Synthesis of Silsesquioxanes with Substituted Triazole Ring Functionalities and Their Coordination Ability †

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Article Synthesis of Silsesquioxanes with Substituted Triazole Ring Functionalities and Their Coordination Ability †

Monika Rzonsowska 1,2,* , Katarzyna Kozakiewicz 1, Katarzyna Mituła 1,2 , Julia Duszczak 1,2, Maciej Kubicki 3 and Beata Dudziec 1,2,*

1 Department of Organometallic Chemistry, Faculty of Chemistry, Adam Mickiewicz University in Poznań, Uniwersytetu Poznańskiego8, 61-614 Poznań,Poland; [email protected] (K.K.); [email protected] (K.M.); [email protected] (J.D.) 2 Centre for Advanced Technologies, Adam Mickiewicz University in Poznań,Uniwersytetu Poznańskiego10, 61-614 Poznań,Poland 3 Faculty of Chemistry, Adam Mickiewicz University in Poznań,Uniwersytetu Poznańskiego8, 61-614 Poznań,Poland; [email protected] * Correspondence: [email protected] (M.R.); [email protected] (B.D.); Tel.: +48-618291878 (B.D.) † Dedicated to Professor Julian Chojnowski on the occasion of his 85th birthday.

Abstract: A synthesis of a series of mono-T8 and difunctionalized double-decker silsesquioxanes bearing substituted triazole ring(s) has been reported within this work. The catalytic protocol for their formation is based on the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) process. Diverse alkynes were in the scope of our interest—i.e., aryl, hetaryl, alkyl, silyl, or germyl—and the latter was shown to be the first example of terminal germane alkyne which is reactive in the applied process’ conditions. From the pallet of 15 compounds, three of them with pyridine-triazole and Citation: Rzonsowska, M.; thiophenyl-triazole moiety attached to T8 or DDSQ core were verified in terms of their coordinating Kozakiewicz, K.; Mituła, K.; properties towards selected transition metals, i.e., Pd(II), Pt(II), and Rh(I). The studies resulted in Duszczak, J.; Kubicki, M.; Dudziec, B. Synthesis of Silsesquioxanes with the formation of four SQs based coordination compounds that were obtained in high yields up to Substituted Triazole Ring 93% and their thorough spectroscopic characterization is presented. To our knowledge, this is the Functionalities and Their first example of the DDSQ-based molecular complex possessing bidentate pyridine-triazole ligand Coordination Ability . Molecules 2021, binding two Pd(II) ions. 26, 439. https://doi.org/10.3390/ molecules26020439 Keywords: polyhedral oligomeric silsesquioxane (SQs); click chemistry; CuAAC; coordination compounds; bidentate ligand Academic Editors: Sławomir Rubinsztajn, Marek Cypryk and Wlodzimierz Stanczyk Received: 21 December 2020 1. Introduction Accepted: 12 January 2021 Published: 15 January 2021 Polyhedral oligomeric silsesquioxanes (SQs) are a large family of compounds that feature diverse structures with Si-O-Si linkages and tetrahedral Si vertices—i.e., random,

Publisher’s Note: MDPI stays neu- amorphous, ladder, and cage-like—and the architecture of the latter has attracted consider- tral with regard to jurisdictional clai- able scientific interest. It is due to the presence of the inorganic, rigid core (thermal stability, ms in published maps and institutio- chemical resistance) and organic moieties attached to it (tunable processability) which is nal affiliations. the essence of hybrid materials. Functionalized SQs derivatives may be regarded as their nanosized, smallest fragments and precursors that affect and drive the directions of their potential applications [1–6]. Significant development of catalytic protocols for effective and selective anchoring of respective organic functionality to the SQs core has been observed Copyright: © 2021 by the authors. Li- during the last years. The crucial aspect of this is the presence of a proper prefunctional censee MDPI, Basel, Switzerland. moiety at the Si-O-Si framework, enabling its modification, e.g., Si-H, Si-OH, Si–CH=CH2 This article is an open access article units, etc. This, in turn, influences the selection of a respective catalytic procedure for distributed under the terms and con- this purpose, e.g., hydrosilylation, cross-metathesis, O-silylation, Friedel-Crafts, silylative, ditions of the Creative Commons At- Heck, Suzuki, or Sonogashira coupling reactions [2,7–20]. Among these methods, the tribution (CC BY) license (https:// copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) may be an alternative but the creativecommons.org/licenses/by/ 4.0/). only route to yield substituted 1,4-triazole ring functionalities regioselectively [21–23]. This

Molecules 2021, 26, 439. https://doi.org/10.3390/molecules26020439 https://www.mdpi.com/journal/molecules Molecules 2021, 26, 439 2 of 15

is a powerful synthetic tool to build covalent connections between dissimilar units, and since its discovery in 2002 (independently by Sharpless, Fokin, and Meldal groups), it is widely utilized in (bio-)organic, medicinal and for some time now, also in surface/materials chemistry [24–27]. Despite the simplicity of the reaction, the immense development in the catalyst design, incl. stabilizing ligands, has be observed in the past few years. This may be visible in the aspect of functional group diversity in both reagents and their resilience to the CuAAC reaction conditions, i.e., solvent type, temperature, time, etc. The variety of Cu-based catalysts for this process requires the presence of the Cu(I) species at the highest concentration whether it is introduced in this state or generated in situ [26]. On the other hand, the Cu(I) favors the Glasser coupling of terminal alkynes [28], so the CuAAC conditions should be optimized to avoid the formation of by-products. For this, the in situ creation of Cu(I) ions seems reasonable [24]. As a result of this evolvement, the process gained popularity in the chemistry of silsesquioxanes as well. There are some examples of CuAAC methodology applied for silsesquioxanes to introduce the triazole moiety(-ies) substituted at 1,4 positions with the SQs core and organic group. The process may be applied in the case of mono- and octa-substituted T8 SQs, linked with the Si-O-Si core via mainly alkyl [29–36] but there are also reports on a phenyl group [37,38]. There are also few examples of using di- substituted double-decker (DDSQ) [39,40] or ladder [41] silsesquioxanes [42]. The application of the resulting products with 1,4-triazole ring(s) depends on the kind of alkyne moiety used as a reagent. Due to the interesting photoelectronic properties of SQs-based systems with aryl-triazole groups, they could be possibly used as luminescent materials with enhanced thermal resistance [29,41,43–45]. One of the promising branches of their application is materials chemistry, e.g., as polymers or dendrimers mod- iﬁers/synthons [30,39,42,46–54]. They may be also found in macromolecular SQs-based surfactants of amphiphilic and self-assembly or encapsulation properties [31,55,56]. Addi- tionally, the CuAAC methodology serves as a tool for the formation of SQs functionalized peptide dendrimers [35] or glycoconjugates and in targeted bioimaging [57,58]. Catalysis has become a very prospective direction of employing the SQs with 1,4- substituted triazole rings, as catalysts by themselves, e.g., in asymmetric Michael or Aldol reactions [32,33]. Even though there have been still very few reports in this area of interest. One of them reported on the potential coordinating character of a pyridine-triazole moiety attached to the SQs core and revealed its use as a ligand for Pd-complexation. Interestingly, this compound was found to be active in Suzuki–Miyaura cross-coupling [59]. Herein, we present our studies on the copper(I)-catalyzed azide-alkyne cycloaddition process of two different types of silsesquioxanes with the variation of alkynes bearing aryl, hetaryl, alkyl, silyl, siloxyl, or even germyl groups. As a result, we report on the preparation of mono-T8 and difunctionalized double-decker silsesquioxanes with substituted triazole ring(s). The second part of the paper is focused on the application of selected SQs with hetaryl substituted triazole moieties as potential ligands in complexing reaction Molecules 2021, 26, x 3 of 15 with transition metals (Pd, Rh, Pt), resulting in the formation of respective SQs-based coordination systems (Figure1).

Figure 1. Mono-TFigure8 1.and Mono-T difunctionalized8 and difunctionalized DDSQ silsesquioxanes DDSQ silsesquioxane with Substituteds with TriazoleSubstituted Ring Triazole and the Ring coordinating and ability of the pyridine-the coordinating and thiophenyl-derivatives ability of the pyridine- towards and selected thiophenyl-derivatives TM ions, presented towards in this work.selected TM ions, presented in this work.

2. Results and Discussion

2.1. The Copper(I)-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) Using iBuT8-N3 and DDSQ-2N3 In the first step, the starting precursors, i.e., the azidopropyl-derivative(s) of mono- iBuT8-N3 and di-DDSQ-2N3 were prepared in a sequence of hydrolytic condensation of respective silanol precursor of SQs and chlorosilane followed by nucleophilic substitution with NaN3 [60,61] (Figure 2). The idea of the synthetic path is presented below.

Figure 2. General route for the synthesis of azide-derivatives iBuT8-N3 and DDSQ-2N3.

The two SQs-based azides iBuT8-N3 and DDSQ-2N3 were used as reagents in Cu- AAC coupling process with a variety of alkynes bearing aryl, alkyl, silyl, and germyl functionalities. The reaction progress was monitored by FT-IR, due to the large mass of the product eliminating the possibility of using GC or GC-MS and confirmed by 1H-NMR. The representative FT-IRs are presented in Figure 3. For all alkynes tested nearly complete conversion of SQs azides was observed within up to 3 days which depended on the type of reaction conditions and Cu catalyst. The stacked FT-IR spectra of starting material iBuT8-N3 and the selected product with 4-pyridine-triazole group iBuT8-A1 are depicted in Figure 3. The established reaction conditions resulted in the complete conversion of azide (-N=N+=N-) group in iBuT8-N3, confirmed by the disappearance of respective bands attributed to stretching asymmetric vibrations of -N=N- at ca. ῡ = 2098 cm−1 (marked in Figure 3). For the CuAAC reaction product, i.e., iBuT8-A1, there are new bands in the spectrum, characteristics of C=C, C=N, N=N stretching vibrations from triazole as well as pyridine ring at ca. ῡ = 1603 cm−1 and ῡ = 1571 cm−1 that confirm the formation of the desired product.

Molecules 2021, 26, x 3 of 15

Molecules 2021, 26, 439Figure 1. Mono-T8 and difunctionalized DDSQ silsesquioxanes with Substituted Triazole Ring and 3 of 15 the coordinating ability of the pyridine- and thiophenyl-derivatives towards selected TM ions, presented in this work.

2. Results and2. Discussion Results and Discussion

2.1. The Copper(I)-Catalyzed2.1. The Copper(I)-Catalyzed Azide-Alkyne Azide-AlkyneCycloaddition Cycloaddition(CuAAC) Using (CuAAC) iBuT8-N3 Using andiBuT 8-N3 and DDSQ-2N3 DDSQ-2N3 In the ﬁrst step, the starting precursors, i.e., the azidopropyl-derivative(s) of mono- In the first step, the starting precursors, i.e., the azidopropyl-derivative(s) of mono- iBuT8-N3 and di-DDSQ-2N3 were prepared in a sequence of hydrolytic condensation of iBuT8-N3 and di-DDSQ-2N3 were prepared in a sequence of hydrolytic condensation of respective silanol precursor of SQs and chlorosilane followed by nucleophilic substitution respective silanol precursor of SQs and chlorosilane followed by nucleophilic substitution with NaN3 [60,61] (Figure2). The idea of the synthetic path is presented below. with NaN3 [60,61] (Figure 2). The idea of the synthetic path is presented below.

Figure 2. General route for the synthesis of azide-derivatives iBuT8-N3 and DDSQ-2N3. Figure 2. General route for the synthesis of azide-derivatives iBuT8-N3 and DDSQ-2N3.

