Chemistry and catalysis advances in organometallic chemistry and catalysis
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- Scheme 29.12
- Scheme 29.13
- Scheme 29.14
- Scheme 29.15
- Scheme 29.16
- Scheme 29.17
- Scheme 29.18
- 29.3.2 Heterometallic-Side Organometallic Polymers
- Scheme 29.19
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393 materials for flow-intensive drug delivery [182, 183], etc. A further important challenge is to extend living self-assembly to other semicrystalline polymers, especially π-conjugated polymers, in order to access colloidal suspensions of nanowires of controlled length [184, 185]. Such materials would possess useful electronic or optical properties. These types of colloidal nanowires might be patterned by spin-coating on substrates structured using electron beam resists and may prove useful as active components in the fabrication of devices [186]. The segmented nanowires show many of the features of the multicolored luminescent nanowire barcodes reported recently by Park et al. [187]. These authors carried out sequential electrochemical polymerization of 3-butylthiophene, 3-methylthiophene, and ethylenedioxythiophene using an anionic alumina oxide nanoporous template. In this way, they obtained uniform elongated structures of diameter ca. 200 nm and length 10 micrometers in which bar-like segments of the individual polymers could be detected by laser confocal fluorescence microscopy (LCFM) through their characteristic fluorescence. The multiblock co-micelles are significantly thinner (ca. 40 nm) and represent an interesting and novel example of barcoded nanowires that might provide a useful platform for sensing applications. The incorporation of transition metals and main group elements into one of the blocks provides an attractive method for expanding the range of properties present in the resulting self-assembled materials [17, 159, 188–198]. Another interesting example of multiblock polymer useful for obtaining colloids was synthesized by self-assembly of the triblock copolymer, poly(ferrocenyldimethylsilane-b-2-vinylpyridine-b-2,5-di-(2 -ethylhexyloxy)-1,4-phenylvinylene) (PFS 30
300 -b-PDEHPV 13 , the subscripts refer to the degree of polymerization) in 2-propanol (2-PrOH) (Scheme 29.12). The resulting polymers provide a useful structure for obtaining complex architectures with particular properties that, in solution, provide colloidally stable entities [199]. These flower-like aggregates that are obtained can be completely disassembled into well-dispersed cylindrical micelles of uniform length upon mild warming of the solutions in 2-PrOH. Using the micelle fragments obtained by sonication and sequentially adding aliquots of PFS 30 -b-P2VP 300 diblock copolymer and PFS 30 -b-P2VP 300 -b-PDEHPV 13 fluorescent triblock copolymer, each as a solution in THF, long uniform cylindrical structures can be obtained, with alternating compartments containing nonfluorescent and fluorescent polymer, with light-emitting segments of a single color. A clever combination of blocks should probably provide multicolor polymers. The research efforts in this field provided a new series of ferrocene-based, well-defined amphiphilic graft copolymers with interesting properties. The obtained HMSOP consists of hydrophilic poly[poly(ethylenglycol)-methyl-ether-acrylate] (PPEGMEA) backbone and hydrophobic poly(2-acryloyloxyethyl-ferrocenecarboxylate) (PAEFC) side chains, which were synthesized by successive single-electron-transfer living radical polymerization (SET-LRP) and atom transfer radical polymerization (ATRP). The backbone was prepared by SET-LRP of poly(ethyleneglycol)-methyl-ether-acrylate (PEGMEA) macromonomer, and it was then treated with lithium di-isopropylamide and 2-bromopropionyl bromide at −78
◦ C to give PPEGMEA-Br macroinitiator [200]. The targeted well-defined graft copolymers with narrow molecular weight distributions (M w /M n ≤ 1.32) were synthesized via ATRP of 2-Acryloyloxoethyl-Ferrocenecarboxylate (AEFC) initiated by PPEGMEA- Br macroinitiator, and, remarkably, the molecular weights of the backbone and side chains were both controllable. The preparation method, the length of PAEFC segment, and the initial water content apparently affected the self-assembly behavior of PPEGMEA-g-PAEFC amphiphilic graft copolymers in aqueous solution (Scheme 29.13). The observed morphologies of Fe Si Me Me (CH 2 ) 3 CH 2 C Ph Ph CH 2 CH C OH CH 3 OR RO RO OR N 12 n Si Me Me n -Bu m R = 2-ethylhexyl PFS 30
300 -b-PDEHPV 13 H
X 1 PFS 30 -b-P2VP 300 Fe
Me Me (CH 2 ) 3 CH 2 C Ph Ph CH 2 CH N n Si Me Me n -Bu m X X 1 H Scheme 29.12 Structure of PFS 30 -b-P2VP 300 -b-PDEHPV 13 and PFS
30 -b-P2VP 300 .
