Name: preparation and reactivity of a triphosphenium bromide salt: a convenient and stable source of phosphorus(i)
Uploaded: 2016-11-22T15:00:00.000+00:00
Duration: 8 min 46 s
Description: Watch this Scientific Journal Video about Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of PhosphorusI at JoVE.com

The authors thank the Natural Sciences and Engineering Research Council (NSERC) of Canada and the Canada Foundation for Innovation (CFI) for funding and scholarship support.

NOTE: Deuterated solvents were dried according to literature procedure when necessary, and all other solvents were dried over a series of Grubbs&#39;-type columns12 and degassed prior to use. Potassium 1,2,4-tris(diphenylphosphino)cyclopentadiene [K][(Ph2P)3C5H2] and the N-heterocyclic carbene 1,3,4,5-tetramethylimidazole-2-ylidene (MeNHCMe) were synthesized according to literature procedures and the latter was sublimed prior to use.9,13 Cyclohexene was dried over CaH2, distilled and degassed prior to use. Acetonitrile-d3 (CD3CN) and dichloromethane-d2 (CD2Cl2) were dried over phosphorus pentoxide and degassed prior to use. Diatomaceous earth was dried in an oven at 150 &#186;C overnight prior to use. All other reagents were used as received.
1. Synthesis of [dppeP][Br]
<ol>
	<li>Dissolve 1.00 g of 1,2-bis(diphenylphosphino)ethane (dppe) in approximately 40 ml of anhydrous, degassed dichloromethane (DCM) in a 250 ml Schlenk flask, under inert gas, equipped with a rubber septum.</li>
	<li>By syringe or cannula transfer, add 2.53 ml of dry, degassed, cyclohexene to the Schlenk flask containing the stirring solution of dppe.</li>
	<li>To this solution, add 0.26 ml of PBr3 via syringe, dropwise with vigorous stirring. The solution should immediately turn pale yellow, and white precipitate forms after stirring the solution for 20 min. Allow the reaction to stir for several hours or overnight.</li>
	<li>After stirring for several hours or overnight, filter the reaction mixture through a fritted flask topped with a one-inch thick diatomaceous earth plug to remove the precipitate.</li>
	<li>Collect the resulting solution and remove the DCM under vacuum on a Schlenk line.</li>
	<li>To the resulting oil, add approximately 75 ml of tetrahydrofuran (THF) while stirring vigorously (or sonicating) to precipitate the product as a white solid.</li>
	<li>Immediately after the white precipitate forms, collect it via filtration with a fritted flask under an inert atmosphere. Collect the solid immediately, and do not leave the suspension to stir for more than 30 min.</li>
	<li>Once collected, dissolve a small amount of [dppeP][Br] in CD2Cl2 or CDCl3 to obtain 31P, 1H and 13C NMR to confirm purity. [dppeP][Br] can be stored indefinitely in an inert atmosphere, or for several weeks on the benchtop.6</li>
</ol>
2. Synthesis of [dppeP][BPh4]
<ol>
	<li>Dissolve 0.5 g of [dppeP][Br] salt in 5 ml of DCM, in a Schlenk flask. Stir the solution under nitrogen gas. Then, add 0.35 g of sodium tetraphenylborate in 5 ml of THF.</li>
	<li>Allow the solution to stir for several hours or overnight, until a fine precipitate forms.</li>
	<li>Centrifuge the suspension to eliminate the precipitate (KBr) and remove the solvent under reduced pressure to yield [dppeP][BPh4] as a white powder.</li>
</ol>
3. Synthesis of [MeNHCMe2P][BPh4]
<ol>
	<li>Load a 100 ml Schlenk flask with 0.200 g of MeNHCMe and a stir bar under an inert atmosphere.</li>
	<li>Load a 100 ml round bottom flask with 0.603 g of [dppeP][BPh4] under an inert atmosphere.</li>
	<li>Cannula transfer 20 ml of THF to the Schlenk flask containing 0.200 g of MeNHCMe and begin magnetic stirring.</li>
	<li>Cannula transfer 20 ml of THF to the 100 ml round bottom flask with 0.603 g of [dppeP][BPh4] and stir until dissolved.</li>
	<li>Cannula transfer the solution of [dppeP][BPh4] in THF to the stirring solution of MeNHCMe in THF and allow the yellow solution to stir for 1 hr.</li>
	<li>Concentrate the yellow solution to a third of the original volume (13 ml) under reduced pressure.</li>
	<li>Add diethyl ether (Et2O) (40 ml) to the stirring concentrated solution to initiate precipitation of the yellow product and allow the resultant suspension to stir for 20 min.</li>
	<li>Place a sealed frit fitted attached to a 100 ml Schlenk flask on the Schlenk line and create an inert atmosphere by evacuating the flask using vacuum and refilling the flask with nitrogen from the Schleck line. Evacuate for 5 min and refill with nitrogen 3 times to insure an inert atmosphere.</li>
	<li>Cannula transfer the Et2O suspension into the apparatus and filter the precipitate.</li>
	<li>Wash the precipitate with 10 ml of Et2O three times and allow the precipitate to dry under reduced pressure for 2 hr.</li>
	<li>Optional) Allow the filtrate and washings to evaporate slowly under nitrogen to recrystallize dppe. Wash the crystals with a minimal amount of hexanes, dry, and collect the crystals for re-use.</li>
</ol>
4. Synthesis of (Ph2P)C5H2(Ph2P)2P
<ol>
	<li>To a 150 ml Schlenk flask containing 0.484g [dppeP][Br] in an inert atmosphere, add 40 ml of dry, degassed THF.</li>
	<li>Place the Schlenk in a dry-ice/acetone bath to cool the suspension to -78 &#176;C.</li>
	<li>Cannula transfer a THF solution of 0.625g [K][(Ph2P)3C5H2] in a round bottom flask, to the Schlenk flash containing [dppeP][Br].</li>
	<li>When the addition is complete, remove the Schlenk flask from the acetone bath and allow to warm to room temperature. After stirring for 2 hr, the solution will be light yellow with a white precipitate present.</li>
	<li>Transfer the suspension to an air-free fritted filter equipped with a 150 ml Schlenk flask, to remove the white precipitate (KBr).</li>
	<li>Collect the yellow solution and remove the THF under vacuum.</li>
	<li>Add an 80:20 mixture of dry and degassed diethyl ether:pentane to the resulting oil and allow to stir for 20 min.</li>
	<li>Collect the product (Ph2P)C5H2(Ph2P)2P as a pale yellow precipitate by filtering the suspension through an air-free, fritted flask. The remaining ether/pentane solution contains the dppe impurity and may be discarded or the solvent may be removed under vacuum and the dppe collected for further use.</li>
</ol>

