Synthesis of Metal-Containing Phosphines and Their Use in Coordination, Polymer, and Materials Chemistry

This thesis describes the investigation of a novel strategy for the synthesis of metal-containing small molecules, polymers, and nanomaterials. In this context, a new family of air-stable, homo- and heterometallic primary, secondary, and tertiary phosphines were prepared via the radical-initiated hydrophosphination reaction of PH3 with vinylferrocene and/or vinylruthenocene. The full characterization of the phosphines confirmed their targeted structures and proved that the properties of the starting metallocenes are reflected in those of the resulting phosphines. To study the coordination behavior of this family of phosphines, primary, secondary, and tertiary ethylferrocene phosphines were reacted with Group 6 metal carbonyl adducts [M(CO)5•THF; where M: Cr, Mo, and W] to generate the corresponding metal complexes. The successful coordination of all three phosphines to M(CO)5 and their purity were confirmed by several characterization methods, such as multinuclear NMR, FT-IR, and UV-vis absorption spectroscopy, cyclic voltammetry (CV), and elemental analysis. FT-IR spectroscopy studies revealed that ethylferrocene substituents act as electron-donating groups and that the σ donating ability of the phosphines were lower than that of PEt3 and higher than that of PPh3. To realize highly metallized polymers, two phosphorous-containing frameworks were targeted: quaternary phosphonium polyelectrolytes and tertiary phosphine polymers. The first iron-containing phosphonium monomer was synthesized by the quaternization reaction of tertiary ethylferrocene phosphine with 3-chloro-1-propanol followed by an esterification reaction with methacryloyl chloride and a salt metathesis reaction with NaOTf. In addition, four styrenic phosphonium monomers were synthesized by the quaternization reaction of 4-vinylbenzyl chloride with the tertiary ethylmetallocene phosphines (where Fe/Ru: 3/0, 2/1, 1/2, 0/3) before their counter-anion was exchanged with triflate. All five monomers were polymerized in the presence of azobisisobutyronitrile (AIBN) and carefully purified. Analysis of the polymers with methods including differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and gel permeation chromatography (GPC) confirmed their macromolecular nature. The pyrolysis of thin films of the phosphonium polymers, under an inert atmosphere, afforded highly metallized crystalline nanomaterials that were characterized with techniques such as scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). Finally, the hydrophosphination reaction of 3-buten-1-ol with a secondary ferrocene- and ruthenocene-containing phosphine followed by a N,N\u27-dicyclohexylcarbodiimide (DCC) coupling reaction with 4-vinyl benzoic acid afforded a tertiary phosphine monomer which was polymerized, in the presence of AIBN, and yielded a heterobimetallic tertiary phosphine polymer. The phosphine polymer was reacted with photogenerated W(CO)5•THF to produce the first example of a heterotrimetallic polymer. The proposed structure of the resulting polymers and their purity were confirmed by methods such as multinuclear NMR, FT-IR, and UV-vis absorption spectroscopy, CV, DSC, TGA, and GPC. The complete coordination of all phosphorous centres in the tertiary phosphine polymer to W(CO)5 was confirmed by 31P NMR spectroscopy and FT-IR studies, where the coordinated-tertiary phosphine polymer gave rise to three diagnostic absorption bands due to CO stretching modes from W(CO)5 moieties

Design, Synthesis, and Characterization of a Phosphine-based Heterotrimetallic (M = Fe, Ru, W) Homopolymer

An organometallic homopolymer containing three different metals per repeating unit was synthesized from an air- and moisture-stable secondary phosphine bearing ethylferrocene and ethylruthenocene groups. Hydrophosphination yielded a tertiary phosphine bearing an alcohol, which was then used to introduce a polymerizable styrene group via DCC coupling. Free-radical polymerization, followed by post-polymerization coordination to photogenerated W(CO)5 units yielded the title polymer, which showed thermal, spectroscopic, and electrochemical properties associated with each of the transition metals involved

A Phosphine-Based Heterotrimetallic (M = Fe, Ru, W) Homo-polymer

An organometallic homopolymer containing three different metals per repeating unit was synthesized from an air- and moisture-stable secondary phosphine bearing ethylferrocene and ethylruthenocene groups. Hydrophosphination yielded a tertiary phosphine bearing an alcohol, which was then used to introduce a polymerizable styrene group via DCC coupling. Free-radical polymerization, followed by post-polymerization coordination to photogenerated W(CO)5 units yielded the title polymer, which showed thermal, spectroscopic, and electrochemical properties associated with each of the transition metals involved

