We are grateful to the National Science Foundation (CHE-1300508) and Mount St. Mary's University (Startup and Summer Faculty Development) for generous support of this work. Ben Rupert (University of Delaware, Mass Spectrometry Facility) is acknowledged for LIFDI mass spectral analyses.

1. Synthesis of an Isomeric Mixture of 3,4,5-Trimethyl-2,5-heptadien-4-ols
<ol>
	<li>Fill an oven dried, 500 mL beaker with 200 mL of hexanes and cover with an oven dried watch glass.
	<ol>
		<li>In an empty hood, use clean scissors to cut half inch pieces of lithium wire. Wipe each lithium piece on a paper towel to remove excess mineral oil, until all oil appears to be removed from the metal&#39;s surface, and place in the beaker containing hexanes.</li>
		<li>Fill an oven dried, 250 mL beaker with 100 mL of hexanes and cover with an oven dried watch glass. Tare this setup on a balance.</li>
		<li>Using oven dried tongs, remove the lithium wire from the first beaker, wipe quickly on a clean paper towel to remove any residual oil or hexanes, and transfer to the tared beaker. Repeat this process until 14.0 g (2.03 mol) of lithium wire have been added to the beaker.</li>
	</ol>
	</li>
	<li>Attach an oven-dried, 1 L three-neck flask equipped with a stir bar to a Schlenk line under a flow of argon in a fume hood. Heat gun the flask for a few minutes and allow it to cool under argon. 
	Caution: It is important to use argon to prevent a potential reaction between lithium and dinitrogen to form lithium nitride.
	<ol>
		<li>Once cooled, use tongs to quickly wipe the lithium pieces on a paper towel and then transfer the lithium into the flask under an argon counter flow.</li>
		<li>Submerge any excess lithium strips in mineral oil for storage. Rinse the tongs and scissors with copious amounts of water in an empty sink. Dry each with a paper towel and submerge the towels in water in the sink. 
		NOTE: No solvent bottles or paper towels should be near the sink.
		<ol>
			<li>Immerse any paper towels or gloves that have been used to cut lithium in a half-filled bowl of water and place in an empty sink. In an empty hood, slowly pour the hexanes from the beakers in 1.1-1.1.3 into a bowl containing water. Add water carefully into the empty beakers to quench any residual lithium.</li>
			<li>Rinse and wipe down the hood where the lithium was cut with water before continuing with the rest of the procedure. Submerge these paper towels in water in the sink before continuing.</li>
		</ol>
		</li>
		<li>Add approximately 500 mL of diethyl ether, collected directly from a solvent purification system, to the reaction flask via cannula transfer.</li>
		<li>Attach an oven dried reflux condenser, an addition funnel equipped with an inert gas sidearm, and a glass stopper to the three neck flask. Place a plastic bowl underneath the reaction setup in case of flask rupture.</li>
		<li>Add 2-bromo-2-butene (29.0 g, 0.218 mol), which has been dried over 4 &#197; molecular sieves overnight, to the addition funnel via syringe.</li>
		<li>Add approximately 3-4 mL of the 2-bromo-2-butene dropwise over the course of 5 minutes to initiate the reaction, whereupon reflux occurs and the solution becomes cloudy. If gentle reflux does not occur on its own after 10-15 minutes of stirring, then warm the flask gently with a heat gun for two-three minutes until reflux is achieved. This is usually adequate to initiate the reaction. 
		Caution: Even if the reaction does not initiate immediately, controlled addition of 2-bromo-2-butene is critical to keep the reaction under control.</li>
		<li>Add the remainder of the 2-bromo-2-butene in the addition funnel dropwise over the course of 90 minutes at a rate that maintains moderate reflux throughout the time period. The reaction mixture will turn a light green color.</li>
		<li>Syringe a mixture of ethyl acetate (40.0 g, 0.454 mol), which has been dried over 4 &#197; molecular sieves overnight, and 2-bromo-2-butene (103.85 g, 0.782 mol) into the addition funnel. Add this mixture to the reaction at a sufficient rate to maintain a controlled but vigorous reflux over the course of four hours.</li>
		<li>After addition is complete, syringe a small amount of ethyl acetate (2.71 g, 0.0308 mol) into the addition funnel and add dropwise to the reaction over 5 minutes. The mixture will be a cloudy orange/yellow color by the end of these additions. Allow the reaction to stir overnight at ambient temperature.</li>
	</ol>
	</li>
	<li>The next day, replace the addition funnel with a rubber septum.
	<ol>
		<li>Under an argon counter flow, remove the septum and use dry tongs to grab a piece of the unreacted lithium. To recover as much product as possible, rinse the lithium wire quickly with diethyl ether from a wash bottle and allow the solution to drip back into the reaction vessel. Then add the lithium piece to a 500 mL beaker filled with 250 mL of water. 
		Caution: The lithium pieces should be added individually to the beaker and the strip should be allowed to fully react before another is added. This minimizes the risk of fire given the significant amount of H2 generated during the quenching process. 
		NOTE: Other methods to quench the excess lithium, such as careful addition to isopropanol, also work but require significantly longer times to fully consume the excess lithium.</li>
		<li>Repeat 1.3.1 until all large pieces of lithium are quenched, which should require 60-90 minutes on the given scale.</li>