<ol>
	<li>Macdonald, C. L. B., Ellis, B. D., Swidan, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-Oxidation-State+Main+Group+Compounds.">Low-Oxidation-State Main Group Compounds.</a> Encyclopedia of Inorganic and Bioinorganic Chemistry. , (2011).</li><li>Coffer (n&#233;e Monks), P. K., Dillon, K. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cyclic+triphosphenium+ions+and+related+species.">Cyclic triphosphenium ions and related species.</a> Coord. Chem. Rev. 257 (5-6), 910-923 (2013).</li><li>Schmidpeter, A., Lochschmidt, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+Products+from+PCl3,+P(NMe2)3,+and+AlCl3.">New Products from PCl3, P(NMe2)3, and AlCl3.</a> Angew. Chem. Internat. Ed. in Engl. 25 (3), 253-254 (1986).</li><li>Schmidpeter, A., Lochschmidt, S., Karaghiosoff, K., Sheldrickb, W. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Triphosphane-l,3-di-ium+Ions.">Triphosphane-l,3-di-ium Ions.</a> J. Chem. Soc. Chem. Commun. , 1447-1448 (1985).</li><li>Ellis, B. D., Carlesimo, M., Macdonald, C. L. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stabilised+phosphorus(I)+and+arsenic(I)+iodide:+readily-synthesised+reagents+for+low+oxidation+state+main+group+chemistry.">Stabilised phosphorus(I) and arsenic(I) iodide: readily-synthesised reagents for low oxidation state main group chemistry.</a> Chem. Commun. 15 (15), 1946-1947 (2003).</li><li>Norton, E. L., Szekely, K. L. S., Dube, J. W., Bomben, P. G., Macdonald, C. L. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+convenient+preparative+method+for+cyclic+triphosphenium+bromide+and+chloride+salts.">A convenient preparative method for cyclic triphosphenium bromide and chloride salts.</a> Inorg. Chem. 47 (3), 1196-1203 (2008).</li><li>Ellis, B. D., Macdonald, C. L. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphorus(I)+iodide:+a+versatile+metathesis+reagent+for+the+synthesis+of+low+oxidation+state+phosphorus+compounds.">Phosphorus(I) iodide: a versatile metathesis reagent for the synthesis of low oxidation state phosphorus compounds.</a> Inorg. Chem. 45 (17), 6864-6874 (2006).</li><li>Kosnik, S. C., Farrar, G. J., Norton, E. L., Cooper, B. F. T., Ellis, B. D., Macdonald, C. L. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low-Valent+Chemistry:+An+Alternative+Approach+to+Phosphorus-+Containing+Oligomers.">Low-Valent Chemistry: An Alternative Approach to Phosphorus- Containing Oligomers.</a> Inorg. Chem. 11 (53), 13061-13069 (2014).</li><li>Kosnik, S. C., Macdonald, C. L. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+zwitterionic+triphosphenium+compound+as+a+tunable+multifunctional+donor.">A zwitterionic triphosphenium compound as a tunable multifunctional donor.</a> Dalton Trans. 45 (14), 6251-6258 (2016).</li><li>Binder, J. F., Swidan, A., Tang, M., Nguyen, J. H., Macdonald, C. L. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Remarkably+stable+chelating+bis-N-heterocyclic+carbene+adducts+of+phosphorus(I)+cations.">Remarkably stable chelating bis-N-heterocyclic carbene adducts of phosphorus(I) cations.</a> Chem. Commun. 51 (36), 7741-7744 (2015).</li><li>Binder, J. F., Corrente, A. M., Macdonald, C. L. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+simple+route+to+phosphamethine+cyanines+from+S,N-heterocyclic+carbenes.">A simple route to phosphamethine cyanines from S,N-heterocyclic carbenes.</a> Dalton Trans. 45 (5), 2138-2147 (2016).</li><li>Pangborn, A. B., Ma Giardello, ., Grubbs, R. H., Rosen, R. K., Timmers, F. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Safe+and+Convenient+Procedure+for+Solvent+Purification.">Safe and Convenient Procedure for Solvent Purification.</a> Organometallics. 15 (5), 1518-1520 (1996).</li><li>Smaliy, R. V., Beaup&#233;rin, M., 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=Hexaphosphine:+A+multifaceted+ligand+for+transition+metal+coordination.">Hexaphosphine: A multifaceted ligand for transition metal coordination.</a> Eur. J. Inorg. Chem. (9), 1347-1352 (2012).</li><li>Klebach, T. C., Lourens, R., Bickelhaupt, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+mesityldiphenylmethylenephosphine:+a+stable+compound+with+a+localized+phosphorus:carbon+bond.">Synthesis of mesityldiphenylmethylenephosphine: a stable compound with a localized phosphorus:carbon bond.</a> J. Amer. Chem. Soc. 100 (15), 4886-4888 (1978).</li><li>Alcarazo, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=&#945;-Cationic+Phosphines:+Synthesis+and+Applications.">&#945;-Cationic Phosphines: Synthesis and Applications.</a> Chem. Eur. J. 20 (26), 7868-7877 (2014).</li></ol>

