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

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 thiophenyl-triazole moiety attached to T8 or DDSQ core were verified in terms of their coordinating properties towards selected transition metals, i.e., Pd(II), Pt(II), and Rh(I). The studies resulted in the formation of four SQs based coordination compounds that were obtained in high yields up to 93% and their thorough spectroscopic characterization is presented. To our knowledge, this is the first example of the DDSQ-based molecular complex possessing bidentate pyridine-triazole ligand binding two Pd(II) ions.


Introduction
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, amorphous, ladder, and cage-like-and the architecture of the latter has attracted considerable scientific interest. It is due to the presence of the inorganic, rigid core (thermal stability, chemical resistance) and organic moieties attached to it (tunable processability) which is 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][2][3][4][5][6]. Significant development of catalytic protocols for effective and selective anchoring of respective organic functionality to the SQs core has been observed during the last years. The crucial aspect of this is the presence of a proper prefunctional moiety at the Si-O-Si framework, enabling its modification, e.g., Si-H, Si-OH, Si-CH=CH 2 units, etc. This, in turn, influences the selection of a respective catalytic procedure for this purpose, e.g., hydrosilylation, cross-metathesis, O-silylation, Friedel-Crafts, silylative, Heck, Suzuki, or Sonogashira coupling reactions [2,[7][8][9][10][11][12][13][14][15][16][17][18][19][20]. Among these methods, the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) may be an alternative but the only route to yield substituted 1,4-triazole ring functionalities regioselectively [21][22][23]. This

The Copper(I)-Catalyzed Azide-Alkyne Cycloaddition (CuAAC) Using iBuT 8 -N3 and DDSQ-2N3
In the first step, the starting precursors, i.e., the azidopropyl-derivative(s) of mono-iBuT 8 -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 NaN 3 [60,61] (Figure 2). The idea of the synthetic path is presented below. Figure 1. Mono-T8 and difunctionalized DDSQ silsesquioxanes with Substituted Triazole Ring and the coordinating ability of the pyridine-and thiophenyl-derivatives towards selected TM ions, presented in this work.

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. 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 1 H-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. The two SQs-based azides iBuT 8 -N3 and DDSQ-2N3 were used as reagents in CuAAC 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 1 H-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.  We based on two types of Cu sources, i.e., CuSO4 with sodium ascorbate [40,59] and CuBr with PMDTA [33]. At first, special conditions were created for the reduction of Cu(II) in situ to Cu(I) and then to maintain the introduction of Cu(I) in this oxidation state into the reaction. The main target was to perform the reaction until full conversion of SQbased azides to avoid the problematic isolation issues of resulting SQ-products with substituted triazole rings(s) from unreacted SQ-based azides. The results of the reactions conducted to obtain products with substituted triazole ring(s) are collected in Table 1 for T8derivatives and in Table 2 for DDSQ-derivatives. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT8-N3 and alkynes. The stacked FT-IR spectra of starting material iBuT 8 -N3 and the selected product with 4-pyridine-triazole group iBuT 8 -A1 are depicted in Figure 3. The established reaction conditions resulted in the complete conversion of azide (-N=N + =N-) group in iBuT 8 -N3, confirmed by the disappearance of respective bands attributed to stretching asymmetric vibrations of -N=N-at ca.ν = 2098 cm −1 (marked in Figure 3). For the CuAAC reaction product, i.e., iBuT 8 -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.ν = 1603 cm −1 and ν = 1571 cm −1 that confirm the formation of the desired product.
We based on two types of Cu sources, i.e., CuSO 4 with sodium ascorbate [40,59] and CuBr with PMDTA [33]. At first, special conditions were created for the reduction of Cu(II) in situ to Cu(I) and then to maintain the introduction of Cu(I) in this oxidation state into the reaction. The main target was to perform the reaction until full conversion of SQ-based azides to avoid the problematic isolation issues of resulting SQ-products with substituted triazole rings(s) from unreacted SQ-based azides. The results of the reactions conducted to obtain products with substituted triazole ring(s) are collected in Table 1 for T 8 -derivatives and in Table 2 for DDSQ-derivatives.  We based on two types of Cu sources, i.e., CuSO4 with sodium ascorbate [40,59] and CuBr with PMDTA [33]. At first, special conditions were created for the reduction of Cu(II) in situ to Cu(I) and then to maintain the introduction of Cu(I) in this oxidation state into the reaction. The main target was to perform the reaction until full conversion of SQbased azides to avoid the problematic isolation issues of resulting SQ-products with substituted triazole rings(s) from unreacted SQ-based azides. The results of the reactions conducted to obtain products with substituted triazole ring(s) are collected in Table 1 for T8derivatives and in Table 2 for DDSQ-derivatives. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT8-N3 and alkynes.  Figure 3. FT-IR spectra of iBuT8-N3 and iBuT8-A1 after completion of CuAAC coupling reaction.
