The authors would like to express their thanks to the King Abdullah University of Science and Technology (KAUST) for financial and human support.

1. Leak check for all the high vacuum vessels and their connection to the HVL
<ol>
	<li>Connect the vessel to the HVL.</li>
	<li>Check whether the pressure increases by alternating the dynamic and the static vacuum.</li>
	<li>In case of a leak, scan the connection with the high-frequency generator to localize leaks and holes.</li>
</ol>
2. Dehydroxylated silica preparation
<ol>
	<li>Cover fumed silica (5 g in a 100 mL beaker) with enough deionized water (ca. 50 mL) till it becomes a compact gel.</li>
	<li>Cover the beaker with some aluminum foil and heat it in the oven at 200 &#176;C overnight.</li>
	<li>Grind the silica and transfer (1 g) to a glass reactor (30 cm in height, with a diameter of 4 cm); then, close it with a cap and seal it with grease.</li>
	<li>Connect the glass reactor to the port of the HVL.</li>
	<li>Start heating it gradually to reach 700 &#176;C and leave it overnight.</li>
	<li>Let the reactor cool down and transfer it to the glovebox.</li>
	<li>Prepare a disc pellet from the silica dehydroxylated at 700 &#176;C for a transmission FTIR measurement in the glovebox.</li>
	<li>Observe the isolated silanol signal in the FTIR spectrum.</li>
</ol>
3. Solvent preparation (removal of oxygen and moisture)
<ol>
	<li>Prepare sodium-mirror-coated solvent bomb equipped with a Teflon stopcok.</li>
	<li>Transfer pentane to the solvent bomb.</li>
	<li>Connect the solvent bomb to the HVL.</li>
	<li>Check for leaks in the connections.</li>
	<li>Freeze the solvent using a liquid-nitrogen-filled dewar.</li>
	<li>Evacuate till the solvent finishes to degas.</li>
	<li>Stop the evacuation.</li>
	<li>Repeat the freeze (step 3.5); then, perform a degas cycle (steps 3.6 and 3.7) at least 2x more to ensure all gases are removed.</li>
</ol>
4. General procedure for grafting metal complexes on dehydroxylated silica using Hf(NMe2)4
<ol>
	<li>Dry a double Schlenk by evacuating it with the HVL and heating it with a heat gun.</li>
	<li>Put the dry double Schlenk into the glovebox.</li>
	<li>In the double Schlenk, add the precursor complex Hf(NMe2)4 (0.33 mmol, 0.089 mL) to one compartment and the dehydroxylated silica (1 g) to the other side with a stir bar.</li>
	<li>Close the two necks of the double Schlenk with cap and seal them with grease.</li>
	<li>Using a T-joint, connect the HVL to the solvent Schlenk on one side and to the double Schlenk on the other side.</li>
	<li>Ensure that all connections are secured by metallic clips and evacuate the line and the double Schlenk until reaching a stable high vacuum (10-5 mbar). All stopcocks should be evacuated.</li>
	<li>Transfer the solvent from the solvent Schlenk to the compartment of the double Schlenk containing the metal precursor by distillation. Once the glassware assembly is under static vacuum, use a liquid nitrogen dewar to cool the compartment to condense the solvent and to dissolve the precursor there.</li>
	<li>Transfer the solution to the silica compartment by gravitation. Stir it for 1&#8211;3 h to complete grafting.</li>
	<li>Introduce extra solvent by distillation to wash the silica.</li>
	<li>Start by washing the material; then, filter the material by transferring the solvent to the solvent compartment and distill the solvent to the solid compartment.</li>
	<li>Remove the waste solvent by distillation using an interceptor (solvent trap). Dry the material by using an HVL with continuous stirring in the beginning; then, leave it under a vacuum overnight.</li>
	<li>Prepare a disc pellet (50-70 mg of prepared material) for an FTIR measurement in the glovebox.</li>
</ol>
5. Preparation of the catalyst
<ol>
	<li>Add the grafted material (1 g) to a Schlenk. Connect it to the HVL.</li>
	<li>Start heating it gradually to reach 200 &#176;C and leave it for 4 h. Leave it to cool down under vacuum.</li>
	<li>Prepare a disc pellet (50-70 mg of prepared material) for an FTIR measurement in the glovebox.</li>
</ol>
6. Imine metathesis catalysis
<ol>
	<li>In an ampule tube (or sealed vial), add the catalyst (0.0031 mmol, 12.47 mg).</li>
	<li>Add two imine substrates, for example, N-(4-phenylbenzylidene)benzylamine (0.0783 mmol, 21.36 mg) with N-benzylidene-tert-butylamine (0.0783 mmol, 13.94 uL). Or, use N-(4-fluorobenzylidene)-4-fluoroaniline (0.0783 mmol, 17.00 mg) with N-(4-phenylbenzylidene)benzylamine (0.0783 mmol, 21.36 mg).</li>
	<li>Add 0.5 mL of toluene. Add a stirring bar. Connect the ampule tube to the vacuum line. Freeze the ampule tube by using liquid nitrogen.</li>
	<li>Use the flame torch (oxygen and propane) to seal the ampule tube. For a sealed vial, just close it tightly by the compressor.</li>
	<li>Place the tube in oil or in a sand bath at 80 &#176;C.</li>
	<li>Leave the experiment run for up to 6 h. Monitor the reaction at different time from 1 to 6 h.</li>
	<li>Freeze the tube and cut the top using a glass cutter.</li>
	<li>Filter the solution into a gas chromatography (GC) vial for GC mass spectrometry (GC-MS) analysis. Dilute the reaction solution to a volume of 1 mL.</li>
</ol>

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The authors have nothing to disclose.