The two SQs-basedThe two azides SQs-based iBuT8-N3 azides and iBuTDDSQ-2N38-N3 and wereDDSQ-2N3 used as reagentswere used in Cu- as reagents in AAC couplingCuAAC process coupling with a variety process of withalkynes a variety bearing of aryl, alkynes alkyl, bearing silyl, and aryl, germyl alkyl, func- silyl, and germyl tionalities. Thefunctionalities. reaction progress The reactionwas monitored progress by was FT-IR, monitored due to bythe FT-IR, large duemass to of the the large mass of product eliminatingthe product the eliminatingpossibility of the using possibility GC or of GC-MS using GCand or confirmed GC-MS and by conﬁrmed 1H-NMR. by 1H-NMR. The representativeThe representative FT-IRs are presented FT-IRs are in presentedFigure 3. For in Figureall alkynes3. For tested all alkynes nearly tested complete nearly complete Molecules 2021, 26, xconversion ofconversion SQs azides of was SQs observed azides was within observed up to within 3 days up which to 3 days depended which on depended the type on the type4 of of 15 of reaction conditionsreaction conditions and Cu catalyst. and Cu catalyst. The stacked FT-IR spectra of starting material iBuT8-N3 and the selected product with 4-pyridine-triazole group iBuT8-A1 are depicted in Figure 3. The established reaction conditions resulted in the complete conversion of azide (-N=N+=N-) group in iBuT8-N3, confirmed by the disappearance of respective bands attributed to stretching asymmetric vibrations of -N=N- at ca. ῡ = 2098 cm−1 (marked in Figure 3). For the CuAAC reaction product, i.e., iBuT8-A1, there are new bands in the spectrum, characteristics of C=C, C=N, N=N stretching vibrations from triazole as well as pyridine ring at ca. ῡ = 1603 cm−1 and ῡ = 1571 cm−1 that confirm the formation of the desired product.

Figure 3. FT-IR spectra of iBuT8-N3 and iBuT8-A1 after completion of CuAAC coupling reaction. Figure 3. FT-IR spectra of iBuT8-N3 and iBuT8-A1 after completion of CuAAC coupling reaction.

TheWe stackedbased on FT-IR two types spectra of ofCu starting sources, material i.e., CuSOiBuT4 with8-N3 sodiumand the ascorbate selected [40,59] product and withCuBr 4-pyridine-triazole with PMDTA [33]. group At iBuTfirst, 8special-A1 are conditions depicted in were Figure created3. The establishedfor the reduction reaction of + conditionsCu(II) in situ resulted to Cu(I) in theand complete then to maintain conversion the introduction of azide (-N=N of Cu(I)=N-) in group this oxidation in iBuT8-N3 state, conﬁrmedinto the reaction. by thedisappearance The main target of was respective to perform bands the attributed reaction until to stretching full conversion asymmetric of SQ- vibrationsbased azides of -N=N- to avoid at ca.the νproblematic¯ = 2098 cm− isolation1 (marked issues in Figure of resulting3). For SQ-products the CuAAC reactionwith sub- product,stituted i.e.,triazoleiBuT rings(s)8-A1, there from are unreacted new bands SQ-b inased the spectrum, azides. The characteristics results of the of reactions C=C, C=N, con- −1 N=Nducted stretching to obtain vibrations products from with triazolesubstituted as well triazole as pyridine ring(s) ringare collected at ca.ν ¯ = in 1603 Table cm 1 forand T8- ν¯derivatives= 1571 cm− and1 that in conﬁrmTable 2 for the DDSQ-derivatives. formation of the desired product.

Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT8-N3 and alkynes.

a 8 a iBuT8-A1 (78%) iBuT8-A2 (90%) a iBuT -A3 (83%)

a a iBuT8-A4 (82%) iBuT8-A5 (90%) iBuT8-A6 (89%) a

iBuT8-A7 (81%) a iBuT8-A9 (70%) b iBuT8-A10 (85%) c iBuT8-A8 (84%) b a Reaction conditions for Cu(II) source: [azide]:[alkyne]:[CuSO4][sodium ascorbate] = 1:1.4–8:0.025– 0.25:0.3–5; 25–60 °C; 72–96 h. b Reaction conditions for Cu(I) source: [azide]:[alkyne]:[CuBr][PMDTA] = 1:1.45:0.1:0.1; 25 °C; 24 h. c additional 12 h at 45 °C. > 99% conversion of iBuT8-N3 was confirmed by FT-IR in situ and 1H-NMR analyses. Value in parenthesis is given for isolation yield (%).

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Figure 3. FT-IR spectra of iBuT8-N3 and iBuT8-A1 after completion of CuAAC coupling reaction. FigureFigureFigureFigure 3. 3.Figure 3.FT3. FT FT FT--IRIR--IR IR3.spectra spectra spectra FTspectra-IR of spectraof of ofiBuT iBuT iBuT iBuT 8of-8-N38N38 -iBuT-N3N3 and and and and8 -iBu N3iBu iBu iBu TandT8T-8T-A18A18 -iBu-A1A1 after after Tafter after8- A1completion completion completion completion after completion of of of ofCuAAC CuAAC CuAAC CuAAC of CuAACcoupling coupling coupling coupling coupling reaction. reaction. reaction. reaction. reaction. FigureFigureFigureFigure 3. 3.Figure 3.FT3. FT FTFT--IRIR--IR IR3.spectra spectra spectraFTspectra-IR of spectraof of ofiBuT iBuT iBuTiBuT8 of-8-N38N38- -iBuTN3N3 and and andand8 -iBu N3iBu iBuiBu TandT8T-8T-A18A18- -iBuA1A1 after after afterTafter8- A1completion completion completioncompletion after completion of of ofofCuAAC CuAAC CuAACCuAAC of CuAACcoupling coupling couplingcoupling coupling reaction. reaction. reaction.reaction. reaction.

WeWe based based on on two two types types of of Cu Cu sources, sources, i.e. i.e.,, CuSO CuSO44 withwith sodium sodium ascorbate ascorbate [40,59] [40,59] and and WeWeWeWe based based basedbasedWe on onbased onon two two twotwo ontypes types typestypes two of of types of ofCu Cu CuCu sources, sources, of sources,sources, Cu sources, i.e. i.e. i.e.i.e., ,CuSO ,CuSO, CuSOCuSO i.e.4,4 with CuSO4with4 withwith sodium sodium4 sodiumsodiumwith sodium ascorbate ascorbate ascorbateascorbate ascorbate [40,59] [40,59] [40,59][40,59] and [40,59]and andand and CuBrCuBrWeWeWeWe withbased withbased basedbasedWe PMDTA on on based onon two two twotwo [typeson types[33]33 typestypes ].two. At Atof of typesof ﬁrst,of CuCu first, CuCu sources, sources, special of sources, sources, special Cu sources, conditionsi.e. i.e. i.e. conditionsi.e., ,CuSO ,CuSO, CuSOCuSO i.e.4 were,4 with CuSO4with4 with werewith createdsodium sodium 4 sodium sodiumwith created forsodium ascorbate ascorbate ascorbate ascorbate the for reduction the ascorbate [40,59] [40,59] reduction [40,59][40,59] of and [40,59]and Cu(II) andand of and CuBrCuBrCuBrCuBr with withCuBr with with PMDTA PMDTA PMDTAwith PMDTA PMDTA [33][33] [33][33]. . At.At. At[33]At first, first, first, first,. At special special special first, special special conditions conditions conditions conditions conditions were were were were created created were created created created for for for for the the the the for reduction reduction reduction reduction the reduction of of of of of CuBrCuBrCuBrCuBrCu(II)in situ with with CuBr with within to situ PMDTA PMDTA Cu(I) PMDTA withPMDTA to Cu(I) and PMDTA [33][33] [33] then[33] and. . At.At. At tothenAt[33] first, first, maintain first, first,. toAt specialmaintain special special first,special the special conditions conditions introduction conditionsthe conditions introduction conditions were were were were of Cu(I) created created of createdwere created Cu(I) in created this for for in for for thethis oxidation the the the for reductionoxidation reduction reduction reduction the state reduction state of of into of of of Cu(II)Cu(II)Cu(II)Cu(II) in inCu(II) in insitu situ situ situ to into to toCu(I) situCu(I) Cu(I) Cu(I) to and and Cu(I)and and then then then then and to to to tothenmaintain maintain maintain maintain to maintain the the the the introduction introduction introduction introduction the introduction of of of ofCu(I) Cu(I) Cu(I) Cu(I) of in in inCu(I) inthis this this this oxidation oxidationin oxidation oxidation this oxidation state state state state state Cu(II)Cu(II)Cu(II)Cu(II)intothe inthe reaction.inCu(II) in insitu situ reaction. situsitu to toin to toCu(I) TheCu(I)situ Cu(I)Cu(I) The mainto and and andCu(I) andmain then targetthen thenthen and target to to was to tomaintainthen maintain maintainmaintain was to to perform tomaintain theperformthe thethe introduction introduction the introductionintroduction the reactionthe introduction reaction of untilof of ofCu(I) Cu(I) Cu(I)Cu(I)until full of in in conversion inCu(I)full inthis this thisthis conversion oxidation oxidationin oxidationoxidation this of oxidation SQ-based state stateof statestate SQ - state intointointointo the the the theinto reaction. reaction. reaction.reaction. the reaction. The The TheThe main main mainmain The target target target maintarget was wastarget waswas to to to to perform wasperform perform perform to perform the the thethe reaction reaction reactionreaction the reaction until until untiluntil full full fulluntilfull conversion conversion conversionconversion full conversion of of of ofSQ SQ SQSQ-- -of- SQ- intointointointobasedazides the the thetheinto reaction. azidesreaction. reaction. toreaction. the avoid toreaction. The Theavoid theTheThe main main problematic main main theThe target targetproblematic targetmaintarget was was targetisolation waswas to to to toisolation perform wasperform performperform issues to perform the issuesthe of thethe resultingreaction reaction reactionreaction of the resulting reaction until until SQ-products untiluntil full full SQ fullfulluntil conversion -conversionproducts conversionconversion full with conversion substituted with of of of ofSQ SQ SQsub-SQ-- -of- SQ- basedbasedbasedbased azides azidesbased azidesazides toazidesto to toavoid avoid avoidavoid to the the avoid thethe problematic problematic problematicproblematic the problematic isolation isolation isolationisolation isolation issues issues issues issues of ofissues of ofresulting resulting resultingresulting of resulting SQ SQ SQSQ--productsproducts--productsproducts SQ-products with with withwith sub- sub- sub-sub-with sub- basedbasedbasedbasedstitutedtriazole azides azides based azidesazides triazole rings(s) to azidesto to toavoid avoid avoidavoid rings(s) from to the the avoid thethe unreacted problematic problematicfrom problematicproblematic the unreacted problematic SQ-based isolation isolation isolationisolation SQ azides. -isolationbased issues issues issuesissues Theazides. of ofissues of of resultsresultingresulting resultingresulting The of ofresultsresulting theSQSQ SQSQ- reactions-productsproducts --ofproductsproducts SQthe- reactionsproducts conductedwith with withwith sub- sub- sub- sub-con-with to sub- stitutedstitutedstitutedstitutedstituted triazole triazole triazole triazole triazole rings(s) rings(s) rings(s) rings(s) rings(s) from from from from unreacted unreacted unreacted fromunreacted unreacted SQ SQ SQ SQ--basedbased--basedbased SQ azides. -azides.based azides. azides. azides.The The The The results results results results The of resultsof of ofthe the the the reactions reactions ofreactions reactions the reactions con- con- con- con- con- stitutedductedobtainstituted triazole to products obtain triazolerings(s) products with rings(s)from substituted with unreacted from substitu triazole unreacted SQted-based ring(s) triazole SQ azides.-based are ring(s) collected Theazides. are results in collectedThe Table ofresults the1 for in reactions ofTable T the8-derivatives reactions1 con-for T8- con- ductedductedductedducted ductedto to to toobtain obtain obtainobtain to products obtainproducts productsproducts products with with withwith substitu substitu substituwithsubstitu substitutedtedtedted triazole triazole triazoletriazoleted triazole ring(s) ring(s) ring(s)ring(s) are ring(s)are areare collected collected collectedcollected are collected in in in inTable Table TableTable in 1 1 Table 1for 1for forfor T T 8 T8-1T-8 8-for- T8- ductedductedductedductedderivativesand ductedto into to to Tableobtainobtain obtainobtain and to2 products forobtainproducts in productsproducts DDSQ-derivatives.Table products with2with withwithfor substituDDSQsubstitu substitusubstituwith- substituderivatives.tedtedtedted triazole triazole triazoletriazoleted triazolering(s) ring(s) ring(s)ring(s) are ring(s)are areare collected collected collectedcollected are collected in in in inTable Table TableTable in 1 1 Table 1for 1for forfor T T 8 T 8-T1-8 8-for- T8- derivativesderivatives and in Tableand in 2 Tablefor DDSQ 2 for- derivatives.DDSQ-derivatives. derivativesderivativesderivativesderivativesderivatives and and andand in in in inTable andTable TableTable in 2 2 Table 2for2for forfor DDSQ DDSQ DDSQ DDSQ2 for- -derivatives.DDSQderivatives.--derivatives.derivatives.-derivatives. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT -N3 and alkynes. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT88-N3 and alkynes. TableTableTableTable 1. 1. Table1.C1. C opperC opperCopperopper 1.- C-catalyzedcatalyzed-opper-catalyzedcatalyzed-catalyzed azide azide azide azide--alkynealkyne- -alkyneazidealkyne cycloaddition- cycloadditionalkyne cycloaddition cycloaddition cycloaddition using using using using iBuT iBuT iBuT usingiBuT8-8-N38N38 -iBuT-N3N3 and and and and8 -alkynes N3alkynes alkynes alkynes and .alkynes . . . . TableTableTableTable 1. 1. 1.TableC1. C opper CopperCopperopper 1.- -catalyzedCcatalyzed--oppercatalyzedcatalyzed-catalyzed azide azide azideazide--alkynealkyne-- alkyneazidealkyne cycloaddition -cycloadditionalkyne cycloadditioncycloaddition cycloaddition using using usingusing iBuT iBuT iBuTusingiBuT8-8-N38N38- -iBuTN3N3 and and andand8 -alkynes N3alkynes alkynesalkynes and. .alkynes .. .

