂COPh)₂(PPh₃)₄](PF₆)2 3.1b•(PF₆)₂, [Pt₂(μ-SCH₂C(O)pyr)₂(PPh₃)₄](PF₆)₂ (pyr = pyrene) 3.2b•(PF₆)₂ and [Pt₂(μ-SCH₂C(O)cyl)₂(PPh₃)₄](PF₆)₂ (cyl = coumaryl) (3.4b•(PF₆)₂. A major outcome of this study is the successful syntheses of the heterodialkylated derivatives [Pt₂(μ-SCH₂C(O)Ph)(μ-SBu)(PPh₃)₄](PF₆)₂ 3.5b•(PF₆)₂ and {Pt₂(μ-SCH₂COPh)(μ-SCH₂CH₃)(PPh₃)₄}(PF₆)₂ 3.6b•(PF₆)₂ through a sequential alkylation with organo-halide electrophiles. The X-ray crystal structures of 3.1b•(PF₆)₂ and 3.5b•(BPh₄)₂ are reported. The secondary products resulting from the displacement of a PPh₃ by Br- in the synthesis of the heterodialkylated derivatives 3.5b•(PF₆)₂ and 3.6b•(PF₆)₂, [Pt₂(μ-SCH₂C(O)Ph) (μ-SBu)(PPh₃)₃Br](PF₆) 3.5c•PF₆ and [Pt₂(μ-SCH₂COPh)(μ-SCH₂CH₃)(PPh₃)₃ Br](PF₆) 3.6c•PF₆ were also isolated and characterised by ESI-MS and X-ray crystallography. Chapter four describes the multifunctional intra- and intermolecular bridging dialkylation of 1.1. The variable alkylation mode of α,ω-dialkylating electrophiles, which is dependent on the nature and the number of spacer atoms, was investigated with functionalised electrophiles, ClCH₂C(O)CH₂Cl 4.1a, ClCH₂C(NNHC(O)NH₂) CH₂Cl 4.2a and ClCH₂C(O)NHNHC(O)CH₂Cl 4.3a. A very important novel result is the stabilisation and isolation of an intramolecular bridged five-membered ring derivative 4.1b•PF₆ [Pt₂{μ-SCH₂C(O)CHS}(PPh₃)₄] (PF₆). The reaction of 4.1a with 1.1 in the presence of dilute aqueous NaOH aided the isolation of 4.1b•PF₆ resulting from intramolecular rearrangement of the four membered ring. The semicarbazone derivative 4.2a and diamide 4.3a dialkylated 1.1 by bridging the two sulfide centres to form stable [Pt₂{μ-SCH₂C(NNHC (O)NH₂)CH₂S-μ}(PPh₃)₄](BPh₄)₂ 4.2b•(BPh₄)₂ and Pt₂{μ-SCH₂C(O)NHNH(O) CH₂S}(PPh₃)₄(PF₆)₂ 4.3b•(PF₆)₂. Both 4.1b•PF₆ and 4.2b•(BPh₄)₂ were characterised by X-ray crystallography. The syntheses and X-ray crystal structure analysis of Pt₄ aggregates formed with amide α,ω-dialkylating agents with longer spacer atoms, o- and p-ClCH₂C(O)NHC₆H₄NHC(O)CH₂Cl through the intermolecular linking of two [Pt₂(μ-S)₂(PPh₃)₄] complexes is also reported. Chapter five is the investigation of the immobilisation of [Pt₂(μ-S)₂ (PPh₃)₄] on electrophilic polymer supports. Following the reactivity of [Pt₂(μ-S)₂(PPh₃)₃] with electrophiles established in chapter two a monomeric electrophilic unit 3-chloropropyltetraethoxysilane 5.1a reacted 1.1 to give 5.1b.BPh₄. Further investigations to immobilised 1.1 on solid polymer supports through the alkylation of one of the sulfide centres with electrophilic polymers, Merrifield’s resin 5.2a, 3-bromopropylpolysiloxane 5.3a 3-chloropropyl silica 5.4a and 3-chloropropyl controlled pore glass 5.5a were done. This gave the corresponding immobilised products which is generally represented as [Pt₂(μ-S)(μ-SCH₂R--P )(PPh₃)₄] (where R = phenyl or -CH₂CH₂- groups). The immobilisation of 1.1 was also achieved through phosphine exchange reactions on polymers, a polyethertriamine phosphine derivative 5.6a and diphenylphosphine polystyrene 5.8a. The products were characterised by Scanning Electron Microscopy, solid state ³¹P{H} (CP MAS) NMR, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and X-ray Photoelectron Spectroscopy (XPS).
Type of thesis
Ujam, O. T. (2011). An Investigation of the Multifunctional Alkylation Chemistry of [Pt₂(μ-S)₂(PPh₃)₄] (Thesis, Doctor of Philosophy (PhD)). University of Waikato, Hamilton, New Zealand. Retrieved from https://hdl.handle.net/10289/5888
University of Waikato
All items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.