This work was supported by a grant from the National Science Foundation, Division of Chemistry, under Award No. CHE-2153240.

1. Setting up the Schlenk line
<ol>
	<li>Ensure all the taps are closed, then secure the cold trap to the Schlenk line using an O-ring (size 229 was used in our set up, although the size may vary depending on the specific Schlenk line used), and clamp.</li>
	<li>Turn on the vacuum pump (gas-ballast closed), and then open the taps of the Schlenk line such that the whole apparatus is open to vacuum. 
	NOTE: Do not open any taps to the hoses or any other taps that are open to the air; the apparatus should be a closed system under a dynamic vacuum.</li>
	<li>Wait at least 5 min while the atmosphere of the Schlenk line is evacuated. 
	NOTE: Some Schlenk lines may be fitted with a barometer to determine the lowest pressure the apparatus will reach under a dynamic vacuum. If that pressure has been reached before 5 min have passed, proceed to the next step.</li>
	<li>Cool the cold trap of the Schlenk line by placing a Dewar flask filled with liquid nitrogen around it. Use a towel to cover the top of the Dewar flask and slow the evaporation of the liquid nitrogen during the experiment. 
	CAUTION: Contact with liquid nitrogen can cause severe damage to the skin and eyes and should only be handled by those trained to use it safely. Wear skin and eye protection. 
	NOTE: Often, it is easier and safer to first place the empty Dewar flask around the cold trap and then use a second Dewar to fill the trap Dewar flask with liquid nitrogen.</li>
	<li>Open the bubbler to a light flow (approximately 3 bubbles/s) of inert gas (N2(g) or Ar(g)).</li>
</ol>
2. Measuring out the solid reagents
<ol>
	<li>Adding tetrakis(triphenylphosphine)palladium(0) and triphenylphosphine modulator into the reaction flask.
	<ol>
		<li>Roll a piece of weighing paper into a cone to use as a solid-addition funnel, and place it in the tap opening of the 10 mL flask. Ensure the bottom of the cone is inserted far enough that it extends past the hose attachment. 
		NOTE: Using an empty NMR tube or a similarly small tubular object to roll the weighing paper over is helpful to attain the small diameter required to fit in the tap opening.</li>
		<li>Weigh by differences the tetrakis(triphenylphosphine)palladium(0) (0.084 g, 0.073 mmol, 1 equiv.) into the 10 mL flask. 
		CAUTION:&#160; Tetrakis(triphenylphosphine)palladium(0) is harmful to the body, especially if swallowed, and may ignite if finely dispersed in the air. Avoid dust formation and all forms of contact, and wear personal protective equipment. 
		NOTE: The flask and weighing paper cone can be gently tapped to ensure all the solid is transferred into the bottom of the flask.</li>
		<li>Repeat step 2.1.2 with triphenylphosphine (1.23 g, 4.67 mmol, 64 equiv.). 
		CAUTION: Triphenylphosphine is harmful to the body and central nervous system. Avoid all forms of contact, and wear personal protective equipment, including chemical-resistant gloves.</li>
		<li>Dispose of the weighing paper cone, and screw the poly(tetrafluoroethylene) (PTFE) tap onto the 10 mL flask.</li>
	</ol>
	</li>
	<li>Measure the tetratopic phosphine linker into a separate 10 mL flask.
	<ol>
		<li>Repeat step 2.1.1 with a second 10 mL flask.</li>
		<li>Using the second 10 mL flask, repeat step 2.1.2 with the tetratopic phosphine linker Sn1 (0.085 g, 0.073 mmol, 1 equiv.). 
		CAUTION: The hazardous properties of Sn1 are unknown. As it is an Sn(IV) compound and a tertiary phosphine, assume it is acutely toxic, and avoid all forms of contact. Wear personal protective equipment, including chemical-resistant gloves.</li>
		<li>Repeat step 2.1.4 with the second 10 mL flask.</li>
	</ol>
	</li>
</ol>
3. Putting the reagents under an inert atmosphere
<ol>
	<li>Connect a hose (black rubber vacuum tubing, 3/16 in inner diameter x 3/16 in wall) from the Schlenk line to each of the 10 mL flasks.</li>
	<li>Open the PTFE tap just enough that the vessel is open to the hose. 
	NOTE: If the tap is too wide open, the solids may be pulled into the hose during evacuation.</li>
	<li>Open both the 10 mL flasks to the vacuum. Wait for 5 min.</li>
	<li>Close the tap on each 10 mL flask, and then close each hose to the vacuum. Switch the hoses to the inert gas, and then slowly open the tap on each 10 mL flask to backfill with inert gas. 