a 8 a iBuT8-A1 (78%aa) a 8 a iBuT -A3 (83%aa)aa a a iBuTiBuT88-A188iBuT-A1 (78%(78%)8-A1) a (a78%a ) iBuT -A2 (90%aaa)a a a iBuTiBuTiBuTiBuTiBuT88--A38A38iBuT--A3-A3A3 ( (83% 83% ((83%)(83%883%-A3)) ) a) ( a83%a ) iBuTiBuTiBuT8-8A18--A1A1 ( 78% ((78%78%)a )) a iBuTiBuTiBuTiBuTiBuT88--A2-A28A28iBuT--A2A2 ( (90%)(90% 90% ((90%890%-A2)) )a ) ( a90%a ) iBuTiBuTiBuT88-8A38--A3A3 ( 83% ((83%883%)a )) a iBuT8-A1iBuT (78%8-A1) (78%) iBuTiBuTiBuTiBuT88--A28A28-iBuT-A2A2 ( (90% 90% ((90%890%-A2)) a ) ) ( 90% ) a iBuT -A3iBuT (83%-A3) (83%)

a a iBuT8-A4 (82%a ) a iBuT8-A5 (90% ) 8 a iBuT88-A488iBuT (82%8-A4) a a(a82%a ) aaa aa a iBuT -A6 (89%aa)aa a a iBuTiBuTiBuT8-8A48--A4-A4A4 ( 82%(82%) ((82%82%)a )) a iBuTiBuTiBuTiBuTiBuT88--A5-A58A58iBuT--A5A5 ( (90%)(90% 90% ((90%890%-A5)) a )a ) ( a90%a ) a iBuTiBuTiBuTiBuTiBuT88--A68A68iBuT--A6-A6A6 ( (89% 89% ((89%)(89%889%-A6)) ) a) ( a89%a ) iBuT8-A4iBuT (82%8-A4) (82%) iBuTiBuTiBuTiBuT88--A58A58-iBuT-A5A5 ( (90% 90% ((90%890%-A5)) ) ) ( 90% ) iBuTiBuTiBuTiBuT88--A68A68-iBuT-A6A6 ( (89% 89% ((89%889%-A6)) a ) ) ( 89% ) a

a b iBuT8-A7 (81%a ) a iBuT8-A9 (70%b ) b c iBuT8 iBuT8-A78-A7 a(a81%a ) 8 iBuT8-A9 b(b70%b )b 8 iBuTiBuTiBuTiBuT8--A78A78--A7A7 ( (81% 81% ((81%81%)) a ) ) a iBuTiBuTiBuTiBuT 8--A98A98--iBuTA9A9 ( (70% 70% ((70%70%-A9)) b ) ) (70%) biBuT -A10iBuT (85%8-A10cc)c c c iBuT8-A7iBuT (a81%8-A7) (81%) iBuT8-A9iBuT (70%8-A9) (70%iBuT)iBuT iBuTiBuT 88--A108A108iBuT--A10A10 ( (85% 885% (-(85%A1085%)) c ) c) ( c85%c ) c (81%) 8 b iBuTiBuTiBuT88-8A108--A10A10 ( 85%8 ((85%85%) )) c iBuT -A8 (84%bb)b b b iBuT -A10iBuT (85%(85%)-A10) (85%) iBuTiBuTiBuTiBuT88--A88A88iBuT--A8A8 ( (84% 84% ((84%884%-A8)b) b )b ) ( b84%b ) b a iBuTiBuTiBuTiBuT88--A8-A88A88-iBuT-A8A8 (84%)( (84% 84% ((84%884%-A8)) ) ) ( 84% ) Reactiona conditions for Cu(II) source: [azide]:[alkyne]:[CuSO4][sodium ascorbate] = 1:1.4–8:0.025– aa aa 4 4 a aReaction aReactiona Reaction aReactiona Reaction conditions conditions conditions conditions conditions for for for for Cu(II) Cu(II) Cu(II) Cu(II) for source: source: Cu(II)source: source: [azide]:[alkyne]:[CuSO source:[azide]:[alkyne]:[CuSO [azide]:[alkyne]:[CuSO [azide]:[alkyne]:[CuSO [azide]:[alkyne]:[CuSO][sodium4][sodium44][sodium][sodium][sodium ascorbate] ascorbate] ascorbate] ascorbate] ascorbate] = = 1:1.4= =1:1.4 1:1.4 1:1.4––8:0.025 –8:0.025=–8:0.025 8:0.0251:1.4–––8:0.025–– – Reaction Reaction ReactionReactionReaction Reaction conditions conditions conditionsconditions conditions conditions for for forfor Cu(II) Cu(II) Cu(II) Cu(II)Cu(II) for source: b source: Cu(II) source:source: [azide]:[alkyne]:[CuSO source:[azide]:[alkyne]:[CuSO [azide]:[alkyne]:[CuSO[azide]:[alkyne]:[CuSO [azide]:[alkyne]:[CuSO4][sodium4][sodium][sodium][sodium][sodium ascorbate]4][sodium ascorbate] ascorbate] ascorbate]ascorbate] = ascorbate] 1:1.4–8:0.025–0.25:0.3–5; = = 1:1.4 ==1:1.4 1:1.41:1.4––8:0.025 8:0.025–=–8:0.025 8:0.0251:1.4–––8:0.025–– – 0.25:0.3–5; 25–60 °C; 72–96 bh. b Reactionb conditions for Cu(I) source: [azide]:[al- 0.25:0.30.25:0.30.25:0.30.25:0.3––0.25:0.35;◦–5;– 5;255; 25 25 –25–60–60–60 605;° °C; C;° 25°C; bC;72 –72 6072 –72–96 –96°–96C; 96h. h. h. 72h. b Reaction –b Reactionb 96Reaction Reaction h. Reaction conditions conditions conditions conditions conditions for for for for Cu(I) Cu(I) Cu(I) Cu(I) for source: source: source: Cu(I)source: [azide]:[al-source:[azide]:[al- [azide]:[al- [azide]:[al- [azide]:[al- ◦ 0.25:0.30.25:0.30.25:0.30.25:0.325–60––0.25:0.35;5;––C; 5;255; 25 72–9625–25–6060–––60 605;° ° h.C; C;°25°C; C;72 72–Reaction 7260–72–9696– –°96C; 96h. h. h.72h.b conditions Reaction –Reaction 96 ReactionReaction h. b Reaction forconditions conditions conditionsconditions Cu(I) source:conditions for for forcfor [azide]:[alkyne]:[CuBr][PMDTA]Cu(I)Cu(I) Cu(I)Cu(I) for source: source: source:source:Cu(I) [azide]:[al- source:[azide]:[al- [azide]:[al-[azide]:[al- [azide]:[al- = 1:1.45:0.1:0.1; 25 C; kyne]:[CuBr][PMDTA] = 1:1.45:0.1:0.1; 25 °C; 24 ch. additionalc 12 h at 45 °C. > 99% conversion of kyne]:[CuBr][PMDTA]kyne]:[CuBr][PMDTA]c = 1:1.45:0.1:0.1;◦ = 1:1.45:0.1:0.1; 25 °C; 24 25 h. ° C; cadditionalc c24 h. additional 12 h at 45 12 ° C.h at > 4599% °C. conversion > 99% conversion 1of of Molecules 2021, 26, x kyne]:[CuBr][PMDTA]kyne]:[CuBr][PMDTA]kyne]:[CuBr][PMDTA]24 h. additional 12 h = at = =1:1.45:0.1:0.1; 451:1.45:0.1:0.1; 1:1.45:0.1:0.1;C. > 99% conversion25 25 25 ° C; °°C;C; 24 24 24 1h. ofh. h.c iBuT additional additional additional8-N3c was 12 12 12conﬁrmed h h hat at at 45 45 45 ° C. °° byC.C. > > FT-IR>99% 99% 99% conversionin conversion conversion situ and H-NMRof of 5of of 15 MoleculesMoleculesMoleculesMolecules 2021Molecules 2021, 2021 202126, x,, , 202126 2626 ,, , x xx, 26 , x kyne]:[CuBr][PMDTA]iBuT8kyne]:[CuBr][PMDTA]-N3 was confirmed = 1:1.45:0.1:0.1; by FT = 1:1.45:0.1:0.1;-IR in 25 situ °C; and 24 25 h. H °C; -additionalNMR 24 h. analyses. additional 12 h atValue 45 12 ° C. hin at> parenthesis 99%45 °C. conversion > 99% is conversion5given of of 15555 of ofoffor 15 15155 of of 15 8 11 11 1 iBuTiBuTiBuTiBuTanalyses.8-8-N38N38-iBuT-N3N3 was was was Valuewas- confirmedN3 confirmed confirmed confirmed inwas parenthesis confirmed by by by by FT FT FT isFT--IR givenIR- -byIR IRin in in FTinsitu forsitu situ -situIR isolationand and inand and situ1 H1 H 11H- yieldHNMR-andNMR--NMRNMR (%). Hanalyses. analyses. -analyses. NMRanalyses. analyses. Value Value Value Value in in Valuein inparenthesis parenthesis parenthesis parenthesis in parenthesis is is isgiven isgiven given given isfor for for givenfor for iBuTiBuTiBuTiBuTisolation8-8-N38N38--iBuTN3N3 was was yield waswas8 -confirmed N3confirmed confirmed confirmed(%) was. confirmed by by byby FT FT FTFT--IRIR- -IRby IRin in in FTinsitu situ situ-situIR and and in andand situ H H H-H-NMR andNMR--NMRNMR 1 Hanalyses. analyses. - analyses.NMRanalyses. analyses. Value Value ValueValue in in inValueinparenthesis parenthesis parenthesisparenthesis in parenthesis is is isgiven isgiven givengiven foris for forgivenfor for isolationisolation yield (%) yield. (%). isolationisolationisolationisolationisolation yield yield yield yield (%) (%) (%) (%)yield. . . . (%). Table 2. DDSQ-2N3 a Table 2. CCopper-catalyzedopper-catalyzed azide azide-alkyne-alkyne cycloaddition using DDSQ-a2N3a a .. a TableTableTableTable 2. CTable opper2. 2.2. C CC opperopper opper2.-catalyzed Copper---catalyzedcatalyzedcatalyzed-catalyzed azide azide azideazide-alkyne azide---alkynealkynealkyne cycloaddition-alkyne cycloaddition cycloadditioncycloaddition cycloaddition using using usingusing DDSQ using DDSQ DDSQDDSQ-2N3 DDSQ---2N3 2N32N3. - 2N3a.. . .