The methodology employed in SOMC was developed to handle sensitive materials (such as highly dehydroxylated silica and sensitive complexes precursors, etc.) in the cleanest way possible. This is necessary to prepare and characterize single-site well-defined surface complexes. Furthermore, these complexes can be isolated and serve as intermediates to various catalytic transformations of interest (e.g., alkane metathesis4,5, imine metathesis7,8,32, and hydroaminoalkylation26).
HVLs (producing a vacuum as high as 10-5 mbar) are necessary to avoid any contamination from inert gases during the grafting reactions. High vacuum techniques are very different from the positive pressure techniques employed in regular Schlenk lines or even gloveboxes. Due to its high surface area (200 m2 per gram), silica tends to adsorb contaminants (water, etc.) that can compromise subsequent reactions.
The glovebox is used mostly to load/unload reactants prior to the reactions and to conduct some reactions. All gloveboxes in this method operate under argon as some catalysts can react with nitrogen. The method requires special attention dedicated to transferring sensitive materials from gloveboxes to HVLs and back. Some steps (i.e., liquid addition and solid washing) require the user to assemble several pieces of glassware on the HVL. Each connection must remain leak-free for the time of the operation (i.e., during the solvent transfer) to protect the chemicals contained.
This technique is rather time-consuming and challenging to upscale but remains unparalleled in producing a significant amount (1-3 g) of clean and well-characterized surface complexes that can be used as catalysts. Future development foreseen is the use of this method to isolate more new catalytic species, such as those containing SOMFs (i.e., metal-nitrido fragment M&#8801;N).
In this study, a SOMF metal amide fragment was isolated. Highly dehydroxylated silica SiO2-700 was treated with about one equivalent of metal precursor (Hf(NMe2)4 [0.089 mL]) to the amount of silanol (0.3 mmol&#183;g-1) in pentane at room temperature to afford catalysts7,8,32. The volatiles were removed, and the powder samples were dried under a dynamic vacuum to afford the desired materials, which were heated to 200 &#176;C to generate imido. All materials should be characterized by FTIR, elemental microanalysis, and SSNMR and DNP-SENS.
The surface silanols were almost completely consumed as evidenced by the disappearing of the signal at 3,747 cm-1 in the FTIR spectra of the grafted complexes. New signals observed around 2,800-3,000 cm-1 and 1,400-1,500 cm-1 correspond to alkyl groups. Further studies by CHNS and ICP analysis provide information about the metal loading for complex 1 (4.49% of Hf in weight per gram of silica (0.91 mmol of Hf per silanol)) that is consistent with a monopodial species. The expected and found M/C, M/H, and M/N ratios are N/M = 3.9 (theory = 3) and C/M = 7.1 (theory = 6) for the grafted material 1 (see Table 1); for 2, the N/M and C/M ratios are 2.5 (theory = 2) and 4.6 (theory = 4), respectively.
To get an insight into the coordination sphere of the surface grafted metal complexes, the materials were examined by advanced SSNMR spectroscopy experiments and DNP-SENS studies. SSNMR results are generally more difficult to interpret compared to liquid NMR spectroscopy; SSNMR is for insoluble macromolecules. Solid samples have less isotropic molecular tumbling compared to liquid samples; the molecules can tumble in all directions as they are homogeneous and diamagnetic, which will result in much broader signals in SSNMR for solid samples40.
From DQ SSNMR, we could observe -CH2 and -CH3,&#160;but from TQ SSNMR, only -CH3 was presented, and from HETCOR correlation, we could elucidate the structure. We focused on the metal-nitrogen fragment which was delivered by the use of 15N DNP-SENS, since we were working on amine complexes.
To conclude, the preparation of new silica-supported hafnium complexes [(&#8801;Si-O-)Hf(&#951;2-MeNCH2)(&#951;1-NMe2)(&#951;1-HNMe2)] 1, and [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] 2 fully characterized by SS NMR and FTIR spectroscopies and elemental analysis. Further characterizations were carried giving structural information about nitrogen atom by 15N MAS DNP SENS data. The data show the presence of surface fragments (MNC) in 1, and ([M]=N) fragment in 2. The essential role of ([M]=NR) fragment in imine metathesis was demonstrated in catalyst testing with two pairs of imine substrates.