		<li>While still under argon, add a saturated ammonium chloride solution (250 mL) slowly dropwise to the stirring reaction mixture over the course of an hour, quenching the reaction mixture and any small pieces of unreacted lithium. The reaction may reflux gently during the process and become more difficult to stir based on solid formation. Continue addition until the layer of sediment completely dissolves at the bottom of the flask, forming a defined aqueous layer.</li>
		<li>Allow the reaction to cool for 30 min after addition of the solution is complete.</li>
		<li>Pour the contents of the flask into a 1 L separatory funnel and isolate the diethyl ether layer.</li>
		<li>Extract the aqueous layers with three 150 mL portions of diethyl ether.</li>
		<li>Combine all four diethyl ether layers and rotavap to a volume of approximately 75-100 mL.</li>
	</ol>
	</li>
</ol>
2. Synthesis of 1,2,3,4,5-Pentamethylcyclopentadiene (Cp*H)
<ol>
	<li>Attach an oven dried 500 mL three neck round bottom flask, equipped with a reflux condenser and stir bar, to a Schlenk line under a flow of inert gas.
	<ol>
		<li>Charge the flask with p-toluene sulfonic acid monohydrate (8.70 g, 0.0457 mol).</li>
		<li>Cannula approximately 50 mL of diethyl ether onto the solid.</li>
		<li>Under inert gas counter flow, attach an oven dried addition funnel to the reaction setup.</li>
		<li>Charge the funnel with the 3,4,5-trimethyl-2,5-heptadien-4-ols/diethyl ether concentrate from Step 1.</li>
		<li>Add the concentrate dropwise to the stirring slurry, maintaining a gentle reflux, over the course of 1 h. Allow the reaction to stir for an additional 1 h after the addition is complete.</li>
		<li>Pour the reaction mixture into 300 mL of a saturated sodium bicarbonate solution containing 4.59&#160;g (0.0433 mol) of sodium carbonate.</li>
		<li>Transfer the contents of the flask into a 1 L separatory funnel and isolate the diethyl ether layer. Extract the aqueous layer with three, 100 mL portions of diethyl ether.</li>
		<li>Combine the four diethyl ether layers and dry over magnesium sulfate for two hours.</li>
		<li>Filter the mixture and rotavap down the liquid until ~75-100 mL of material remains. At this stage, the concentrate can be stored in a refrigerator overnight prior to purification the following day.</li>
	</ol>
	</li>
	<li>Transfer the concentrate to an oven dried, round bottom flask equipped with a stir bar. Connect this flask to an oven dried transfer manifold equipped with another 100 mL round bottom flask.
	<ol>
		<li>Cool the receiving flask in ice while submerging the concentrate in an ambient temperature water bath.</li>
		<li>Apply dynamic vacuum to the setup, while stirring the concentrate, for 30-60 min to remove any residual diethyl ether.</li>
		<li>Seal the transfer setup and switch the bath for the receiving flask to a dry ice/acetone slurry while submerging the concentrate in a warm water bath. Allow the trap-to-trap distillation to continue while stirring over the course of 2-3 h, being careful to refresh the vacuum periodically (every 15-20 min) while the baths are also monitored over the same time period. 
		NOTE: After transfer, 39.0 g (0.286 moles, 58% based on 2-bromo-2-butene) of Cp*H can be isolated as a pale yellow oil.</li>
	</ol>
	</li>
</ol>
3. Synthesis of [Cp*RuCl2]229
<ol>
	<li>Charge 1.00 g (3.95 mmol) of ruthenium(III) chloride trihydrate in an oven dried 100 mL Schlenk flask equipped with a stir bar under a flow of inert gas on a Schlenk line.
	<ol>
		<li>Cannula transfer 50 mL of methanol, dried over Mg and distilled prior to use, onto the solid and stir for 30 min.</li>
		<li>Filter the solution under inert gas through an oven dried air free filter funnel, filled with an inch of oven dried Celite, into another 100 mL Schlenk flask equipped with a stir bar.</li>
		<li>Remove the air-free filter funnel and replace with a septum.</li>
		<li>Add Cp*H (1.20 g, 8.81 mmol) by syringe, attach an oven dried reflux condenser equipped with an inert gas sidearm adapter under a flow of inert gas.</li>
		<li>Seal the sidearm on the Schlenk flask and reflux for 4 h under a flow of inert gas.</li>
	</ol>
	</li>
	<li>Allow the reaction to cool and replace the reflux condenser with a glass stopper under a flow of inert gas.
	<ol>
		<li>Remove the solvent in vacuo and dry on a Schlenk line for three hours. Transfer the flask to a glovebox.</li>
		<li>Inside the glovebox, rinse the solid with pentane and scrape the solid from the sides of the flask. Filter the black solid onto a medium porosity frit, rinse with 50 mL of pentane, and dry for an additional hour in vacuo. 
		Note: [Cp*RuCl2]2 (1.53 g, 63% based on Ru) is isolated as a dark solid. Characterization matches literature reports.29</li>
	</ol>
	</li>
</ol>
4. Synthesis of [Cp*IrCl2]230
<ol>
	<li>Charge 1.00 g (2.60 mmol) of iridium(III) chloride hydrate in an oven dried 100 mL Schlenk flask equipped with a stir bar under a flow of inert gas on a Schlenk line.
	<ol>
		<li>Cannula transfer 50 mL of methanol onto the solid.</li>
		<li>Add Cp*H (0.50 g, 3.67 mmol) by syringe, attach an oven dried reflux condenser equipped with an inert gas sidearm adapter under a flow of inert gas.</li>
		<li>Seal the sidearm on the Schlenk flask and reflux for 48 h under inert gas flow.</li>
	</ol>
	</li>
	<li>Allow the reaction to cool and replace the reflux condenser with a septum under a flow of inert gas.
	<ol>
		<li>Cool the flask in an ice bath for 30 min.</li>
		<li>Filter the reaction in air through a 15 mL medium porosity frit.</li>
		<li>Rinse with 50 mL of diethyl ether and dry the solid in vacuo for two hours. 
		NOTE: [Cp*IrCl2]2 (1.23 g, 59% based on Ir) is isolated as an orange/red solid. Characterization matches literature reports.30</li>
	</ol>
	</li>
</ol>