The authors have nothing to disclose.

Crystal structures and multi-nuclear NMR (31P, 1H, and 13C) were obtained for all products reported to confirm connectivity. Electrospray-ionization mass spectrometry was used to confirm presence of the cations and elemental analysis was used to confirm analytical purity of the samples.
It is imperative that all reactions are done in an air-free and dry environment to ensure that no unexpected by-products or decomposition products are formed. Using a slight excess of dppe as well as an excess (10 equivalents) of cyclohexene is necessary, to ensure good yields of [dppeP][Br].
There are no major limitations of the techniques described herein. The ligand displacement reactions with [dppeP][Br] are only limited to ligands of sufficient donor ability to displace the dppe from the [dppeP][Br] molecule. Notwithstanding, the significant advantage to this methodology is the controlled release of &#34;P+&#34; without the generation of unanticipated by-products or the use of harsh reagents. Thus, this methodology can be employed in the future to generate novel molecules containing PI moieties.

The chemistry of main group elements in unusually low oxidation or valence states has been an area of significant interest over the last two decades.1 Aside from the fundamental interest arising from their unique bonding and structure, such compounds often display reactivities that are very different from those of their more typical oxidation state counterparts. In this sense, they offer significant potential as reagents to build more complex main group-element containing materials.
A landmark class of low-valent phosphorus containing molecules are &#34;triphosphenium&#34; cations which were first reported by Schmidpeter in the 1980s.2 These ions feature a dicoordinate phosphorus(I) ion ligated by two phosphonio substituents, with the more stable variants built from a chelating framework.3,4 Our group has optimized the syntheses of triphosphenium halide salts5-7 and has demonstrated that these stable compounds are versatile P+ transfer agents that are useful for the controlled synthesis of phosphorus(I)-containing oligomers,8 zwitterions,9 and phosphamethine cyanine dyes.10,11 While the original syntheses of such compounds often involve dangerous phosphorus-containing reagents and/or highly reducing conditions, the controlled route we present is safe, P-atom efficient, and convenient. The method results in high purity materials which may be used as dyes, ligands for transition metal complexes and precursors for more complex phosphorus-containing species.