SOMC has a rich library of surface complexes active for a wide range of catalytic reactions and an unparalleled track record to isolate the catalytic intermediates in heterogeneous catalysis. Single-site catalysts have been prepared by the reaction of an organometallic compound (or a coordination compound) with a very clean surface of highly dehydroxylated metal oxide (e.g., silica). Recently, we have identified surface organometallic fragments (SOMF) (e.g., M=C, M-C, M-H, M-NC, M=O, M=CR2,andM=NR) that have a pivotal role toward targeted catalysis reactivity (e.g., alkane oxidation1,2,3, alkane metathesis4,5, alkene metathesis6, imine metathesis7,8,9). [M]=NR fragments have received less attention; their characterization and reactivity studies remain limited, yet they can act as an intermediate in carbon-nitrogen transformation reactions10. The importance of imido complexes (bearing a [M]=NR) is their well-established organic synthesis and catalysis11,12. Stoichiometric or catalytic reactions may occur at the M=NR fragment itself13, or the imido group may remain a spectator, as in Schrock&#39;s catalysts for olefin metathesis14 or some Ziegler-Natta-type olefin polymerization catalysts15. This paper deals with a reaction of imine metathesis with a group IV organometallic complex bearing a metallaaziridine fragment which transfers to a metal-imido fragment that promotes the catalysis16. Catalytic imine metathesis is analogous to olefin metathesis in that two different imines afford a statistical mixture of all possible =NR exchange products.
Metathesis reactions were discovered in 196417 by Phillips Petroleum Co., Bartlesville, Oklahoma. A variety of heterogeneous catalysts were developed for olefin metathesis (e.g., tungsten, molybdenum oxide on silica or alumina, or rhenium oxide on alumina)18. Most progresses were reported in olefin metathesis19,20 and advanced the general understanding of hydrocarbon transformations. They were recognized in 2005 by the award of the Nobel Prize to scientists who worked in olefin metathesis, namely Richard R. Schrock, Yves Chauvin, and Robert Grubbs21. The chemistry of metal-alkylidene-mediated olefin metathesis processes has broadened not only pure hydrocarbon organic synthesis possibilities22 but also made it possible to deliver chemicals with new carbon-heteroatom double bonds7,16. Alkane metathesis was discovered later by Basset&#39;s group and requires multifunctional catalysts23,24,25. Less attention has been dedicated to imine metathesis, yet it can be a promising route to a variety of nitrogen-containing compounds.
Metal-mediated catalytic systems can selectively metathesize carbon-nitrogen bonds26,27,28. Homogeneous catalytic systems have been employed for imine metathesis, yet no definite mechanism has been validated29. This has hindered the rational development of new efficient synthetic pathways to yield new compounds. A practical perspective developing a metal-catalyzed imine metathesis may improve its selectivity and its tolerances toward functional groups compared to acid-catalyzed imine exchange30,31.
Employing rigorous SOMC methodology, we have isolated two new well-defined hafnium nitrogen-containing fragments (metallaaziridine and metal-imido) that were fully characterized (FTIR, solid-state NMR, elemental microanalysis)7. Using highly dehydroxylated silica with isolated silanols, SiO2-700 (Figure 1) allows the isolation of well-defined single-site catalysts. This work is considering the M-N, MNC, and M=N surface fragments (SFs) as key reaction intermediates that direct the reaction toward hydroaminoalkylation26 or imine metathesis7,8,32. This study can potentially bring a better general understanding of transition metal imido functional groups bore by group IV metal grafted on silica.
One major issue with a heteroatom containing SFs, including nitrogen ones, has been the limited amount of characterization methods available to identify the metal-heteroatom coordination. This work is showing that 15N DNP-SENS can provide a clear insight into the silica-supported nitrogen moieties (metallaaziridine and metal-imido). Herein, we isolate a silica-supported well-defined (imido) complex and demonstrate its capability as a highly efficient imine metathesis catalyst7,33.
Overall, this work leads to an improved understanding of the imine metathesis mechanism catalyzed by surface complexes. This protocol can be generalized to other early transition metal imine complexes grafted on highly dehydroxylated silica surfaces. Those surface species could be employed as catalysts but only for the hydroamination and hydroaminoalkylation of alkenes or alkynes26,34,35,36,37, but also for the metathesis of imines representing a 2 + 2 mechanism including the imine and the imido groups see (Figure 2). Imine products are valuable in pharmaceutical and agricultural applications35,38.

<table>
	<tbody>
		<tr>
			<td>Fumed silica (AEROSIL&#174; 200)</td>
			<td>Sigma-Aldrich</td>
			<td>112945-52-5</td>
			<td></td>
		</tr>
		<tr>
			<td>tetrakis(dimethylamido)hafnium(iv) Hf(NMe2)4</td>
			<td>Strem Chemicals</td>
			<td>19782-68-4</td>
			<td></td>
		</tr>
		<tr>
			<td>Pentane</td>
			<td></td>
			<td>109-66-0</td>
			<td></td>
		</tr>
		<tr>
			<td>Nicolet 6700 FT-IR spectrometer</td>
			<td>Thermo Scientific</td>
			<td>IQLAADGAAGFAEFMAAI</td>
			<td>equipped with a controlled-atmosphere cell</td>
		</tr>
		<tr>
			<td>Ultashield 600WB plus 600 MHz NMR Bruker AVANCE III solid-state NMR spectrometer</td>
			<td>Bruker</td>
			<td>-</td>
			<td>Magnet BZH 09/600/107B</td>
		</tr>
		<tr>
			<td>5110 ICP-OES</td>
			<td>Agilent Technologies</td>
			<td>G8015A</td>
			<td>EPA 3052 method for digestion</td>
		</tr>
		<tr>
			<td>Ethos1 (Advanced Digestion System)</td>
			<td>Milestone</td>
			<td>-</td>
			<td></td>
		</tr>
		<tr>
			<td>Gass Chromatography (GC)</td>
			<td>Agilent Technologies</td>
			<td>G1701EA</td>
			<td>inert XL MSD With Triple-Axis Detector</td>
		</tr>
		<tr>
			<td>DNP-SENS-NMR 400 MHz (1H/electron Larmor frequencies) Bruker Avance III solid-state NMR spectrometer</td>
			<td>Bruker</td>
			<td>-</td>
			<td>equipped with a 263-GHz gyrotron.</td>
		</tr>
		<tr>
			<td>FLASH 2000 CHNS/O Analyzer</td>
			<td>Thermo Scientific</td>
			<td>-</td>
			<td></td>
		</tr>
		<tr>
			<td>N-(4-Phenylbenzylidene)benzylamine</td>
			<td>Sigma-Aldrich</td>
			<td>118578-71-5</td>
			<td></td>
		</tr>
		<tr>
			<td>N-(4-Fluorobenzylidene)-4-fluoroaniline</td>
			<td>Sigma-Aldrich</td>
			<td>39769-09-0</td>
			<td></td>
		</tr>
		<tr>
			<td>N-Benzylidenetert-butylamine</td>
			<td>Sigma-Aldrich</td>
			<td>6852-58-0</td>
			<td></td>
		</tr>
		<tr>
			<td>Toluene</td>
			<td>Sigma-Aldrich</td>
			<td>108-88-3</td>
			<td></td>
		</tr>
	</tbody>
</table>

imine metathesis by silica-supported catalysts using the methodology of surface organometallic chemistry