a a DDSQ-2A1 (a85%) a DDSQ-2A3 (82%a )a a a a DDSQ-2A1 (85%) a aaa a DDSQ-2A2 (60%a a)a a a DDSQDDSQDDSQ-2A3DDSQDDSQ-2A3--2A3 2A3(82%- 2A3( (82%)82% (82%)()82%) a ) DDSQDDSQDDSQDDSQ-2A1DDSQ---2A12A1 2A1(85%- 2A1( ((85%85%)85% ())85%) ) DDSQDDSQDDSQDDSQDDSQ-2A2-2A2DDSQ---2A22A2 2A2(60%- (60%) 2A2( ((60%60%)60% ())60%) a ) DDSQ-2A3 (82%)

a a a DDSQ-2A4 (78%a) DDSQDDSQ-2A11-2A11(84%) (84%a )aa a a DDSQDDSQDDSQDDSQDDSQ-2A4-2A4DDSQ---2A42A4 2A4(78%- (78%)2A4( ((78%78%)78% a ())78%) a aa ) a DDSQDDSQDDSQDDSQ-2A11DDSQ---2A112A112A11 (84%-2A11 ( ((84%84%)84% ())84%) ) a Reactiona conditions for Cu(II) source: [azide]:[alkyne]:[CuSO4][sodium ascorbate] = 1:1.4–8:0.025– a aaa a 4 44 4 Reaction Reaction ReactionReactionReaction Reactionconditions conditions conditionsconditions conditions for Cu(II) forfor forfor Cu(II) Cu(II) Cu(II)Cu(II) for source: Cu(II) source: source: source:source: [azide]:[alkyne]:[CuSO source: [azide]:[alkyne]:[CuSO [azide]:[alkyne]:[CuSO [azide]:[alkyne]:[CuSO[azide]:[alkyne]:[CuSO [azide]:[alkyne]:[CuSO4][sodium4][sodium][sodium][sodium ascorbate]][sodium ascorbate] ascorbate] ascorbate]ascorbate] =ascorbate] 1:1.4–8:0.025–0.25:0.3–5;= 1:1.4 = == 1:1.4 1:1.4–1:1.48:0.025 = ––1:1.4–8:0.0258:0.0258:0.025––8:0.025––– – 0.25:0.3◦ –5; 25–60 °C; 72–96 h. > 99% conversion of DDSQ-2N3 was confirmed by FT-IR in situ and 0.25:0.30.25:0.30.25:0.30.25:0.325–60–5;0.25:0.3 25––C;–5;5;–5;60 72–96 25 2525– °––5;–C;606060 25 h. 72 ° °°C;– >C;C;–60 99%96 72 7272 ° h.C;––– conversion969696 >72 h. 99%h.h.– 96 > >> 99% 99%99%conversionh. of> conversion 99%conversionDDSQ-2N3conversion conversion of DDSQ wasof ofof DDSQ DDSQDDSQ conﬁrmed of-2N3 DDSQ---2N3 2N32N3was by - was2N3wasconfirmedwas FT-IR confirmedconfirmedwasconfirmed in situ confirmed by and FT by by1byH-NMR-IR FT FTFT byin---IRIRIR situFT analyses.in inin- IR situ andsitusitu in and andandsitu Value and 1H-NMR analyses. Value in parenthesis is given for isolation yield (%). 1H-NMR111HHHin---NMRNMR parenthesisNMR 1analyses.H-NMR analyses. analyses.analyses. analyses. isValue given Value ValueValue in for parenthesisValue isolation in inin parenthesis parenthesisparenthesis in parenthesis yield is (%).given is isis given givengiven for is given isolation for forfor isolation isolationisolation for isolationyield y yy ieldield(%)ield y. (%)(%)ield(%).. . (%). The results of DDSQ-based systems with substituted triazole rings are collected in TheThe TheTheresultsThe Theresultsresultsresults results ofresults DDSQ ofofof of DDSQDDSQDDSQ DDSQ-basedof-based DDSQ---basedbasedbased systems-based systemssystemssystems systems systemswith withwithwith withsubstituted with substitutedsubstitutedsubstituted substituted substituted triazole triazoletriazoletriazole triazole triazolerings ringsringsrings ringsare rings arearecollectedare are collectedcollectedcollectedare collected collected in ininin in in Table 2 and involves the selective formation of DDSQ-compounds with the two above- TableTableTableTableTable 2 Tableand 222 and andinvolves 2 andinvolves involves involves the thetheselective the selectiveselective selectivethe selective formation formationformation formation formation of DDSQ ofof of DDSQDDSQDDSQ DDSQ-compounds of-compounds DDSQ---compoundscompoundscompounds-compounds with withwithwith withthe with thethetwothe the two twotwothe twoabove- twoabove-above-above- above- above- mentioned triazole moieties. The spectrum of used alkynes varies as they contain aryl, mentionedmentionedmentionedmentionedmentionedmentioned triazole triazoletriazoletriazole triazole triazolemoieties. moieties.moieties.moieties. moieties. moieties. The The TheThespectrum The Thespectrumspectrumspectrum spectrum spectrum of used ofofof of usedusedused of usedalkynes used alkynesalkynesalkynes alkynes alkynesvaries variesvariesvaries varies as varies they asasas as theytheythey theycontainas they containcontaincontain contain containaryl, aaa ryl,ryl, aryl,ryl, a ryl, hetaryl, alkyl, and silyl derivatives of commercial availability. Additionally, we tested hetaryl,hetaryl,hetaryl,hetaryl, hetaryl, alkyl alkyl alkyl alkyl, and alkyl,, , and andand silyl, and silyl silyl silyl derivatives silyl derivatives derivatives derivatives derivatives of commercial of of of commercial commercial commercial of commercial availability. availability. availability. availability. availability. Additionally, Additionally, Additionally, Additionally, Additionally, we we testedwe we tested tested testedwe tested ethynyl(triethyl)germane (A9) and ethynylsiloxysubstituted-iBuT8 (A8) to verify their po- ethynyl(triethyl)germaneethynyl(triethyl)germaneethynyl(triethyl)germaneethynyl(triethyl)germaneethynyl(triethyl)germane (A9) (A9) (A9)(A9) and (A9) and andandethynylsiloxysubstituted ethynylsiloxysubstituted andethynylsiloxysubstitutedethynylsiloxysubstituted ethynylsiloxysubstituted-iBuT---iBuTiBuTiBuT8 (A8)-iBuT888 (A8) (A8)(A8) to 8verify (A8) to toto verify verifyverify to their verify their theirtheir po- their po- po-po- po- tential in the CuAAC process. tentialtentialtentialtential intential the in inin the CuAACthethe in CuAAC CuAACCuAACthe CuAAC process. process. process.process. process. The tested reaction conditions based on Cu(II) and Cu(I) catalysts seem to be analo- TheThe TheThetested testedThetestedtested reaction tested reactionreactionreaction reactionconditions conditionsconditionsconditions conditions based basedbasedbased on based Cu( ononon Cu(II)Cu(Cu( on andII) II)II)Cu( and andandCu(I)II) Cu(I)andCu(I)Cu(I) catalysts Cu(I) catalystscatalystscatalysts catalysts seem seemseemseem to seembe tototo analo- bebebe to analo-analo-analo- be analogous in the case of less demanding alkynes, i.e., simple aryl or alkyl derivatives. Interest- gousgousgousgous in thegous in inin the casethethe in case case casetheof less caseof ofof less lesslessdemanding of demanding lessdemandingdemanding demanding alkynes, alkynes, alkynes,alkynes, alkynes, i.e., i.e.i.e.simplei.e.,, , simple simplei.e.simple ,aryl simple aryl aryl arylor alkyl arylor oror alkyl alkylalkyl orderivatives. alkyl derivatives. derivatives.derivatives. derivatives. Interest- Interest- Interest-Interest- Interest- ingly, for the 5-hexynenitrile, the applied catalytic conditions did not affect the present - ingly,ingly,ingly,ingly, foringly, the forforfor the5the thefor-hexynenitrile, 555the---hexynenitrile,hexynenitrile,hexynenitrile, 5-hexynenitrile, the theappliedthethe appliedappliedappliedthe appliedcatalytic catalyticcatalyticcatalytic catalytic conditions conditionsconditionsconditions conditions did diddidnotdid notnotaffectdidnot affectaffectnotaffect the affect thepresentthethe presentpresentpresentthe present- --- - CN moiety that in general may also be reactive and susceptible to alkyne-azide coupling CN CNCNmoietyCN moietymoietyCNmoiety thatmoiety thatthat thatin general that ininin generalgeneralgeneral in maygeneral maymaymay also may aa abelsolsolso reactive a bebebelso reactivereactivereactive be reactiveand and andandsusceptible susceptibleandsusceptiblesusceptible susceptible to alkyne tototo alkynealkynealkyne to- azidealkyne---azideazideazide coupling-azide couplingcouplingcoupling coupling reaction conditions to form respective 5-substituted tetrazoles [62]. For this, the presence reactionreactionreactionreaction reactionconditions conditionsconditionsconditions conditions to form tototo formformform respectiveto form respectiverespectiverespective respective 5-substituted 555---substitutedsubstitutedsubstituted 5-substituted tetrazoles tetrazolestetrazolestetrazoles tetrazoles [62] [62].[62][62] For. . .[62] ForForthis,For. this,this,Forthis, the this, thepresencethethe presence presencepresencethe presence of a reactive -CN moiety could be used in further modifications of the obtained products: of aof ofofreactive a aa reactive ofreactivereactive a reactive-CN - -- CNCNmoietyCN - moiety moietyCNmoiety couldmoiety could couldcould be could used be bebe used usedused bein furtherused in inin further furtherfurther in modfurther mod modmodifications modificationsificationsificationsifications of the of ofof the obtainedthethe of obtained obtainedobtainedthe obtained products: products: products:products: products: iBuT8-A4 and DDSQ-2A4. The reactivity of ethynylsilane (A9), ethynylgermane (A10) iBuTiBuTiBuTiBuT8-A4iBuT888- --A4andA4A4 8 -and andandA4DDSQ andDDSQDDSQDDSQ- 2A4DDSQ---2A42A4.2A4 The-..2A4 . The TheThereactivity. Thereactivityreactivityreactivity reactivity of ethynylsilane ofofof ethynylsilaneethynylsilaneethynylsilane of ethynylsilane (A9), (A9),(A9),(A9), ethynylgermane (A9), ethynylgermaneethynylgermaneethynylgermane ethynylgermane (A10) (A10)(A10)(A10) (A10) and also ethynylsiloxysubstituted iBuT8 (A8) compounds was tested with positive results. andand andandalso also andalso alsoethynylsiloxysubstituted ethynylsiloxysubstitutedalso ethynylsiloxysubstitutedethynylsiloxysubstituted ethynylsiloxysubstituted iBuT iBuT iBuTiBuT8 (A8) iBuT888 (A8) (A8)(A8) compounds8 (A8) compounds compoundscompounds compounds was was was wastested testedwas testedtested with tested with withwith positive with positive positivepositive positiveresults. results. results.results. results. However, the use of silyl (A9) or germyl (A10) alkyne proceeded with >99% conversion However,However,However,However,However, the theusethethe useuseofusethe silyl ofofuseof silylsilylsilyl (A9)of silyl (A9)(A9)(A9) or germyl (A9) ororor germylgermylgermyl or (A10)germyl (A10)(A10)(A10) alkyne (A10) aaalkynelkynelkyne proceededalkyne proceededproceededproceeded proceeded with withwithwith >99% with >99%>99%>99% conversion >99% conversionconversionconversion conversion of SQs-based azides (iBuT8-N3 and DDSQ-2N3) only when modified reaction conditions of SQsofofof SQs SQs-SQsbasedof- -SQs-basedbasedbased azides-based azides azidesazides ( iBuTazides ( ((iBuTiBuTiBuT8-N3 (iBuT888- --andN3N3N3 8 and -andandDDSQN3 DDSQ andDDSQDDSQ- 2N3DDSQ---2N32N3)2N3 only-))2N3) only onlyonly when) only when whenwhen modified when modified modifiedmodified modified reaction reaction reactionreaction reactionconditions