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G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=1,2,3,4,5-pentamethylcyclopentadiene.">1,2,3,4,5-pentamethylcyclopentadiene.</a> Org. Synth. 65, (1987).</li><li>Koelle, U., Kossakowski, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Di-&#181;-chloro-bis[(&#951;5-pentachlororuthenium(III)],+[Cp*RuCl2]2+and+Di-&#181;-methoxo-bis(&#951;5-pentamethylcyclomethylcyclopentadienyl)+diruthenium(II),+[Cp*RuOMe]2.">Di-&#181;-chloro-bis[(&#951;5-pentachlororuthenium(III)], [Cp*RuCl2]2 and Di-&#181;-methoxo-bis(&#951;5-pentamethylcyclomethylcyclopentadienyl) diruthenium(II), [Cp*RuOMe]2.</a> Inorg. Synth. 29, 225-228 (1992).</li><li>White, C., Yates, A., Maitlis, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=&#951;5-pentamethylcyclopentadienyl)rhodium+and+-iridium+compounds.">&#951;5-pentamethylcyclopentadienyl)rhodium and -iridium compounds.</a> Inorg. Synth. 29, 228-234 (1992).</li><li>Andersen, R. A., Blom, R., Boncella, J. M., Burns, C. J., Volden, H. V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+thermal+average+molecular+structures+of+bis(pentamethylcyclopentadienyl)magnesium(II),+-calcium(II),+and+-ytterbium(II)+in+the+gas+phase.">The thermal average molecular structures of bis(pentamethylcyclopentadienyl)magnesium(II), -calcium(II), and -ytterbium(II) in the gas phase.</a> Acta Chem. Scand. 41A, 24-35 (1987).</li><li>Gross, J. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Liquid+injection+field+desorption/ionization+of+reactive+transition+metal+complexes.">Liquid injection field desorption/ionization of reactive transition metal complexes.</a> Anal. Bioanal. Chem. 386 (1), 52-58 (2006).</li></ol>

The authors have nothing to disclose.