With this protocol, a well-defined singlesite silica-supported heterogeneous catalyst [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is designed and prepared according to the methodology developed by surface organometallic chemistry (SOMC). In this framework, catalytic cycles can be determined by isolating crucial intermediates. All air-sensitive materials are handled under inert atmosphere (using gloveboxes or a Schlenk line) or high vacuum lines (HVLs, &#60;10-5 mbar). The preparation of SiO2-700 (silica dehydroxylated at 700 &#176;C) and subsequent applications (the grafting of complexes and catalytic runs) requires the use of HVLs and double-Schlenk techniques. Several well-known characterization methods are used, such as Fourier-transform infrared spectroscopy (FTIR), elemental microanalysis, solid-state nuclear magnetic resonance spectroscopy (SSNMR), and state-of-the-art dynamic nuclear polarization surface enhanced NMR spectroscopy (DNP-SENS). FTIR and elemental microanalysis permit scientists to establish the grafting and its stoichiometry. 1H and 13C SSNMR allows the structural determination of the hydrocarbon ligands coordination sphere. DNP SENS is an emerging powerful technique in solid characterization for the detection of poorly sensitive nuclei (15N, in our case). SiO2-700 is treated with about one equivalent of the metal precursor compared to the amount of surface silanol (0.30 mmol&#183;g-1) in pentane at room temperature. Then, volatiles are removed, and the powder samples are dried under dynamic high vacuum to afford the desired materials [(&#8801;Si-O-)Hf(&#951;2&#960;-MeNCH2)(&#951;1-NMe2)(&#951;1-HNMe2)]. After a thermal treatment under high vacuum, the grafted complex is converted into metal imido silica complex [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)]. [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] effectively promotes the metathesis of imines, using the combination of two imine substrates, N-(4-phenylbenzylidene)benzylamine, or N-(4-fluorobenzylidene)-4-fluoroaniline, with N-benzylidenetert-butylamine as substrates. A significantly lower conversion is observed with the blank runs; thus, the presence of the imido group in [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is correlated to the catalytic performance.