conditions conditionsconditions conditions with Cu(I) [33] were applied (heating at 45 °C). Even though, for ethynylsiloxysubstituted- withwithwithwith Cu(I)with Cu(I) Cu(I)Cu(I) [33] Cu(I) [33] [33][33]were were were[33]were applied were applied appliedapplied (heatingapplied (heating (heating(heating (heating at 45 at atat ° C).45 4545 at ° °°EvenC).C). C).45 Even °EvenEvenC). though, Even though, though,though, though,for ethynylsiloxysubstituted for forfor ethynylsiloxysubstituted ethynylsiloxysubstitutedethynylsiloxysubstituted for ethynylsiloxysubstituted- --- - iBuT8 (A8) up to 10% of unreacted iBuT8-N3 was observed. It could be separated from the iBuTiBuTiBuTiBuT8 (A8)iBuT888 (A8)(A8) (A8) up8 (A8)to up upup 10% to toto up 10% 10% 10%of to unreacted 10%of ofof unreacted unreactedunreacted of unreacted iBuT iBuT iBuTiBuT8-N3 iBuT888- --wasN3N3N3 8 was -was wasobserved.N3 wasobserved. observed.observed. observed. It could It ItIt could couldcould Itbe could separated be bebe separated separatedseparated be separated from from fromfrom the from the thethe the resulting product iBuT8-A8 during the purification with the use of chromatography col- resultingresultingresultingresultingresulting product productproductproduct productiBuT iBuTiBuTiBuT8-A8 iBuT888- --duringA8A8A8 8 during-duringduringA8 theduring thepurificationthethe purificationpurificationpurificationthe purification with withwithwith the with theusethethe useuseofusethe chromatography ofofuseof chromatographychromatographychromatography of chromatography col- col-col-col- col- umn and proper eluent selection (hexane:DCM 3:1 for separation of iBuT8-N3 from iBuT8- umnumnumnumn andumn and andandproper proper andproperproper eluent proper eluent eluenteluent selection eluent selection selectionselection selection (hexane:DCM (hexane:DCM (hexane:DCM(hexane:DCM (hexane:DCM 3:1 for 3:1 3:13:1 separation for forfor 3:1 separation separationseparation for separation of iBuT of ofof iBuT iBuTiBuT8 of-N3 iBuT888- --fromN3N3N3 8 from -fromfromN3 iBuT from iBuT iBuTiBuT8- iBuT888--- 8- A8). Lower reactivity of A8 may derive from the presence of oxygen as the silicon atom in A8).A8A8A8 Lower).).). A8Lower LowerLower). reactivity Lower reactivity reactivityreactivity reactivity of A8 of ofof mayA8 A8A8 of may may may A8derive may derive derivederive from derive from fromfrom the from thepresence thethe presence presence presencethe presence of oxygen of ofof oxygen oxygenoxygen of asoxygen the as asas thesilicon thethe as silicon silicon siliconthe a silicontom a aatomtom tomin a intom inin in the vicinity of ethynyl-moiety and its electron-withdrawing impact. It should be noted the thethevicinitythe vicinityvicinitythevicinity vicinityof ethynyl ofofof ethynylethynylethynyl of -ethynylmoiety---moietymoietymoiety -andmoiety and andandits electron anditsitsits electronelectron electronits -electronwithdrawing---withdrawingwithdrawingwithdrawing-withdrawing impact. impact.impact.impact. impact.It should ItItIt shouldshouldshould It beshould noted bebebe notednoted notedbe noted that ethynylsilanes exhibit reactivity in this process, but conditions created by us seem to thatthatthat thatethynylsilanes thatethynylsilanes ethynylsilanesethynylsilanes ethynylsilanes exhibit exhibit exhibitexhibit reactivity exhibit reactivity reactivityreactivity reactivity in this in inin this thisthisprocess, in process, thisprocess,process, process,but but butconditionsbut conditionsconditionsbutconditions conditions created cr crcreatedeatedeated bycreated us by byby seem us usus by seem seemseem usto seem to toto to be milder for lower reaction temperature [63]. On the other hand, it would be the first be milderbebebe mildermildermilderbe formilder forlowerforfor lower lowerlowerfor reaction lower reactionreactionreaction reactiontemperature temperaturetemperaturetemperature temperature [63] [63].[63][63] On .. .[63] OnOntheOn . thetheothertheOn otherothertheother hand, other hand,hand,hand, it hand,would ititit wouldwouldwould it bewould the bebebe thethefirst thebe firstfirst thefirst first example for ethynylgermane (A10) to exhibit high reactivity in the CuAAC reaction. One exampleexampleexampleexampleexample for ethynyfor forfor ethyny ethyny ethynyforlgermane ethynylgermanelgermanelgermanelgermane (A10) (A10) (A10)(A10) to (A10)exhibit to toto exhibit exhibitexhibit to high exhibit high highhigh reactivity high reactivity reactivityreactivity reactivity in the in inin the CuAACthethe in CuAAC CuAACCuAACthe CuAAC reaction. reaction. reaction.reaction. reaction. One One One One One report on the formation of 4-germyl-substituted triazole ring derivative concerns using reportreportreportreport onreport the ononon thetheformation theon formationformationtheformation formation of 4 ofof-ofgermyl 444 ---ofgermylgermylgermyl 4--substitutedgermyl---substitutedsubstitutedsubstituted-substituted triazole triazoletriazoletriazole triazolering ringring ringderivative ring derivativederivativederivative derivative concerns concernsconcernsconcerns concerns using usingusingusing using internal alkyne, i.e., 3-(trimethylgermyl)-2-propynal [64]. Additionally, the reports on the internalinternalinternalinternal internalalkyne, alkyne, alkyne,alkyne, i.e.alkyne,, i.e. i.e.3i.e.-(trimethylgermyl),, , 33i.e.3---(trimethylgermyl)(trimethylgermyl)(trimethylgermyl), 3-(trimethylgermyl)-2-propynal---222---propynalpropynalpropynal-2-propynal [64] [64] .[64][64] Additionally,. . .[64] Additionally, Additionally,Additionally,. Additionally, the the reportsthethe reports reportsreportsthe onreports the on onon the thethe on the reactivity of the ethynylsiloxy-moiety (meaning A8) in the CuAAC process are very scarce reactivityrrreactivityeactivityeactivityreactivity of the of ofof theethynylsiloxy thethe of ethynylsiloxy ethynylsiloxy ethynylsiloxythe ethynylsiloxy-moiety---moietymoietymoiety -(meaningmoiety (meaning (meaning(meaning (meaning A8) A8) A8)inA8) the in inA8)in theCuAAC thethe in CuAAC CuAAC CuAACthe CuAAC process process processprocess areprocess veryare areare very very very arescarce very scarce scarcescarce scarce [65]. [65][65].[65][65] .. .[65] . An interesting relationship was found for 1H-NMR analyses of DDSQs bearing tria- An AninterestingAnAn interestinginterestinginterestingAn interesting relationship relationshiprelationshiprelationship relationship was waswas wasfou ndwas foufoufou forndnd ndfou 1 forforHfornd- NMR 11 1HHforH---NMRNMR NMR1H analyses-NMR analysesanalysesanalyses analyses of DDSQs ofofof DDSQsDDSQsDDSQs of bearingDDSQs bearingbearingbearing bearingtria- tria-tria-tria- tria- zole ring substituted at 4-positition with an aryl (DDSQ-2A1) and alkyl (DDSQ-2A4) zolezolezole zole ring zole ring ring ring substituted ring substituted substituted substituted substituted at 4 at at- atpositition 4 4 4 -- at-posititionposititionpositition 4-positition with with with with an with aryl an an an aryl aryl aryl an(DDSQ aryl ( ( (DDSQDDSQDDSQ - (2A1DDSQ---2A12A1)2A1 and-))2A1) and and and alkyl) and alkyl alkyl alkyl (DDSQ alkyl ( ( (DDSQDDSQDDSQ - (2A4DDSQ---2A42A4)2A4 -))2A4) ) group. The resonance line of a very significant triazole proton N=C-Ht at 5H-position of group.group.group.group. Thegroup. The TheTheresonance resonanceTheresonanceresonance resonance line linelinelineof a ofline ofofvery aaa ofveryveryvery significant a very significantsignificantsignificant significant triazole triazoletriazoletriazole triazoleproton protonprotonproton N=Cproton N=CN=CN=C-Ht N=C-at--HHH t5t t atHatat-H- 5position55tH HHat---position positionposition5H-position of ofofof of triazole ring depends on the type of the moiety at 4-position of the latter. The crucial as- triazoletriazoletriazoletriazole triazolering ringring ringdepends ring dependsdependsdepends depends on the ononon thetypethethe on typetypetypethe of the type ofofof themoietythethe of moietymoietymoietythe atmoiety 4 at-atatposition 444- --positionatpositionposition 4-position of the ofofof thelatter.thethe of latter.latter.latter.the The latter. The TheThecrucial crucialThecrucialcrucial as- crucial as-as-asas- pect may be its electronic property and the respective shielding effect of alkyl and pectpectpectpect may pect may may may be may itsbe be be electronicits its its be electronic electronic electronic its electronic property property property property property and and and and the and the the therespective respective therespective respective respective shielding shielding shielding shielding shielding effect effect effect effect of effect alkyl of of of alkyl alkyl alkyl of and alkyl and and and and deshielding effect characteristic for the aryl moiety presence. It affects the N=C-Ht signal deshieldingdeshieldingdeshieldingdeshieldingdeshielding effect effecteffecteffect characteristic effect characteristiccharacteristiccharacteristic characteristic for the forforfor thearylthe thefor arylaryl arylthemoiety aryl moietymoietymoiety presence.moiety presence.presence.presence. presence. It affects ItItIt affectsaffectsaffects It the affects theN=Cthethe N=CN=CN=Cthe-Ht N=C-signal--HHHtt t signalsignalsignal-H t signal shift and it is upfield for DDSQ-2A1 to be present at 6.75 ppm and downfield for DDSQ- shiftshiftshiftshift and shift and andandit is itanditupfieldit is isis upfield upfielditupfield is forupfield DDSQfor forfor DDSQ DDSQ DDSQfor- 2A1DDSQ---2A12A1 2A1to be- 2A1to toto present be bebe to present presentpresent be atpresent 6.75 at atat 6.75 6.75 6.75ppm at 6.75ppm ppmppm and ppm and andanddownfield downfield anddownfielddownfield downfield for DDSQfor forfor DDSQ DDSQ DDSQfor- DDSQ--- - 2A4, to appear at 7.84 ppm, which gives a total change in resonance lines of 1.09 ppm 2A42A42A4,2A4 to ,,2A4appear , tototo appearappear,appear to atappear 7.84 atatat 7.847.84 7.84 ppm,at 7.84 ppm,ppm,ppm, which ppm, whichwhichwhich gives which givesgivesgives a totalgives aaa totaltotaltotal change a total changechangechange inchange resonance ininin resonanceresonanceresonance in resonance lines lineslineslines of lines1.09 ofofof 1.091.09 1.09 ppmof 1.09 ppmppmppm ppm