During preparation of the heptadienol mixture, it is important to clean the lithium prior to initiating the reaction with the 2-bromo-2-butene. This is accomplished by wiping off residual mineral oil used for storage on paper towels, to the point that the oil appears fully removed from the surface, and by dissolving any remaining oil in the beaker of hexanes. The hexanes were used as received and not further dried before use in the procedure. Because of both the large scale of the reaction and an excess of lithium used, ...

Since the discovery and structural elucidation of ferrocene in the 1950s,1,2,3,4 cyclopentadienyl (Cp) substituted ligands have played a vital role in the development of organometallic chemistry. These ligands have served as versatile ancillary supports for a range of metals, leading to studies of unusual structure and bonding,5,6,7 the activation and functionalization of small molecules,8,9,10,11,12,13 and catalysis, including olefin polymerization.14,15
The 1,2,3,4,5-pentamethylcyclopentadienyl (Cp*) anion has proven to be a particularly valuable ligand in transition and main group metal chemistry, as the methyl groups impart greater steric protection, increased electron donation by the anionic ligand, and block potential activation of the cyclopentadienyl ring.16,17 The Cp* ligand remains relevant even today, as the anion has recently been utilized to support H/D exchange by Ir(III),18 hydride transfer by Rh,19 and conjugate aminations mediated by Ti(III).20
Our interest in the Cp* ligand stems from the desire to access reactive sources of cobalt(I) for use in small molecule activation.21 These studies have resulted in the generation of both Cp*CoI and Cp*CoIL (L = N-heterocyclic carbene) equivalents for use in sp3 and sp2 C-H bond oxidative addition.22,23,24 As access to our Cp*Co(II) starting materials necessitate significant quantities of 1,2,3,4,5-pentamethylcyclopentadiene, we desired a multigram synthesis of Cp*H, given the substantial commercial cost of the ligand.
Two major methods currently exist for the large scale preparation of Cp*H, each of which presents inherent technical challenges. A procedure developed by Marks and coworkers involves a two-step synthesis of 2,3,4,5-tetramethylcyclopent-2-enone followed by installation of the final methyl group using methyl lithium.25 The synthesis is described on a massive scale, using a 12 L reaction vessel and mechanical stirring, while also requiring sustained low temperature cooling at 0 &#176;C for four days.
An alternative procedure originally developed by Bercaw and coworkers,26 and later adapted by Marks,27 utilizes in situ generation of an alkenyl lithium for nucleophilic attack of ethyl acetate to produce an isomeric mixture of 3,4,5-trimethyl-2,5-heptadien-4-ols followed by acid mediated cyclization to provide Cp*H. The initial reports of this method were performed on a large (3-5 L) scale and required mechanical stirring. In addition, a significant excess of lithium metal was used, complicating quenching and subsequent workup of the intermediate heptadienols. A subsequent revision of the procedure scales down the reaction and the amount of lithium,28 but safe quenching of the reaction mixture remains an issue. Reproducibility in the initiation of the alkenyl lithium, due to differences in lithium source and purity or dryness of the 2-bromo-2-butene reactant are further noted concerns. Given these issues with the commonly used procedures for preparing Cp*H, we looked to develop better access to the ligand on an intermediate scale (30-40 g) which would circumvent use of specialty laboratory glassware and equipment, improve reaction reproducibility and safety, and simplify workup and ligand purification.
Here we report that synthesis of 1,2,3,4,5-pentamethylcyclopentadiene, based on modifications of the existing procedure developed by Bercaw and coworkers. The revised synthesis and purification of the ligand accomplishes the major goals outlined above, while permitting access to substantial amounts (39 g) of Cp*H in good yield (58%). The procedure offers other additional benefits, including a more controlled quench of excess lithium during the production of the intermediate heptadienols and a simplified isolation of Cp*H of adequate purity for subsequent metallation with transition metals. To demonstrate the utility of the prepared ligand, it was used to synthesize two [Cp*MCl2]2 (M = Ir, Ru) complexes. The revised protocol outlined below complements existing procedures and provides a simpler and more accessible entry point into the chemistry of a ubiquitous ancillary ligand support in organometallic chemistry.