Controlled Polymerization of Ethyl Glyoxylate Using Alkyllithium and Alkoxide Initiators

The synthesis of poly(ethyl glyoxylate)s (PEtGs) by anionic polymerization was explored. PEtGs are a subclass of stimuli-responsive self-immolative polymers with promising properties for applications as coatings, sensors, and drug delivery vehicles. In this report, a new purification procedure for the preparation of highly pure ethyl glyoxylate (EtG), suitable for anionic polymerization reactions, and the first successful examples of controlled polymerization of EtG are described. n-BuLi, PhLi, and t-BuLi were employed as initiators under different experimental conditions and their behavior was examined using NMR spectroscopy, size exclusion chromatography, and thermal analysis to develop an optimized procedure. As functional alkoxide initiators, propargyl alkoxide was employed in optimization studies and poly(ethylene glycol) (PEG) dialkoxide was utilized for the direct synthesis of PEtG-PEG-PEtG copolymers. The new polymerization method revealed many features of controlled polymerization reactions, yielding PEtGs with predictable molar masses and relatively low dispersity values

Metal-containing polymers bearing pendant nickel(II) complexes of Goedken\u27s macrocycle

The design, synthesis, and polymerization of a norbornene-based monomer bearing a nickel(II) complex of Goedken\u27s macrocycle (endo-13) and the characterization of the resulting polymer are described. Detailed studies of the ring-opening metathesis polymerization of endo-13 using the 3-bromopyridine adduct of Grubbs\u27 3rd generation catalyst revealed that the polymerization shares many characteristics associated with a living polymer, but deviated from ideal behavior when high degrees of polymerization were targeted. The installation of a 3-hexylphenyl substituent at the macrocyclic backbone allowed for the realization of soluble polymers (14) and shut down an oxidative dimerization pathway commonly associated with metal complexes of Goedken\u27s macrocycle. The cyclic voltammogram of the polymer 14 was comprised of two one-electron oxidation waves (0.21 V and 0.70 V relative to ferrocene/ferrocenium) associated with the stepwise oxidation of the macrocyclic ligand backbone and a one electron reduction wave associated with the reduction of nickel(II) to nickel(I) (-2.07 V). Solution and solid-state UV-vis absorption spectra recorded for polymer 14 revealed a strong p®p* absorption (lmax = 390 nm) and a ligand-to-metal charge transfer band (lmax = 590 nm) typical of nickel(II) complexes of Goedken\u27s macrocycle, and confirmed the absence of macrocycle-macrocycle interactions. This work has ultimately led to the development of a controlled polymerization route to a rare example of a side-chain nickel-containing polymer with potentially useful properties

Transesterification of Poly(ethyl glyoxylate): A Route to Structurally Diverse Polyglyoxylates

Polyglyoxylates are a class of self-immolative polymers that depolymerize in solution and the solid state. The glyoxylic acid degradation product is a metabolite in the glyoxylate cycle and can also be processed in the liver in humans, making polyglyoxylates attractive for applications in the environment and in medicine. Although expanding the scope of available polyglyoxylates would enable new properties and applications, highly pure glyoxylate monomers are required for polymerization, and this level of purity is difficult to achieve for many potential monomers. To address this challenge, we report here the 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD)-catalyzed post-polymerization transesterification of poly(ethyl glyoxylate) (PEtG) as a general method for the synthesis of directly inaccessible polyglyoxylates. Using a new end-capping strategy, PEtG compatible with the transesterification reaction was developed. n-Propanol, i-propanol, n-butanol, t-butanol, n-pentanol, n-hexanol, n-octanol, and benzyl alcohol were employed and the reactivities of these different alcohols were investigated. The resulting polyglyoxylates were characterized chemically and their thermal properties were compared. In all cases, the transesterified polyglyoxylates retained the stimuli-responsive depolymerization properties of the parent PEtG. In addition, functional polyglyoxylates based on allyl, propargyl, and furfuryl esters, which are suitable for subsequent click reactions, were prepared. The propargyl-functionalized polyglyoxylate was used to conjugate pyrene, and the resulting molecules underwent a change in fluorescence properties upon depolymerization

Group 6 Metal Pentacarbonyl Complexes of Air-Stable Primary, Secondary, and Tertiary Ferrocenylethylphosphines