Molecules 2021, 26, 439 5 of 15

hetaryl, alkyl, and silyl derivatives of commercial availability. Additionally, we tested ethynyl(triethyl)germane (A9) and ethynylsiloxysubstituted-iBuT8 (A8) to verify their potential in the CuAAC process. The tested reaction conditions based on Cu(II) and Cu(I) catalysts seem to be analogous in the case of less demanding alkynes, i.e., simple aryl or alkyl derivatives. Interestingly, for the 5-hexynenitrile, the applied catalytic conditions did not affect the present -CN moiety that in general may also be reactive and susceptible to alkyne-azide coupling reaction conditions to form respective 5-substituted tetrazoles [62]. For this, the presence of a reactive -CN moiety could be used in further modifications of the obtained products: iBuT8-A4 and DDSQ-2A4. The reactivity of ethynylsilane (A9), ethynylgermane (A10) and also ethynylsiloxysubstituted iBuT8 (A8) compounds was tested with positive results. However, the use of silyl (A9) or germyl (A10) alkyne proceeded with >99% conversion of SQs-based azides (iBuT8-N3 and DDSQ-2N3) only when modified reaction conditions with Cu(I) [33] were applied (heating at 45 ◦C). Even though, for ethynylsiloxysubstituted- iBuT8 (A8) up to 10% of unreacted iBuT8-N3 was observed. It could be separated from the resulting product iBuT8-A8 during the purification with the use of chromatography column and proper eluent selection (hexane:DCM 3:1 for separation of iBuT8-N3 from iBuT8-A8). Lower reactivity of A8 may derive from the presence of oxygen as the silicon atom in the vicinity of ethynyl-moiety and its electron-withdrawing impact. It should be noted that ethynylsilanes exhibit reactivity in this process, but conditions created by us seem to be milder for lower reaction temperature [63]. On the other hand, it would be the first example for ethynylgermane (A10) to exhibit high reactivity in the CuAAC reaction. One report on the formation of 4-germyl-substituted triazole ring derivative concerns using internal alkyne, i.e., 3-(trimethylgermyl)-2-propynal [64]. Additionally, the reports on the reactivity of the ethynylsiloxy-moiety (meaning A8) in the CuAAC process are very scarce [65]. An interesting relationship was found for 1H-NMR analyses of DDSQs bearing triazole ring substituted at 4-positition with an aryl (DDSQ-2A1) and alkyl (DDSQ-2A4) group. The resonance line of a very significant triazole proton N=C-Ht at 5H-position of triazole ring depends on the type of the moiety at 4-position of the latter. The crucial aspect may be its electronic property and the respective shielding effect of alkyl and deshielding effect characteristic for the aryl moiety presence. It affects the N=C-Ht signal shift and it is upfield for DDSQ-2A1 to be present at 6.75 ppm and downfield for DDSQ-2A4, to appear at 7.84 ppm, which gives a total change in resonance lines of 1.09 ppm (Figure4). Due to the presence of a triazole, aromatic ring, this effect is also insensibly perceptible for -CH2- group at 1N-position of this ring (for DDSQ-2A1 δ = 4.15 ppm and DDSQ-2A4 δ = 4.21 ppm) (Figure4). This is a notable difference in chemical shifts of N=C-H t at triazole ring for its alkyl and aryl derivatives when compared with analogous compounds of iBu-SQs, i.e., iBuT8-A4 (alkyl δ = 7.31 ppm) and iBuT8-A1 (aryl δ = 8.12 ppm) that equals 0.82 ppm (Figure5). It is even more significant when comparing analogous products with alkyl groups at triazole ring but with diverse Si-O-Si cores, i.e., DDSQ-2A4, N=C-Ht proton t present at 6.75 ppm with iBuT8-A4, =C-H at 7.31 ppm. These differences in result may be explained by the presence and electronic effect of the DDSQ core with phenyl substituents. Molecules 2021, 26, x 6 of 15 Molecules 2021, 26, x 6 of 15

(Figure 4). Due to the presence of a triazole, aromatic ring, this effect is also insensibly (Figure 4). Due to the presence of a triazole, aromatic ring, this effect is also insensibly perceptible for -CH2- group at 1N-position of this ring (for DDSQ-2A1 δ = 4.15 ppm and DDSQ-2A4perceptible δfor = 4.21-CH ppm)2- group (Figure at 1N 4).-position This is aof notable this ring difference (for DDSQ-2A1 in chemical δ = shifts4.15 ppm of N=C- and HDDSQ-2A4t at triazole δring = 4.21 for ppm) its alkyl (Figure and 4).aryl This de rivativesis a notable when difference compared in chemical with analogous shifts of com-N=C- Ht at triazole ring for its alkyl and aryl derivatives when compared with analogous compounds of iBu-SQs, i.e., iBuT8-A4 (alkyl δ = 7.31 ppm) and iBuT8-A1 (aryl δ = 8.12 ppm) thatpounds equals of iBu-SQs,0.82 ppm i.e., (Figure iBuT 5).8-A4 It (alkylis even δ =more 7.31 significantppm) and iBuTwhen8-A1 comparing (aryl δ = analogous 8.12 ppm) productsthat equals with 0.82 alkyl ppm groups (Figure at triazole 5). It is ri evenng but more with significant diverse Si-O-Si when cores, comparing i.e., DDSQ-2A4 analogous, productst with alkyl groups at triazole ring but with diverset Si-O-Si cores, i.e., DDSQ-2A4, N=C-H proton present at 6.75 ppm with iBuT8-A4, =C-H at 7.31 ppm. These differences Molecules 2021 26 t t , , 439 inN=C-H result protonmay be present explained at 6.75 by theppm presence with iBuT and8-A4 electronic, =C-H ateffect 7.31 of ppm. the DDSQThese6 of differencescore 15 with phenylin result substituents. may be explained by the presence and electronic effect of the DDSQ core with phenyl substituents.

1 FigureFigure 4. Selected 4. Selected range range of ofstacked stacked H-NMR1H-NMR spectra of ofDDSQ-2A1 DDSQ-2A1and andDDSQ-2A4 DDSQ-2A4. . Figure 4. Selected range of stacked 1H-NMR spectra of DDSQ-2A1 and DDSQ-2A4.

Figure 5. Selected range of stacked 1H-NMR spectra of iBuT8-A1 and iBuT8-A4. 11 FigureFigure 5. Selected 5. Selected range range of of stacked stacked H-NMRH-NMR spectra spectra of iBuTof iBuT8-A18-A1and iBuTand 8iBuT-A4. 8-A4.

Molecules 2021, 26, 439 7 of 15

2.2. X-ray Analysis of DDSQ-2A1

Molecules 2021, 26, x A DDSQ-based pyridine-triazole derivative, i.e., DDSQ-2A1 proved to be a solid7 of 15 and acquired the form of crystals amenable to X-ray crystal structure determination (Figure6) . The molecule is Ci-symmetrical, as it lies across the center of inversion in the space group P21/c. The structure of the core may be described as built of four rings, two2.2. 8-memberedX-ray Analysis (four of DDSQ-2A1 Si, four O), and two 10-membered (five Si, five O), which can be notedA as DDSQ-based 82102. The geometry pyridine-triazole of the core derivative, of the molecule i.e., DDSQ-2A1 is determined proved by two to be factors: a solid one and rigid—Si-Oacquired the distance, form of whichcrystals has amenable a very narrow to X-ray spread crystal (mean structure value determination 1.615(8) Å), and (Figure one ◦ ◦ flexible6). The Si-O-Simolecule angles is Ci (140.77(16)-symmetrical,–162.43(16) as it lies ).across Similar the tendencies center of inversion were noted in inthe similar space moleculesgroup P21/c[16. The,66] .structure The architecture of the core of may the crystalbe described is determined as built of by four weak rings, but two numerous 8-mem- interactionsbered (four Si, (C-H four··· O,O), C-Hand··· twoπ, π10-membered···π etc.). These (five multiple Si, five O), interactions which can give be noted rise to as quite 82102. significantThe geometry interaction of the core energies. of the molecule Calculations is determined with PIXEL by method two factors: give resultsone rigid—Si-O as high asdistance,−160.5, which−95.7, has and a very−85.4 narrow kJ/mol spread for the (mean three value highest 1.615(8) interaction Å), and energies one flexible between Si-O- molecules,Si angles (140.77(16)°–162.43(16)°). and −555.5 kJ/mol as total Similar packing tendencies energy [67 were,68]. noted in similar molecules [16,66].All The of the architecture T8 and DDSQ-based of the crystal compounds is determined with by substituted weak but numerous triazole ring(s) interactions were isolated(C-H···O, in C-H··· high,π up, π to···π 90% etc.). yields. These Theymultiple are air-stableinteractions white give or rise light-yellow to quite significant solids with in- goodteraction solubility energies. in DCM, Calculations CHCl3 ,with THF, PIXEL toluene. method The solubilitygive results in MeOH,as high as MeCN −160.5, and −95.7, for hexaneand −85.4 depends kJ/mol onfor thethe typethree of highest SQ’s core, intera i.e.,ctioniBuT energies8 derivatives between are molecules, more soluble and − than555.5 DDSQkJ/mols. as total packing energy [67,68].

FigureFigure 6.6. A perspective view view of of the the molecule. molecule. Ellipso Ellipsoidsids are are drawn drawn at atthe the 50% 50% probability probability level, level, hydrogenhydrogen atoms atoms are are shown shown as as spheres spheres of of arbitrary arbitrary radii radii (grey-C, (grey-C, white-H, white-H, blue-N, blue-N, red-O, red-O, yellow-Si). yellow- Si). 2.3. SQs-Based Pyridyl- and Thiophenyl-Triazole Derivatives (iBuT8-A1, DDSQ-2A1, iBuT8All-A7 of) asthe Bidentate T8 and DDSQ-based Ligands in the compounds Formation of with Coordination substituted Complexes triazole with ring(s) Selected were iso- Transitionlated in high, Metals up (TM to 90% = Pd, yields. Pt, Rh) They are air-stable white or light-yellow solids with good solubilityThe next in DCM, step wasCHCl to3, verifyTHF, toluene. the coordination The solubility properties in MeOH, of selected MeCN Tand8 and for DDSQhexane productsdepends typeon the possessing type of SQ’s heteroatom core, i.e., atiBuT 4C8triazole derivatives ring, are i.e., more N ( iBuTsoluble8-A1 than, DDSQ-2A1 DDSQs. ) and S (iBuT8-A7). Using 2-ethynylpyridine and 2-ethynylthiophene derivatives created the2.3. possibility SQs-Based toPyridyl- form bidentate and Thiophenyl-Triazole ligands of NˆN Derivatives and NˆS kind (iBuT donation.8-A1, DDSQ-2A1 For this purpose,, iBuT8- weA7) chose as Bidentate TM metals Ligands that in arethe knownFormation to of form Coordination coordination Complexes compounds with Selected with SQs-basedTransition ligands,Metals (TM i.e., = Pd(II) Pd, Pt, [59 Rh),69 ], Rh(I) [70], and Pt(II) [71].The general scheme for using T8-type ligands, i.e., iBuT8-A1 and iBuT8-A7 is disclosed in Figure7 for Pd(II), Pt(II), and Rh(I) The next step was to verify the coordination properties of selected T8 and DDSQ and DDSQ-based ligand with Pd(II) in Figure8. products type possessing heteroatom at 4C triazole ring, i.e., N (iBuT8-A1, DDSQ-2A1) and S (iBuT8-A7). Using 2-ethynylpyridine and 2-ethynylthiophene derivatives created the possibility to form bidentate ligands of N^N and N^S kind donation. For this purpose, we chose TM metals that are known to form coordination compounds with SQs-based ligands, i.e., Pd(II) [59,69], Rh(I) [70], and Pt(II) [71].The general scheme for using T8-type ligands, i.e., iBuT8-A1 and iBuT8-A7 is disclosed in Figure 7 for Pd(II), Pt(II), and Rh(I) and DDSQ-based ligand with Pd(II) in Figure 8.