	NOTE: When switching from the vacuum to the inert gas, ensure that the bubble flow of the inert gas is high enough to prevent oil from being pulled into the Schlenk line but low enough not to disturb the solids in the flask. Never open the system to vaccum and inert gas at the same time.</li>
	<li>Repeat steps 3.3-3.4 two more times for a total of three cycles.</li>
</ol>
4. Adding solvent to the reagents under an inert atmosphere
<ol>
	<li>Under a positive pressure of inert gas sufficient to prevent air from entering the flask, remove the PTFE tap, and replace it with a septum for each 10 mL flask.</li>
	<li>Add toluene and methylene chloride to the palladium and phosphine mixture.
	<ol>
		<li>Use a syringe and needle to transfer 1.5 mL of dry and deoxygenated toluene into the flask containing the tetrakis(triphenylphosphine)palladium(0) and triphenylphosphine. 
		CAUTION: Toluene is both toxic and flammable. Avoid all forms of contact, keep away from heat sources, work in the fume hood, and wear personal protective equipment. 
		NOTE: Solvents can be dried by passing them through an activated aluminum column under inert gas and deoxygenated by sparging them with inert gas for 30 min. Be sure to purge the syringe and needle with inert gas three times before drawing the solution.</li>
		<li>Repeat step 4.2.1 with 1.5 mL of dry and deoxygenated methylene chloride. 
		CAUTION: Methylene chloride is toxic and carcinogenic. Avoid all forms of contact, work in a fume hood, and wear personal protective equipment.</li>
		<li>Swirl the flask until all the solids have dissolved (approximately 30 s).</li>
	</ol>
	</li>
	<li>Add methylene chloride to the tetratopic phosphine linker.
	<ol>
		<li>Use a syringe and needle to transfer 3.0 mL of dry and deoxygenated toluene into the flask containing the tetratopic phosphine linker Sn1.</li>
		<li>Swirl the flask until all the solid has dissolved (approximately 30 s).</li>
	</ol>
	</li>
</ol>
5. Adding the linker to the palladium and phosphine mixture
<ol>
	<li>Use a syringe and needle to transfer the entire Sn1 linker solution into the flask containing the tetrakis(triphenylphosphine)palladium(0) and triphenylphosphine.</li>
	<li>Swirl the solution for 30 s to thoroughly mix it, then replace the septum with the PTFE tap under a positive pressure of inert gas sufficient to prevent air from entering the flask, and seal the flask.</li>
	<li>Sonicate (40 kHz) the reaction solution for an additional 30 s.</li>
</ol>
6. Heating the reaction
<ol>
	<li>Place the sealed flask into a pre-heated oil bath at 60 &#176;C, and leave it for 24 h without agitating it.</li>
</ol>
7. Isolating the MOF product
<ol>
	<li>Remove the flask from the oil bath, and allow it to cool to room temperature. 
	CAUTION: When handling hot glassware and/or surfaces, be sure to wear heat-resistant gloves.</li>
	<li>Set up a vacuum filtration apparatus using a small Buchner funnel and filter paper (8 &#181;m pore size).</li>
	<li>Remove the PTFE tap from the flask, and then use a pipette to transfer the total volume of the suspension to the filter. 
	NOTE: A light flow of inert gas over the top of the filter can help to avoid the decomposition of the oxygen-sensitive MOF product.</li>
	<li>Rinse the solid with 2 mL of deoxygenated 3:1 methylene chloride/toluene solution. Repeat this step two more times, and allow the solid to dry on the filter paper for 3 min.</li>
	<li>Scrape the solid into a pre-weighed vial, and then weigh the vial to obtain the yield of Sn1-Pd. 
	&#8203;NOTE: Store the LVMOF material under inert gas or a dynamic vacuum in order to avoid decomposition in the presence of oxygen in the air.</li>
</ol>
8. Characterization of the MOF product by powder X-ray diffraction (PXRD)
<ol>
	<li>Transfer approximately 20-30 mg of the crystalline solid to a silicon PXRD sample holder. 
	NOTE: While Sn1-Pd is sufficiently stable in air for the characterization by PXRD, more air-sensitive LVMOF materials can be transferred to an inert atmosphere glovebox and loaded into a sealable capillary PXRD sample holder.</li>
	<li>Place the sample holder in a diffractometer, and close the door to the instrument.</li>
	<li>Collect the PXRD pattern from 4 to 40 2&#952; (scan speed of 0.5 s/step, step size of 0.0204&#176; 2&#952;), and compare the data to the simulated powder pattern of Sn1-Pd.</li>
</ol>