Firstly, preparing silica 700 as described in section 2 of the protocol, the fumed silica should be mixed with enough deionized water to make it compact, left overnight in the oven at 120 &#176;C, and then, loaded to a quartz reactor (Figure 3). Dehydroxylated silica SiO2-700 was obtained by heating the silica gradually to 700 &#176;C under a dynamic vacuum, FTIR spectrum for SiO2-700 in (Figure 1) shows the characteristic isolated silanol of SiO2-700.
The grafting of metal complex to the silica was achieved by a protonolysis reaction of the amido ligands (NMe2) by surface silanols. For the grafting of organometallic complexes onto highly dehydroxylated silica surface SiO2-700 (Figure 4), dehydroxylated silica was loaded with complex Hf(NMe2)4 into a double Schlenk inside a glovebox. The double Schlenk was moved out of the glovebox for the reaction to occur. The grafting reaction lasted around 3 h. Three washing cycles were then carried out by filtration; more solvent was transferred by distillation when needed. Finally, the solvent was distilled and then removed, with all volatiles, using an interceptor (solvent trap). All solids were dried by connecting the double Schlenk to the HVL (Figure 4 and Figure 5).
Elemental analysis using inductively coupled plasma (ICP) (using the EPA 3052 method for digestion) and carbon, hydrogen, nitrogen, and sulfur analyzer (CHNS) accompanied with FTIR was first verified for the determination of grafting stoichiometry. Elemental analysis showed that N/M = 3.9 (theory = 3) and C/M = 7.1 (theory = 6) for the grafted material (see Table 1); for 2, the N/M and C/M ratios were 2.5 (theory = 2) and 4.6 (theory = 4), respectively. Thus, the carbon and nitrogen contents were declined. For the preparation of the samples for the FTIR measurement, using the designed FTIR cell, see Figure 6. The first sample is the dehydroxylated SiO2-700, which displayed a characteristic peak for isolated silanol. After grafting the complex on dehydroxylated silica, this characteristic peak almost completely disappeared, and new peaks appeared in the alkyl region at 2,776-2,970 cm-1 and 1,422-1,465 cm1. After a heat treatment of prepared material at 200 &#176;C for 1 h, its infrared (IR) spectrum showed a new peak for the imido fragment at 1,595 cm-1.
SSNMR experiments were carried out for a deeper understanding of the surface structure. Samples for SSNMR (Figure 7) were loaded in a specific rotor (32.1 &#181;L). The 1H SSNMR spectrum of the grafted material displayed broad peaks at 2.2 and 2.7 ppm for alkyl groups bonded to the nitrogen ligands. The breadth of the resonances was expected in 1H SSNMR (in contrast to liquid NMR) and was also associated with less mobile surface species (Figure 7B).
The 13C cross-polarized magic angle spinning (CP-MAS) spectrum displayed signals that were less broadened but had a low sensitivity (alike liquid NMR). The spectrum of the grafted material revealed two overlapping peaks at 37 ppm -N-(CH3)2 and at 46 ppm, attributed to the nonequivalent methyl group in -N-(CH3) alongside a low-intensity peak at 81 ppm. A heteronuclear correlation spectroscopy (HETCOR) experiment was carried out to show the correlation between proton and carbon directly bonded to each other. The 81 ppm signal was correlated with the proton peak at 2.7 ppm in the HETCOR spectrum7. As previously reported with zirconiaaziridene, this peak represented the methylene (CH2) group in a metallaaziridine cycle39.
A multiple-quantum experiment makes it possible to visualize the correlation between proximal protons. Double-quantum (DQ) NMR indicates the sum of the two single quantum NMR frequencies to provide an autocorrelation peak located where &#969;1 = 2&#969;2. Similarly, for triple-quantum (TQ) NMR impart from the sum of three protons single quantum frequencies where &#969;1 = 3&#969;2. CH2 and CH3 afford characteristic autocorrelation peaks in the double- and triple-quantum dimensions, respectively. DQ and TQ proton SSNMR experiments were performed with the grafted material. For the strongest autocorrelation peak observed for the signal at 2.2 ppm in both the DQ and TQ spectra (appearing at 4.4 ppm and 6.6 ppm in DQ and TQ, respectively), revealing -CH3 protons, see Figure 7B. The second overlapping peak for the proton at 2.7 ppm showed an autocorrelation only in the double quantum (DQ) spectrum; thus, it confirms the presence of a methylene group (-CH2-) in the grafted species.
15N SSNMR experiments using the DNP-SENS technique (Figure 7B) were carried out to characterize the nitrogen atoms coordinated to the metal center. The spectrum obtained for the grafted material displayed two peaks, around 7 and 32 ppm. On the basis of its relative intensity, the intense signal downfield at 32 ppm was assigned to the nitrogen nuclei of the (&#951;2-NMeCH2) and (-NMe2) functionalities. The weak upfield-shifted peak at 7 ppm was attributed to an NH(CH3)2 moiety; upon heat treatment, -HNMe2 remains on the surface.
For the imido metal fragment in catalyst 2, generated after heat treatment, one broad peak appeared at 2.2 ppm, and the weak peaks at 1.2 and 0.7 ppm in the 1H NMR spectrum attributed to some minor impurities, dimethylamine moieties. For 13C CP-MAS, NMR spectrum displays two peaks at 37 and 48 ppm. Interestingly, the peak for (-CH2-) in metallaaziridine disappeared (Figure 7C). Additionally, we inferred from the multiple quantum experiments that the 1H peak appearing at 2.2 ppm represented the (-CH3) protons. For the 15N SSNMR spectrum of the imido metal fragment in 2 (Figure 7C), an additional downfield-shifted peak at 113 ppm along with a peak at 34 ppm became much less intense after the heat treatment of the grafted material. The 113 ppm peak was assigned to the new fragment generated from the hafnium imido moieties.
In a glovebox, imine substrates with a catalyst were loaded either in an ampule tube or a sealed vial with toluene, and Figure 8 shows the reaction of imine metathesis with three imine compounds, namely N-(4-phenylbenzylidene)benzylamine, N-(4-fluorobenzylidene)-4-fluoroaniline, and N-benzylidenetert-butylamine. Mass spectra for products analyzed by GC-MS (Figure 8) are a&#34; (1-([1,1&#39;-biphenyl]-4-yl)-N-(tert-butyl)methanimine), c&#39; (N,1-diphenylmethanimine),&#160;a&#39; (1-([1,1&#39;-biphenyl]-4-yl)-N-(3-fluorophenyl)methanimine) and b&#39; (1-(4-fluorophenyl)-N-phenylmethanimine).
Imine metathesis is a combination of two imine substrates mixed with the catalyst to produce a new two imine substrates after characterizing by GC-MS. To calculate the conversion percentage as shown in (Table 2), use the following formulas. 
<img alt="Equation 1" src="/files/ftp_upload/59409/59409eq1.jpg" /> 
<img alt="Equation 2" src="/files/ftp_upload/59409/59409eq2.jpg" />
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/59409/59409fig1.jpg" /> 
Figure 1: Dehydroxylation. Formation of isolated silanols by dehydroxylation to produce silica dehydroxylated at 700 &#176;C (SiO2-700). <a href="https://www.jove.com/files/ftp_upload/59409/59409fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/59409/59409fig2.jpg" /> 
Figure 2: General reaction scheme of the imine metathesis mechanism7. <a href="https://www.jove.com/files/ftp_upload/59409/59409fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/59409/59409fig3.jpg" /> 
Figure 3: Dehydroxylation of silica. The reactor was inserted into the oven and connected to a high vacuum line (HVL). The photograph shows the actual setup. <a href="https://www.jove.com/files/ftp_upload/59409/59409fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/59409/59409fig4.jpg" /> 
Figure 4: Grafting in a double Schlenk. Schematic representation of the grafting process. The photograph shows the actual setup. <a href="https://www.jove.com/files/ftp_upload/59409/59409fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/59409/59409fig5.jpg" /> 
Figure 5: Handling grafting in a double Schlenk with a high vacuum line (HVL). First, the solvent transfer procedure was performed, followed by the washing procedure, the solvent removal, and drying the material. <a href="https://www.jove.com/files/ftp_upload/59409/59409fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/59409/59409fig6.jpg" /> 
Figure 6: Fourier-transform infrared spectroscopy (FTIR) measurement. (A) FTIR disc pellet preparation. (B) FTIR spectra of the support, SiO2-700 have a characteristic signal for isolated silanols observed at 3,747 cm-1 and silica undertone between 1,400-2000 cm-1. For the grafted complex, strong new signals appeared in the regions of 2,800-3,000 cm-1 and 1,400-1,500 cm-1. They represent the alkyl groups. After heat treatment, spectrum shows a new signal appeared at 1,595 cm-1 for the imido group7. <a href="https://www.jove.com/files/ftp_upload/59409/59409fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/59409/59409fig7.jpg" /> 
Figure 7: NMR data from the grafted material and the catalyst. (A) Preparing a solid-state NMR sample. (B) (B-1) 1D 13C cross-polarized magic angle spinning (CP-MAS) with 2D 1H-13C heteronuclear correlation (HETCOR( NMR spectra of the grafted complex before treatment. (B-2) 1D 1H NMR spectrum with 1H-1H double-quantum (DQ) and 1H-1H triple quantum (TQ) spectra of the grafted complex. (B-3) 15N dynamic nuclear polarization surface enhanced the NMR spectroscopy (DNP-SENS) spectrum and (inset 1) the proposed structure of the grafted surface hafnium complex [(&#8801;Si-O-)Hf(&#951;2-MeNCH2)(&#951;1-NMe2)(&#951;1-HNMe2)]. (C) (C-1) 1D 13C CP-MAS with 2D 1H-13C HETCOR NMR spectra of the grafted complex after heat treatment to generate an imido fragment. (C-2) 1D 1H NMR spectrum with 1H-1H DQ and 1H-1H TQ spectra of the grafted complex after heat treatment which is the catalyst 2. (C-3) 15N DNP-SENS spectrum, and (inset 2) proposed a structure of the surface hafnium complex catalyst [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)]7. <a href="https://www.jove.com/files/ftp_upload/59409/59409fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/59409/59409fig8.jpg" /> 
Figure 8: Imine metathesis catalysis and mass spectral data of products. Three imine compounds were tested: N-(4-phenylbenzylidene)benzylamine (a), N-(4-fluorobenzylidene)-4-fluoroaniline (b), and N-benzylidene-tert-butylamine (c). Gas chromatography-mass spectrometry (GC-MS) was used to analyze the products obtained, namely 1-([1,1&#39;-biphenyl]-4-yl)-N-(tert-butyl)methanimine (a&#34;), N,1-diphenylmethanimine (c&#39;), 1-([1,1&#39;-biphenyl]-4-yl)-N-(3-fluorophenyl)methanimine (a&#39;), and 1-(4-fluorophenyl)-N-phenylmethanimine (b&#39;)7. <a href="https://www.jove.com/files/ftp_upload/59409/59409fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td></td>
			<td>Metal </td>
			<td>%Metal</td>
			<td>M/Silanol</td>
			<td>%C</td>
			<td>%N</td>
			<td>C/N</td>
			<td>N/M</td>
			<td>C/M</td>
		</tr>
		<tr>
			<td>1</td>
			<td>Hf</td>
			<td>4.94</td>
			<td>0.92</td>
			<td>2.49</td>
			<td>1.5</td>
			<td>2</td>
			<td>3.9</td>
			<td>7.1</td>
		</tr>
		<tr>
			<td>2</td>
			<td>Hf</td>
			<td>4.48</td>
			<td>0.81</td>
			<td>1.4</td>
			<td>0.8</td>
			<td>1.8</td>
			<td>2.5</td>
			<td>4.6</td>
		</tr>
	</tbody>
</table>
Table 1: Elemental analysis7.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Catalyst</td>
			<td>Time</td>
			<td>substrate conversion %</td>
			<td>Substrate conversion %</td>
		</tr>
		<tr>
			<td>2</td>
			<td>1</td>
			<td>a (54)</td>
			<td>c (54)</td>
		</tr>
		<tr>
			<td>no catalyst</td>
			<td>1</td>
			<td>a (11)</td>
			<td>c (11)</td>
		</tr>
		<tr>
			<td>2</td>
			<td>6</td>
			<td>a (50)</td>
			<td>b (55)</td>
		</tr>
		<tr>
			<td>no catalyst</td>
			<td>6</td>
			<td>a (25)</td>
			<td>b (20)</td>
		</tr>
		<tr>
			<td>2</td>
			<td>4</td>
			<td>a (36)</td>
			<td>b (30)</td>
		</tr>
	</tbody>
</table>
Table 2: Catalysis Conversion7.

