Phosphorus-Containing Block Copolymer Templates Can Control the Size and Shape of Gold Nanostructures

From phosphanylphosphaalkenes to coordination copper and silver polymers containing P-P bonds

This study was focused on the activation of the CP bond via reactions of Ph2CP-PtBu2 (1) with 1,6-hexanediol and selected dithiols (1,4-butanedithiol, 1,4-benzenedithiol and 1,4-benzenedimethanethiol). These reactions proceed according to a 1,2-addition mechanism, providing new compounds with formulas {(Ph)2(H)C-P-PtBu2}{μ2-(O-(CH2)6-O)}{tBu2P-P-C(H)(Ph)2} (2), {(Ph)2(H)C-P-PtBu2}{μ2-(S-(CH2)4-S)}{tBu2P-P-C(H)(Ph)2} (3a), {(Ph)2(H)C-P-PtBu2}{μ2-(S-C6H4-S)}{tBu2P-P-C(H)(Ph)2} (3b), and {(Ph)2(H)C-P-PtBu2}{μ2-(S-CH2-C6H4-CH2-S)}{tBu2P-P-C(H)(Ph)2} (3c). Next, the reactions of 3a and 3c with metal chlorides led to the growth of desired coordination polymers of copper(I) and silver(I). All the obtained compounds remained stable under atmospheric conditions.

Synthesis of platinum(II)-complex end-tethered polymers: spectroscopic properties and nanostructured particles

Although metal-containing polymers have been widely studied as a novel class of functional soft materials, the microphase separation between polymeric segments and metal-ligand complexes has been less addressed, which is critical to control their structures and functions. To do this, short-chain polystyrenes (PSs) have been end-functionalized with nanosized square-planar platinum(II) complexes. The platinum(II)-comprising polymers were found to show significant luminescence enhancement in chloroform/methanol solvent mixtures upon increasing the methanol composition. By modulating both the PS length and solvent quality, various self-assembled morphologies formed controllably in the mixed solvents and typical examples include nanofibers, nanoellipsoids, and nanospheres. More interestingly, the inside structures of these polymer particles are shown to be lamellar with sub-10 nm spacings, wherein the PS blocks are alternatively aligned with the platinum(II) units. Such a luminescence enhancement and hierarchical nanostructured particles originate from a subtle combination of directional Pt(II)⋯Pt(II) and/or π-π stacking interactions between the platinum(II) units and the solvophobic effect between the PS blocks. This work suggests that by microphase separating polymer chains with nanosized metal-ligand complexes, metal-containing polymers can self-assemble to form sub-10 nm scale nanostructures showcasing desired properties and functions.

Fabrication of Cellulase Catalysts Immobilized on a Nanoscale Hybrid Polyaniline/Cationic Hydrogel Support for the Highly Efficient Catalytic Conversion of Cellulose

A novel conductive nanohydrogel hybrid support was prepared by in situ polymerization of polyaniline nanorods on an electrospun cationic hydrogel of poly(ε-caprolactone) and a cationic phosphine oxide macromolecule. Subsequently, the cellulase enzyme was immobilized on the hybrid support. Field-emission scanning electron microscopy and Brunauer-Emmett-Teller analyses confirmed a mesoporous, rod-like structure with a slit-like pore geometry for the immobilized support and exhibiting a high immobilization capacity and reduced diffusion resistance of the substrate. For comparison, the catalytic activity, storage stability, and reusability of the immobilized and free enzymes were evaluated. The results showed that the immobilized enzymes have higher thermal stability without changes in the optimal pH (5.5) and temperature (55 °C) for enzyme activity. A high immobilization efficiency (96%) was observed for the immobilized cellulose catalysts after optimization of parameters such as the pH, temperature, incubation time, and protein concentration. The immobilized enzyme retained almost 90% of its original activity after 4 weeks of storage and 73% of its original activity after the ninth reuse cycle. These results strongly suggest that the prepared hybrid support has the potential to be used as a support for protein immobilization.

Chemical- and light-induced isomerization of the P=C bond of a 1-phosphabutadiene

Treatment of Mes*P=C(Si(CH3)3)Br with CH2=CHMgBr in the presence of Pd(0) affords 1-phosphabutadiene Mes*P=C(Si(CH3)3)–CH=CH2 (1) selectively as the Z isomer. Remarkably, treatment of Z-1 with n-BuLi (0.1 equiv.) resulted in quantitative formation of E-1. The exact role of the n-BuLi is unknown; however, it appears to be required to promote the isomerization in the absence of light. The isomerization of Z-1 to E-1 was also mediated by sunlight with the reaction mixture consisting of a ca. 1:9 ratio of Z-1 to E-1. DFT calculations were consistent with the thermodynamic favorability of the isomerization of Z-1 to E-1.