Synthesis of Low-Valent MOFs from Multitopic Phosphine Linkers

<ol><li>Zhou, H. -C., Long, J. R., Yaghi, O. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Introduction+to+metal-organic+frameworks%5BTitle%5D)+AND+%22Chemical+Reviews%22%5BJournal%5D)">Introduction to metal-organic frameworks.</a> Chemical Reviews. 112 (2), 673674(2012).</li>
<li>Furukawa, H., Cordova, K. E., O'Keefe, M., Yaghi, O. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((The+chemistry+and+applications+of+metal-organic+frameworks%5BTitle%5D)+AND+%22Science%22%5BJournal%5D)">The chemistry and applications of metal-organic frameworks.</a> Science. 341 (6149), 1230444(2013).</li>
<li>Li, J., Bhatt, P. M., Li, J., Eddaoudi, M., Liu, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Recent+progress+on+microfine+design+of+metal-organic+frameworks%3A+Structure+regulation+and+gas+sorption+and+separation%5BTitle%5D)+AND+%22Advanced+Materials%22%5BJournal%5D)">Recent progress on microfine design of metal-organic frameworks: Structure regulation and gas sorption and separation.</a> Advanced Materials. 32 (44), 2002563(2020).</li>
<li>Lin, R. -B., Xiang, S., Zhou, W., Chen, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Microporous+metal-organic+framework+materials+for+gas+separation%5BTitle%5D)+AND+%22Chem%22%5BJournal%5D)">Microporous metal-organic framework materials for gas separation.</a> Chem. 6 (2), 337363(2020).</li>
<li>Mendes, R. F., Figueira, F., Leite, J. P., Gales, L., Almeida Paz, F. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Metal-organic+frameworks%3A+a+future+toolbox+for+biomedicine%5BTitle%5D)+AND+%22Chemical+Society+Reviews%22%5BJournal%5D)">Metal-organic frameworks: a future toolbox for biomedicine.</a> Chemical Society Reviews. 49 (24), 91219153(2020).</li>
<li>Wei, Y. -S., Zhang, M., Zou, R., Xu, Q. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Metal-organic+framework-based+catalysts+with+single+metal+sites%5BTitle%5D)+AND+%22Chemical+Reviews%22%5BJournal%5D)">Metal-organic framework-based catalysts with single metal sites.</a> Chemical Reviews. 120 (21), 1208912174(2020).</li>
<li>Cornils, B., Herrmann, W. A., Beller, M., Paciello, R. <a target="_blank" href="http://scholar.google.com/scholar?hl=en&safe=off&q=author%3aCornils%2C+B+%22Applied+Homogeneous+Catalysis+with+Organometallic+Compounds%3A+A+Comprehensive+Handbook+in+Four+Volumes%22">Applied Homogeneous Catalysis with Organometallic Compounds: A Comprehensive Handbook in Four Volumes</a>. , Wiley VCH. Weinheim, Germany. (2017).</li>
<li>Young, R. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Isolating+reactive+metal-based+species+in+metal-organic+frameworks+-+Viable+strategies+and+opportunities%5BTitle%5D)+AND+%22Chemical+Science%22%5BJournal%5D)">Isolating reactive metal-based species in metal-organic frameworks - Viable strategies and opportunities.</a> Chemical Science. 11 (16), 40314050(2020).</li>
<li>Drake, T., Ji, P., Lin, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Site+isolation+in+metal-organic+frameworks+enables+novel+transition+metal+catalysis%5BTitle%5D)+AND+%22Accounts+of+Chemical+Research%22%5BJournal%5D)">Site isolation in metal-organic frameworks enables novel transition metal catalysis.</a> Accounts of Chemical Research. 51 (9), 21292138(2018).</li>
<li>Dunning, S. G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+metal-organic+framework+with+cooperative+phosphines+that+permit+post-synthetic+installation+of+open+metal+sites%5BTitle%5D)+AND+%22Angewandte+Chemie+-+International+Edition%22%5BJournal%5D)">A metal-organic framework with cooperative phosphines that permit post-synthetic installation of open metal sites.</a> Angewandte Chemie - International Edition. 57 (30), 92959299(2018).</li>
<li>Sikma, R. E., Balto, K. P., Figueroa, J. S., Cohen, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Metal-organic+frameworks+with+low-valent+metal+nodes%5BTitle%5D)+AND+%22Angewandte+Chemie+-+International+Edition%22%5BJournal%5D)">Metal-organic frameworks with low-valent metal nodes.</a> Angewandte Chemie - International Edition. 61 (33), e202206353(2022).</li>
<li>Agnew, D. W., Gembicky, M., Moore, C. E., Rheingold, A. L., Figueroa, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Robust%2C+transformable%2C+and+crystalline+single-node+organometallic+networks+constructed+from+ditopic+m-terphenyl+isocyanides%5BTitle%5D)+AND+%22Journal+of+the+American+Chemical+Society%22%5BJournal%5D)">Robust, transformable, and crystalline single-node organometallic networks constructed from ditopic m-terphenyl isocyanides.</a> Journal of the American Chemical Society. 138 (46), 1513815141(2016).</li>
<li>Agnew, D. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Crystalline+coordination+networks+of+zero-valent+metal+centers%3A+Formation+of+a+3-dimensional+Ni%280%29+framework+with+m-Terphenyl+diisocyanides%5BTitle%5D)+AND+%22Journal+of+the+American+Chemical+Society%22%5BJournal%5D)">Crystalline coordination networks of zero-valent metal centers: Formation of a 3-dimensional Ni(0) framework with m-Terphenyl diisocyanides.</a> Journal of the American Chemical Society. 139 (48), 1725717260(2017).</li>
<li>Voigt, L., Wugt Larsen, R., Kubus, M., Pedersen, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Zero-valent+metals+in+metal-organic+frameworks%3A+fac-M%28CO%29%283%29%28pyrazine%29%283%2F2%29%5BTitle%5D)+AND+%22Chemical+Communications%22%5BJournal%5D)">Zero-valent metals in metal-organic frameworks: fac-M(CO)(3)(pyrazine)(3/2).</a> Chemical Communications. 57 (3), 3861(2021).</li>
<li>Sikma, R. E., Cohen, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Metal-organic+frameworks+with+zero+and+low-valent+metal+nodes+connected+by+tetratopic+phosphine+ligands%5BTitle%5D)+AND+%22Angewandte+Chemie+-+International+Edition%22%5BJournal%5D)">Metal-organic frameworks with zero and low-valent metal nodes connected by tetratopic phosphine ligands.</a> Angewandte Chemie - International Edition. 61 (11), e202115454(2022).</li>
<li>Xu, Z., Han, L. L., Zhuang, G. L., Bai, J., Sun, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((In+situ+construction+of+three+anion-dependent+cu%28i%29+coordination+networks+as+promising+heterogeneous+catalysts+for+azide-alkyne+%26%2334%3Bclick%26%2334%3B+reactions%5BTitle%5D)+AND+%22Inorganic+Chemistry%22%5BJournal%5D)">In situ construction of three anion-dependent cu(i) coordination networks as promising heterogeneous catalysts for azide-alkyne &#34;click&#34; reactions.</a> Inorganic Chemistry. 54 (10), 47374743(2015).</li>
<li>Llabresixamena, F., Abad, A., Corma, A., Garcia, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((MOFs+as+catalysts%3A+Activity%2C+reusability+and+shape-selectivity+of+a+Pd-containing+MOF%5BTitle%5D)+AND+%22Journal+of+Catalysis%22%5BJournal%5D)">MOFs as catalysts: Activity, reusability and shape-selectivity of a Pd-containing MOF.</a> Journal of Catalysis. 250 (2), 294298(2007).</li>
<li>Dong, Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+palladium-carbon-connected+organometallic+framework+and+its+catalytic+application%5BTitle%5D)+AND+%22Chemical+Communications%22%5BJournal%5D)">A palladium-carbon-connected organometallic framework and its catalytic application.</a> Chemical Communications. 55 (96), 14414(2019).</li>
<li>Moosavi, S. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Capturing+chemical+intuition+in+synthesis+of+metal-organic+frameworks%5BTitle%5D)+AND+%22Nature+Communications%22%5BJournal%5D)">Capturing chemical intuition in synthesis of metal-organic frameworks.</a> Nature Communications. 10 (1), 17(2019).</li>
</ol>

