Alkylation of [PT2(µ-S)2(PPH3)4] with Boronic Acid Derivatives by Pressurized Sample Infusion Electrospray Ionization Mass Spectrometry (PSI-ESI-MS) Technique.
ABSTRACT
This project work present the alkylating reaction of [Pt2(μ-S)2(PPh3)4] with boronic acid alkylating agents.
The reactivity of the metalloligand [Pt2(μ-S)2(PPh3)4] with the boron-functionalized alkylating agents BrCH2(C6H4) B(OR)2 (R = H or C(CH3)2) was investigated by electrospray ionization mass spectrometry (ESI-MS) in real time using the pressurized sample infusion (PSI).
The macroscopic reaction of [Pt2(μ-S)2(PPh3)4] with one mole equivalent of alkylating agents BrCH2(C6H4)B{OC(CH3)2}2and BrCH2(C6H4)B(OH)2 gave the dinuclear monocationic µ-sulfide thiolate complexes [Pt2(µ-S){µ-SCH2(C6H4)B{OC(CH3)2}2}(PPh3)4]+ and [Pt2(µ-S){µ-S+CH2 (C6H4)B(OH)(O–)}(PPh3)4].
The products were isolated as the [PF6]– salts and zwitterion respectively, and fully characterized by ESI-MS, IR, 1H and 31P NMR spectroscopy and single crystal X-ray structure determinations.
The alkylation reaction of BrCH2(C6H4)B{OC(CH3)2}2 with [Pt2(µ-S)2(PPh3)4 + H]+was determined via kinetic analysis by PSI-ESI-MS to be second order consistent with the expected SN2 mechanism for an alkylation reaction.
The PSI-ESI-MS microscale synthesis showed that[Pt2(µ-S)2(PPh3)4]disappeared rapidly with consequent formation of onlymonoalkylated cationic product, [Pt2(µ-S){µ- SCH2(C6H4)B{OC(CH3)2}2}(PPh3)4]+. This was indicated by the immediate appearance of the monoalkylated product peak at m/z 1720.6.
The reaction came to completion within 6 minutes after injection and no trace of any other product or dialkylated species. The desk top synthesis observed after further stirring for six hours also show the formation of no other product.
The reaction ofBrCH2(C6H4)B(OH)2, with({[Pt2(µ-S)2(PPh3)4] + H}+)within same time interval yielded three monocationic species that were detected by ESI-MS and assignable to the three alkylated products:
[Pt2(µ-S){µ-SCH2C6H5)(PPh3)4]+, m/z 1593.4 from the loss of B(OH)2 moiety; a hemiketal-like species [Pt2(µ-S){µ-SCH2(C6H4)B(OH)(OCH3)}(PPh3)4]+, m/z 1651.5 and [Pt2(µ-S){µ-SCH2(C6H4)OH}(PPh3)4]+, m/z 1609.5. The laboratory scale synthesis indicated the same products.
The masses were identified by comparing the experimental isotope patterns with calculated ones. No peak was observed in the mass spectrum that was attributable to the formation of the expected product [Pt2(µ- S){µ-SCH2(C6H4)B(OH)2}(PPh3)4]+.
The structural determination by X-ray diffraction showed that the compound formed was a zwitter ion (neutral complex) [Pt2(µ-S){µ-S+CH2(C6H4)B(OH)(O–)}(PPh3)4]. [Pt2(µ-S){µ-S+CH2(C6H4)B(OH)(O– )}(PPh3)4] is a neutral species and not detectable in ESI-MS. 1
H NMR spectra showed a complicated set of resonances in the aromatic region due to the terminal triphenylphosphine ligands and were broadly assigned as such.
However, SCH2 hydrogen atoms were easily identified as broad peaks at δ 3.59 ppm and 3.60 ppm for [Pt2(µ-S){µ-SCH2(C6H4)B{OC(CH3)2}2}(PPh3)4]+PF6 and [Pt2(µ-S){µ- S+CH2(C6H4)B(OH)(O–)}(PPh3)4], respectively.
The monoalkylated products shows IR and 31P{1H} NMR spectra expected of the complexes. The OH vibration (3336 cm– 1) in 2.1 shifted to 3435 cm-1 in 2.1a.
The absorption bands of the B-O bond in 2.2 (1355 cm-1) and 2.1 (1350 cm-1) shifted to 1360 cm-1 and 1367 cm-1 in 2.2a·(PF6) and 2.1a respectively. The 31P{1H} NMR spectra showed nearly superimposed central resonances and clearly separated satellite peaks due to 195Pt coupling.
The 1J(PtP) coupling constants showed the differences due to the trans influences of the substituted and the unsubstituted sulfide centers.
The trans influence of the unsubstituted sulfide is greater than the thiolate (substituted) species demonstrated by the coupling constants at (2628 and 3291 Hz) for 2.2a·(PF6) and (2632 and 3272 Hz) 2.1a,respectively.