394 ORGANOMETALLIC POLYMERS PEGMEA CuBr, Me
6 TREN, 2-MBP THF/H 2
°C CH O O O H 3 C 9 CH 2 19 PPEGMEA 1 1. LDA, THF 2. BrCO(CH 3 )CHBr, −78 °C AEFC, CuBr, PMDETA DMF, 40 °C, 48h
CH O O O H 3 C 9 CH 2 CH 2 14 C O O O H 3 C 9 5 O Br PPEGMEA-Br 2 CH O O O CH 2 n O Fe PPEGMEA-g-PAEFC 3 O O O H 3 C 9
Synthesis of PPEGMEA-g-PAEFC amphiphilic graft copolymer. micelles in water could transform from cylinders to spheres or rods on changing the preparation condition and the length of the side chains. The resulting micelles should be particularly interesting for a variety of potential applications such as amperometric biosensors and redox drug controlled-release carriers. In addition, the self-assembly of block copolymers with immiscible segments is known to generate a variety of different morphologies because of phase separation in the solid state and selective solvation in block-selective solvents and provides an attractive route to different nanostructures [201–203]. Using the living anionic and the photocontrolled living anionic protocols and combining the obtained polyferrocenylsilane block with a second readily tuned block was possible the rational design of nanostructures such as block co-micelles, which are available via crystallization-directed living supramolecular polymerization processes. Finally, the rare organometallic-inorganic diblock copolymer polyferrocenylsilane- b-polyphosphazene was obtained (Scheme 29.14). METALLIC-SIDE ORGANOMETALLIC POLYMERS 395 Fe Si Me Me 1. n-BuLi, THF, 25 °C 2. ClPPh
2 Fe Si PPh 2 Me Me n-Bu n C 2 Cl 6 , CH 2 Cl 2 , 25 °C −C 2 Cl 4 Fe Si PPh 2 Cl 2 Me Me
n m Cl 3 P=NSiMe 3 −m ClSiMe 3 Fe
P Me Me n-Bu n Ph Ph N P Cl Cl N PCl 4
Fe Si
Me Me
n Ph Ph N P OCH
2 CF 3 OCH 2 CF 3 N P(OCH
2 CF 3 ) 4
NaOCH 2
3 −NaCl
Scheme 29.14 Synthesis of end-functionalized poly(ferrocenylsilane) homopolymer and poly(ferrocenylsilane)-b-polyphosphazene diblock copolymers. Bu Si Fe Si Me NMe 3 (MeSO 4 ) − n Me Me m O O
O O − O 3 S ISA Hierarchical self-assembly 10–100 nm 2–3 nm
Schematic representation of the formation of hierarchically self-assembled architectures, illustrating the concept of structure-within-structure formation. Newly, Manners et al. [204] have synthesized and characterized the first example of an organic– organometallic hierarchically organized nanostructure from the ionic complexation of polyferrocenylmethyl-dimethylaminopropynylsilane diblock copolymer with low molecular weight amphiphilic molecules. A fine structural tuning can be achieved by careful selection of the amphiphile for complexation. In addition, the method can provide a simple route to achieve hierarchical organization at different length scales, the generation of nanostructured materials, and inducing certain functionality by careful selection of starting materials. Self-assembly of block copolymer– surfactant complexes was also studied in bulk and thin films and produced materials with structural hierarchy over multiple length scales (Scheme 29.15). Compared to widely studied ferrocene and ferrocene polymers, cobaltocene has received far less attention, partly because of the greater difficulty in preparing substituted derivatives [205–210]. Cobaltocene (19-e) has one more valence electron than ferrocene (18-e) but it can lose an electron readily to form the cobaltocenium cation (18-e), isoelectronic with ferrocene [211]. Given the ease oxidation of cobaltocene and the great inertness of cobaltocenium salts, it is extremely difficult to prepare substituted derivatives from cobaltocene or cobaltocenium. A few main-chain cobaltocenium polymers were synthesized via condensation or ROP [212–214]. Owing to their cationic nature, side-chain cobaltocenium polymers exhibit interesting solubility behaviors in solvents such as water and acetone, in which solvents the polymer may present interesting self-assembly in solution and provide new materials with possible useful catalytic, magnetic, and redox properties. 