Molecules 2021, 26, 439 8 of 15 Molecules 2021, 26, x 8 of 15

Molecules 2021, 26, x 8 of 15

Figure 7. General procedure for the synthesis of T8-based N^N and N^S type mononuclear coordi- Figure 7. General procedure for the synthesis of T8-based NˆN and NˆS type mononuclear coordination compounds with Pd(II) (iBuT8-A7-Pt(N^S)), Pt(II) (iBuT8-A1-Pt(N^N)), and binuclear with nationFigure compounds 7. General procedure with Pd(II) for (iBuT the synthesis8-A7-Pt(NˆS) of T),8-based Pt(II) (N^NiBuT and8-A1-Pt(NˆN) N^S type ),mononuclear and binuclear coordi- with nationRh(I) ((compoundsiBuT8-A1)2 -Rh(N^N)with Pd(II)). (iBuT8-A7-Pt(N^S)), Pt(II) (iBuT8-A1-Pt(N^N)), and binuclear with Rh(I) ((iBuT8-A1)2-Rh(NˆN)). Rh(I) ((iBuT8-A1)2-Rh(N^N)).

Figure 8. General procedure for the synthesis of DDSQ-based N^N coordination compound FigureFigurewith Pd(II) 8.8. GeneralGeneral (DDSQ-A1-[Pd(N^N)] procedureprocedure forfor thethe2). synthesissynthesis ofof DDSQ-basedDDSQ-based NˆNN^N coordinationcoordination compoundcompound with with Pd(II) (DDSQ-A1-[Pd(N^N)]2). Pd(II) (DDSQ-A1-[Pd(NˆN)]2). The analogous verification was performed in terms of DDSQ-2A1 possessing biden- tateThe TheN^N analogous analogous ligand Pd(II). veriﬁcationverification The 1:2 waswas (ligand: performedperformed metal) inin stoichiometry termsterms ofof DDSQ-2A1 of the reaction possessing enabled biden- the tatetateformation NˆN N^N ligand ligand of a molecular Pd(II). Pd(II). The The system 1:2 1:2 (ligand: (ligand: with two metal) metal) Pd(II) stoichiometry stoichiometry ions captured ofof to thethe the reactionreaction opposite enabledenabled parts of thethe the formationformationDDSQ core of of a (Figurea molecular molecular 8). system system with with two two Pd(II) Pd(II) ionsions capturedcaptured toto thethe oppositeopposite partsparts ofof thethe DDSQDDSQTo core core our (Figure (Figure knowledge,8 ).8). this is the first example of the DDSQ-based molecular complex possessingToTo our our knowledge, aknowledge, bidentate pyridine-triazole thisthis isis the the ﬁrst first example example ligand ofwithof thethe coordination DDSQ-basedDDSQ-based TM molecularmolecular Pd(II) ion. complexcomplex Further- possessingpossessingmore, it is a aan bidentate bidentate interesting pyridine-triazolepyridine-triazole example of using ligandligand difunctionalized withwith coordinationcoordination DDSQ TMTM compounds Pd(II)Pd(II) ion. Further- to anchor more,more,metal it itions is is an an and interesting interesting the reports example example on these of of using usingsystems difunctionalizeddifunctionalized have been still DDSQ DDSQprofoundly compoundscompounds limited toto [71,72] anchoranchor. metalmetal ionsFor ions the and and reaction the the reports reports aiming on on these theseat palladium systems systems have andhave rhodium beenbeen stillstill complexes, profoundlyprofoundly their limitedlimited cyclooctadiene [[71,72]71,72].. precursorsForFor the the reactionwere reaction used aiming aiming and for at at platinum, palladium palladium the andand tetrachloroplatinate(II) rhodiumrhodium complexes,complexes, was theirtheir applied. cyclooctadienecyclooctadiene The mon- precursorsprecursorsonuclear compounds werewere used and andiBuT for for8-A7-Pt(N^S) platinum, platinum, the and the tetrachloroplatinate(II) iBuT tetrachloroplatinate(II)8-A1-Pt(N^N) are was air-stable, was applied. applied. pale The yellowmon- The mononuclearonuclearsolids. The compounds dinuclear compounds iBuT Rh(I)iBuT8-A7-Pt(N^S) based8-A7-Pt(NˆS) complex and iBuT((andiBuT8iBuT-A1-Pt(N^N)8-A1)8-A1-Pt(NˆN)2-Rh(N^N) are air-stable,) areis rather air-stable, pale an yellowair- pale and yellowsolids.moisture solids.The sensitive dinuclear The dinuclear orange Rh(I) Rh(I)basedsolid basedandcomplex its complex synthesis ((iBuT ((8iBuT-A1) was28-Rh(N^N)-A1) performed2-Rh(NˆN)) is withrather) is the rather an use air- an ofand air- the andmoistureSchlenk moisture technique.sensitive sensitive orange The orange iBuT solid8 solid-derivatives and and its itssynthesis are synthesis soluble was was in performedDCM, performed CHCl with with3, THF, the the toluene,use use of thethe and SchlenkSchlenkof very technique. technique. low solubility The The iBuT iBuT in8-derivatives 8-derivativesmethanol. are Theare soluble solubleDDSQ-based in in DCM, DCM, CHClPd(II) CHCl3, THF,3complex, THF, toluene, toluene, DDSQ-A1- and and of veryof[Pd(N^N)] very low solubilitylow2 is solubilityan air-stable in methanol. in palemethanol.The yellow DDSQ-based solidThe DDSQ-basedwith Pd(II) very limited complex Pd(II) solubilityDDSQ-A1-[Pd(NˆN)] complex in DCM,DDSQ-A1- CHCl2 3, is[Pd(N^N)]and an air-stable THF and2 is palean soluble air-stable yellow in solidDMF pale withyellowand veryDMSO. solid limited withThe solubility fourvery coordinationlimited in DCM, solubility CHClSQ-based in3, DCM, and compounds THF CHCl and3, solubleandwere THF isolated in DMFand solublein and yields DMSO. in 55%–93% DMF The and four and DMSO. coordination characterized The four SQ-based usingcoordination spectroscopic compounds SQ-based were analysis compounds isolated proving in yieldsweretheir isolated 55%–93%formation in and yields(forcharacterized details 55%–93% see ESI).and using characterizedThe spectroscopic respective using comparison analysis spectroscopic proving of the analysis their1H-NMR formation proving stacked 1 1 (fortheirspectra details formation of seeligand ESI). (for DDSQ-A1 The details respective see and ESI). respective comparison The respective complex of the comparison DDSQ-A1-[Pd(N^N)]H-NMR stacked of the spectraH-NMR2 are of presented stacked ligand DDSQ-A1spectrabelow (Figureof ligandand respective9). DDSQ-A1 complex and respectiveDDSQ-A1-[Pd(NˆN)] complex DDSQ-A1-[Pd(N^N)]2 are presented below2 are (Figurepresented9). below (Figure 9).

Molecules 2021, 26, 439 9 of 15 Molecules 2021, 26, x 9 of 15

11 FigureFigure 9. 9. SelectedSelected range range of of stacked stacked H-NMRH-NMR spectra spectra of of DDSQ-A1DDSQ-A1 andand DDSQ-A1-[Pd(N^N)]DDSQ-A1-[Pd(NˆN)]22..

TheThe presence presence of of Pd Pd with with its its chloro-ligands chloro-ligands in in DDSQ-A1-[Pd(N^N)]DDSQ-A1-[Pd(NˆN)]22 affectsaffects the the po- po- laritylarity of of the the complex complex and and restricts restricts its its solubility solubility in in a a common, common, less less polar polar solvent solvent and and for for 1 thisthis reason reason DMF- DMF-dd77 waswas selected selected in in order order to to compare compare 1H-NMRH-NMR spectra. spectra. As As expected expected from from thethe results results obtained obtained for for the the iBuT iBuT88-based-based Pd, Pd, Pt, Pt, and and Rh Rh complexes complexes and and from from the the literature literature reportsreports [59], [59], the the placement ofof resonanceresonance lineline of of the the triazole triazole proton proton N=C-H N=C-Ht ist is susceptible susceptible to tothe the chemical chemical surrounding surrounding and and presence presence of of a differenta different type type of of TM TM ion. ion. However, However, in general,in gen- t eral,in each in each complex complex its shiftits shift is downfield is downfield significantly. significantly. For ForDDSQ-A1-[Pd(NˆN)] DDSQ-A1-[Pd(N^N)]2 N=C-H2 N=C- Htheret there is ais notable a notable difference difference in itsin chemicalits chemical shift shift to appear to appear at δ at= 9.18δ = 9.18 ppm ppm when when compared com- t paredwith a with bare a ligand, bare ligand, i.e., DDSQ-A1 i.e., DDSQ-A1: N=C-H: N=C-Hat δ =t 8.53at δ = ppm 8.53 (Figure ppm (Figure9). Additionally, 9). Additionally, the res- theonance resonance lines derived lines derived from the from pyridine the pyridine ring are ring also are shifted also downfieldshifted downfield due to the due changes to the changesin the electron in the electron density density on the hetaryl on the moietyhetaryl whilemoiety coordinating while coordinating to Pd ion, to Pd especially ion, espe- for 5 ciallythe =C-H for the. =C-H5. 3. Materials and Methods 3. Materials and Methods 3.1. Materials 3.1. Materials The chemicals were purchased from the following sources: Hybrid Plastics (Hy- The chemicals were purchased from the following sources: Hybrid Plastics (Hybrid brid Plastics, Hattiesburg, MS, USA) for DDSQ tetrasilanol form (C48H44O14Si8) (DDSQ- Plastics, Hattiesburg, MS, USA) for DDSQ tetrasilanol form (C48H44O14Si8) (DDSQ-4OH), 4OH), trisilanol (C28H66O12Si7)(iBuT8-3OH); Sigma-Aldrich (Saint Louis, MO, USA) for: trisilanoldichloromethane (C28H66O12 (DCM),Si7)(iBuT tetrahydrofuran8-3OH); Sigma-Aldrich (THF), (Saint dimethylformamide Louis, MO, USA) (DMF), for: dichloro- toluene, methane (DCM), tetrahydrofuran (THF), dimethylformamide (DMF), toluene, methanol, methanol, acetonitrile (MeCN), chloroform (CHCl3), hexane, chloroform-d, dimethyl acetonitrile (MeCN), chloroform (CHCl3), hexane, chloroform-d, dimethyl sulfoxide-d6 sulfoxide-d6 (DMSO-d6), dichloromethane-d2 (DCM-d2), (dimethylphenylsilyl)acetylene, (DMSO-2-ethynylpyridine,d6), dichloromethane-N-methyl-dN2 (DCM--propargylbenzylamine,d2), (dimethylphenylsilyl)a 3-butynylbenzene,cetylene, 2-ethynylpyr- phenylacety- idine,lene, n-heptyne,N-methyl- 1,4-diethynylbenzene,N-propargylbenzylamine, 5-hexynenitrile, 3-butynylbenzene, 2-ethynylthiophene; phenylacetylene, ABCR (ABCR,n-heptyne,Karlsruhe, 1,4-diethynylbenzene, Germany) for dichloro(3-chloropropyl)methylsilane, 5-hexynenitrile, 2-ethynylthiophene; molecular ABCR (ABCR, sieves, triethy-Karls- ruhe,lamine, Germany) and silica for gel dichloro(3-chloropropyl) 60. Chemat (Gdansk, Poland)methylsilane, for: sodium molecular L-ascorbate sieves, crystalline,triethylamine,ammonium and silica chloride, gel 60. copper(II)Chemat (Gdansk, sulfate pentahydrate,Poland) for: sodium copper(I) L-ascorbate bromide, crystalline,N,N,N0,N 0am-,N00- moniumpentamethyldiethylenetriamine chloride, copper(II) sulfate (PMDTA), pentahydrate, sodium copper(I) azide, bromide, sodium sulfateN,N,N′,N anhydrous,′,N′′-pen- tamethyldiethylenetriaminedichloro(1,5-cyclooctadiene)palladium(II), (PMDTA), sodium chloro(1,5-cyclooctadiene)rhodium(I) azide, sodium sulfate anhydrous, dimer, dichloro(1,5-cyclooctadiene)palladium(II),potassium tetrachloroplatinate(II). Tetrahydrofuran chloro(1,5-cyclooctadiene)rhodium(I) (THF) was refluxed over dimer, sodium/ po- tassiumbenzophenone tetrachloroplatinate(II). and distilled. Triethylamine Tetrahydrofuran (Et3 N)(THF) was was distilled refluxed over over calcium sodium/ben- hydride zophenonebefore use. and DMF distilled. was stored Triethylamine under argon. (Et3N) Ethynyl(triethyl)germane was distilled over calcium (A10) hydride and ethynyl before use.(dimethylsiloxy)hepta(i-butyl)octasilsesquioxane DMF was stored under argon. Ethynyl(triethyl)germane (A8) was synthesized (A10) and according ethynyl(dime- to the