<table><tbody><tr><td>&lt;strong&gt;Materials&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Lithium wire (in mineral oil)</td><td>Aldrich</td><td>278327-100G</td><td>&gt;98%</td></tr><tr><td>2-bromo-2-butene (mixture of cis/trans isomers)</td><td>Acros</td><td>200016-364&amp;nbsp;&amp;nbsp;</td><td>98%, dried over molecular sieves from an oven overnight before use</td></tr><tr><td>Hexanes</td><td>Millipore</td><td>HX0299-3</td><td>GR ACS, used as received</td></tr><tr><td>Ethyl actetate</td><td>Millipore</td><td>EX0240-3</td><td>GR ACS, dried over molecular sieves from an oven overnight before use</td></tr><tr><td>Ammonium chloride</td><td>Aldrich</td><td>213330-2.5kg</td><td>ACS Reagent</td></tr><tr><td>Diethyl ether</td><td>Millipore</td><td>EX0190-5</td><td>GR ACS, collected from a solvent purification system before use</td></tr><tr><td>Magnesium sulfate</td><td>Aldrich</td><td>793612-500g</td><td>Anhydrous, reagent grade</td></tr><tr><td>&lt;em&gt;p&lt;/em&gt;-toluene sulfonic acid monohydrate</td><td>Fisher</td><td>A320-500</td><td>ACS Certified</td></tr><tr><td>Sodium bicarbonate</td><td>Fisher</td><td>5233-500</td><td>ACS Certified</td></tr><tr><td>Sodium carbonate</td><td>Amresco</td><td>0585-500g</td><td></td></tr><tr><td>Ruthenium(III) chloride trihydrate</td><td>Pressure Chemical</td><td>4750</td><td>40% Metal</td></tr><tr><td>Iridium(III) chloride hydrate</td><td>Pressure Chemical</td><td>5730</td><td>53% Metal</td></tr><tr><td>Methanol</td><td>Avantor</td><td>3016-22</td><td>AR ACS, distilled from Mg before use</td></tr><tr><td>Pentane</td><td>J. T. Baker</td><td>T007-09</td><td>&gt;98%, dried with a solvent purification system before use</td></tr><tr><td>Chloroform-&lt;em&gt;d&lt;/em&gt;</td><td>Aldrich</td><td>151823-150G</td><td>99.8 atom % D</td></tr><tr><td>Molecular sieves 4&amp;nbsp;&amp;Aring;</td><td>Aldrich</td><td>208590-1KG</td><td>dried in an oven at 140&amp;nbsp;&amp;deg;C before use</td></tr><tr><td>Celite 545</td><td>Acros</td><td>AC34967-0025</td><td>dried in an oven at 140&amp;nbsp;&amp;deg;C before use</td></tr><tr><td>&lt;strong&gt;Name&lt;/strong&gt;</td><td>&lt;strong&gt;Company&lt;/strong&gt;</td><td>&lt;strong&gt;Catalog Number&lt;/strong&gt;</td><td>&lt;strong&gt;Comments&lt;/strong&gt;</td></tr><tr><td>&lt;strong&gt;Equipment&lt;/strong&gt;</td><td></td><td></td><td></td></tr><tr><td>Schlenk line, with vacuum and inert gas manifolds</td><td>Custom</td><td>NA</td><td>Used in Preps 1-4</td></tr><tr><td>Solvent transfer manifold</td><td>Chemglass</td><td>AF-0558-01</td><td>Used in 2.2</td></tr><tr><td>Airfree filter funnel</td><td>Chemglass</td><td>AF-0542-22</td><td>Used in 3.1.3</td></tr><tr><td>Glovebox</td><td>Vacuum Atmospheres</td><td>OMNI</td><td>Used in 3.2.2</td></tr></tbody></table>

accessing valuable ligand supports for transition metals: a modified, intermediate scale preparation of 1,2,3,4,5-pentamethylcyclopentadiene

A reliable, intermediate scale preparation of 1,2,3,4,5-pentamethylcyclopentadiene (Cp*H) is presented, based on modifications of existing protocols that derive from initial 2-bromo-2-butene lithiation followed by acid mediated dienol cyclization. The revised synthesis and purification of the ligand avoids the use of mechanical stirring while still permitting access to significant quantities (39 g) of Cp*H in good yield (58%). The procedure offers other additional benefits, including a more controlled quench of excess lithium during the production of the intermediate heptadienols and a simplified isolation of Cp*H of sufficient purity for metallation with transition metals. The ligand was subsequently used to synthesize [Cp*MCl2]2 complexes of both iridium and ruthenium to demonstrate the utility of the Cp*H prepared and purified by our method. The procedure outlined herein affords substantial quantities of a ubiquitous ancillary ligand support used in organometallic chemistry while minimizing the need for specialized laboratory equipment, thus providing a simpler and more accessible entry point into the chemistry of 1,2,3,4,5-pentamethylcyclopentadiene.

