|
Recently, the discovery of a general Ag(I)-catalyzed azide–alkyne cycloaddition reaction (Ag-AAC) leading to 1,4-triazoles is reported. Mechanistic features are similar to the generally accepted mechanism of the copper(I)-catalyzed process. Silver(I)-salts alone are not sufficient to promote the cycloaddition. However the ligated Ag(I) source has proven to be exceptional for AgAAC reaction.<ref>{{cite journal |author1=McNulty, J. |author2=Keskar, K |author3=Vemula, R. | title = The First Well-Defined Silver(I)-Complex-Catalyzed Cycloaddition of Azides onto Terminal Alkynes at Room Temperature | year = 2011 | journal = [[Chemistry: A European Journal]] | volume = 17 | issue = 52 | pages = 14727–14730 | doi = 10.1002/chem.201103244 | pmid= 22125272}}</ref><ref>{{cite journal |author1=McNulty, J. |author2=Keskar, K. | title = Discovery of a Robust and Efficient Homogeneous Silver(I) Catalyst for the Cycloaddition of Azides onto Terminal Alkynes | year = 2012 | journal = [[Eur. J. Org. Chem.]] | doi = 10.1002/ejoc.201200930 | volume=2012 |issue=28 | pages=5462–5470}}</ref>
Curiously, pre-formed silver acetylides do not react with azides; however, silver acetylides do react with azides under catalysis with copper(I).<ref>{{cite journal | authors = Proietti Silvestri, I., Andemarian, F., Khairallah, G.N., Yap, S., Quach, T., Tsegay, S., Williams, C.M., O'Hair, R.A.J., Donnelly, P.S., Williams, S.J.| title = Copper(i)-catalyzed cycloaddition of silver acetylides and azides: Incorporation of volatile acetylenes into the triazole core | year = 2011 | journal = [[Organic and Biomolecular Chemistry]] | volume = 9 | issue = 17 | pages = 6082–6088 | doi = 10.1039/c1ob05360d | pmid= 21748192}}</ref>
=== <big>Topochemical azide-alkyne cycloaddition (TAAC)</big>[edit source] ===
Kana M. Sureshan at [[IISER Thiruvananthapuram]] has developed and popularized a new branch namely, Topochemical Azide-Alkyne Cycloaddition (TAAC) reaction<ref>{{Cite journal |last=Hema |first=Kuntrapakam |last2=Sureshan |first2=Kana M. |date=2019-11-19 |title=Topochemical Azide-Alkyne Cycloaddition Reaction |url=https://pubmed.ncbi.nlm.nih.gov/31600046 |journal=Accounts of Chemical Research |volume=52 |issue=11 |pages=3149–3163 |doi=10.1021/acs.accounts.9b00398 |issn=1520-4898 |pmid=31600046}}</ref> or topochemical click reaction.<ref>{{Cite journal |last=Pathigoolla |first=Atchutarao |last2=Gonnade |first2=Rajesh G. |last3=Sureshan |first3=Kana M. |date=2012-04-27 |title=Topochemical click reaction: spontaneous self-stitching of a monosaccharide to linear oligomers through lattice-controlled azide-alkyne cycloaddition |url=https://pubmed.ncbi.nlm.nih.gov/22431207 |journal=Angewandte Chemie (International Ed. in English) |volume=51 |issue=18 |pages=4362–4366 |doi=10.1002/anie.201201023 |issn=1521-3773 |pmid=22431207}}</ref> As topochemical reactions occur in the crystal lattice, they are green reactions, which neither require catalysts nor solvents.