The synthesis and characterization of a series of Group 6 metal pentacarbonyl complexes of air stable primary, secondary, and tertiary phosphines containing ferrocenylethyl substituents are reported [M(CO)5L: M = Cr, Mo, W; L = PH2(CH2CH2Fc), PH(CH2CH2Fc)2, P(CH2CH2Fc)3]. The structure and composition of the complexes were confirmed by multinuclear NMR spectroscopy, IR and UV-Vis absorption spectroscopy, mass spectrometry, X-ray crystallography, and elemental analysis. The solid-state structural data reported revealed trends in M-C and M-P bond lengths that mirrored those of the atomic radii of the Group 6 metals involved. UV-Vis absorption spectroscopy and cyclic voltammetry highlighted characteristics consistent with electronically isolated ferrocene units including wavelengths of maximum absorption between 435 and 441 nm and reversible one-electron (per ferrocene unit) oxidation waves between 10 and -5 mV relative to the ferrocene/ferrocenium redox couple. IR spectroscopy confirmed that the σ donating ability of the phosphines increased as ferrocenylethyl substituents were introduced and that the tertiary phosphine ligand described is a stronger σ donor than PPh3 and a weaker σ donor than PEt3, respectively

Aluminum Complexes of N2O23‒ Formazanate Ligands Supported by Phosphine Oxide Donors

The synthesis and characterization of a new family of phosphine-oxide-supported aluminum formazanate complexes (7a, 7b, 8a, 9a) are reported. X-ray diffraction studies revealed that the aluminum atoms in the complexes adopt an octahedral geometry in the solid state. The equatorial positions are occupied by an N2O23‒ formazanate ligand, and the axial positions are occupied by L-type phosphine oxide donors. UV-vis absorption spectroscopy revealed that the complexes were strongly absorbing (ε ~ 30,000 M‒1 cm‒1) between 500 and 700 nm. The absorption maxima in this region were simulated using time-dependent density-functional theory. With the exception of 3-cyano substituted complex 7b, which showed maximum luminescence intensity in the presence of excess phosphine oxide, the title complexes are non-emissive in solution and the solid state. The electrochemical properties of the complexes were probed using cyclic voltammetry. Each complex underwent sequential one-electron oxidations in potential ranges of ‒0.12 to 0.29 V and 0.62 to 0.97 V, relative to the ferrocene/ferrocenium redox couple. Electrochemical reduction events were observed at potentials between ‒1.34 and ‒1.75 V. When combined with tri-n-propylamine as a coreactant, complex 7b acted as an electrochemiluminescence emitter with a maximum electrochemiluminescence intensity at a wavelength of 735 nm, red-shifted relative to the photoluminescence maximum of the same compound

Synthesis and Characterization of a Family of Air-Stable Ferrocene- and Ruthenocene-Containing Primary, Secondary, and Tertiary Phosphines

The synthesis and characterization of a family of air-stable primary, secondary, and tertiary phosphines containing all possible combinations of ethylferrocene and ethylruthenocene substituents are reported. Each phosphine was characterized by 1H, 13C, and 31P NMR spectroscopy, IR and UV-vis absorption spectroscopy, mass spectrometry, and elemental analysis. With the exception of primary ethylruthenocene phosphine 8a, all of the title compounds have been studied by single crystal X-ray crystallography. Ferrocene-containing phosphines showed maximum absorption at wavelengths of ca. 440 nm and qualitatively reversible oxidation waves in their cyclic voltammograms with intensities scaling to the number of ferrocene units present. The average metal-cyclopentadienyl centroid distances observed for ferrocene-containing phosphines were shorter than those of ruthenocene-containing phosphines, which also had maximum absorption wavelengths of ca. 320 nm and underwent irreversible electrochemical oxidation. Phosphines containing both ethylferrocene and ethylruthenocene substituents displayed properties consistent with the presence of both metallocene types

Polyglyoxylamides: Tuning Structure and Properties of Self-Immolative Polymers

© 2018 American Chemical Society. Self-immolative polymers (SIPs) are a class of stimuli-responsive materials that undergo controlled end-to-end depolymerization in response to stimuli. Their unique degradation and amplification properties have made them of interest for a diverse array of applications including sensors, vehicles for controlled release, and transient objects. Thus far, a limited number of SIP backbones exist, each with its own advantages and limitations. We report here the preparation and study of polyglyoxylamides (PGAms) as a new class of SIPs. PGAms were synthesized by simple postpolymerization modifications of poly(ethyl glyoxylate) (PEtG). While retaining the important stimuli-responsive depolymerization properties of polyglyoxylates, PGAms exhibited much different thermal properties, and some were even water-soluble. Furthermore, a depolymerizable PGAm analogue of poly(ethylene glycol) was prepared, demonstrating the capability to synthesize more complex PGAm graft copolymers. Overall, PGAms are a new class of SIPs with unique combinations of physical, thermal, and degradative properties that provide avenues for novel applications