We based on two types of Cu sources, i.e., CuSO4 with sodium ascorbate [40,59] and CuBr with PMDTA [33]. At first, special conditions were created for the reduction of Cu(II) in situ to Cu(I) and then to maintain the introduction of Cu(I) in this oxidation state into the reaction. The main target was to perform the reaction until full conversion of SQbased azides to avoid the problematic isolation issues of resulting SQ-products with substituted triazole rings(s) from unreacted SQ-based azides. The results of the reactions conducted to obtain products with substituted triazole ring(s) are collected in Table 1 for T8derivatives and in Table 2 for DDSQ-derivatives. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT8-N3 and alkynes.  We based on two types of Cu sources, i.e., CuSO4 with sodium ascorbate [40,59] and CuBr with PMDTA [33]. At first, special conditions were created for the reduction of Cu(II) in situ to Cu(I) and then to maintain the introduction of Cu(I) in this oxidation state into the reaction. The main target was to perform the reaction until full conversion of SQbased azides to avoid the problematic isolation issues of resulting SQ-products with substituted triazole rings(s) from unreacted SQ-based azides. The results of the reactions conducted to obtain products with substituted triazole ring(s) are collected in Table 1 for T8derivatives and in Table 2 for DDSQ-derivatives. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT8-N3 and alkynes.  We based on two types of Cu sources, i.e., CuSO4 with sodium ascorbate [40,59] and CuBr with PMDTA [33]. At first, special conditions were created for the reduction of Cu(II) in situ to Cu(I) and then to maintain the introduction of Cu(I) in this oxidation state into the reaction. The main target was to perform the reaction until full conversion of SQbased azides to avoid the problematic isolation issues of resulting SQ-products with substituted triazole rings(s) from unreacted SQ-based azides. The results of the reactions conducted to obtain products with substituted triazole ring(s) are collected in Table 1 for T8derivatives and in Table 2 for DDSQ-derivatives. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT8-N3 and alkynes.  We based on two types of Cu sources, i.e., CuSO4 with sodium ascorbate [40,59] and CuBr with PMDTA [33]. At first, special conditions were created for the reduction of Cu(II) in situ to Cu(I) and then to maintain the introduction of Cu(I) in this oxidation state into the reaction. The main target was to perform the reaction until full conversion of SQbased azides to avoid the problematic isolation issues of resulting SQ-products with substituted triazole rings(s) from unreacted SQ-based azides. The results of the reactions conducted to obtain products with substituted triazole ring(s) are collected in Table 1 for T8derivatives and in Table 2 for DDSQ-derivatives. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT8-N3 and alkynes.  We based on two types of Cu sources, i.e., CuSO4 with sodium ascorbate [40,59] and CuBr with PMDTA [33]. At first, special conditions were created for the reduction of Cu(II) in situ to Cu(I) and then to maintain the introduction of Cu(I) in this oxidation state into the reaction. The main target was to perform the reaction until full conversion of SQbased azides to avoid the problematic isolation issues of resulting SQ-products with substituted triazole rings(s) from unreacted SQ-based azides. The results of the reactions conducted to obtain products with substituted triazole ring(s) are collected in Table 1 for T8derivatives and in Table 2 for DDSQ-derivatives. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT8-N3 and alkynes.  We based on two types of Cu sources, i.e., CuSO4 with sodium ascorbate [40,59] and CuBr with PMDTA [33]. At first, special conditions were created for the reduction of Cu(II) in situ to Cu(I) and then to maintain the introduction of Cu(I) in this oxidation state into the reaction. The main target was to perform the reaction until full conversion of SQbased azides to avoid the problematic isolation issues of resulting SQ-products with substituted triazole rings(s) from unreacted SQ-based azides. The results of the reactions conducted to obtain products with substituted triazole ring(s) are collected in Table 1 for T8derivatives and in Table 2 for DDSQ-derivatives. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT8-N3 and alkynes.  