Watch this Scientific Journal Video about Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry at JoVE.com

Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry

A new group IV metal catalyst for imine metathesis is prepared by grafting amine metal complex onto dehydroxylated silica. Surface metal fragments are characterized using FT-IR, elemental microanalysis, and solid-state NMR spectroscopy. Further dynamic nuclear polarization surface enhanced NMR spectroscopy experiments complement the determination of the coordination sphere.

With this protocol, a well-defined singlesite silica-supported heterogeneous catalyst [(&#8801;Si-O-)Hf(=NMe)(&#951;1-NMe2)] is designed and prepared ...

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9.4K Views.  King Abdullah University of Science and Technology (KAUST). A new group IV metal catalyst for imine metathesis is prepared by grafting amine metal complex onto dehydroxylated silica. Surface metal fragments are characterized using FT-IR, elemental microanalysis, and solid-state NMR spectroscopy. Further dynamic nuclear polarization surface enhanced NMR spectroscopy experiments complement the determination of the coordination sphere.

Video: Imine Metathesis by Silica-Supported Catalysts Using the Methodology of Surface Organometallic Chemistry

Exploring the Radical Nature of a Carbon Surface by Electron Paramagnetic Resonance and a Calibrated Gas Flow

While the first Electron Paramagnetic Resonance (EPR) studies regarding the effects of oxidation on the structure and stability of carbon radicals date back to the early 1980s the focus of these early papers primarily characterized the changes to the structures under extremely harsh conditions (pH or temperature)1-3. It is also known that paramagnetic molecular oxygen undergoes a Heisenberg spin exchange interaction with stable radicals that extremely broadens the EPR signal4-6. Recently, we reported interesting results where this interaction of molecular oxygen with a certain part of the existing stable radical structure can be reversibly affected simply by flowing a diamagnetic gas through the carbon samples at STP7. As flows of He, CO2, and N2 had a similar effect these interactions occur at the surface area of the macropore system.
This manuscript highlights the experimental techniques, work-up, and analysis towards affecting the existing stable radical nature in the carbon structures. It is hoped that it will help towards further development and understanding of these interactions in the community at large.