The authors have nothing to disclose.

There are several critical steps in the protocol that must be followed in order to achieve the desired phosphine-based LVMOF product with sufficient crystallinity. The first is that the metal precursor and modulator mixture (in this case, tetrakis(triphenylphosphine)palladium(0) and triphenylphosphine, respectively) must be dissolved independently of the multitopic phosphine linker (in this case, Sn1). This is to avoid the rapid and irreversible formation of amorphous coordination polymers, which occurs ...

Metal-organic frameworks, or MOFs, are a class of crystalline, porous materials1. MOFs are constructed from metal ions or metal ion cluster nodes, often referred to as secondary building units (SBUs), and multitopic organic linkers to give two- and three-dimensional network structures2. Over the past three decades, MOFs have been studied extensively due to their potential use in gas storage3 and separation4, biomedicine5, and catalysis6. The overwhelming majority of MOFs reported are composed of high-oxidation state metal nodes and hard, anionic donor linkers, such as carboxylates2. However, many homogeneous catalysts utilize soft, low-valent metals in combination with soft donor ligands, such as phosphines7. Therefore, expanding the scope of MOFs that contain low-valent metals can increase the range of catalytic transformations to which MOFs can be applied.
The established strategies for the incorporation of low-valent metals into MOFs using embedded soft donor sites are limited in scope and reduce the free pore volume of the parent MOF structure6,8,9,10. An alternative approach is to use low-valent metals directly as nodes or SBUs in combination with multitopic soft donor ligands as linkers to construct the MOF. This strategy not only provides a high loading of low-valent metal sites in the MOF but may also reduce or prevent metal leaching into the solution as a result of the stability of the framework structure11. For example, Figueroa and co-workers used multitopic isocyanide ligands as soft donor linkers and Cu(I)12 or Ni(0)13 as low-valent metal nodes to produce two- and three-dimensional MOFs. Similarly, Pederson and co-workers synthesized MOFs containing zero-valent group 6 metal nodes using pyrazine as a linker14. More recently, our laboratory reported tetratopic phosphine ligands as linkers for the construction of MOFs containing Pd(0) or Pt(0) nodes (Figure 1)15. These MOFs are particularly interesting due to the prevalence of phosphine-ligated low-valent metal complexes in homogeneous catalysis7. Nevertheless, low-valent MOFs (LVMOFs) as a general class of materials are relatively underexplored in the MOF literature but have great promise for applications in heterogeneous catalysis for reactions such as azide-alkyne coupling16, Suzuki-Miyaura coupling17,18, hydrogenation17, and others11.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/65317/65317fig01v2.jpg" /> 
Figure 1: Synthesis of LVMOFs using phosphine linkers. Sikma and Cohen15 reported the synthesis of three-dimensional LVMOFs, E1-M, using tetratopic phosphine ligands, E1, as linkers, Pd(0) and Pt(0) as nodes, and triphenylphosphine as a modulator. The central atom, E, can be Si or Sn. <a href="https://www.jove.com/files/ftp_upload/65317/65317fig01largev2.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
While the differences in the nature of the linkers and nodes of LVMOFs may give them unique properties compared to conventional MOF materials, these differences also introduce synthetic challenges. For example, many of the metal precursors and linkers that are commonly used in the MOF literature can be used in air2. In contrast, the successful synthesis of phosphine-based LVMOFs requires the exclusion of both air and water15. Similarly, the types of modulators used to promote crystallinity and the solvents used in the synthesis of phosphine-based LVMOFs are unusual compared to those used in most of the MOF literature15. As a result, the synthesis of these materials requires equipment and experimental techniques that even experienced MOF chemists may be less familiar with. Therefore, in an effort to minimize the impact of these obstacles, a step-by-step method for the synthesis of this new class of materials is provided here. The protocol outlined here covers all aspects of the synthesis of phosphine-based LVMOFs, including the overall experimental procedure, air-free techniques, the required equipment, the proper storage and handling of LVMOFs, and characterization methods. The choice of the metal precursor, modulator, and solvent are also discussed. Enabling the entry of new researchers into this field will help accelerate the discovery of novel LVMOFs and related materials for applications in catalysis.