Phosphorus-Containing Block Copolymers from the Sequential Living Anionic Copolymerization of a Phosphaalkene with Methyl Methacrylate

Although living polymerization methods are widely applicable to organic monomers, their application to inorganic monomers is rare. For the first time, we show that the living poly(methylenephosphine) (PMP_n ^- ) anion can function as a macroinitiator for olefins. Specifically, the phosphaalkene, MesP=CPh₂ (PA), and methyl methacrylate (MMA) can be sequentially copolymerized using the BnLi-TMEDA initiator system in toluene. A series of PMP_n -b-PMMA_m copolymers with narrow dispersities are accessible (Đ=1.05-1.10). Analysis of the block copolymers provided evidence for -P-CPh₂ -CH₂ -CMe(CO₂ Me)- switching groups. Importantly, this indicates that the -P-CPh₂ ^- anion directly initiates the anionic polymerization of MMA and stands in stark contrast to the isomerization mechanism followed for the homopolymerization of PA. For the first time, the glass transition of a PMP_n homopolymer has been measured (T_g =45.1 °C, n=20). The PMP_n -b-PMMA_m copolymers do not phase separate and show a single T_g which increases with higher PMMA content.

Intensely phosphorescent block copolymer micelles containing gold(i) complexes

The electrostatic combination of anionic block copolymers with cationic gold(i) complexes leads to the formation of spherical micelles, where gold(i)-containing ionic cores were formed with anionic blocks and further stabilized by neutral blocks of polystyrene or poly(ethylene oxide). This self-assembled strategy induces remarkable phosphorescence enhancement of the gold(i) complexes in solution. The emissive intensity increases unexpectedly with increasing molecular weight of the anionic block that is not coordinated onto the gold(i) complexes. The intensely phosphorescent micelles formed in water can be utilized as a luminescence bioimaging probe in living cells.

Coordination-driven micellelization of block copolymers with gold(i) complexes induces remarkable phosphorescence enhancements with reversible mechanochromism

The coordination-driven self-assembly of block copolymers with gold(i) complexes leads to the formation of spherical micelles with remarkable phosphorescence enhancements. The rising luminescence level increases unexpectedly with increasing the degree of polymerization of the noncoordinated block. Furthermore, one of the gold(i)-containing metallopolymers shows reversible mechanochromic luminescence.

Mass spectrometric characterization of oligomeric phosphaalkenes

Oligomeric phosphaalkenes are readily characterized using electrospray ionization mass spectrometry (ESI-MS). The high affinity of phosphines for silver ions permits the detection of the unadulterated polymer as [M + xAg]x+ions (x = 2–3). When the oligomers are oxidized using H2O2, the resulting phosphine oxide polymer may be treated with sodium ions to produce [M + xNa]x+ions (x = 2–3). Both methods predict a similar distribution of oligomers: Mnvalues of 3450 ± 100 Da and a PDI of 1.09 ± 0.01 cover both analyses. This distribution represents oligomers of the general formula Me(PMesCPh2)nH from n = 4–20, maximizing at ∼n = 10.

Phosphaalkene-oxazoline copolymers with styrene as chiral ligands for rhodium(I)

The radical-initiated copolymerization of phosphaalkene-oxazoline, MesP[double bond, length as m-dash]C(Ph)CMe2Ox [1, Ox = CNOCH(iPr)CH2] with different loadings of styrene affords poly(methylenephosphine-co-styrene)s [2a (1 : S = 1 : 2): Mw = 7400 g mol(-1), PDI = 1.1; 2b (1 : S = 1 : 5): Mw = 18 000 g mol(-1), PDI = 1.2; 2c (1 : S = 1 : 10): Mw = 16 000 g mol(-1), PDI = 1.3]. Copolymers 2a-2c are demonstrated as viable macromolecular ligands for rhodium(i). By comparison with the crystallographically characterized model P,N-bidentate complex, [Mes(Me)P-CH(Ph)CMe2Ox·Rh(cod)]BF4, the polymer complexes [2·Rh(cod)]BF4 were prepared. The macromolecular metal complexes were characterized by GPC {for [2a·Rh(cod)]BF4: Mw = 14 000 g mol(-1), PDI = 1.2}, UV/Vis spectroscopy, (1)H, (13)C and (31)P NMR spectroscopy. Integration of the (31)P NMR spectra of mixtures of 2 and [Rh(cod)2]BF4 permitted the determination of the mol% of incorporation of monomer 1 in copolymer 2 (2a: 17%; 2b: 5%; 2c: 4%). These results compared favorably with those determined by elemental analysis (2a: 17%; 2b: 6%).