<table><tbody><tr><td>bis(diphenyl)phosphino ethane (dppe)</td><td>Strem</td><td>1663-45-2</td><td>98% Stored in gloved box, used as is.&amp;nbsp;</td></tr><tr><td>Anhydrous Dichloromethane (DCM)</td><td>Sigma Aldrich</td><td>270997</td><td>Purified through solvent purification system, or standard methods</td></tr><tr><td>Anhydrous Cyclohexene</td><td>Sigma Aldrich</td><td>29240</td><td>Dried over calcium hydride and distilled.</td></tr><tr><td>Phosphorus Tribromide (PBr&lt;sub&gt;3&lt;/sub&gt;)</td><td>Sigma Aldrich</td><td>157783</td><td>99% Stored in glove box, used as is. Air sensitive.</td></tr><tr><td>Anyhydrous Tetrahydrofuran (THF)</td><td>Sigma Aldrich</td><td>401757</td><td>Purified through solvent purification system, or standard methods</td></tr><tr><td>Methylene Chloride-D&lt;sub&gt;2&lt;/sub&gt; (CD&lt;sub&gt;2&lt;/sub&gt;Cl&lt;sub&gt;2&lt;/sub&gt;)</td><td>Sigma Aldrich</td><td>DLM-23-25</td><td>Dried over phosphorus pentoxide, vacuum transferred or distilled</td></tr><tr><td>Acetonitrile</td><td>Alfa Aesar</td><td>5/8/1975</td><td>Stored in glove box, used as is</td></tr><tr><td>Sodium Tetraphenylborate</td><td>Sigma Aldrich</td><td>T25402</td><td>Stored in glove box, used as is</td></tr><tr><td>Anyhydrous Diethyl Ether&amp;nbsp;</td><td>Sigma Aldrich</td><td>673811</td><td>Purified through solvent purification system, or standard methods</td></tr><tr><td>Anhydrous Pentane</td><td>Sigma Aldrich</td><td>236705</td><td>Purified through solvent purification system, or standard methods</td></tr></tbody></table>

preparation and reactivity of a triphosphenium bromide salt: a convenient and stable source of phosphorus(i)

We present herein the optimized synthesis of a triphosphenium bromide salt. Apart from being a versatile metathesis reagent, this unusually stable low-valent-phosphorus-containing compound acts as a useful P+ transfer agent. Unlike traditional methods employed to access low-coordinate phosphorus species which usually require pyrophoric phosphorus-containing precursors (white phosphorus, Tris(trimethylsilyl)phosphine, etc.), or harsh reducing agents (alkali metals, potassium graphite, etc.), the current approach does not involve pyrophoric or explosive reagents and can be done on large scales (&#62;20 g) in excellent yields by undergraduates with basic air-free synthetic training. The bromide counter ion is readily exchanged with other anions such as tetraphenyl borate (described herein) using typical salt metathesis reagents to obtain materials with desired properties and reactivities. The versatility of this P+ transfer approach is exemplified by the reactions of these triphosphenium precursors with an N-heterocyclic carbene and an anionic bisphosphine, each of which readily displace the neutral bisphosphine to give an NHC-stabilized phosphorus(I) cation and a phosphorus(I) containing zwitterion, respectively.