We based on two types of Cu sources, i.e., CuSO4 with sodium ascorbate [40,59] and CuBr with PMDTA [33]. At first, special conditions were created for the reduction of Cu(II) in situ to Cu(I) and then to maintain the introduction of Cu(I) in this oxidation state into the reaction. The main target was to perform the reaction until full conversion of SQbased azides to avoid the problematic isolation issues of resulting SQ-products with substituted triazole rings(s) from unreacted SQ-based azides. The results of the reactions conducted to obtain products with substituted triazole ring(s) are collected in Table 1 for T8derivatives and in Table 2 for DDSQ-derivatives. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT8-N3 and alkynes.  We based on two types of Cu sources, i.e., CuSO4 with sodium ascorbate [40,59] and CuBr with PMDTA [33]. At first, special conditions were created for the reduction of Cu(II) in situ to Cu(I) and then to maintain the introduction of Cu(I) in this oxidation state into the reaction. The main target was to perform the reaction until full conversion of SQbased azides to avoid the problematic isolation issues of resulting SQ-products with substituted triazole rings(s) from unreacted SQ-based azides. The results of the reactions conducted to obtain products with substituted triazole ring(s) are collected in Table 1 for T8derivatives and in Table 2 for DDSQ-derivatives. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT8-N3 and alkynes.   We based on two types of Cu sources, i.e., CuSO4 with sodium ascorbate [40,59] and CuBr with PMDTA [33]. At first, special conditions were created for the reduction of Cu(II) in situ to Cu(I) and then to maintain the introduction of Cu(I) in this oxidation state into the reaction. The main target was to perform the reaction until full conversion of SQbased azides to avoid the problematic isolation issues of resulting SQ-products with substituted triazole rings(s) from unreacted SQ-based azides. The results of the reactions conducted to obtain products with substituted triazole ring(s) are collected in Table 1 for T8derivatives and in Table 2 for DDSQ-derivatives. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT8-N3 and alkynes.   We based on two types of Cu sources, i.e., CuSO4 with sodium ascorbate [40,59] and CuBr with PMDTA [33]. At first, special conditions were created for the reduction of Cu(II) in situ to Cu(I) and then to maintain the introduction of Cu(I) in this oxidation state into the reaction. The main target was to perform the reaction until full conversion of SQbased azides to avoid the problematic isolation issues of resulting SQ-products with substituted triazole rings(s) from unreacted SQ-based azides. The results of the reactions conducted to obtain products with substituted triazole ring(s) are collected in Table 1 for T8derivatives and in Table 2 for DDSQ-derivatives. Table 1. Copper-catalyzed azide-alkyne cycloaddition using iBuT8-N3 and alkynes.   The results of DDSQ-based systems with substituted triazole rings are collected in Table 2 and involves the selective formation of DDSQ-compounds with the two abovementioned triazole moieties. The spectrum of used alkynes varies as they contain aryl, 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. Interest-  The results of DDSQ-based systems with substituted triazole rings are collected in Table 2 and involves the selective formation of DDSQ-compounds with the two abovementioned triazole moieties. The spectrum of used alkynes varies as they contain aryl, 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 analo-  The results of DDSQ-based systems with substituted triazole rings are collected in Table 2 and involves the selective formation of DDSQ-compounds with the two abovementioned triazole moieties. The spectrum of used alkynes varies as they contain aryl, 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 analo-  The results of DDSQ-based systems with substituted triazole rings are collected in Table 2 and involves the selective formation of DDSQ-compounds with the two abovementioned triazole moieties. The spectrum of used alkynes varies as they contain aryl, 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 analo-  The results of DDSQ-based systems with substituted triazole rings are collected in Table 2 and involves the selective formation of DDSQ-compounds with the two abovementioned triazole moieties. The spectrum of used alkynes varies as they contain aryl, 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 analo-  The results of DDSQ-based