Stable radicals that are present in carbon substrates interact with paramagnetic oxygen through a Heisenberg spin exchange. This interaction can be significantly reduced under STP conditions by flowing a diamagnetic gas over the carbon system. This manuscript describes a simple method to characterize the nature of those radicals.

While the first Electron Paramagnetic Resonance (EPR) studies regarding the effects of oxidation on the structure and stability of carbon radicals date ...

Synthetic Methodology for Asymmetric Ferrocene Derived Bio-conjugate Systems via Solid Phase Resin-based Methodology

Early detection is a key to successful treatment of most diseases, and is particularly imperative for the diagnosis and treatment of many types of cancer. The most common techniques utilized are imaging modalities such as Magnetic Resonance Imaging (MRI), Positron Emission Topography (PET), and Computed Topography (CT) and are optimal for understanding the physical structure of the disease but can only be performed once every four to six weeks due to the use of imaging agents and overall cost. With this in mind, the development of &#8220;point of care&#8221; techniques, such as biosensors, which evaluate the stage of disease and/or efficacy of treatment in the clinician&#8217;s office and do so in a timely manner, would revolutionize treatment protocols.1 As a means to exploring ferrocene based biosensors for the detection of biologically relevant molecules2, methods were developed to produce ferrocene-biotin bio-conjugates described herein. This report will focus on a biotin-ferrocene-cysteine system that can be immobilized on a gold surface.

The synthesis of asymmetric species of ferrocene is challenging using solution techniques. This report focuses on the methods carried out to produce a ferrocene-biotin bioconjugate using facile and clean reactions accomplished via solid-phase synthesis. Incorporation of a thiolate moiety is shown to impart the ability for immobilization on gold surfaces.

Early detection is a key to successful treatment of most diseases, and is particularly imperative for the diagnosis and treatment of many types of cancer. ...

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 ...

Facile Synthesis of Worm-like Micelles by Visible Light Mediated Dispersion Polymerization Using Photoredox Catalyst

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins with the synthesis of a hydrophilic poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) homopolymer using reversible addition-fragmentation chain-transfer (RAFT) polymerization. Under mild visible light irradiation (&#955; = 460 nm, 0.7 mW/cm2), this macro-chain transfer agent (macro-CTA) in the presence of a ruthenium based photoredox catalyst, Ru(bpy)3Cl2 can be chain extended with a second monomer to form a well-defined block copolymer in a process known as Photoinduced Electron Transfer RAFT (PET-RAFT). When PET-RAFT is used to chain extend POEGMA with benzyl methacrylate (BzMA) in ethanol (EtOH), polymeric nanoparticles with different morphologies are formed in situ according to a polymerization-induced self-assembly (PISA) mechanism. Self-assembly into nanoparticles presenting POEGMA chains at the corona and poly(benzyl methacrylate) (PBzMA) chains in the core occurs in situ due to the growing insolubility of the PBzMA block in ethanol. Interestingly, the formation of highly pure worm-like micelles can be readily monitored by observing the onset of a highly viscous gel in situ due to nanoparticle entanglements occurring during the polymerization. This process thereby allows for a more reproducible synthesis of worm-like micelles simply by monitoring the solution viscosity during the course of the polymerization. In addition, the light stimulus can be intermittently applied in an ON/OFF manner demonstrating temporal control over the nanoparticle morphology.

This article describes a process for producing polymeric self-assembled nanoparticles using visible light mediated dispersion polymerization. Using low energy visible light to control the polymerization allows for the reproducible formation of self-assembled worm-like micelles at high solids content.

Presented herein is a protocol for the facile synthesis of worm-like micelles by visible light mediated dispersion polymerization. This approach begins ...

Temperature-programmed Deoxygenation of Acetic Acid on Molybdenum Carbide Catalysts

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system includes a reactor, furnace, gas and vapor sources, flow control, instrumentation to quantify reaction products (e.g., gas chromatograph), and instrumentation to monitor the reaction in real time (e.g., mass spectrometer). Here, we apply the TPRxn methodology to study molybdenum carbide catalysts for the deoxygenation of acetic acid, an important reaction among many in the upgrading/stabilization of biomass pyrolysis vapors. TPRxn is used to evaluate catalyst activity and selectivity and to test hypothetical reaction pathways (e.g., decarbonylation, ketonization, and hydrogenation). The results of the TPRxn study of acetic acid deoxygenation show that molybdenum carbide is an active catalyst for this reaction at temperatures above ca. 300 &#176;C and that the reaction favors deoxygenation (i.e., C-O bond-breaking) products at temperatures below ca. 400 &#176;C and decarbonylation (i.e., C-C bond-breaking) products at temperatures above ca. 400 &#176;C.

Presented here is a protocol for the operation of a micro-scale temperature-programmed reactor for evaluating the catalytic performance of molybdenum carbide during acetic acid deoxygenation.

Temperature programmed reaction (TPRxn) is a simple yet powerful tool for screening solid catalyst performance at a variety of conditions. A TPRxn system ...

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of NixNb1-xO nanoparticles with different atomic compositions (x = 0.03, 0.08, 0.15, and 0.20) have been prepared by chemical precipitation. These NixNb1-xO catalysts are characterized by X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The study revealed the sponge-like and fold-like appearance of Ni0.97Nb0.03O and Ni0.92Nb0.08O on the NiO surface, and the larger surface area of these NixNb1-xO catalysts, compared with the bulk NiO. Maximum surface area of 173 m2/g can be obtained for Ni0.92Nb0.08O catalysts. In addition, the catalytic hydroconversion of lignin-derived compounds using the synthesized Ni0.92Nb0.08O catalysts have been investigated.

Chemical Precipitation Method for the Synthesis of Nb2O5 Modified Bulk Nickel Catalysts with High Specific Surface Area

A protocol for the synthesis of sponge-like and fold-like Ni1-xNbxO nanoparticles by chemical precipitation is presented.