A stable salt ([dppeP][Br]) containing a low valent phosphorus(I) source can be synthesized easily by the addition of PBr3 to diphenylphosphinoethane (dppe) in the presence of excess cyclohexene (Figure 1)6.
Upon work up of the reaction, 31P NMR spectra show the presence of a triplet signal that is significantly shielded at -220 ppm, and a doublet signal at 50 ppm. Strong coupling between the nuclei is observed on the order of 500 Hz (Figure 2).
Single crystals can be grown from concentrated acetonitrile or dichloromethane solutions and single crystal X-ray diffraction analysis reveals that [dppeP][Br] has an ion-separated structure with two formula units present in the asymmetric unit (Figure 4). The bromide ion may be exchanged for a less reactive anion, such as trifluoromethane sulfonate (triflate, OTf) or tetraphenylborate (BPh4). The 31P NMR spectrum of this product is almost identical to that of the starting material [dppeP][Br] (Figure 3).
Addition of [dppeP][BPh4] to a solution containing two equivalents of the carbene MeNHCMe results in displacement of the chelating bis-phosphine by the more strongly donating NHC ligands and generates the yellow phosphamethine cyanine dye [MeNHCMe2P][BPh4] (Figure 1). Because [MeNHCMe2P][BPh4] is soluble in THF but insoluble in diethyl ether, the latter is used to remove the bisphosphine byproduct, which is highly soluble in most solvents. Once separated by filtration, washed and dried, [MeNHCMe2P][BPh4] is obtained as an analytically pure yellow powder. The 31P NMR spectrum of this material dissolved in acetonitrile-d3 features a singlet signal at -113 ppm, which is significantly shielded relative to typical phosphaalkenes (cf. 31P NMR &#948; for P-mesityldiphenylmethylenephosphine = 233.06 ppm14) which is consistent with the phosphorus(I) assignment (Figure 5).
Likewise, the relatively long C-P bond lengths, the acute C-P-C angle and twisting of the heterocycles from the C-P-C plane observed in the crystal structure of [MeNHCMe2P][BPh4] (Figure 6) are also most consistent with the phosphorus(I) description. In addition to its potential applications as a dye, compounds such as [MeNHCMe2P][BPh4] have also proven to be useful ligands and reagents for the preparation of cationic phosphines of a type that are useful components in catalytic applications.15
The reaction of potassium 1,2,4-tris(diphenylphosphino)cyclopentadiene in a 1:1 stoichiometric ratio with [dppeP][Br] yields (Ph2P)C5H2(Ph2P)2P in quantitative yield (Figure 1)9. The only byproducts from this reaction, namely KBr and dppe, can be removed by filtrations in THF and diethyl ether/pentane respectively. The 31P NMR spectrum obtained from a concentrated solution of (Ph2P)C5H2(Ph2P)2P in CD2Cl2 (Figure 7) reveals the presence of a triplet signal at -174 ppm, attributable to the dicoordinate phosphorus(I) center, a singlet signal at -16.9 ppm for the Ph2P fragment on the backbone, and a doublet signal attributable to the two Ph2P groups that chelate the phosphorus(I) center.
This structure of this molecule obtained from a single crystal X-ray diffraction analysis is shown in Figure 8. Crystals can be grown via slow evaporation of a concentrated solution of DCM, THF, or even a dilute solution of diethyl ether. The ligand chemistry of (Ph2P)C5H2(Ph2P)2P is of interest because the molecule features three different types of donor sites with which it may interact with metals: it features a phosphine site, a phosphide-like site, and a cyclopentadienide site.9
<img alt="Figure 1" src="/files/ftp_upload/55021/55021fig1.jpg" /> 
Figure 1. Reaction of dppe with PBr3 and cyclohexene, [dppeP][BPh4] with MeNHCMe, and dppeP][Br] with [K][(Ph2P)3C5H2]. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55021/55021fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" src="/files/ftp_upload/55021/55021fig2.jpg" /> 
Figure 2. 31P (A), 1H (B), and 13C (C) NMR spectra of [dppeP][Br] collected in CD2Cl2 prepared as described in the protocol. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55021/55021fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/55021/55021fig3.jpg" /> 
Figure 3. 31P (A), 1H (B), 11B (C), and 13C (D) [dppeP][BPh4] collected in CD2Cl2 prepared as described in the protocol. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55021/55021fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/55021/55021fig4.jpg" /> 
Figure 4. Molecular Structure of [dppeP][Br] (A) and [dppeP][BPh4] (B). <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55021/55021fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/55021/55021fig5.jpg" /> 
Figure 5. 31P (A), 1H (B), 11B (C) and 13C (D) NMR spectra of [MeNHCMe2P][BPh4] collected in CD3CN prepared as described in the protocol. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55021/55021fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" src="/files/ftp_upload/55021/55021fig6.jpg" /> 
Figure 6. Molecular Structure of [MeNHCMe2P][BPh4]. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55021/55021fig6large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" src="/files/ftp_upload/55021/55021fig7.jpg" /> 
Figure 7. 31P (A), 1H (B), and 13C (C) NMR spectra of (Ph2P)C5H2(Ph2P)2P collected in CD2Cl2 prepared as described in the protocol. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55021/55021fig7large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" src="/files/ftp_upload/55021/55021fig8.jpg" /> 
Figure 8. Molecular Structure of (Ph2P)C5H2(Ph2P)2P. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55021/55021fig8large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of PhosphorusI at JoVE.com

Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of PhosphorusI

The synthesis of a triphosphenium bromide salt is described and its use as a P+ transfer agent is outlined by reactions with an N-heterocyclic carbene and an anionic bisphosphine, yielding an NHC-stabilized P(I) cation and a P(I) containing zwitterion, respectively.

Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of Phosphorus(I)

We present herein the optimized synthesis of a triphosphenium bromide salt. Apart from being a versatile metathesis reagent, this unusually stable ...

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7.7K Views.  University of Windsor. The synthesis of a triphosphenium bromide salt is described and its use as a P+ transfer agent is outlined by reactions with an N-heterocyclic carbene and an anionic bisphosphine, yielding an NHC-stabilized P(I) cation and a P(I) containing zwitterion, respectively.

Video: Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of PhosphorusI

Nucleoside Triphosphates - From Synthesis to Biochemical Characterization

The traditional strategy for the introduction of chemical functionalities is the use of solid-phase synthesis by appending suitably modified phosphoramidite precursors to the nascent chain. However, the conditions used during the synthesis and the restriction to rather short sequences hamper the applicability of this methodology. On the other hand, modified nucleoside triphosphates are activated building blocks that have been employed for the mild introduction of numerous functional groups into nucleic acids, a strategy that paves the way for the use of modified nucleic acids in a wide-ranging palette of practical applications such as functional tagging and generation of ribozymes and DNAzymes. One of the major challenges resides in the intricacy of the methodology leading to the isolation and characterization of these nucleoside analogues.
	
	In this video article, we present a detailed protocol for the synthesis of these modified analogues using phosphorous(III)-based reagents. In addition, the procedure for their biochemical characterization is divulged, with a special emphasis on primer extension reactions and TdT tailing polymerization. This detailed protocol will be of use for the crafting of modified dNTPs and their further use in chemical biology.