systems with substituted triazole rings are collected in Table 2 and involves the selective formation of DDSQ-compounds with the two abovementioned triazole moieties. The spectrum of used alkynes varies as they contain aryl, 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 analo- The results of DDSQ-based systems with substituted triazole rings are collected in Table 2 and involves the selective formation of DDSQ-compounds with the two abovementioned triazole moieties. The spectrum of used alkynes varies as they contain aryl, hetaryl, alkyl, and silyl derivatives of commercial availability. Additionally, we tested ethynyl(triethyl)germane (A9) and ethynylsiloxysubstituted-iBuT 8 (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: iBuT 8 -A4 and DDSQ-2A4. The reactivity of ethynylsilane (A9), ethynylgermane (A10) and also ethynylsiloxysubstituted iBuT 8 (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 (iBuT 8 -N3 and DDSQ-2N3) only when modified reaction conditions with Cu(I) [33] were applied (heating at 45 • C). Even though, for ethynylsiloxysubstituted-iBuT 8 (A8) up to 10% of unreacted iBuT 8 -N3 was observed. It could be separated from the resulting product iBuT 8 -A8 during the purification with the use of chromatography column and proper eluent selection (hexane:DCM 3:1 for separation of iBuT 8 -N3 from iBuT 8 -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 1 H-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-H t 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-H t 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 (Figure 4). Due to the presence of a triazole, aromatic ring, this effect is also insensibly perceptible for -CH 2 -group at 1N-position of this ring (for DDSQ-2A1 δ = 4.15 ppm and DDSQ-2A4 δ = 4.21 ppm) ( Figure 4). 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., iBuT 8 -A4 (alkyl δ = 7.31 ppm) and iBuT 8 -A1 (aryl δ = 8.12 ppm) that equals 0.82 ppm ( Figure 5). 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-H t proton present at 6.75 ppm with iBuT 8 -A4, =C-H t at 7.31 ppm. These differences in result may be explained by the presence and electronic effect of the DDSQ core with phenyl substituents. pounds 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 ( Figure 5). 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-H t proton present at 6.75 ppm with iBuT8-A4, =C-H t at 7.31 ppm. These differences in result may be explained by the presence and electronic effect of the DDSQ core with phenyl substituents.   H t at triazole ring for its alkyl and aryl derivatives when compared with analogous com pounds 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 ( Figure 5). It is even more significant when comparing analogou products with alkyl groups at triazole ring but with diverse Si-O-Si cores, i.e., DDSQ-2A4 N=C-H t proton present at 6.75 ppm with iBuT8-A4, =C-H t at 7.31 ppm. These difference in result may be explained by the presence and electronic effect of the DDSQ core wit phenyl substituents.

X-ray Analysis of DDSQ-2A1
A DDSQ-based pyridine-triazole derivative, i.e., DDSQ-2A1 proved to be a solid and acquired the form of crystals amenable to X-ray crystal structure determination ( Figure 6). The molecule is C i -symmetrical, as it lies across the center of inversion in the space group P2 1 /c. The structure of the core may be described as built of four rings, two 8-membered (four Si, four O), and two 10-membered (five Si, five O), which can be noted as 8 2 10 2 . The geometry of the core of the molecule is determined by two factors: one rigid-Si-O distance, which has a very narrow spread (mean value 1.615(8) Å), and one flexible Si-O-Si angles (140.77 (16) • -162.43(16) • ). Similar tendencies were noted in similar molecules [16,66]. The architecture of the crystal is determined by weak but numerous interactions (C-H···O, C-H···π, π···π etc.). These multiple interactions give rise to quite significant interaction energies. Calculations with PIXEL method give results as high as −160.5, −95.7, and −85.4 kJ/mol for the three highest interaction energies between molecules, and −555.5 kJ/mol as total packing energy [67,68].
All of the T 8 and DDSQ-based compounds with substituted triazole ring(s) were isolated in high, up to 90% yields. They are air-stable white or light-yellow solids with good solubility in DCM, CHCl 3 , THF, toluene. The solubility in MeOH, MeCN and for hexane depends on the type of SQ's core, i.e., iBuT 8 derivatives are more soluble than DDSQs.