<table><tbody><tr><td>2800 Ultrasonic Cleaner, 3/4 Gallon, 40 kHz</td><td>Branson</td><td>CPX2800H</td><td>Used for sonicating</td></tr><tr><td>Argon, Ultra High Purity</td><td>Matheson</td><td>G1901101</td><td>Used as inert gas source</td></tr><tr><td>D8 ADVANCE Powder X-Ray Diffractometer</td><td>Bruker</td><td></td><td>Used to collect PXRD patterns</td></tr><tr><td>Dewar Flask</td><td>Chemglass Life Sciences</td><td>CG159303</td><td>Dewar used for liquid nitrogen</td></tr><tr><td>Flask,&amp;nbsp;High Vacuum Valve, Capacity (mL) 10, Valve Size 0-4 mm</td><td>Synthware Glass</td><td>F490010</td><td>Reaction vessel referred to as &quot;10 mL flask&quot;</td></tr><tr><td>Grade 2 Qualitative Filter Paper, Standard, 42.5 mm circle</td><td>Whatman</td><td>1002-042</td><td>Used for product isolation</td></tr><tr><td>Methylene Chloride (HPLC)</td><td>Fisher Scientific</td><td>MFCD00000881</td><td>Dried and deoxygenated prior to use</td></tr><tr><td>Sn1 (tetratopic phosphine linker)</td><td></td><td></td><td>Prepared according to literature procedure (ref. 15)</td></tr><tr><td>SuperNuova+ Stirring Hotplate</td><td>Thermo Fisher Scientific</td><td>SP88850190</td><td>Used to heat oil bath</td></tr><tr><td>Tetrakis(triphenylphosphine) palladium(0), 99% (99.9+%-Pd)</td><td>Strem Chemicals</td><td>46-2150</td><td>Commercial Pd(0) source</td></tr><tr><td>Toluene (HPLC)</td><td>Fisher Scientific</td><td>MFCD00008512</td><td>Dried and deoxygenated prior to use</td></tr><tr><td>Triphenylphosphine, &amp;ge;95.0% (GC)</td><td>Sigma-Aldrich</td><td>93092</td><td>Used as a modulator</td></tr><tr><td>Weighing Paper</td><td>Fisher Scientific</td><td>09-898-12B</td><td>Used for solid addition</td></tr></tbody></table>

experimental approaches for the synthesis of low-valent metal-organic frameworks from multitopic phosphine linkers

Metal-organic frameworks (MOFs) are the subject of intense research focus due to their potential applications in gas storage and separation, biomedicine, energy, and catalysis. Recently, low-valent MOFs (LVMOFs) have been explored for their potential use as heterogeneous catalysts, and multitopic phosphine linkers have been shown to be a useful building block for the formation of LVMOFs. However, the synthesis of LVMOFs using phosphine linkers requires conditions that are distinct from those in the majority of the MOF synthetic literature, including the exclusion of air and water and the use of unconventional modulators and solvents, making it somewhat more challenging to access these materials. This work serves as a general tutorial for the synthesis of LVMOFs with phosphine linkers, including information on the following: 1) the judicious choice of the metal precursor, modulator, and solvent; 2) the experimental procedures, air-free techniques, and required equipment; 3) the proper storage and handling of the resultant LVMOFs; and 4) useful characterization methods for these materials. The intention of this report is to lower the barrier to this new subfield of MOF research and facilitate advancements toward novel catalytic materials.

The successful synthesis of Sn1-Pd produces a bright yellow, crystalline solid. The Pd(0) MOF products using analogous tetratopic phosphine linkers are also yellow. The most effective way to determine if the reaction was successful is to collect the PXRD pattern and evaluate the crystallinity of the sample. For example, Figure 2 shows the PXRD pattern of crystalline Sn1-Pd. The key features to verify that the sample is crystalline are that the reflection pea...

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Author Spotlight: Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers  

Here, we describe a protocol for the synthesis of low-valent metal-organic frameworks (LVMOFs) from low-valent metals and multitopic phosphine linkers under air-free conditions. The resulting materials have potential applications as heterogeneous catalyst mimics of low-valent metal-based homogeneous catalysts.

Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers

Metal-organic frameworks (MOFs) are the subject of intense research focus due to their potential applications in gas storage and separation, biomedicine, ...

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Video: Auteur in de schijnwerpers: Experimentele benaderingen voor de synthese van laagvalente metaal-organische raamwerken uit multitopische fosfinelinkers  

Preparation of Hydrophobic Metal-Organic Frameworks via Plasma Enhanced Chemical Vapor Deposition of Perfluoroalkanes for the Removal of Ammonia

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high surface area microporous materials, such as metal-organic frameworks (MOFs), unique challenges present themselves for PECVD treatments. Herein the protocol for development of a MOF that was previously unstable to humid conditions is presented. The protocol describes the synthesis of Cu-BTC (also known as HKUST-1), the treatment of Cu-BTC with PECVD of perfluoroalkanes, the aging of materials under humid conditions, and the subsequent ammonia microbreakthrough experiments on milligram quantities of microporous materials. Cu-BTC has an extremely high surface area (~1,800 m2/g) when compared to most materials or surfaces that have been previously treated by PECVD methods. Parameters such as chamber pressure and treatment time are extremely important to ensure the perfluoroalkane plasma penetrates to and reacts with the inner MOF surfaces. Furthermore, the protocol for ammonia microbreakthrough experiments set forth here can be utilized for a variety of test gases and microporous materials.