The protocol described above for Cp*H synthesis relies on modification of the three step procedure developed by Bercaw and coworkers and modified by Marks (Figure 1). The air sensitive alkenyl lithium is prepared in situ from a mixture of cis and trans-2-butene via a lithium/halogen exchange reaction and is subsequently quenched with ethyl acetate to prepare an isomeric mixture of heptadienols. The mixture can be used without further purificatio...

Watch this Scientific Journal Video about Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene at JoVE.com

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Reliable, intermediate scale preparation of 1,2,3,4,5-pentamethylcyclopentadiene (Cp*H) is presented. The revised protocol for the synthesis and purification of the ligand minimizes the need for specialized laboratory equipment while simplifying reaction workups and product purification. Use of Cp*H in the synthesis of [Cp*MCl2]2 complexes (M = Ru, Ir) is also described.

A reliable, intermediate scale preparation of 1,2,3,4,5-pentamethylcyclopentadiene (Cp*H) is presented, based on modifications of existing protocols that ...

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10.3K Views.  Mount St. Mary's University. Reliable, intermediate scale preparation of 1,2,3,4,5-pentamethylcyclopentadiene (Cp*H) is presented. The revised protocol for the synthesis and purification of the ligand minimizes the need for specialized laboratory equipment while simplifying reaction workups and product purification. Use of Cp*H in the synthesis of [Cp*MCl2]2 complexes (M = Ru, Ir) is also described. 

Video: Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium Under Mild Reaction Conditions

Dichloro-bis(aminophosphine) complexes of palladium with the general formula of [(P{(NC5H10)3-n(C6H11)n})2Pd(Cl)2] (where n = 0-2), belong to a new family of easy accessible, very cheap, and air stable, but highly active and universally applicable C-C cross-coupling catalysts with an excellent functional group tolerance. Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium [(P(NC5H10)3)2Pd(Cl)2] (1), the least stable complex within this series towards protons; e.g. in the form of water, allows an eased nanoparticle formation and hence, proved to be the most active Heck catalyst within this series at 100 &#176;C and is a very rare example of an effective and versatile catalyst system that efficiently operates under mild reaction conditions. Rapid and complete catalyst degradation under work-up conditions into phosphonates, piperidinium salts and other, palladium-containing decomposition products assure an easy separation of the coupling products from catalyst and ligands. The facile, cheap, and rapid synthesis of 1,1',1"-(phosphinetriyl)tripiperidine and 1 respectively, the simple and convenient use as well as its excellent catalytic performance in the Heck reaction at 100 &#176;C make 1 to one of the most attractive and greenest Heck catalysts available.
We provide here the visualized protocols for the ligand and catalyst syntheses as well as the reaction protocol for Heck reactions performed at 10 mmol scale at 100 &#176;C and show that this catalyst is suitable for its use in organic syntheses.

Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1',1''-phosphinetriyltripiperidine]}palladium Under Mild Reaction Conditions

Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium [(P(NC5H10)3)2Pd(Cl)2] (1) is an easy accessible, cheap, and air stable, but highly active Heck catalyst with an excellent functional group tolerance that efficiently operates under mild reaction conditions to give the coupling products in very high yields.

Dichloro-bis(aminophosphine) complexes of palladium with the general formula of [(P{(NC5H10)3-n(C6H11)n})2Pd(Cl)2] (where n = 0-2), belong to a new family ...

Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

The main purpose of this video is to show 6 reaction steps of a convergent synthesis and prepare a complex molecule containing up to three nonplanar polyaromatic units, which are two corannulene moieties and a racemic hexahelicene linking them. The compound described in this work is a good host for fullerenes. Several common organic reactions, such as free-radical reactions, C-C coupling or click chemistry, are employed demonstrating the versatility of functionalization that this compound can accept. All of these reactions work for planar aromatic molecules. With subtle modifications, it is possible to achieve similar results for nonplanar polyaromatic compounds.

Preparation of a Corannulene-functionalized Hexahelicene by CopperI-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

Here, we present a protocol to synthesize a complex organic compound comprised of three nonplanar polyaromatic units, assembled easily with reasonable yields.

The main purpose of this video is to show 6 reaction steps of a convergent synthesis and prepare a complex molecule containing up to three nonplanar ...

A Protocol for Safe Lithiation Reactions Using Organolithium Reagents

Organolithium reagents are powerful tools in the synthetic chemist&#39;s toolbox. However, the extreme pyrophoric nature of the most reactive reagents warrants proper technique, thorough training, and proper personal protective equipment. To aid in the training of researchers using organolithium reagents, a thorough, step-by-step protocol for the safe and effective use of tert-butyllithium on an inert gas line or within a glovebox is described. As a model reaction, preparation of lithium tert-butyl amide by the reaction of tert-butyl amine with one equivalent of tert-butyl lithium is presented.