X-ray Analysis of DDSQ-2A1
A DDSQ-based pyridine-triazole derivative, i.e., DDSQ-2A1 proved to be a solid and acquired the form of crystals amenable to X-ray crystal structure determination ( Figure  6). 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, two 8-membered (four Si, four O), and two 10-membered (five Si, five O), which can be noted as 8 2 [16,66]. The architecture of the crystal is determined by weak but numerous interactions (C-H···O, C-H···π, π···π etc.). These multiple interactions give rise to quite significant interaction energies. Calculations with PIXEL method give results as high as −160.5, −95.7, and −85.4 kJ/mol for the three highest interaction energies between molecules, and −555.5 kJ/mol as total packing energy [67,68]. All of the T8 and DDSQ-based compounds with substituted triazole ring(s) were isolated in high, up to 90% yields. They are air-stable white or light-yellow solids with good solubility in DCM, CHCl3, THF, toluene. The solubility in MeOH, MeCN and for hexane depends on the type of SQ's core, i.e., iBuT8 derivatives are more soluble than DDSQs.
To our knowledge, this is the first example of the DDSQ-based molecular complex possessing a bidentate pyridine-triazole ligand with coordination TM Pd(II) ion. Furthermore, it is an interesting example of using difunctionalized DDSQ compounds to anchor metal ions and the reports on these systems have been still profoundly limited [71,72].
For the reaction aiming at palladium and rhodium complexes, their cyclooctadiene precursors were used and for platinum, the tetrachloroplatinate(II) was applied. The mononuclear compounds iBuT8-A7-Pt(N^S) and iBuT8-A1-Pt(N^N) are air-stable, pale yellow solids. The dinuclear Rh(I) based complex ((iBuT8-A1)2-Rh(N^N)) is rather an air-and moisture sensitive orange solid and its synthesis was performed with the use of the Schlenk technique. The iBuT8-derivatives are soluble in DCM, CHCl3, THF, toluene, and of very low solubility in methanol. The DDSQ-based Pd(II) complex DDSQ-A1-[Pd(N^N)]2 is an air-stable pale yellow solid with very limited solubility in DCM, CHCl3, and THF and soluble in DMF and DMSO. The four coordination SQ-based compounds were isolated in yields 55%-93% and characterized using spectroscopic analysis proving their formation (for details see ESI). The respective comparison of the 1 H-NMR stacked spectra of ligand DDSQ-A1 and respective complex DDSQ-A1-[Pd(N^N)]2 are presented below (Figure 9).  The analogous verification was performed in terms of DDSQ-2A1 possessing bidentate N^N ligand Pd(II). The 1:2 (ligand: metal) stoichiometry of the reaction enabled the formation of a molecular system with two Pd(II) ions captured to the opposite parts of the DDSQ core ( Figure 8).
To our knowledge, this is the first example of the DDSQ-based molecular complex possessing a bidentate pyridine-triazole ligand with coordination TM Pd(II) ion. Furthermore, it is an interesting example of using difunctionalized DDSQ compounds to anchor metal ions and the reports on these systems have been still profoundly limited [71,72].
For the reaction aiming at palladium and rhodium complexes, their cyclooctadiene precursors were used and for platinum, the tetrachloroplatinate(II) was applied. The mononuclear compounds iBuT8-A7-Pt(N^S) and iBuT8-A1-Pt(N^N) are air-stable, pale yellow solids. The dinuclear Rh(I) based complex ((iBuT8-A1)2-Rh(N^N)) is rather an air-and moisture sensitive orange solid and its synthesis was performed with the use of the Schlenk technique. The iBuT8-derivatives are soluble in DCM, CHCl3, THF, toluene, and of very low solubility in methanol. The DDSQ-based Pd(II) complex DDSQ-A1-[Pd(N^N)]2 is an air-stable pale yellow solid with very limited solubility in DCM, CHCl3, and THF and soluble in DMF and DMSO. The four coordination SQ-based compounds were isolated in yields 55%-93% and characterized using spectroscopic analysis proving their formation (for details see ESI). The respective comparison of the 1 H-NMR stacked spectra of ligand DDSQ-A1 and respective complex DDSQ-A1-[Pd(N^N)]2 are presented below (Figure 9). The analogous verification was performed in terms of DDSQ-2A1 possessing bidentate NˆN ligand Pd(II). The 1:2 (ligand: metal) stoichiometry of the reaction enabled the formation of a molecular system with two Pd(II) ions captured to the opposite parts of the DDSQ core ( Figure 8).