<ref>{{Cite journal |last=Hema |first=Kuntrapakam |last2=Ravi |first2=Arthi |last3=Raju |first3=Cijil |last4=Sureshan |first4=Kana M. |date=2021-02-23 |title=Polymers with advanced structural and supramolecular features synthesized through topochemical polymerization |url=https://pubmed.ncbi.nlm.nih.gov/34168781 |journal=Chemical Science |volume=12 |issue=15 |pages=5361–5380 |doi=10.1039/d0sc07066a |issn=2041-6520 |pmc=8179609 |pmid=34168781}}</ref> <ref>{{Cite journal |last=Hema |first=Kuntrapakam |last2=Ravi |first2=Arthi |last3=Raju |first3=Cijil |last4=Pathan |first4=Javed R. |last5=Rai |first5=Rishika |last6=Sureshan |first6=Kana M. |date=2021-03-21 |title=Topochemical polymerizations for the solid-state synthesis of organic polymers |url=https://pubmed.ncbi.nlm.nih.gov/33543741 |journal=Chemical Society Reviews |volume=50 |issue=6 |pages=4062–4099 |doi=10.1039/d0cs00840k |issn=1460-4744 |pmid=33543741}}</ref>Sureshan group used crystal engineering to design molecular crystals of various monomers decorated with azide and alkyne units and polymerized such clickable monomers in the crystal state. The molecular design allowed Sureshan group to obtain crystals having head-to-tail arrangement of the monomer molecules with azide and alkyne groups at proximity in the crystal lattice. Apart from the strong supramolecular glues such as hydrogen bonding which dictated the molecular packing, weaker non-covalent interactions ''viz.'' the azide…oxygen interaction<ref>{{Cite journal |last=Bursch |first=Markus |last2=Kunze |first2=Lukas |last3=Vibhute |first3=Amol M. |last4=Hansen |first4=Andreas |last5=Sureshan |first5=Kana M. |last6=Jones |first6=Peter G. |last7=Grimme |first7=Stefan |last8=Werz |first8=Daniel B. |date=2021-03-08 |title=Quantification of Noncovalent Interactions in Azide–Pnictogen, –Chalcogen, and –Halogen Contacts |url=https://onlinelibrary.wiley.com/doi/10.1002/chem.202004525 |journal=Chemistry – A European Journal |language=en |volume=27 |issue=14 |pages=4627–4639 |doi=10.1002/chem.202004525 |issn=0947-6539}}</ref><ref>{{Cite journal |last=Madhusudhanan |first=Mithun C. |last2=Balan |first2=Haripriya |last3=Werz |first3=Daniel B. |last4=Sureshan |first4=Kana M. |date=2021-10-11 |title=Azide⋅⋅⋅Oxygen Interaction: A Crystal Engineering Tool for Conformational Locking |url=https://pubmed.ncbi.nlm.nih.gov/34399025 |journal=Angewandte Chemie (International Ed. in English) |volume=60 |issue=42 |pages=22797–22803 |doi=10.1002/anie.202106614 |issn=1521-3773 |pmid=34399025}}</ref> and azide…alkyne interaction<ref>{{Cite journal |last=Bhandary |first=Subhrajyoti |last2=Pathigoolla |first2=Atchutarao |last3=Madhusudhanan |first3=Mithun C. |last4=Sureshan |first4=Kana M. |date=2022-05-16 |title=Azide-Alkyne Interactions: A Crucial Attractive Force for Their Preorganization for Topochemical Cycloaddition Reaction |url=https://pubmed.ncbi.nlm.nih.gov/35302679 |journal=Chemistry (Weinheim an Der Bergstrasse, Germany) |volume=28 |issue=28 |pages=e202200820 |doi=10.1002/chem.202200820 |issn=1521-3765 |pmid=35302679}}</ref> have been recognized as additional supramolecular forces that help in proximal packing. Such crystals, upon mild heaing, undergo regiospecific lattice-controlled azide-alkyne cycloaddition reaction to yield triazole-linked polymers. In some cases, the reaction occurs spontaneously at room temperature also.
