Inorganic and organometallic polymers

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<ul><li><p>Inorganic and organometallic polymers</p><p>Kevin J. T. Noonan and Derek P. Gates*DOI: 10.1039/b612872f</p><p>The synthesis of macromolecules composed partially or entirely of inor-ganic elements in the main chain is an area of widespread interest. Thisreport summarizes the many advances that were made in the area ofinorganic polymer science in 2006.</p><p>Highlights</p><p>Major accomplishments in the synthesis of inorganic polymers include: the observa-</p><p>tion of molecular weight doubling when polysilanes are synthesized in chiral</p><p>solvents, the synthesis of PH polyphosphazenes, the development of polyphos-</p><p>phole-based sensors, the ring-opening polymerization of phosphirenes, the living</p><p>anionic polymerization of PQC bonds, the ring-opening polymerization of [1]sila-trochrocenophanes, and the development of palladium-containing polymers as</p><p>supramolecular cruciforms.</p><p>1 Introduction</p><p>The synthesis of macromolecules composed partially or entirely of inorganic</p><p>elements in the main chain is an area of widespread interest. A major challenge</p><p>facing researchers in this area is the development of general synthetic methods to</p><p>link inorganic elements into long chains. Despite these hurdles, researchers are</p><p>motivated to develop polymers containing main group elements or transition metals</p><p>due to their novel properties and possible applications.</p><p>In this article, the 2006 literature in the area of inorganic and organometallic</p><p>polymers shall be surveyed. This report complements previous articles in this series,1</p><p>and is divided into eight sections beginning with this introductory part. The next</p><p>subsection will give an overview of recent books, reviews and highlight articles that</p><p>have been published in the area. This is followed by three subsections devoted to the</p><p>well-established polysiloxanes (silicones), polysilanes, and polyphosphazenes. This is</p><p>followed by a summary of advances in the development of new types of macro-</p><p>molecules composed partially or entirely of main group elements. A section will then</p><p>be devoted to the growing field of ferrocene and related organometallic polymers.</p><p>The final section will highlight progress in the synthesis of macromolecules contain-</p><p>ing transition metals within the main chain.</p><p>In this review, emphasis will be placed on synthetic advances in the development</p><p>of linear macromolecules containing main group elements or transition metals</p><p>within the main chain.</p><p>Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver,Canada BC V6T 1Z1</p><p>Annu. Rep. Prog. Chem., Sect. A, 2007, 103, 407427 | 407</p><p>This journal is c The Royal Society of Chemistry 2007</p><p>REVIEW www.rsc.org/annrepa | Annual Reports APu</p><p>blis</p><p>hed </p><p>on 2</p><p>2 Ju</p><p>ne 2</p><p>007.</p><p> Dow</p><p>nloa</p><p>ded </p><p>by U</p><p>nive</p><p>rsity</p><p> of </p><p>Illin</p><p>ois </p><p>at C</p><p>hica</p><p>go o</p><p>n 28</p><p>/10/</p><p>2014</p><p> 01:</p><p>59:1</p><p>3. </p><p>View Article Online / Journal Homepage / Table of Contents for this issue</p><p>http://dx.doi.org/10.1039/b612872fhttp://pubs.rsc.org/en/journals/journal/IChttp://pubs.rsc.org/en/journals/journal/IC?issueid=IC007103</p></li><li><p>2 Books and reviews of inorganic polymer science</p><p>A book entitled Metal-Containing and Metallosupramolecular Polymers and Materi-</p><p>als has been published in 2006 as part of the ACS symposium series.2 The editors,</p><p>Schubert, Newkome, and Manners have assembled a wonderful collection of articles</p><p>from a variety of leading researchers in the field. An excellent monograph entitled</p><p>Frontiers in Transition Metal-Containing Polymers has appeared which features</p><p>chapters written by leaders in the field.3 A special issue of Current Organic Chemistry</p><p>has appeared on organophosphorus chemistry in which phosphorus-containing</p><p>macrocycles and dendrimers are described.4</p><p>An interesting review of the literature on the Pt content in commercial silicones</p><p>and its implications for biomedical applications has appeared.5 The use of acyclic</p><p>diene