Polymers and the p-block elements

A survey of the state-of-the-art in the development of synthetic methods to incorporate p-block elements into polymers is given. The incorporation of main group elements (groups 13-16) into long chains provides access to materials with fascinating chemical and physical properties imparted by the presence of inorganic groups. Perhaps the greatest impedance to the widespread academic and commercial use of p-block element-containing macromolecules is the synthetic challenge associated with linking inorganic elements into long chains. In recent years, creative methodologies have been developed to incorporate heteroatoms into polymeric structures, with perhaps the greatest advances occurring with hybrid organic-inorganic polymers composed of boron, silicon, phosphorus and sulfur. With these developments, materials are currently being realized that possess exciting chemical, photophysical and thermal properties that are not possible for conventional organic polymers. This review focuses on highlighting the most significant recent advances whilst giving an appropriate background for the general reader. Of particular focus will be advances made over the last two decades, with emphasis on the novel synthetic methodologies employed.

Probing the structural and electronic properties of bimetallic chromium-gold clusters CrmAun(m+n≤6): comparison with pure chromium and gold clusters

Bimetallic chromium-gold CrmAun(m+n≤6) clusters are systematically investigated using the density functional theory at PW91P86 level with LanL2TZ basis set to understand the evolution of various structural, electronic, magnetic, and energetic properties as a function of size (m+n) and composition (m/n) of the system. Theoretical results show a logical evolution of the properties depending on the size and the composition of the system. Cr m clusters clearly prefer 3D structures while Au n clusters favor planar configurations. The geometry of the bimetallic Cr m Au n clusters mainly depends on their composition, i.e., clusters enriched in Cr atoms prefer 3D structures while increasing Au contents promotes planar configurations. The stability is maximized when the composition of binary Cr m Au n clusters is nearly balanced. Meanwhile, the number of hetero Cr-Au bonds and charge transfer from Cr to Au are maximized for clusters with m≈n. The most probable dissociation channels of the Cr m Au n clusters are calculated and analyzed. Natural population analysis reveals that Au atoms tend to be negatively charged while Cr atoms tend to be positively charged. Combined with the trend that Au atoms favor the surface/edges/vertices and Cr atoms tend to be inside, the outer part of the cluster tends to be negatively charged, and the inner part tends to be positively charged.

Highly-metallized phosphonium polyelectrolytes

The synthesis, characterization, and pyrolysis of a novel class of highly-metallized, redox-active polyelectrolytes that employ phosphorus as a scaffold for the installation of transition metals is described.

A cooperative role for the counteranion in the PCl5-initiated living, cationic chain growth polycondensation of the phosphoranimine Cl3P═NSiMe3

The counteranion associated with the cationic initiator [Cl(3)P═N═PCl(3)](+) ([4](+)) generated during the PCl(5)-initiated living, cationic chain growth polycondensation of the N-silylphosphoranimine Cl(3)P═NSiMe(3) (3) to give poly(dichlorophosphazene), [N═PCl(2)](n) (2), has been found to have a dramatic effect on the polymerization. When the counteranion of [4](+) was changed from PCl(6)(-) or Cl(-) to the weakly coordinating anions [BAr*(F)(4)](-) and [BAr(F)(4)](-) (Ar*(F) = 3,5-{CF(3)}(2)C(6)H(3), Ar(F) = C(6)F(5)) instead of the polymerization of 3 being complete in 4-6 h, no reaction was observed after 24 h. Remarkably, the polymerization of 3 may be initiated by Cl(-) anions even in the absence of an active cation such as [4](+). However, in the presence of [4](+), the reaction proceeded significantly faster and allowed for molecular weight control. These results reveal that the currently accepted mechanism for the PCl(5)-initiated living polymerization of 3 needs to be revised to reflect the key role of the counteranion present.