TAAC reaction is highly regiospecific and the regiochemistry is dictated by the relative orientation of the azide and alkyne units in the crystal lattice. Sureshan group could achieve the synthesis of various 1,5-triazole-linked polymers and1,4-triazole-linked polymers exclusively. Rarely, they have observed the formation two different polymers in a single crystal; one polymer with 1,4-triazole linkage and other polymer with 1,5-triazole-linkage.<ref>{{Cite journal |last=Hema |first=Kuntrapakam |last2=Sureshan |first2=Kana M. |date=2019-02-25 |title=Solid-State Synthesis of Two Different Polymers in a Single Crystal: A Miscible Polymer Blend from a Topochemical Reaction |url=https://pubmed.ncbi.nlm.nih.gov/30609210 |journal=Angewandte Chemie (International Ed. in English) |volume=58 |issue=9 |pages=2754–2759 |doi=10.1002/anie.201813198 |issn=1521-3773 |pmid=30609210}}</ref> Authors employed cocrystal strategy to finetune the selectivity in such cases to yield one type of polymer.<ref>{{Cite journal |last=Hema |first=Kuntrapakam |last2=Raju |first2=Cijil |last3=Bhandary |first3=Subhrajyoti |last4=Sureshan |first4=Kana M. |date=2022-10-04 |title=Tuning the Regioselectivity of Topochemical Polymerization through Cocrystallization of the Monomer with an Inert Isostere |url=https://pubmed.ncbi.nlm.nih.gov/35947531 |journal=Angewandte Chemie (International Ed. in English) |volume=61 |issue=40 |pages=e202210733 |doi=10.1002/anie.202210733 |issn=1521-3773 |pmid=35947531}}</ref>
This reaction has been used successful for the polymerisation of peptides,<ref>{{Cite journal |last=Krishnan |first=Baiju P. |last2=Rai |first2=Rishika |last3=Asokan |first3=Aromal |last4=Sureshan |first4=Kana M. |date=2016-11-16 |title=Crystal-to-Crystal Synthesis of Triazole-Linked Pseudo-proteins via Topochemical Azide-Alkyne Cycloaddition Reaction |url=https://pubmed.ncbi.nlm.nih.gov/27791357 |journal=Journal of the American Chemical Society |volume=138 |issue=45 |pages=14824–14827 |doi=10.1021/jacs.6b07538 |issn=1520-5126 |pmid=27791357}}</ref> carbohydrates,<ref>{{Cite journal |last=Pathigoolla |first=Atchutarao |last2=Sureshan |first2=Kana M. |date=2013-08-12 |title=A crystal-to-crystal synthesis of triazolyl-linked polysaccharide |url=https://pubmed.ncbi.nlm.nih.gov/23818337 |journal=Angewandte Chemie (International Ed. in English) |volume=52 |issue=33 |pages=8671–8675 |doi=10.1002/anie.201303372 |issn=1521-3773 |pmid=23818337}}</ref><ref>{{Cite journal |last=Hema |first=Kuntrapakam |last2=Gonnade |first2=Rajesh G. |last3=Sureshan |first3=Kana M. |date=2020-02-10 |title=Crystal-to-Crystal Synthesis of Helically Ordered Polymers of Trehalose by Topochemical Polymerization |url=https://pubmed.ncbi.nlm.nih.gov/31804011 |journal=Angewandte Chemie (International Ed. in English) |volume=59 |issue=7 |pages=2897–2903 |doi=10.1002/anie.201914164 |issn=1521-3773 |pmid=31804011}}</ref> cyclitols,<ref>{{Cite journal |last=Ravi |first=Arthi |last2=Shijad |first2=Amina |last3=Sureshan |first3=Kana M. |date=2021-09-15 |title=Single-crystal-to-single-crystal synthesis of a pseudostarch via topochemical azide-alkyne cycloaddition polymerization |url=https://pubmed.ncbi.nlm.nih.gov/34659700 |journal=Chemical Science |volume=12 |issue=35 |pages=11652–11658 |doi=10.1039/d1sc03727g |issn=2041-6520 |pmc=8442703 |pmid=34659700}}</ref> nucleic acids,<ref>{{Cite journal |last=Pathigoolla |first=Atchutarao |last2=Sureshan |first2=Kana M. |date=2014-09-01 |title=Synthesis