Herein the procedures for plasma enhanced chemical vapor deposition of perfluoroalkanes on microporous materials such as metal-organic frameworks to enhance their stability and hydrophobicity are described. Furthermore, breakthrough testing of milligram quantities of samples is described in detail.

Plasma enhanced chemical vapor deposition (PECVD) of perfluoroalkanes has long been studied for tuning the wetting properties of surfaces. For high ...

Synthesis and Characterization of Functionalized Metal-organic Frameworks

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and technological applications. Their signature property is their ultrahigh porosity, which however imparts a series of challenges when it comes to both constructing them and working with them. Securing desired MOF chemical and physical functionality by linker/node assembly into a highly porous framework of choice can pose difficulties, as less porous and more thermodynamically stable congeners (e.g., other crystalline polymorphs, catenated analogues) are often preferentially obtained by conventional synthesis methods. Once the desired product is obtained, its characterization often requires specialized techniques that address complications potentially arising from, for example, guest-molecule loss or preferential orientation of microcrystallites. Finally, accessing the large voids inside the MOFs for use in applications that involve gases can be problematic, as frameworks may be subject to collapse during removal of solvent molecules (remnants of solvothermal synthesis). In this paper, we describe synthesis and characterization methods routinely utilized in our lab either to solve or circumvent these issues. The methods include solvent-assisted linker exchange, powder X-ray diffraction in capillaries, and materials activation (cavity evacuation) by supercritical CO2 drying. Finally, we provide a protocol for determining a suitable pressure region for applying the Brunauer-Emmett-Teller analysis to nitrogen isotherms, so as to estimate surface area of MOFs with good accuracy.

Synthesis, activation, and characterization of intentionally designed metal-organic framework materials is challenging, especially when building blocks are incompatible or unwanted polymorphs are thermodynamically favored over desired forms. We describe how applications of solvent-assisted linker exchange, powder X-ray diffraction in capillaries and activation via supercritical CO2 drying, can address some of these challenges.

Metal-organic frameworks have attracted extraordinary amounts of research attention, as they are attractive candidates for numerous industrial and ...

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the development of antibody drug conjugates (ADCs) and nanomedicine, fluorescent microscopy and systems chemistry. For many of these applications, specificity of the bioconjugation method used is of prime concern. The Michael addition of maleimides with cysteine(s) on the target proteins is highly selective and proceeds rapidly under mild conditions, making it one of the most popular methods for protein bioconjugation.
We demonstrate here the modification of the only surface-accessible cysteine residue on yeast cytochrome c with a ruthenium(II) bisterpyridine maleimide. The protein bioconjugation is verified by gel electrophoresis and purified by aqueous-based fast protein liquid chromatography in 27% yield of isolated protein material. Structural characterization with MALDI-TOF MS and UV-Vis is then used to verify that the bioconjugation is successful. The protocol shown here is easily applicable to other cysteine - maleimide coupling of proteins to other proteins, dyes, drugs or polymers.

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

This protocol details the important steps required for the bioconjugation of a cysteine containing protein to a maleimide, including reagent purification, reaction conditions, bioconjugate purification and bioconjugate characterization.

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the ...

Synthesis of a Water-soluble Metal&#8211;Organic Complex Array

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as Ru(II), Pt(II), and Rh(III). The compound, named as a water-soluble metal-organic complex array (WSMOCA), is obtained through 1) the conventional solution-chemistry-based preparation of the corresponding metal complex monomers having a 9-fluorenylmethyloxycarbonyl (Fmoc)-protected amino acid moiety and 2) their sequential coupling together with other water-soluble organic building units on the surface-functionalized polymeric resin by following the procedures originally developed for the solid-phase synthesis of polypeptides, with proper modifications. Traces of reactions determined by mass spectrometric analysis at the representative coupling steps in stage 2 confirm the selective construction of a predetermined sequence of metal centers along with the peptide backbone. The WSMOCA cleaved from the resin at the end of stage 2 has a certain level of solubility in aqueous media dependent on the pH value and/or salt content, which is useful for the purification of the compound.

A potential general method for the synthesis of water-soluble multimetallic peptidic arrays containing a predetermined sequence of metal centers is presented.

We demonstrate a method for the synthesis of a water-soluble multimetallic peptidic array containing a predetermined sequence of metal centers such as ...