To our knowledge, this is the first example of the DDSQ-based molecular complex possessing a bidentate pyridine-triazole ligand with coordination TM Pd(II) ion. Furthermore, it is an interesting example of using difunctionalized DDSQ compounds to anchor metal ions and the reports on these systems have been still profoundly limited [71,72].
For the reaction aiming at palladium and rhodium complexes, their cyclooctadiene precursors were used and for platinum, the tetrachloroplatinate(II) was applied. The mononuclear compounds iBuT 8  The presence of Pd with its chloro-ligands in DDSQ-A1-[Pd(N^N)]2 affects the polarity of the complex and restricts its solubility in a common, less polar solvent and for this reason DMF-d7 was selected in order to compare 1 H-NMR spectra. As expected from the results obtained for the iBuT8-based Pd, Pt, and Rh complexes and from the literature reports [59], the placement of resonance line of the triazole proton N=C-H t is susceptible to the chemical surrounding and presence of a different type of TM ion. However, in general, in each complex its shift is downfield significantly. For DDSQ-A1-[Pd(N^N)]2 N=C-H t there is a notable difference in its chemical shift to appear at δ = 9.18 ppm when compared with a bare ligand, i.e., DDSQ-A1: N=C-H t at δ = 8.53 ppm (Figure 9). Additionally, the resonance lines derived from the pyridine ring are also shifted downfield due to the changes in the electron density on the hetaryl moiety while coordinating to Pd ion, especially for the =C-H 5 .

Methods
Nuclear magnetic resonance spectroscopy (NMR) measurements ( 1 H, 13 C, and 29 Si NMR) were conducted using spectrometers: Bruker Ultrashield 300 MHz and 400 MHz respectively (Bruker, Faellanden, Switzerland) with CDCl 3 , CD 2 Cl 2 , DMF-d 7 , and DMSOd 6 as a solvent. Chemical shifts are reported in ppm with reference to the residual solvent signal peaks for 1 H and 13 C and to TMS for 29 Si.
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 .
High-resolution mass spectra (HRMS) were obtained using Impact HD mass spectrometerQ-TOF type instrument equipped with electrospray ion source (Bruker Daltonics, 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 CH 3 ) times Ueq of appropriate carrier atoms.
Crystallographic data for the structural analysis has been deposited with the Cambridge 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: deposit@ccdc.cam.ac.uk, or www.ccdc.cam.ac.uk.
Crystal data. C 70   The exemplary synthetic procedure is presented for iBuT 8 -A1. To a solution of iBuT 8 -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 iBuT 8 -N3, confirmed 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 1 H, 13 C, and 29 Si NMR and EA to confirm its structure. For the spectroscopic analysis please see Supplementary Materials.

Synthetic Procedure with Use of CuBr as Cu(I) Ion Source
The exemplary synthetic procedure is presented for iBuT 8 -A7 [33]. To a solution of iBuT 8 -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 1 H, 13 C, and 29 Si NMR and EA to confirm its structure. The procedure for the synthesis of iBuT 8 -A7-Pd(NˆS) is described as an example. A mixture of 1 equiv. of iBuT8-A7 ligand and a stoichiometric amount of Pd(cod)Cl 2 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 iBuT 8 -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 (iBuT 8 -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.

Procedure for Synthesis of iBuT 8 -A1-Pt(NˆN)
The complex was synthesized as described by Galanski and Keppler et al. with slight modifications [78]. To a solution of ligand iBuT 8 -A1 (0.051 g, 0.05 mmol, 1.005 eq.) in THF, a solution of K 2 PtCl 4 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 iBuT 8 -A1-Pt(NˆN) as pale pale-yellow solid in 87% yield (55 mg) and then dried in vacuo.

Conclusions
In conclusion, we reported on the synthesis and characterization of a series of T 8 -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 thiophenylderivatives 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., two mononuclear iBuT 8 -based Pt-and Pd-with NˆN and NˆS ligands, dinuclear iBuT 8based 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, 1 H, 13 C, 29 Si NMR spectra of all obtained compounds (Figures S1-S53).