of triazole-linked homonucleoside polymers through topochemical azide-alkyne cycloaddition |url=https://pubmed.ncbi.nlm.nih.gov/25044244 |journal=Angewandte Chemie (International Ed. in English) |volume=53 |issue=36 |pages=9522–9525 |doi=10.1002/anie.201404797 |issn=1521-3773 |pmid=25044244}}</ref><ref>{{Cite journal |last=Pathigoolla |first=Atchutarao |last2=Sureshan |first2=Kana M. |date=2016-01-18 |title=The topochemical synthesis of triazole-linked homobasic DNA |url=https://pubmed.ncbi.nlm.nih.gov/26565720 |journal=Chemical Communications (Cambridge, England) |volume=52 |issue=5 |pages=886–888 |doi=10.1039/c5cc08834h |issn=1364-548X |pmid=26565720}}</ref> and fumaramides.<ref>{{Cite journal |last=Pathan |first=Javed R. |last2=Sureshan |first2=Kana M. |date=2021-07-26 |title=Solvent-Free and Catalyst-Free Synthesis of Cross-Linkable Polyfumaramides via Topochemical Azide-Alkyne Cycloaddition Polymerization |url=https://pubs.acs.org/doi/10.1021/acssuschemeng.1c02796 |journal=ACS Sustainable Chemistry & Engineering |language=en |volume=9 |issue=29 |pages=9871–9878 |doi=10.1021/acssuschemeng.1c02796 |issn=2168-0485}}</ref> One of the important advantages of TAAC polymerization is that the reaction often follows a single-crystal-to-single-crystal (SCSC) pathway, which allow these researchers to dissect the structure and conformation of the resultant polymers by single crystal X-ray diffraction. This is a feat not possible for polymers synthesized by normal solution-phase chemistry. TAAC polymerization of peptide-monomers gave crystalline protein-mimics having secondary structures such as beta-sheet,<ref>{{Cite journal |last=Krishnan |first=Baiju P. |last2=Sureshan |first2=Kana M. |date=2017-02-01 |title=Topochemical Azide-Alkyne Cycloaddition Reaction in Gels: Size-Tunable Synthesis of Triazole-Linked Polypeptides |url=https://pubmed.ncbi.nlm.nih.gov/28068764 |journal=Journal of the American Chemical Society |volume=139 |issue=4 |pages=1584–1589 |doi=10.1021/jacs.6b11549 |issn=1520-5126 |pmid=28068764}}</ref> beta-meander,<ref>{{Cite journal |last=Athiyarath |first=Vignesh |last2=Madhusudhanan |first2=Mithun C. |last3=Kunnikuruvan |first3=Sooraj |last4=Sureshan |first4=Kana M. |date=2022-01-21 |title=Secondary Structure Tuning of a Pseudoprotein Between β-Meander and α-Helical Forms in the Solid-State |url=https://pubmed.ncbi.nlm.nih.gov/34699112 |journal=Angewandte Chemie (International Ed. in English) |volume=61 |issue=4 |pages=e202113129 |doi=10.1002/anie.202113129 |issn=1521-3773 |pmid=34699112}}</ref> and helix,<ref>{{Cite journal |last=Hema |first=Kuntrapakam |last2=Sureshan |first2=Kana M. |date=2020-06-02 |title=β-Sheet to Helical-Sheet Evolution Induced by Topochemical Polymerization: Cross-α-Amyloid-like Packing in a Pseudoprotein with Gly-Phe-Gly Repeats |url=https://pubmed.ncbi.nlm.nih.gov/32149438 |journal=Angewandte Chemie (International Ed. in English) |volume=59 |issue=23 |pages=8854–8859 |doi=10.1002/anie.201914975 |issn=1521-3773 |pmid=32149438}}</ref> and having novel cross-laminated<ref>{{Cite journal |last=Athiyarath |first=Vignesh |last2=Sureshan |first2=Kana M. |date=2019-01-08 |title=Spontaneous Single-Crystal-to-Single-Crystal Evolution of Two Cross-Laminated Polymers |url=https://pubmed.ncbi.nlm.nih.gov/30461147 |journal=Angewandte Chemie (International Ed. in English) |volume=58 |issue=2 |pages=612–617 |doi=10.1002/anie.201812094 |issn=1521-3773 |pmid=30461147}}</ref> and twist-stacked<ref>{{Cite