The protocol described herein aims to explain and abridge the numerous obstacles in the way of the intricate route leading to modified nucleoside triphosphates. Consequently, this protocol facilitates both the synthesis of these activated building-blocks and their availability for practical applications.

The  traditional strategy for the introduction of chemical functionalities is the  use of solid-phase synthesis by appending suitably modified ...

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 and Use of Carbonyl-decorated Carbenes in the Activation of White Phosphorus

Here we present a protocol for the synthesis of two distinct carbonyl-decorated carbenes. Both carbenes can be prepared using nearly identical procedures in multi-gram scale quantities. The goal of this manuscript is to clearly detail how to handle and prepare these unique carbenes such that a synthetic chemist of any skill level can work with them. The two carbenes described are a diamidocarbene (DAC, carbene 1) and a monoamidoaminocarbene (MAAC 2). These carbenes are highly electron-deficient and as such display reactivity profiles that are atypical of more traditional N-heterocyclic carbenes. Additionally, these two carbenes only differ in their electrophilic character and not their steric parameters, making them ideal for studying how carbene electronics influence reactivity. To demonstrate this phenomenon, we are also describing the activation of white phosphorus (P4) using these carbenes. Depending on the carbene used, two very different phosphorus-containing compounds can be isolated. When the DAC 1 is used, a tris(phosphaalkenyl)phosphane can be isolated as the exclusive product. Remarkably however, when MAAC 2 is added to P4 under identical reaction conditions, an unexpected carbene-supported P8&#160;allotrope of phosphorus is isolated exclusively. Mechanistic studies demonstrate that this carbene-supported P8allotrope forms via a [2+2] cycloaddition dimerization of a transient diphosphene which has been trapped by treatment with 2,3-dimethyl-1,3-butadiene.

Here, we present a protocol for the synthesis of two carbonyl-decorated carbenes. The protocol makes these interesting compounds readily available to chemists of all skill levels. In addition to the synthesis of these two carbenes, their use in the activation of white phosphorus is also described.

Here we present a protocol for the synthesis of two distinct carbonyl-decorated carbenes. Both carbenes can be prepared using nearly identical procedures ...

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

Herein we report the synthesis of a tridentate phosphine ligand N(CH2PPh2)3 (N-triphosPh) (1) via a phosphorus based Mannich reaction of the hydroxylmethylene phosphine precursor with ammonia in methanol under a nitrogen atmosphere. The N-triphosPh ligand precipitates from the solution after approximately 1 hr of reflux and can be isolated analytically pure via simple cannula filtration procedure under nitrogen. Reaction of the N-triphosPh ligand with [Ru3(CO)12] under reflux affords a deep red solution that show evolution of CO gas on ligand complexation. Orange crystals of the complex [Ru(CO)2{N(CH2PPh2)3}-&#954;3P] (2) were isolated on cooling to RT. The 31P{1H} NMR spectrum showed a characteristic single peak at lower frequency compared to the free ligand. Reaction of a toluene solution of complex 2 with oxygen resulted in the instantaneous precipitation of the carbonate complex [Ru(CO3)(CO){N(CH2PPh2)3}-&#954;3P] (3) as an air stable orange solid. Subsequent hydrogenation of 3 under 15 bar of hydrogen in a high-pressure reactor gave the dihydride complex [RuH2(CO){N(CH2PPh2)3}-&#954;3P] (4), which was fully characterized by X-ray crystallography and NMR spectroscopy. Complexes 3 and 4 are potentially useful catalyst precursors for a range of hydrogenation reactions, including biomass-derived products such as levulinic acid (LA). Complex 4 was found to cleanly react with LA in the presence of the proton source additive NH4PF6 to give [Ru(CO){N(CH2PPh2)3}-&#954;3P{CH3CO(CH2)2CO2H}-&#954;2O](PF6) (6).

The Synthesis, Characterization and Reactivity of a Series of Ruthenium N-triphosPh Complexes

Ruthenium phosphine complexes are widely used for homogeneous catalytic reactions such as hydrogenations. The synthesis of a series of novel tridentate ruthenium complexes bearing the N-triphos ligand N(CH2PPh2)3 is reported. Additionally, the stoichiometric reaction of a dihydride Ru&#8211;N-triphos complex with levulinic acid is described.

Herein we report the synthesis of a tridentate phosphine ligand N(CH2PPh2)3 (N-triphosPh) (1) via a phosphorus based Mannich reaction of the ...

Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of Chalcogenidoplumbates(II or IV)

The phases of &#34;PbCh2&#34; (Ch = Se, Te) are obtained from solid-state syntheses (i.e., by the fusion of the elements under inert conditions in silica glass ampules). Reduction of such phases by elemental alkaline metals in amines affords crystalline chalcogenidoplumbate(II) salts comprised of [PbTe3]2- or [Pb2Ch3]2- anions, depending upon which sequestering agent for the cations is present: crown ethers, like 18-crown-6, or cryptands, like [2.2.2]crypt. Reactions of solutions of such anions with transition-metal compounds yield (poly-)chalcogenide anions or transition-metal chalcogenide clusters, including one with a &#181;-PbSe ligand (i.e., the heaviest-known CO homolog).
In contrast, the solid-state synthesis of a phase of the nominal composition &#34;K2PbSe2&#34; by successive reactions of the elements and by the subsequent solvothermal treatment in amines yields the first non-oxide/halide inorganic lead(IV) compound: a salt of the ortho-selenidoplumbate(IV) anion [PbSe4]4-. This was unexpected due to the redox potentials of Pb(IV) and Se(-II). Such methods can further be applied to other elemental combinations, leading to the formation of solutions with binary [HgTe2]2- or [BiSe3]3- anions, or to large-scale syntheses of K2Hg2Se3 or K3BiSe3 via the solid-state route.
All compounds are characterized by single-crystal X-ray diffraction and elemental analysis; solutions of plumbate salts can be investigated by 205Pb and 77Se or 127Te NMR techniques. Quantum chemical calculations using density functional theory methods enable energy comparisons. They further allow for insights into the electronic configuration and thus, the bonding situation. Molecular Rh-containing Chevrel-type compounds were found to exhibit delocalized mixed valence, whereas similar telluridopalladate anions are electron-precise; the cluster with the &#181;-PbSe ligand is energetically favored over a hypothetical CO analog, in line with the unsuccessful attempt at its synthesis. The stability of formal Pb(IV) within the [PbSe4]4- anion is mainly due to a suitable stabilization within the crystal lattice.

Combining Solid-state and Solution-based Techniques: Synthesis and Reactivity of ChalcogenidoplumbatesII or IV

The synthesis of chalcogenidoplumbates(II,IV) via the in situ reduction of nominal "PbCh2" (Ch = Chalcogen) and via a solid-state reaction and subsequent solvothermal reactions is presented. Additionally, reactivities of plumbate(II) solutions are portrayed, which yield the heaviest-known CO homolog known to date: the &#181;-PbSe ligand.

The phases of &#34;PbCh2&#34; (Ch = Se, Te) are obtained from solid-state syntheses (i.e., by the fusion of the elements under inert conditions in silica ...

Synthesis of High Purity Nonsymmetric Dialkylphosphinic Acid Extractants

We present the synthesis of (2,3-dimethylbutyl)(2,4,4&#39;-trimethylpentyl)phosphinic acid as an example to demonstrate a method for the synthesis of high purity nonsymmetric dialkylphosphinic acid extractants. Low toxic sodium hypophosphite was chosen as the phosphorus source to react with olefin A (2,3-dimethyl-1-butene) to generate a monoalkylphosphinic acid intermediate. Amantadine was adopted to remove the dialkylphosphinic acid byproduct, as only the monoalkylphosphinic acid can react with amantadine to form an amantadine&#8729;mono-alkylphosphinic acid salt, while the dialkylphosphinic acid cannot react with amantadine due to its large steric hindrance. The purified monoalkylphosphinic acid was then reacted with olefin B (diisobutylene) to yield nonsymmetric dialkylphosphinic acid (NSDAPA). The unreacted monoalkylphosphinic acid can be easily removed by a simple base-acid post-treatment and other organic impurities can be separated out through the precipitation of the cobalt salt. The structure of the (2,3-dimethylbutyl)(2,4,4&#39;-trimethylpentyl)phosphinic acid was confirmed by 31P NMR, 1H NMR, ESI-MS, and FT-IR. The purity was determined by a potentiometric titration method, and the results indicate that the purity can exceed 96%.

A protocol for the synthesis of high purity nonsymmetric dialkylphosphinic acid extractants is presented, taking (2,3-dimethylbutyl)(2,4,4&#39;-trimethylpentyl)phosphinic acid as an example.

We present the synthesis of (2,3-dimethylbutyl)(2,4,4&#39;-trimethylpentyl)phosphinic acid as an example to demonstrate a method for the synthesis of high ...

Preparation of N-(2-alkoxyvinyl)sulfonamides from N-tosyl-1,2,3-triazoles and Subsequent Conversion to Substituted Phthalans and Phenethylamines

Decomposition of N-tosyl-1,2,3-triazoles with rhodium(II) acetate dimer in the presence of alcohols forms synthetically versatile N-(2-alkoxyvinyl)sulfonamides, which react under a variety of conditions to afford useful N- and O-containing compounds. Acid-catalyzed addition of alcohols or thiols to N-(2-alkoxyvinyl)sulfonamide-containing phthalans provides access to ketals and thioketals, respectively. Selective reduction of the vinyl group in N-(2-alkoxyvinyl)sulfonamide-containing phthalans via hydrogenation yields the corresponding phthalan in good yield, whereas reduction with sodium bis(2-methoxyethoxy)aluminumhydride generates a ring-opened phenethylamine analogue. Because the N-(2-alkoxyvinyl)sulfonamide functional group is synthetically versatile, but often hydrolytically unstable, this protocol emphasizes key techniques in preparing, handling, and reacting these pivotal substrates in several useful transformations.