The safe and proper use of organolithium reagents is described.

Organolithium reagents are powerful tools in the synthetic chemist&#39;s toolbox. However, the extreme pyrophoric nature of the most reactive reagents ...

Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions

Detailed and generalized protocols are presented for the synthesis and subsequent purification of four palladium N-heterocyclic carbene complexes from benzimidazolium salts. Detailed and generalized protocols are also presented for testing the catalytic activity of such complexes in arylation and Suzuki-Miyaura cross-coupling reactions. Representative results are shown for the catalytic activity of the four complexes in arylation and Suzuki-Miyaura type reactions. For each of the reactions investigated, at least one of the four complexes successfully catalyzed the reaction, qualifying them as promising candidates for catalysis of many carbon-carbon bond-forming reactions. The protocols presented are general enough to be adapted for the synthesis, purification and catalytic activity testing of new palladium N-heterocyclic carbene complexes.

Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions

Detailed and generalized protocols are presented for the synthesis and subsequent purification of four palladium N-heterocyclic carbene complexes from benzimidazolium salts. The complexes were tested for catalytic activity in arylation and Suzuki-Miyaura reactions. For each reaction investigated, at least one of the four complexes successfully catalyzed the reaction.

Detailed and generalized protocols are presented for the synthesis and subsequent purification of four palladium N-heterocyclic carbene complexes from ...

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 ...

Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of &#945;-Imino &#947;-Lactones and Alkylidene Pyrazolones

Bispirocyclic scaffolds are one of the important structural subunits in many natural products that exhibit diverse and attractive biological activities. Recently, we have developed an efficient organocatalytic strategy, which provides facile access to a variety of enantiomerically enriched bispiro[&#947;-butyrolactone-pyrrolidin-4,4&#39;-pyrazolone] skeletons. In this paper, we demonstrate a detailed protocol for the asymmetric synthesis of drug-like bispirocyclic compounds with two spirocyclic carbon centers via an organocatyltic 1,3-dipolar cycloaddition reaction. Spirocyclization synthons &#945;-imino &#947;-lactones and alkylidene pyrazolones are prepared first, which are then subjected to a cycloaddition reaction in the presence of a bifunctional squaramide organocatalyst to afford the desired bispirocycles in high yields and excellent stereoselectivities. Chiral high-performance liquid chromatography (HPLC) is carried out to determine the enantiomeric purity of the products, and the d.r. value is examined by proton nuclear magnetic resonance (1H NMR). The absolute configuration of the product is assigned according to an X-ray crystallographic analysis. This synthetic strategy allows scientists to prepare a diversity of bispirocyclic scaffolds in high yields and excellent diastereo- and enantioselectivities.

Enantiomerically enriched bispiro[&#947;-butyrolactone-pyrrolidin-4,4&#39;-pyrazolone] skeletons are asymmetrically synthesized through a simple organocatalytic 1,3-dipolar cycloaddition reaction.

Bispirocyclic scaffolds are one of the important structural subunits in many natural products that exhibit diverse and attractive biological activities. ...

Preparation of 6-aminocyclohepta-2,4-dien-1-one Derivatives via Tricarbonyl(tropone)iron

aza-Michael adducts of tricarbonyl(tropone)iron are synthesized by two different methods. Primary aliphatic amines and cyclic secondary amines participate in a direct aza-Michael reaction with tricarbonyl(tropone)iron under solvent-free conditions. Less nucleophilic aniline derivatives and more hindered secondary amines add efficiently to the cationic tropone complex formed by protonation of tricarbonyl(tropone)iron. While the protocol utilizing the cationic complex is less efficient overall for accessing the aza-Michael adducts than the direct, solvent-free addition to the neutral complex, it allows the use of a broader range of amine nucleophiles. Following protection of the amine of the aza-Michael adduct as a tert-butyl carbamate, the diene is decomplexed from the iron tricarbonyl fragment upon treatment with cerium(IV) ammonium nitrate to provide derivatives of 6-aminocyclohepta-2,4-dien-1-one. These products can serve as precursors to diverse compounds containing a seven-membered carbocyclic ring. Because the demetallation requires protection of the amine as a carbamate, the aza-Michael adducts of secondary amines cannot be decomplexed using the protocol described here.

Preparation of 6-aminocyclohepta-2,4-dien-1-one Derivatives via Tricarbonyltroponeiron

Representative experimental procedures for the addition of amine nucleophiles to tricarbonyl(tropone)iron and subsequent demetallation of the resulting complexes are presented in detail.

aza-Michael adducts of tricarbonyl(tropone)iron are synthesized by two different methods. Primary aliphatic amines and cyclic secondary amines participate ...