396 ORGANOMETALLIC POLYMERS Manners et al. [214] described the synthesis of the high molecular weight, water-soluble polycobaltocenium polyelectrolytes by ROP of dicarba[2]cobaltocenophanes (19-e). Anionic polymerization of the cobaltocenophane (19-e) and dicarba[2]cobaltocenophane using Li[t-BuC 5 H 4 ] as initiator resulted in the formation of oligomers with up to nine repeat units. The observation that this process occurs in the absence of light, in contrast to the case for corresponding [1]ferrocenophanes, indicates that the M–Cp bond in the 19-electron dicarba[2]cobaltocenophane is intrinsically weaker, presumably because the unpaired electron occupies an antibonding orbital. Thermal ROP of the dicarba[2]cobaltocenophane followed by oxidation resulted in an interesting high molecular weight, water-soluble, redox-active polycobaltocenium (Scheme 29.16). Soon after, Tang et al. synthesized highly pure monosubstituted carboxycobaltocenium and subsequently prepared side- chain cobaltocenium-containing block copolymers. These block copolymers exhibited self-assembled vesicle and nanotube structures depending on the solvent used (Scheme 29.17) [215]. Transmission electron microscopy (TEM) images showed that these micellar aggregates exhibited nonuniform vesicle morphology with diameter ranging from 50 to 300 nm. Co 1a. h ν, 0.1 equiv Li[ t BuC
5 H 4 ], THF, 1 h
or 1b. 0.1 equiv Li[ t BuC
5 H 4 ], THF, 16 h 2. NH 4
2 O, O
2 , 16 h
Co Cl t Bu
1a: x ≤ 5, 44%
2a: x ≤ 9, 62%
Co 1. 140
°C, 1 h 2. NH
4 NO 3 , MeOH/H 2 O, O 2 ,16 h Co NO 3 n Scheme 29.16 Syntheses of water-soluble polymer derived from the dicarba[2]cobaltocenophane. Co PF 6
COOH Co PF
6 − CH 3 i. CoBr
2 , Pyrrolidine ii. NaPF 6 , H 2 O Co PF 6 − Co PF 6 − ii. NaPF 6 iii. HCl
Co PF 6 − Co PF 6 − COOH HOOC
Multiple extraction Recrystallization Co PF
6 − COOH SOCl 2 Co PF 6 − C O Cl O O HO O O O O O O Co PF 6 − Br m n Br O O HO O O m n Et 3 N, DMF i. KMnO
4 , NaOH
Scheme 29.17 Synthesis of monocarboxycobaltocenium and side-chain cobaltocenium-containing block copolymers. METALLIC-SIDE ORGANOMETALLIC POLYMERS 397 (
6 -C
H 6 )Cr(CO) 3 Bu 2 O, 120 °C, 5 days Cr
Reactions of single-walled carbon nanotubes with ( η 6
Probably one of the most exciting new research lines on side-chain organometallic polymers is the functionalization of carbon derivatives such as nanotubes and, more recently, graphene [216]. Nonetheless, research toward the wider application of side-chain graphene organometallic polymers is still in its infancy and much work remains to be done in facilitating the practical applications of graphene-based materials and broadening the scope of their electrochemical applications in the future. Apart from the electronic structure, the chemical reactivity of carbon nanotubes is governed by the curvature-induced pyramidalization and the misalignment of the π-orbitals, which renders carbon nanotubes a distinct class of materials between the usually more reactive fullerenes (commented previously) and graphene. The end-group functionalization and side-wall chemical addition reactions of carbon nanotubes have received a great deal of attention [217, 218]. Also, the endohedral filling of the nanotubes with various molecules, atoms, and complexes has been extensively investigated for fabrication of nanowires and in energy storage and drug delivery applications. The inner carbon nanotube cavities have been filled with fullerenes, metals [219–221], metal oxides [222, 223] and (noncovalently encapsulated) transition metal complexes [224]. The first reported [225] side-chain covalent organometallic complexation of carbon nanotubes was synthesized by reaction of purified single-walled carbon nanotubes with [Cr(CO) 6 ] and [Cr( η 6 -benzene)(CO) 3 ] (Scheme 29.18). The bonding of the {Cr(CO)
3 } and {Cr(η 6 -benzene) } moieties on the single-walled carbon nanotubes is primarily covalent in nature, with slight charge-transfer character in the case of {Cr(CO) 3