Enzymatic Cascade Reactions for the Synthesis of Chiral Amino Alcohols from L-lysine

Amino alcohols are versatile compounds with a wide range of applications. For instance, they have been used as chiral scaffolds in organic synthesis. Their synthesis by conventional organic chemistry often requires tedious multi-step synthesis processes, with difficult control of the stereochemical outcome. We present a protocol to enzymatically synthetize amino alcohols starting from the readily available L-lysine in 48 h. This protocol combines two chemical reactions that are very difficult to conduct by conventional organic synthesis. In the first step, the regio- and diastereoselective oxidation of an unactivated C-H bond of the lysine side-chain is catalyzed by a dioxygenase; a second regio- and diastereoselective oxidation catalyzed by a regiodivergent dioxygenase can lead to the formation of the 1,2-diols. In the last step, the carboxylic group of the alpha amino acid is cleaved by a pyridoxal-phosphate (PLP) decarboxylase (DC). This decarboxylative step only affects the alpha carbon of the amino acid, retaining the hydroxy-substituted stereogenic center in a beta/gamma position. The resulting amino alcohols are therefore optically enriched. The protocol was successfully applied to the semipreparative-scale synthesis of four amino alcohols. Monitoring of the reactions was conducted by high performance liquid chromatography (HPLC) after derivatization by 1-fluoro-2,4-dinitrobenzene. Straightforward purification by solid-phase extraction (SPE) afforded the amino alcohols with excellent yields (93% to &#62;95%).

Chiral amino alcohols are versatile molecules for use as scaffolds in organic synthesis. Starting from L-lysine, we synthesize amino alcohols by an enzymatic cascade reaction combining diastereoselective C-H oxidation catalyzed by dioxygenase followed by cleavage of the carboxylic acid moiety of the corresponding hydroxyl amino acid by a decarboxylase.

Amino alcohols are versatile compounds with a wide range of applications. For instance, they have been used as chiral scaffolds in organic synthesis. ...

Synthesis of a Thiol Building Block for the Crystallization of a Semiconducting Gyroidal Metal-sulfur Framework

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and porous metal-dithiolene network in the highly ordered single crystalline state. Unlike the highly reactive free-standing thiols, which tend to decompose and complicate the crystallization of metal-thiolate open frameworks, the thioester reacts in situ to provide the thiol species, serving to mitigate the reaction between the mercaptan units and the metal centers, and to improve crystallization consequently. Specifically, the thioester was synthesized in a one-pot procedure: an aromatic bromide (hexabromotriphenylene) reacted with excess sodium thiomethoxide under vigorous conditions to first form the thioether intermediate product. The thioether was then demethylated by the excess thiomethoxide to provide the thiolate anion that was acylated to form the thioester product. The thioester was conveniently purified by standard column chromatography, and then used directly in the framework synthesis, wherein NaOH and ethylenediamine serve to revert in situ the thioester to the thiol linker for assembling the single-crystalline Pb(II)-dithiolene network. Compared with other methods for thiol synthesis (e.g., by cleaving alkyl thioether using sodium metal and liquid ammonia), the thioester synthesis here uses simple conditions and economical reagents. Moreover, the thioester product is stable and can be conveniently handled and stored. More importantly, in contrast to the generic difficulty in accessing crystalline metal-thiolate open frameworks, we demonstrate that using the thioester for in situ formation of the thiol linker greatly improves the crystallinity of the solid-state product. We intend to encourage broader research efforts on the technologically important metal-sulfur frameworks by disclosing the synthetic protocol for the thioester as well as the crystalline framework solid.

Here, we present a one-pot, transition-metal-free synthesis of thiols and thioesters from aromatic halides and sodium thiomethoxide, followed by the preparation of single crystals of a metal-dithiolene network using thiol species generated in situ from the more stable and tractable thioester.

We present a method for preparing thioester molecules as the masked form of the thiol linkers and their utilization for accessing a semiconducting and ...

Surface Functionalization of Metal-Organic Frameworks for Improved Moisture Resistance

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. However, the main issue limiting their applicability is their poor stability in humid conditions. The common methods to overcome this problem involve the formation of strong metal-linker bonds by using highly charged metals, which is limited to a number of structures, the introduction of alkylic groups to the framework by post-synthetic modification (PSM) or chemical vapour deposition (CVD) to enhance overall hydrophobicity of the framework. These last two usually provoke a drastic reduction of the porosity of the material. These strategies do not permit to exploit the properties of the MOF already available and it is imperative to find new methods to enhance the stability of MOFs in water while keeping their properties intact. Herein, we report a novel method to enhance the water stability of MOF crystals featuring Cu2(O2C)4&#160;paddle-wheel units, such as HKUST (where HKUST stands for Hong Kong University of Science &#38; Technology), with the catechols functionalized with alkyl and fluoro-alkyl chains. By taking advantage of the unsaturated metal sites and the catalytic catecholase-like activity of CuII ions, we are able to create robust hydrophobic coatings through the oxidation and subsequent polymerization of the catechol units on the surface of the crystals under anaerobic and water-free conditions without disrupting the underlying structure of the framework. This approach not only affords the material with improved water stability but also provides control over the function of the protective coating, which enables the development of functional coatings for the adsorption and separations of volatile organic compounds. We are confident that this approach could also be extended to other unstable MOFs featuring open metal sites.

Robust functional catechol coatings were produced in one step by direct reaction of the material known as HKUST with synthetic catechols under anaerobic conditions. The formation of homogeneous coatings surrounding the entire crystal is ascribed to the biomimetic catalytic activity of Cu(II) dimers on the external surface of the crystals.

Metal-organic frameworks (MOFs) are a class of porous inorganic materials with promising properties in gas storage and separation, catalysis and sensing. ...