metathesis (ADMET) to prepare siliconcarbon hybrid materials has been</p><p>highlighted.6 Divinylarene-silylene copolymers have been reviewed in a Chemical</p><p>Communications feature article.7 A review of Wurtz-type coupling to synthesize</p><p>polysilanes in high yields has been compiled by Jones and Holder.8 Weak non</p><p>covalent Si FC interactions of fluorosilane polymers have been highlighted.9Several reviews of phosphazene macromolecules have appeared on topics ranging</p><p>from ion conductivity,10 the use of polyphosphazenes as hydrophobic surfaces,11 to</p><p>recent developments of metal-containing phosphazene macromolecules.12</p><p>New directions in main group polymers have been reviewed fairly extensively in</p><p>2006. A comprehensive review of p-conjugated phosphorus-containing materials byBaumgartner and Reau has been published.13 A review of the synthesis and</p><p>properties of bithiophenes containing heteroatoms has appeared.14 Jakle has high-</p><p>lighted the incorporation of Lewis acidic boron centres into macromolecules.15 Two</p><p>reviews highlighting recent advances in dehydrocoupling as a route to polymers</p><p>possessing inorganic elements have been published.16,17</p><p>Advances in ring opening polymerization (ROP) and supramolecular polymer self</p><p>assembly has been highlighted.18 An overview of the recent advances in transition</p><p>metal containing conjugated polymers has appeared.19 Conjugated organometallic</p><p>polymer networks and metal-containing supramolecular architectures have been</p><p>reviewed.20,21 Organometallic structures p bonded to quinonoids forming coordina-tion networks has been highlighted.22,23 Using metallo-supramolecular initiators for</p><p>controlled polymerization has been reviewed.24 An article on organometallic poly-</p><p>mer nanostructures has appeared.25 Reviews on phosphorus-, metal- and silicone-</p><p>containing dendrimers have appeared in the literature.2632</p><p>3 Polysiloxanes (silicones) and related polymers</p><p>The field of polysiloxanes is the most mature area of inorganic polymer science and a</p><p>large number of papers were published in 2006. Consequently, there is not enough</p><p>space to highlight all the developments in this vast area and this section will focus on</p><p>advances in the synthesis of novel silicone macromolecules.</p><p>Weber and coworkers have prepared a monomer containing a tricyclic and</p><p>tetracyclic siloxane ring (1) and have selectively polymerized the tricyclic ring using</p><p>anionic and cationic ROP to prepare 2.33 This interesting development represents the</p><p>first selective polymerization of one ring of a bicyclic siloxane monomer and could</p><p>prove to be a valuable route to copolymers and crosslinked macromolecules.</p><p>Polystyrene-polysiloxane multiblock copolymers 3 with moderate molecular weight</p><p>(ca. 25 000 g mol1) were synthesized from hydrosilylation coupling and were</p><p>408 | Annu. Rep. Prog. Chem., Sect. A, 2007, 103, 407427</p><p>This journal is c The Royal Society of Chemistry 2007</p><p>Publ</p><p>ishe</p><p>d on</p><p> 22 </p><p>June</p><p> 200</p><p>7. D</p><p>ownl</p><p>oade</p><p>d by</p><p> Uni</p><p>vers</p><p>ity o</p><p>f Il</p><p>linoi</p><p>s at</p><p> Chi</p><p>cago</p><p> on </p><p>28/1</p><p>0/20</p><p>14 0</p><p>1:59</p><p>:13.</p><p> View Article Online</p><p>http://dx.doi.org/10.1039/b612872f</p></li><li><p>characterized by differential scanning calorimetry (DSC) and scanning electron</p><p>microscopy (SEM).34 Poly(ethylene oxide)-polydimethylsiloxane-poly(ethylene</p><p>oxide) triblock copolymers were observed to form aggregates with a variety of</p><p>morphologies that can be controlled by altering the self-assembly conditions.35</p><p>Two different strategies have been developed for the preparation of polydi-</p><p>phenylsiloxane-polydimethylsiloxane-polydiphenylsiloxane triblock copolymers.36</p><p>The anionic ring-opening polymerization (ROP) of hexamethylcyclotrisiloxane</p><p>(D3) using the bifunctional initiator Li2(Ph2SiO2) followed by treatment with</p><p>hexaphenyltrisiloxane affords polymer 4. In the second strategy, the hydrosilylation</p><p>of vinyl-terminated polydiphenylsiloxane with a,o-bis(hydrido)polydimethylsilox-ane is employed to afford triblock copolymer 5. The number average molecular</p><p>weights (Mn) for these novel copolymers ranged from 8800 g mol1 to 31 300 g</p><p>mol1 with polydispersity indices (PDIs) ranging from 1.41.8.