showed electronic conductivity different to that of the starting nanotube. 29.3.2 Heterometallic-Side Organometallic Polymers There are not too many examples of side-chain hetero-organometallic polymers, which indicates the difficulty in synthesizing this kind of polymers. The first examples of ferrocenyl-containing dendronized polysiloxanes were prepared some years ago from polysiloxanes containing small pendant electroactive wedges possessing electronically communicated ferrocenyl moieties [226]. The synthesis via hydrosilylation chemistry of a series of new polysiloxanes functionalized with small appended dendritic wedges containing both electron-donor ferrocenyl units and electron-acceptor ( η 6
aryl)tricarbonylchromium fragments were presented by Cuadrado et al. (Scheme 29.19) [227]. The novel ferrocenyl- polysiloxanes are stable under air and moisture, and soluble in common organic solvents. The TGA analysis showed that the thermal stability of the novel ferrocenyl-polysiloxanes strongly depends on the size of the ferrocenyl dendritic fragment appended to the siloxane backbones, some of them at temperature higher than 250 ◦ C, yielding ceramic residues in relatively high amounts. Electrochemical studies in dissolution showed that all the ferrocenyl redox units present in the ferrocenyl dendronized polysiloxanes are electrochemically independent. In addition, the authors have demonstrated the feasibility of modifying electrode surfaces with stable electroactive films of these siloxane-based polyferrocenyl dendronized molecules. A very interesting heterometal polymer that can be considered as a combination of MSOP and MBOP were synthesized by living photocontrolled ROP of block copolymers based on ferrocene and cobaltocenium repeat units. This synthetic procedure, which had never been used before (Scheme 29.20), constituted a very interesting approach to obtaining new heterometallic materials [228]. The self-assembly procedure allows access to new heterobimetallic block co-micelle architectures through living self-assembly. The presented Fe–Co block copolymers display interesting redox properties owing to the electroactive ferrocene and cobaltocenium centers that yield oxidation and reduction waves separated by around 1.5 V. As a result, the Fe-Co block copolymers may have utility as three-stage switches in polymer-based functional materials. 398 ORGANOMETALLIC POLYMERS Fe Si
Si O O Me Si O Me Me Si Me Me Me Si Me Me Me n m Cr(CO)
6 Bu 2 O / THF Δ Fe Si Me Si O O Me Si O Me Me Si Me O Me Cr OC CO CO Si Me Me Me Si Me Me Me Fe Si Me Si O O Me Si O Me Me Si Me O Me Cr OC CO CO Fe Si Me Si Me Fe Si Me Si O O Me Si Me Me Me Si Me Me Me
(MeCN) 3
3 THF
Δ Fe Si Me Si O O Me Si O Me Si Me Me Me Cr OC CO CO Fe Si Me Fe Si Me Si O Me Si O Me Fe Si Me Cr CO CO OC Si Me Me Me Scheme 29.19 Synthesis of polysiloxanes with pendant silicon-bridged {(η 5
5 H 4 )Fe( η 5 -C 5 H 5 ) } and {(η 6 -C 6 H 5 )Cr(CO) 3 } units.
Luo et al. made a very interesting contribution to the synthesis of heterometallic-side organometallic polymers (Het- MSOP). They envisioned that if a soluble Ag(I)-NHC-based side-chain polymer could be synthesized, then it could be further utilized as a carbene transfer agent to prepare a functional N-heterocyclic-based organometallic polymer with higher metal loading [229]. They describe the synthesis of a novel soluble and interesting Ag(I)–NHC-based side-chain heterometal- organometallic polymer by postpolymerization modification of polychloromethylstyrene and its application in the synthesis of the Pd–NHC-containing polymer by the transmetalation reaction of the Ag(I)–NHC moieties (Scheme 29.21). This development offers a new methodology for constructing novel functional NHC-based organometallic polymers by a simple three-step synthesis under mild conditions. The resulting Pd–NHC-containing polymer showed high catalytic activity and reusability in the Suzuki reactions of the challenging, relatively inactive aryl chlorides and aryl boronic acids. Remarkably, even ortho-substituted and electronically deactivated 2-chloroanisole can be coupled with aryl boronic acids in good yields. In addition, the less reactive aryl boronic acids containing nitryl groups undergo the Suzuki reactions smoothly with this procedure, although the yield decreases. Download 11.05 Mb. Do'stlaringiz bilan baham: 
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