journal |last=Athiyarath |first=Vignesh |last2=Sureshan |first2=Kana M. |date=2020-09-01 |title=Designed Synthesis of a 1D Polymer in Twist-Stacked Topology via Single-Crystal-to-Single-Crystal Polymerization |url=https://pubmed.ncbi.nlm.nih.gov/32779302 |journal=Angewandte Chemie (International Ed. in English) |volume=59 |issue=36 |pages=15580–15585 |doi=10.1002/anie.202006758 |issn=1521-3773 |pmid=32779302}}</ref> packing topologies. The crystallinity offered interesting properties such as water sorption,<ref>{{Cite journal |last=Mohanrao |first=Raja |last2=Sureshan |first2=Kana M. |date=2018-09-17 |title=Synthesis and Reversible Hydration of a Pseudoprotein, a Fully Organic Polymeric Desiccant by Multiple Single-Crystal-to-Single-Crystal Transformations |url=https://pubmed.ncbi.nlm.nih.gov/30044034 |journal=Angewandte Chemie (International Ed. in English) |volume=57 |issue=38 |pages=12435–12439 |doi=10.1002/anie.201806451 |issn=1521-3773 |pmid=30044034}}</ref><ref>{{Cite journal |last=Mohanrao |first=Raja |last2=Hema |first2=Kuntrapakam |last3=Sureshan |first3=Kana M. |date=2020-11-13 |title=Scalable Topochemical Synthesis of a Pseudoprotein in Aerogel for Water-Capturing Applications |url=https://pubs.acs.org/doi/10.1021/acsapm.0c00849 |journal=ACS Applied Polymer Materials |language=en |volume=2 |issue=11 |pages=4985–4992 |doi=10.1021/acsapm.0c00849 |issn=2637-6105}}</ref> mechanical properties<ref>{{Cite journal |last=Rai |first=Rishika |last2=Krishnan |first2=Baiju P. |last3=Sureshan |first3=Kana M. |date=2018-03-20 |title=Chirality-controlled spontaneous twisting of crystals due to thermal topochemical reaction |url=https://pubmed.ncbi.nlm.nih.gov/29507233 |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=115 |issue=12 |pages=2896–2901 |doi=10.1073/pnas.1718965115 |issn=1091-6490 |pmc=5866578 |pmid=29507233}}</ref> etc. to these materials.
One of the limitations of the CuAAC click reaction is the non-reactivity of internal alkynes. The Sureshan group has proven that the TAAC reaction works well with internal alkynes too.<ref>{{Cite journal |last=Raju |first=Cijil |last2=Kunnikuruvan |first2=Sooraj |last3=Sureshan |first3=Kana M. |date=2022-09-12 |title=Topochemical Cycloaddition Reaction between an Azide and an Internal Alkyne |url=https://pubmed.ncbi.nlm.nih.gov/35857815 |journal=Angewandte Chemie (International Ed. in English) |volume=61 |issue=37 |pages=e202210453 |doi=10.1002/anie.202210453 |issn=1521-3773 |pmid=35857815}}</ref> Furthermore, TAAC reaction has great potentials in developing different polymorphs of the same polymer, which is almost impossible using polymers synthesized via the conventional solution-phase synthesis due to the thermodynamic factors that prevent their crystallization.<ref>{{Cite journal |last=Mohanrao |first=Raja |last2=Hema |first2=Kuntrapakam |last3=Sureshan |first3=Kana M. |date=2020-02-13 |title=Topochemical synthesis of different polymorphs of polymers as a paradigm for tuning properties of polymers |url=https://pubmed.ncbi.nlm.nih.gov/32054844 |journal=Nature Communications |volume=11 |issue=1 |pages=865 |doi=10.1038/s41467-020-14733-y |issn=2041-1723 |pmc=7018732 |pmid=32054844}}</ref><ref>{{Cite journal |last=Rai |first=Rishika |last2=Sureshan |first2=Kana M. |date=2022-04-11 |title=Topochemical Synthesis of a Heterochiral Peptide Polymer in Different Polymorphic Forms from Crystals and Aerogels |url=https://pubmed.ncbi.nlm.nih.gov/35076971 |journal=Angewandte Chemie (International Ed. in English) |volume=61 |issue=16 |pages=e202111623 |doi=10.1002/anie.202111623 |issn=1521-3773 |pmid=35076971}}</ref> Many a times, TAAC polymerization occurred even when the monomer packing was not conducive for proximity-driven reaction. Authors established that the molecular motion in the crystal lattice allow the reaction partners to reach an orientation suitable for their reaction transiently.