</p><p>Annu. Rep. Prog. Chem., Sect. A, 2007, 103, 407427 | 409</p><p>This journal is c The Royal Society of Chemistry 2007</p><p>Publ</p><p>ishe</p><p>d on</p><p> 22 </p><p>June</p><p> 200</p><p>7. D</p><p>ownl</p><p>oade</p><p>d by</p><p> Uni</p><p>vers</p><p>ity o</p><p>f Il</p><p>linoi</p><p>s at</p><p> Chi</p><p>cago</p><p> on </p><p>28/1</p><p>0/20</p><p>14 0</p><p>1:59</p><p>:13.</p><p> View Article Online</p><p>http://dx.doi.org/10.1039/b612872f</p></li><li><p>Alternating copolymers (8) were obtained from the hydrosilylation of the divinyl</p><p>monomer 6 with the SiH terminated oligosiloxane 7.37 The coupling of oligosilane 7</p><p>(21004000 g mol1) with 6 afforded the copolymer 8 with molecular weights up to</p><p>78 100 g mol1.</p><p>Poly(dimethylsiloxane) zinc and sodium ionomers (0.31.3 mol% of metal) have</p><p>been prepared and their gel formation has been described.38 Chojnowski and</p><p>410 | Annu. Rep. Prog. Chem., Sect. A, 2007, 103, 407427</p><p>This journal is c The Royal Society of Chemistry 2007</p><p>Publ</p><p>ishe</p><p>d on</p><p> 22 </p><p>June</p><p> 200</p><p>7. D</p><p>ownl</p><p>oade</p><p>d by</p><p> Uni</p><p>vers</p><p>ity o</p><p>f Il</p><p>linoi</p><p>s at</p><p> Chi</p><p>cago</p><p> on </p><p>28/1</p><p>0/20</p><p>14 0</p><p>1:59</p><p>:13.</p><p> View Article Online</p><p>http://dx.doi.org/10.1039/b612872f</p></li><li><p>coworkers have completed oligomerization reactions of 9 in the presence of B(C6F5)3to form oligosilicone 10 (m = 1, 2, etc.).39 The formation of 10 was accompanied by</p><p>hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4) and dimethylsi-</p><p>lane. Kinetic studies to elucidate the mechanism of chain formation are described.</p><p>Siloxane oligomers with ethylene glycol side groups 11 were prepared from either</p><p>hydrosilation or dehydrocoupling reactions to test their use as electrolytes for</p><p>lithium batteries.40 After doping with lithium bis(oxalato)borate or lithium bis(tri-</p><p>fluorosulfonyl) imide, ambient temperature conductivities between 2 104 S cm1and 6 104 S cm1 were obtained. Polysiloxanes with pendant glycol and methoxysilane groups allow for the formation of comb structures which are of interest as</p><p>electrolyte membranes.41 Rodlike polysiloxanes with acrylamido side groups have</p><p>been prepared and crosslinked to prepare hydrogels.42</p><p>Polycondensation of monomer 12 with water (1 equiv.) in the presence of catalytic</p><p>quantities of tetrabutylammonium fluoride (or HCl) produced insoluble powders.43</p><p>X-ray diffraction data suggested that these solids are ordering themselves on the</p><p>nanometer scale. A mesoporous material with free phosphines was synthesized and</p><p>proved capable of complexing several lanthanide ions.44</p><p>A cis-isotactic ladder polysilsesquioxane (14) was obtained in a confined supra-</p><p>molecular channel.45 This exciting development was made possible by employing</p><p>dischotic Si-substituents, which self-assemble to form H-bonded channels (i.e. 13)</p><p>prior to their base-catalysed condensation to form the ladder structure 14. Poly-</p><p>silesquioxane materials with bound sulfonic acid groups have been prepared and</p><p>Annu. Rep. Prog. Chem., Sect. A, 2007, 103, 407427 | 411</p><p>This journal is c The Royal Society of Chemistry 2007</p><p>Publ</p><p>ishe</p><p>d on</p><p> 22 </p><p>June</p><p> 200</p><p>7. D</p><p>ownl</p><p>oade</p><p>d by</p><p> Uni</p><p>vers</p><p>ity o</p><p>f Il</p><p>linoi</p><p>s at</p><p> Chi</p><p>cago</p><p> on </p><p>28/1</p><p>0/20</p><p>14 0</p><p>1:59</p><p>:13.