TABLE OF CONTENTS
Title Page i
Certification ii
Declaration iii
Dedication iv
Acknowledgement v
Abstract vi
Table of Contents viii
List of Tables x
List of Figures xi
List of Abbreviations xiii
CHAPTER ONE
1.0 Introduction 1
1.1 Background of the Study 1
1.2 Statement of Problem 4
1.3 Justification of Study 5
1.4 Aims and Objectives of the Study 6
CHAPTER TWO
2.0 Literature Review 7
2.1 Brief Summary of [Pt2(μ-S)2(PPh3)4] 7
2.2 Electronic and Molecular Features of [Pt2(μ-S)2(PPh3)4] 8
2.3 Protonation of [Pt2(μ-S)2(PPh3)4] 10
2.4 Role of [Pt2(μ-S)2(PPh3)4] as a Metalloligand 11
2.5 Mono-, Homo- and Heterodi Alkylation reactions of [Pt2(μ-S)2(PPh3)4]13
2.6 Effect of Alkylation on {Pt2(μ-S)2} Geometry 18
2.7 Effect of Leaving Group (Halogens) in Alkylation Reactions 20
2.8 Formation of Inter and Intramolecular Bridging Di-Alkylation Reactivity of [Pt2(μ-S)2(PPh3)4] 21
2.9 Spectroscopic Methods For Structural Characterization 25
2.9.1Electrospray Ionisation Mass Spectrometry(ESI-MS) 25
2.9.1.1 Application of ESI-MS in Chemical Analysis 29
2.9.1.2 Electrospray Ionization Mass Spectrometry- An Indispensible Tool for the Preliminary Screening of [Pt2(μ-S)2(PPh3)4] Chemistry 30
CHAPTER THREE
3.0 Experimental 34
3.1 General Reagent Information 34
3.2 General Analytical Information 34
3.3 Synthesis of the Alkylated Derivatives of [Pt2(μ-S)2(PPh3)4] 35
3.3.1 Pre-Synthetic Kinetic Profile of the Reaction of [Pt2(μ-S)2(PPh3)4]
withBrCH2(C6H4)B{OC(CH3)2}2 35
3.3.2 Synthesis of [Pt2(μ-S){μ-CH2(C6H4)B{OC(CH3)2}2} (PPh3)4](PF6), 2.2a·(PF6) 36
3.3.3 Synthesis of [Pt2(μ-S){μ-S+CH2(C6H4)B(OH)(O-)}(PPh3)4] 2.1a 37
CHAPTER FOUR
4.0 Results and Discussion 38
4.1 Synthesis and Spectroscopic Characterization 39
4.2 X-Ray Crystal Structures 46
4.3 X-Ray Structure Determinations of 2.2a·(PF6) and 2.1a 51
4.4 [Pt2(μ-S){μ-SCH2(C6H4)B{OC(CH3)2}2}(PPh3)4](PF6), 2.2a·(PF6) 54
4.5 [Pt2(μ-S){μ-S+CH2(C6H4)B(OH)(O-)}(PPh3)4], 2.1a 55
Conclusions 58
References 59
INTRODUCTION
1.1 Background of Study
The diverse study on platinum and sulfur element has been possible due to their rich individual chemistries. Their compounds have been extensively studied due to their wide range of applications in both biology and industry1. Platinum was first discovered in 1735 by Don Antonio de Ulloa.
It has high melting point and good resistance to corrosion and chemical attack2. Consequence to its resistance to wear and tarnish and its beautiful looks, it is employed in jewellery production3,4.
It is also used in laboratory equipment, electrical contacts, catalytic converters, dentistry equipment, electrodes, antioxidation processes, catalysis, biomedical applications and hard disk4,5,6,7, 8-11. Platinum compounds like cisplatin, carboplatin and oxaliplatin are used in cancer treatments12,13,14.
The use of cisplatin in cancer chemotherapy is limited by ototoxicity, emetogenesis effect, neurotoxicity, and nephrotoxicity of the drug15-18. It has been suggested that the toxicity of the drug is as a result of bonding between platinum and protein sulfur atoms19.
Platinum exists in different oxidation states, 0 to +6, due to its vacant d orbitals. The most common oxidation state is +2 including non-even20 with +1 and +3 found in dinuclear Pt-Pt bonded complexes. These properties make platinum form coordination compounds easily.
REFERENCES
Stiefel E.I and Matsumoto K. (1996), Transition Metal Sulfur Chemistry: Biological and Industrial Significance, J. American Chemical Society, Washington. DC pp 2-38.
Encyclopædia Britannica Online. (2012) Encyclopædia Britannica Inc. Web.
Yang P. J., Halbach V. V., Higashida R. T., and Hieshima G. B., (1988), Platinum Wire: New Transvascular Embolic Agent, Am. J. Neuroradiol.,9, 547-550.
Johnson Matthey (2012) The Platinum Decathlon J. Archive56, 165-176.
Curry S. W., (1957) Platinum Metals Rev, J. Archive1, 38.
Nakano M., Fujita N., Takase M. and Fukunaga H., (2006) Electrodeposited Co-Pt Thin Films with High Coercivity. Elect. Eng. Jpn., 157,7.
Fisher J. M., Potter R. J. and Barnard C. F. J., (2004) Platinum Metals Review., 48,101.