Electrophoretic Crystallization of Ultrathin High-performance Metal-organic Framework Membranes

We report the synthesis of thin, highly intergrown, polycrystalline metal-organic framework (MOF) membranes on a wide range of unmodified porous and non-porous supports (polymer, ceramic, metal, carbon, and graphene). We developed a novel crystallization technique, which is termed the ENACT approach: the electrophoretic nuclei assembly for the crystallization of highly intergrown thin films (ENACT). This approach allows for a high density of heterogeneous nucleation of MOFs on a chosen substrate via the electrophoretic deposition (EPD) directly from the precursor sol. The growth of well-packed MOF nuclei leads to a highly intergrown polycrystalline MOF film. We show that this simple approach can be used for the synthesis of thin, intergrown zeolite imidazole framework (ZIF)-7 and ZIF-8 films. The resulting 500 nm-thick ZIF-8 membranes show a considerably high H2 permeance (8.3 x 10-6 mol m-2 s-1 Pa-1) and ideal gas selectivities (7.3 for H2/CO2, 15.5 for H2/N2, 16.2 for H2/CH4, and 2655 for H2/C3H8). An attractive performance for C3H6/C3H8 separation is also achieved (a C3H6 permeance of 9.9 x 10-8 mol m-2 s-1 Pa-1 and a C3H6/C3H8 ideal selectivity of 31.6 at 25 &#176;C). Overall, the ENACT process, owing to its simplicity, can be extended to synthesize intergrown thin films of a wide range of nanoporous crystalline materials.

A simple, reproducible, and versatile approach for the synthesis of intergrown, polycrystalline metal-organic framework membranes on a wide range of unmodified porous and non-porous supports is presented.

We report the synthesis of thin, highly intergrown, polycrystalline metal-organic framework (MOF) membranes on a wide range of unmodified porous and ...

Triazole and Tetrazole Functionalized Zr-MOFs Synthesis and Characterization

Synthesis of Triazole and Tetrazole-Functionalized Zr-Based Metal-Organic Frameworks Through Post-Synthetic Ligand Exchange

Metal-organic frameworks (MOFs) are a class of porous materials that are formed through coordination bonds between metal clusters and organic ligands. Given their coordinative nature, the organic ligands and strut framework can be readily removed from the MOF and/or exchanged with other coordinative molecules. By introducing target ligands to MOF-containing solutions, functionalized MOFs can be obtained with new chemical tags via a process called post-synthetic ligand exchange (PSE). PSE is a straightforward and practical approach that enables the preparation of a wide range of MOFs with new chemical tags via a solid-solution equilibrium process. Furthermore, PSE can be performed at room temperature, allowing the incorporation of thermally unstable ligands into MOFs. In this work, we demonstrate the practicality of PSE by using heterocyclic triazole- and tetrazole-containing ligands to functionalize a Zr-based MOF (UiO-66; UiO = University of Oslo). After digestion, the functionalized MOFs are characterized via various techniques, including powder X-ray diffraction and nuclear magnetic resonance spectroscopy.

Author Spotlight: Functionalizing Metal-Organic Frameworks: Advancements, Challenges, and the Power of Post-Synthetic Ligand Exchange 

Post-synthetic ligand exchange (PSE) is a versatile and powerful tool for installing functional groups into metal-organic frameworks (MOFs). Exposing MOFs to solutions containing triazole- and tetrazole-functionalized ligands can incorporate these heterocyclic moieties into Zr-MOFs through PSE processes.

Metal-organic frameworks (MOFs) are a class of porous materials that are formed through coordination bonds between metal clusters and organic ligands. ...

Synthesis and Discovery of Phosphonate-Based MOFs: A Solvothermal Approach

Discovery and Synthesis Optimization of Isoreticular Al(III) Phosphonate-Based Metal-Organic Framework Compounds Using High-Throughput Methods

High-throughput (HT) methods are an important tool for the fast and efficient screening of synthesis parameters and the discovery of new materials. This manuscript describes the synthesis of metal-organic frameworks (MOFs) from solution using an HT reactor system, resulting in the discovery of various phosphonate-based MOFs of the composition [Al2H12-x(PMP)3]Clx&#8729;6H2O (H4PMP = N,N &#39;-piperazine bis(methylenephosphonic acid)) for x = 4, 6, denoted as Al-CAU-60-xHCl, containing trivalent aluminum ions. This was accomplished under solvothermal reaction conditions by systematically screening the impact of the molar ratio of the linker to the metal and the pH of the reaction mixture on the product formation. The protocol for the HT investigation includes six steps: a) synthesis planning (DOE = design of&#160;experiment) within the HT methodology, b) dosing and working with in-house developed HT reactors, c) solvothermal synthesis, d) synthesis workup using in-house developed filtration blocks, e) characterization by HT powder X-ray diffraction, and f) evaluation of the data. The HT methodology was first used to study the influence of acidity on the product formation, leading to the discovery of Al-CAU-60&#8729;xHCl (x = 4 or 6).

Author Spotlight: Accelerating Discovery in Microporous Material Chemistry 

The targeted synthesis of new metal-organic frameworks (MOFs) is difficult, and their discovery depends on the knowledge and creativity of the chemist. High-throughput methods allow complex synthetic parameter fields to be explored quickly and efficiently, accelerating the process of finding crystalline compounds and identifying synthetic and structural trends.

High-throughput (HT) methods are an important tool for the fast and efficient screening of synthesis parameters and the discovery of new materials. This ...

Experimental Approaches for the Synthesis of Low-Valent Metal-Organic Frameworks from Multitopic Phosphine Linkers

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