</p><p> View Article Online</p><p>http://dx.doi.org/10.1039/b612872f</p></li><li><p>investigated as proton exchange membranes for fuel cell applications. Moreover,</p><p>their conductivity was found to increase as a function of sulfonic acid content up to a</p><p>maximum of 6.2 103 S cm1.46</p><p>Polystyrene-block-butadiene-block-polystyrene was grafted with oligomeric silses-</p><p>quioxanes using hydrosilation to afford the functional polymer 15.47 The morpho-</p><p>logy of the copolymer was investigated using small angle X-ray scattering (SAXS)</p><p>and rheology. Miniemulsion (co)polymerization of styrene and g-methacryloxy-propyltrimethoxysilane has been used to synthesize organic-inorganic nanocapsules</p><p>which have been characterized by transmission electron microscopy (TEM),</p><p>dynamic light scattering, NMR and IR.48</p><p>4 Polysilanes, polygermanes, polystannanes, polycarbosilanes andrelated polymers</p><p>It is widely known that performing polymerization reactions in chiral solvents can</p><p>influence the tacticity and/or helicity of the resultant polymer. In a surprising</p><p>development, Holder and coworkers have shown that the Wurtz polymerization</p><p>of silanes in a chiral solvent can also influence the molecular weight of the resultant</p><p>polysilane.49 Specifically, the Wurtz-type polymerization of PhMeSiCl2 in enantio-</p><p>nerically pure (R) or (S)-limonene produced helical polymer 16 with double the</p><p>molecular weight than if the analogous polymerization was performed in racemic (R/</p><p>S)-limonene at 90 1C. The authors suggested that a reduction in helical reversals inchiral solvents is responsible for the higher molecular weights.</p><p>412 | Annu. Rep. Prog. Chem., Sect. A, 2007, 103, 407427</p><p>This journal is c The Royal Society of Chemistry 2007</p><p>Publ</p><p>ishe</p><p>d on</p><p> 22 </p><p>June</p><p> 200</p><p>7. D</p><p>ownl</p><p>oade</p><p>d by</p><p> Uni</p><p>vers</p><p>ity o</p><p>f Il</p><p>linoi</p><p>s at</p><p> Chi</p><p>cago</p><p> on </p><p>28/1</p><p>0/20</p><p>14 0</p><p>1:59</p><p>:13.</p><p> View Article Online</p><p>http://dx.doi.org/10.1039/b612872f</p></li><li><p>Helical polysilanes with fluoroalkyl substituents (17) have been prepared and</p><p>analysis of isolated polymer chains by AFM revealed that the polymer topology was</p><p>related to the chain length.50 In particular, the longer chains tend to adopt circular</p><p>structures whilst the shorter chains form rods. It was shown that the chiral</p><p>supramolecular complexation of the helical amylose to oligosilane Me(SiMe2)6Me</p><p>was pH-dependent and that the optical activity switched from an on to an off</p><p>state at pH r 7.51 CD spectroscopy was used to study aggregates of the solutions ofoptically active polysilane 18 in ethanol (a nonsolvent) and THF (an associative</p><p>solvent) which were confined to microcapsules.52</p><p>Bromo-functional polysilane 19 was reacted with an azocrown complex to afford</p><p>photosensitive polysilane 20 (Mn = 70 000 g mol1; PDI = 1.2).53 Interestingly, UV</p><p>irradiation of solutions of 20 with 400 nm filtered light resulted in 6570% transcis</p><p>isomerization as indicated by the enhancement of the band at 480 nm characteristic</p><p>of np* transition of cis-configured azobenzene. Polymethylphenylsilane-supportedPd and Pt nanoparticles have been used as solid recoverable supports for catalytic</p><p>Suzuki, Sonagashira and hydrosilylation reactions.54</p><p>Polysilanes with all anti conformations of the main chain (i.e. SiSiSiSi dihedral</p><p>angles of 1801) are believed to provide the highest degree of s-conjugation. A majorstep towards the realization of an all-anti-polysilane was made with the synthesis of a</p><p>(tetramethylene)-tethered octasilane 21 by Fukazawa, Tsuji and Tamao. Currently,</p><p>this is the longest silicon chain where the silicon atoms are conformationally</p><p>controlled to be in the all anti state. Remarkably, octasilane 21 exhibits a molar</p><p>extinction coefficient 3 larger than the unrestricted n-Si8Me18 at 0 1C which isconsistent with increased s delocalization in the former.55</p><p>Annu. Rep. Prog. Chem., Sect. A, 2007, 103, 407427 | 413</p><p>This journal is c The Royal Society of Chemistry 2007</p><p>Publ</p><p>ishe</p><p>d on</p><p> 22 </p><p>June</p><p> 200</p><p>7. D</p><p>ownl</p><p>oade</p><p>d by</p><p> Uni</p><p>vers</p><p>ity o</p><p>f Il</p><p>linoi</p><p>s at</p><p> Chi</p><p>cago</p><p> on </p><p>28/1</p><p>0/20</p><p>14 0</p><p>1:59</p><p>:13.</p><p> View Article Online</p><p>http://dx.doi.org/10.1039/b612872f</p></li><li><p>A polysilane-containing ABA block copolymer 22 has been employed to prepare</p><p>shaped calcium carbonate films as 2D model systems for CaCO3 biomateria...</p></li></ul>

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