Molecules 2021, 26, 439 10 of 15

literature procedures [73,74]. (3-chloropropyl)hepta(i-butyl)octasilsesquioxane (iBuT8-Cl) and DDSQ-2Cl were obtained via corner- and side-capping hydrolytic condensation procedure, and mono- and diazido-functionalized silsesquioxanes (iBuT8-N3, DDSQ-2N3) were synthesized via nucleophilic substitution according to the literature procedures [60,61]. All syntheses were conducted under argon atmosphere using standard Schlenk-line and vacuum techniques.

3.2. Methods Nuclear magnetic resonance spectroscopy (NMR) measurements (1H, 13C, and 29Si NMR) were conducted using spectrometers: Bruker Ultrashield 300 MHz and 400 MHz respectively (Bruker, Faellanden, Switzerland) with CDCl3, CD2Cl2, DMF-d7, and DMSO- d6 as a solvent. Chemical shifts are reported in ppm with reference to the residual solvent signal peaks for 1H and 13C and to TMS for 29Si. Fourier transform-infrared (FT-IR) spectra were recorded on a Nicolet iS5 (Thermo Scientific, Waltham, MA, USA) spectrophotometer equipped with a SPECAC Golden Gate, diamond ATR unit with a resolution of 2 cm−1. In all cases, 16 scans were collected to record the spectra in a range of 4000–430 cm−1. Elemental analyses (EA) were performed using a Vario EL III instrument (Elementar Analysensysteme GmbH, Langenselbold, Germany). High-resolution mass spectra (HRMS) were obtained using Impact HD mass spectrometerQ-TOF type instrument equipped with electrospray ion source (Bruker Dal- tonics, GmbH, Bremen, Germany). The sample solutions (DCM:MeOH) were infused into the ESI source by a syringe pump (direct inlet) at the flow rate of 3 µL/min. The instrument was operated under the following optimized settings: endplate voltage 500 V; capillary voltage 4.2 kV; nebulizer pressure 0.3 bar; dry gas (nitrogen) temperature 200 ◦C; dry gas flow rate 4 L/min. The spectrometer was previously calibrated with the standard tune mixture. X-ray crystallography. Diffraction data were collected by the ω-scan technique, using graphite-monochromated MoKα radiation (λ = 0.71073 Å), at 100(1) on Rigaku XCalibur (Rigaku OD, Neu-Isenburg, Germany) four-circle diffractometer with EOS CCD detector. The data were corrected for Lorentz-polarization as well as for absorption effects [75]. Precise unit-cell parameters were determined by a least-squares fit of the 6861 reflections of the highest intensity, chosen from the whole experiment. The structures were solved with SHELXT [76] and refined with the full-matrix least-squares procedure on F2 by SHELXL [77]. All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were placed in idealized positions and refined as ‘riding model’ with isotropic displacement parameters set at 1.2 (1.5 for CH3) times Ueq of appropriate carrier atoms. Crystallographic data for the structural analysis has been deposited with the Cam- bridge Crystallographic Data Centre, no. CCDC–2045899. Copies of this information may be obtained free 589 of charge from: The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK; e-mail: [email protected], or www.ccdc.cam.ac.uk. Crystal data. C70H68N8O14Si10,Mr = 1526.22, monoclinic, P21/c, a = 14.8188(5) Å, b = 22.6566(9) Å, c = 11.1567(3) Å, β = 101.194(3)◦, V = 3674.5(2) Å3, Z = 2, dx = 1.379 g·cm−3, F(000) = 1592, µ = 0.248 mm−1, 16,862 reflections collected, 6455 symmetry-independent (Rint = 2.40%), 5402 with I > 2σ(I). Final R(F) [I > 2σ(I)] = 0.0580, wR2 [I > 2σ(I) = = 0.1257, R(F) [all data] = 0.0709, wR2 [all data] = 0.1298, ∆ρmax/min = 1.398/−0.627 e/Å−3.

3.3. General Procedure for Copper(I)-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) 3.3.1. Synthetic Procedure with the Use of CuSO4 as Cu(II) Ion Source The exemplary synthetic procedure is presented for iBuT8-A1. To a solution of iBuT8- N3 (300 mg, 0.33 mmol) in THF (15 mL), sodium L-ascorbate crystalline (in general 0.3–5 eq., herein 5 eq.), A1 (in general 1.4–8 eq., herein 7.85 eq.) and copper(II) sulfate pentahydrate (in general 0.025–0.25eq., herein 0.25 eq.) diluted in water, were added respectively. The reaction was conducted in a closed system until full conversion of iBuT8-N3, conﬁrmed Molecules 2021, 26, 439 11 of 15

by FT-IR analysis (typically 72–96 h depending on alkyne used). The crude product was ﬁltered off by column chromatography (silica gel 60, THF) to remove solid impurities and the solvent was evaporated. It was extracted with DCM and water. Organic layer was dried with anhydrous sodium sulfate. Then the solvent was removed under reduced pressure, and the product was precipitated in methanol as white solid. The product (83 mg, i.e., 78% isolated yield) was analyzed by 1H, 13C, and 29Si NMR and EA to conﬁrm its structure. For the spectroscopic analysis please see Supplementary Materials.

3.3.2. Synthetic Procedure with Use of CuBr as Cu(I) Ion Source

The exemplary synthetic procedure is presented for iBuT8-A7 [33]. To a solution of iBuT8-N3 (200 mg, 0,22 mmol) and A7 (35 µL, 0.33 mmol) in THF (3 mL) stirring under argon, CuBr (3.2 mg, 0.02 mmol) and PMDTA (4.6 µL, 0.02 mmol) were added. The reaction mixture was stirred at room temperature for 30 h. After the reaction was completed (FT-IR analysis), the crude product was ﬁltered off by column chromatography (silica gel 60, THF) to remove solid impurities and solvent was evaporated. The resulted solid was washed with methanol and dried in vacuo. Second option for isolation is the extraction in DCM and water. Organic layer was dried with sodium anhydrous sulfate, solvent was removed under reduced pressure, and product was precipitated in methanol as a pale yellow solid in 81% yield (181 mg). Product was analyzed by 1H, 13C, and 29Si NMR and EA to conﬁrm its structure.

3.4. General Procedure for Using SQs-Based Pyridyl-Triazole- and Thiophenyl-Triazole Derivatives as Ligands in the Formation of Coordination Complexes with Selected Transition Metals (Pd, Pt, Rh) 3.4.1. Procedure for the Synthesis of iBuT8-A7-Pd(NˆS), DDSQ-A1-[Pd(NˆN)]2, and (iBuT8-A1)2-Rh(NˆN)

The procedure for the synthesis of iBuT8-A7-Pd(NˆS) is described as an example. A mixture of 1 equiv. of iBuT8-A7 ligand and a stoichiometric amount of Pd(cod)Cl2 was dissolved in dichloromethane and stirred at room temperature for 24 h. After this time, a solvent was evaporated. The crude product was dissolved in hexane and ﬁltrated off via cannula. The solvent was evaporated and afforded in pure iBuT8-A7-Pd(NˆS) as yellow solid in 60% yield (91 mg). It was dried in vacuo. Complex DDSQ-A1-[Pd(NˆN)]2 was obtained analogously, however, it precipitated from the DCM solution. After 24 h, the solvent was evaporated and washed with hexane and dried in vacuo. Obtained products were yellow DDSQ-A1-[Pd(NˆN)]2 (93%, 228 mg) and orange (iBuT8-A1)2-Rh(NˆN) (for Rh, the complexation was performed within 96 h) (55%, 70 mg) solids. DDSQ-A1-[Pd(NˆN)]2 exhibits very restricted solubility in DCM, chloroform, THF or hexane and is soluble in DMF and DMSO.

3.4.2. Procedure for Synthesis of iBuT8-A1-Pt(NˆN) The complex was synthesized as described by Galanski and Keppler et al. with slight modiﬁcations [78]. To a solution of ligand iBuT8-A1 (0.051 g, 0.05 mmol, 1.005 eq.) in THF, a solution of K2PtCl4 in water-MeOH (1:1) was added. The mixture was stirred overnight in a light-protected ﬂask at 40 ◦C. After this time, the mixture was in a form of suspension and the addition of MeOH resulted in crude product precipitation. It was washed with methanol and afforded in pure iBuT8-A1-Pt(NˆN) as pale pale-yellow solid in 87% yield (55 mg) and then dried in vacuo.

4. Conclusions

In conclusion, we reported on the synthesis and characterization of a series of T8- and DDSQ-based double-decker silsesquioxanes bearing 4-substituted triazole ring with aryl, hetaryl, alkyl, silyl, and germyl groups via copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). From this group of compounds hetaryl-triazole i.e., pyridine- and thiophenyl- derivatives were selected and veriﬁed in terms of their coordinating properties towards Pd(II), Pt(II), and Rh(I) ions. As a result of performed tests, four types of complexes, i.e., Molecules 2021, 26, 439 12 of 15

two mononuclear iBuT8-based Pt- and Pd- with NˆN and NˆS ligands, dinuclear iBuT8- based Rh with NˆN ligand as well as DDSQ-based with two Pd ions coordinated with NˆN bidentate ligand were obtained and fully characterized. For the DDSQ-2A1 ligand, this is the ﬁrst example of using the pyridine-triazole moiety to anchor TM ion in the chemistry of DDSQ-compounds. These may be potentially valuable systems of catalytic activity that will be tested in our future studies.

Supplementary Materials: The following are available online, 1H, 13C, 29Si NMR spectra of all obtained compounds (Figures S1–S53). Author Contributions: Designed and supervised, B.D.; Synthesis and characterization of the reported compounds, K.K., M.R., K.M., and J.D.; X-ray analysis and description M.K.; Writing—original draft preparation, M.R. and B.D. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by National Science Centre (Poland) Project OPUS UMO- 2016/23/B/ST5/00201. Data Availability Statement: The data presented in this study are available in this article or in a Supplementary Materials. Acknowledgments: The authors are grateful to Rafał Januszewski for donation of iBu-SQ-Cl and to Jan Jarozek˙ for the project of graphical abstract. Conﬂicts of Interest: The authors declare no conﬂict of interest. Sample Availability: Not available.

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