We demonstrate a method for the synthesis of NixNb1-xO catalysts with sponge-like and fold-like nanostructures. By varying the Nb:Ni ratio, a series of ...

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. ...

Preparation of Polyoxometalate-based Photo-responsive Membranes for the Photo-activation of Manganese Oxide Catalysts

This paper presents a method to prepare charge-transfer chromophores using polyoxotungstate (PW12O403-), transition metal ions (Ce3+ or Co2+), and organic polymers, with the aim of photo-activating oxygen-evolving manganese oxide catalysts, which are important components in artificial photosynthesis. The cross-linking technique was applied to obtain a self-standing membrane with a high PW12O403- content. Incorporation and structure retention of PW12O403- within the polymer matrix were confirmed by FT-IR and micro-Raman spectroscopy, and optical characteristics were investigated by UV-Vis spectroscopy, which revealed successful construction of the metal-to-metal charge transfer (MMCT) unit. After deposition of MnOx oxygen evolving catalysts, photocurrent measurements under visible light irradiation verified the sequential charge transfer, Mn &#8594; MMCT unit &#8594; electrode, and&#160;the photocurrent intensity was consistent with the redox potential of the donor metal (Ce or Co). This method provides a new strategy for preparing integrated systems involving catalysts and photon-absorption parts for use with photo-functional materials.

Here, we present a protocol to prepare charge transfer chromophores based on a polyoxometalate/polymer composite membrane.

This paper presents a method to prepare charge-transfer chromophores using polyoxotungstate (PW12O403-), transition metal ions (Ce3+ or Co2+), and organic ...

Surface Properties of Synthesized Nanoporous Carbon and Silica Matrices

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) with a 4.6 nm pore size, and ordered silica porous matrix, SBA-15, with a 5.3 nm pore size. This work describes the surface properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the differently ordered porous materials with similar pore sizes. For this purpose, OMC and SBA-15 with highly ordered nanoporous structures are synthesized via impregnation of the silica matrix by applying a carbon precursor and by the sol-gel method, respectively. The porous structure of investigated systems is characterized by an N2 adsorption-desorption analysis at 77 K. To determine the electrochemical character of the surface of synthesized materials, potentiometric titration measurements are conducted; the obtained results for OMC shows a significant pHpzc shift toward the higher values of pH, relative to SBA-15. This suggests that investigated OMC has surface properties related to oxygen-based functional groups. To describe the surface properties of the materials, the contact angles of liquids penetrating the studied porous beds are also determined. The capillary rise method has confirmed the increased wettability of the silica walls relative to the carbon walls and an influence of the pore roughness on the fluid/wall interactions, which is much more pronounced for silica than for carbon mesopores. We have also studied the melting behavior of D2O confined in OMC and SBA-15 by applying the dielectric method. The results show that the depression of the melting temperature of D2O in the pores of OMC is about 15 K higher relative to the depression of the melting temperature in SBA-15 pores with a comparable 5 nm size. This is caused by the influence of adsorbate/adsorbent interactions of the studied matrices.

Here we report the synthesis and characterization of ordered nanoporous carbon (with a 4.6 nm pore size) and SBA-15 (with a 5.3 nm pore size). The work describes the surface and textural properties of nanoporous molecular sieves, their wettability, and the melting behavior of D2O confined in the materials.

In this work, we report the synthesis and characterization of ordered nanoporous carbon material (also called ordered mesoporous carbon material [OMC]) ...

Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization

We report a method to generate the N-heterocyclic carbene (NHC) 1,3-dimesitylimidazol-2-ylidene (IMes) under UV-irradiation at 365 nm to characterize IMes and determine the corresponding photochemical mechanism. Then, we describe a protocol to perform ring-opening metathesis polymerization (ROMP) in solution and in miniemulsion using this NHC-photogenerating system. To photogenerate IMes, a system comprising 2-isopropylthioxanthone (ITX) as the sensitizer and 1,3-dimesitylimidazolium tetraphenylborate (IMesH+BPh4-) as the protected form of NHC is employed. IMesH+BPh4- can be obtained in a single step by anion exchange between 1,3-dimesitylimidazolium chloride and sodium tetraphenylborate. A real-time steady-state photolysis setup is described, which hints that the photochemical reaction proceeds in two consecutive steps: 1) ITX triplet is photo-reduced by the borate anion and 2) subsequent proton transfer takes place from the imidazolium cation to produce the expected NHC IMes. Two separate characterization protocols are implemented. Firstly, CS2 is added to the reaction media to evidence the photogeneration of NHC through formation of the IMes-CS2 adduct. Secondly, the amount of NHC released in situ is quantified using acid-base titration. The use of this NHC photo-generating system for the ROMP of norbornene is also discussed. In solution, a photopolymerization experiment is conducted by mixing ITX, IMesH+BPh4-, [RuCl2(p-cymene)]2 and norbornene in CH2Cl2, then irradiating the solution in a UV reactor. In a dispersed medium, a monomer miniemulsion is first formed then irradiated inside an annular reactor to produce a stable poly(norbornene) latex.

We describe a protocol to photogenerate N-heterocyclic carbenes (NHCs) by UV irradiation of a 2-isopropylthioxanthone/imidazolium tetraphenylborate salt system. Methods to characterize the photoreleased NHC and elucidate the photochemical mechanism are proposed. The protocols for ring-opening metathesis photopolymerization in solution and miniemulsion illustrate the potential of this 2-component NHC photogenerating system.

We report a method to generate the N-heterocyclic carbene (NHC) 1,3-dimesitylimidazol-2-ylidene (IMes) under UV-irradiation at 365 nm to characterize IMes ...