<ref>{{Cite journal |last=Ravi |first=Arthi |last2=Hassan |first2=Syed Zahid |last3=Bhandary |first3=Subhrajyoti |last4=Sureshan |first4=Kana M. |date=2022-06-07 |title=Topochemical Postulates: Are They Relevant for Topochemical Reactions Occurring at Elevated Temperatures? |url=https://pubmed.ncbi.nlm.nih.gov/35258143 |journal=Angewandte Chemie (International Ed. in English) |volume=61 |issue=23 |pages=e202200954 |doi=10.1002/anie.202200954 |issn=1521-3773 |pmid=35258143}}</ref> Apart from polymer synthesis, TAAC reaction has also been successful for synthesizing a homodimer,<ref>{{Cite journal |last=Ravi |first=Arthi |last2=Sureshan |first2=Kana M. |date=2018-07-20 |title=Tunable Mechanical Response from a Crystal Undergoing Topochemical Dimerization: Instant Explosion at a Faster Rate and Chemical Storage of a Harvestable Explosion at a Slower Rate |url=https://pubmed.ncbi.nlm.nih.gov/29870594 |journal=Angewandte Chemie (International Ed. in English) |volume=57 |issue=30 |pages=9362–9366 |doi=10.1002/anie.201804589 |issn=1521-3773 |pmid=29870594}}</ref> heterodimer<ref>{{Cite journal |last=Krishnan |first=Baiju P. |last2=Ramakrishnan |first2=Shyama |last3=Sureshan |first3=Kana M. |date=2013-02-21 |title=Supramolecular design of a bicomponent topochemical reaction between two non-identical molecules |url=https://pubmed.ncbi.nlm.nih.gov/23208380 |journal=Chemical Communications (Cambridge, England) |volume=49 |issue=15 |pages=1494–1496 |doi=10.1039/c2cc37067k |issn=1364-548X |pmid=23208380}}</ref> and oligomers<ref>{{Cite journal |last=Hema |first=Kuntrapakam |last2=Sureshan |first2=Kana M. |date=2018-03-12 |title=Three-way competition in a topochemical reaction: permutative azide–alkyne cycloaddition reactions leading to a vast library of products in the crystal |url=https://pubs.rsc.org/en/content/articlelanding/2018/ce/c8ce00131f |journal=CrystEngComm |language=en |volume=20 |issue=11 |pages=1478–1482 |doi=10.1039/C8CE00131F |issn=1466-8033}}</ref> of carbohydrate derived monomers. Advancing this green chemistry further, Sureshan group has developed the novel Topochemical Ene-Azide Cycloaddition (TEAC) reaction<ref>{{Cite journal |last=Khazeber |first=Ravichandran |last2=Sureshan |first2=Kana M. |date=2021-11-15 |title=Topochemical Ene-Azide Cycloaddition Reaction |url=https://pubmed.ncbi.nlm.nih.gov/34379367 |journal=Angewandte Chemie (International Ed. in English) |volume=60 |issue=47 |pages=24875–24881 |doi=10.1002/anie.202109344 |issn=1521-3773 |pmid=34379367}}</ref> which has been exploited for the synthesis helical covalent polymers.<ref>{{Cite journal |last=Khazeber |first=Ravichandran |last2=Sureshan |first2=Kana M. |date=2022-07-19 |title=Single-crystal-to-single-crystal translation of a helical supramolecular polymer to a helical covalent polymer |url=https://pubmed.ncbi.nlm.nih.gov/35858342 |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=119 |issue=29 |pages=e2205320119 |doi=10.1073/pnas.2205320119 |issn=1091-6490 |pmc=9303982 |pmid=35858342}}</ref>
==References==
|