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks (MOFs)

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of the reaction site in metal-organic framework (MOF)&#8211;based catalysts in an enantioselective catalytic reaction system. Therefore, a method of validating the reaction site of MOF-based catalysts is necessary to investigate this issue. Substrate size discrimination by pore size was accomplished by comparing the substrate size versus the reaction rate in two different types of carbonyl-ene reactions with two kinds of MOFs. The MOF catalysts were used to compare the performance of the two reaction types (Zn-mediated stoichiometric and Ti-catalyzed carbonyl-ene reactions) in two different media. Using the proposed method, it was observed that the entire MOF crystal participated in the reaction, and the interior of the crystal pore played an important role in exerting chiral control when the reaction was stoichiometric. Homogeneity of the chiral environment of MOF catalysts was established by the size control method for a particle used in the Zn-mediated stoichiometric reaction system. The protocol proposed for the catalytic reaction revealed that the reaction mainly occurred on the catalyst surface regardless of the substrate size, which reveals the actual reaction sites in MOF-based heterogeneous catalysts. This method for reaction site validation of MOF catalysts suggests various considerations for developing heterogeneous enantioselective MOF catalysts.

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks MOFs

Here, we present a protocol for active site validation of metal-organic framework catalysts by comparing stoichiometric and catalytic carbonyl-ene reactions to find out whether a reaction takes place on the inner or outer surface of metal-organic frameworks.

Substrate size discrimination by the pore size and homogeneity of the chiral environment at the reaction sites are important issues in the validation of ...

Structure Of Ferrocene

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University&#160;
In 1951, Kealy and Pauson reported to Nature the synthesis of a new organometallic compound, ferrocene.1&#160;In their original report, Pauson suggested a structure for ferrocene in which the iron is singly bonded (sigma bonds) to one carbon atom of each cyclopentadiene ligand (Figure 1, Structure I).1,2,3&#160;This initial report led to wide-spread interest in the structure of ferrocene, and many leading scientists participated in the structure elucidation of this interesting new molecule. Wilkinson and Woodward were quick to suggest an alternative formulization where the iron is &#34;sandwiched&#34; between two cyclopentadiene ligands, with equal binding to all 10 carbon atoms (Figure 1, Structure II).4&#160;Here, we will synthesize ferrocene and decide, based on experimental data (IR and 1H NMR), which of these structures is observed. In addition, we will study the electrochemistry of ferrocene by collecting a cyclic voltammogram. In the course of this experiment, we introduce the 18-electron rule and discuss valence electron counting for transition metal complexes.
<img alt="Figure 1" src="/files/ftp_upload/10347/10347fig1v2.jpg" /> 
Figure 1. Two proposed structures of ferrocene.

Structure Determination of Ferrocene-an Organometallic Complex

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University&#160;
In 1951, Kealy and Pauson reported to Nature the synthesis of a new ...

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Inorganic Chemistry

Molecular Orbital (MO) Theory

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University
This protocol serves as a guide in the synthesis of two metal complexes featuring the ligand 1,1&#39;-bis(diphenylphosphino)ferrocene (dppf): M(dppf)Cl2, where M = Ni or Pd. While both of these transition metal complexes are 4-coordinate, they exhibit different geometries at the metal center. Using molecular orbital (MO) theory in conjunction with 1H NMR and Evans method, we will determine the geometry of these two compounds.

Molecular Orbital MO Theory: Predicting Geometry of Transition Metal Complexes

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University
This protocol serves as a guide in the synthesis of two metal complexes ...

Accessing Valuable Ligand Supports for Transition Metals: A Modified, Intermediate Scale Preparation of 1,2,3,4,5-Pentamethylcyclopentadiene

Summary

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Mizoroki-Heck Cross-coupling Reactions Catalyzed by Dichloro{bis[1,1',1''-(phosphinetriyl)tripiperidine]}palladium Under Mild Reaction Conditions

Preparation of a Corannulene-functionalized Hexahelicene by Copper(I)-catalyzed Alkyne-azide Cycloaddition of Nonplanar Polyaromatic Units

A Protocol for Safe Lithiation Reactions Using Organolithium Reagents

Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions

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

Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones

Preparation of 6-aminocyclohepta-2,4-dien-1-one Derivatives via Tricarbonyl(tropone)iron

Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks (MOFs)

Structure Of Ferrocene

Molecular Orbital (MO) Theory