Preparation of N-2-alkoxyvinylsulfonamides from N-tosyl-1,2,3-triazoles and Subsequent Conversion to Substituted Phthalans and Phenethylamines

Representative experimental procedures for the synthesis of N-(2-alkoxyvinyl)sulfonamides and subsequent conversion to phthalan and phenethylamine derivatives are presented in detail.

Decomposition of N-tosyl-1,2,3-triazoles with rhodium(II) acetate dimer in the presence of alcohols forms synthetically versatile ...

Synthesis of Low-Valent MOFs from Multitopic Phosphine Linkers

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

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

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

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

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

Chemical Triphosphorylation of Oligonucleotides

The 5&#8242;-triphosphate is an essential nucleic acid modification found throughout all life and increasingly used as a functional modification of oligonucleotides in biotechnology and synthetic biology. Oligonucleotide 5&#8242;-triphosphates have historically been prepared in vitro by enzymatic methods. However, these methods are limited to natural RNA oligonucleotides, have strong sequence preferences, and tend to produce heterogeneous products. New methods of chemical triphosphorylation complement both the reduced cost of automated oligonucleotide synthesis by phosphoramidite chemistry and the diverse range of nucleotide modifications now available. Thus, the synthesis of oligonucleotide triphosphates of arbitrary sequence and length, and optionally containing various nonnatural modifications, is now accessible.
This paper presents the appropriate methods and techniques for chemical triphosphorylation of oligonucleotides using salicyl phosphorochloridite and pyrophosphate. This method uses commercially available reagents, is compatible with most oligonucleotides prepared by standard solid-phase synthesis methods, and can be completed in 2 h following oligonucleotide synthesis, before deprotection and purification. Two uses of chemically triphosphorylated oligonucleotides as substrates for catalytic RNA enzymes are demonstrated, including the synthesis of a mirror-image version of the hammerhead ribozyme from nonbiological L-RNA triphosphates.

Oligonucleotide 5&#8242;-triphosphates are ubiquitous components in essential biological pathways and have seen increasing use in biotechnology applications. Here, we describe techniques for the routine synthesis and purification of oligonucleotide 5&#8242;-triphosphates, starting from oligonucleotides prepared by standard automated synthesis techniques.

The 5&#8242;-triphosphate is an essential nucleic acid modification found throughout all life and increasingly used as a functional modification of ...

Bioengineering

Lewis Acid-Base Interaction in Ph3P-BH3

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University&#160;
One of the goals of chemistry is to use models that account for trends and provide insights into the properties of reactants that contribute to reactivity. Substances have been classified as acids and bases since the time of the ancient Greeks, but the definition of acids and bases has been modified and expanded over the years.1
The ancient Greeks would characterize substances by taste, and defined acids as those that were sour-tasting, such as lemon juice and vinegar. The term &#34;acid&#34; is derived from the Latin term for &#34;sour-tasting.&#34; Bases were characterized by their ability to counteract or neutralize acids. The first bases characterized were those of ashes from a fire, which were mixed with fats to make soap. In fact, the term &#34;alkaline&#34; is derived from the Arabic word for &#34;roasting.&#34; Indeed, it has been known since ancient times that acids and bases can be combined to give a salt and water.
The first widely-used description of an acid is that of the Swedish chemist, Svante Arrhenius, who in 1894 defined acids as substances which dissociate in water to give hydronium ions, and bases as substances which dissociate in water to give hydroxide ions. This definition is thus limited to aqueous acids and necessitates that an acid contribute a proton.2 For example, in water, HCl is an acid, as it dissociates to give the hydronium ion (H3O)+ and the chloride ion. Boron trichloride would not be considered an acid, as in water it hydrolyzes to give B(OH)3 and 3 HCl; the product HCl though is an Arrhenius acid.
In 1923, Johannes Nicolaus Br&#248;nsted and Martin Lowry independently defined acids and bases on their ability to donate and accept hydrogen ions, or protons. Thus came the concept of acid-base conjugate pairs, and the expansion of the definition of acids and bases in solvents other than water. For example, ammonium is an acid, as it can donate a proton and generate ammonia. Ammonia can accept a proton, to give ammonium. Thus, ammonia is the conjugate base of ammonium. This acid-base reaction can occur in water, ammonia, or other solvents.
This video deals with the acid-base definition of the American chemist, Gilbert N. Lewis, who also defined acids and bases in 1923. Indeed, this is the same Lewis from Lewis-dot structures in General Chemistry. His approach focuses not on the ability of acids and bases to donate and accept protons, but rather on their ability to accept and donate electron pairs, respectively. This encompasses the Br&#248;nsted-Lowry definition, as H+ accepts an electron pair from a Br&#248;nsted base during protonation. However, it greatly expands the definition of an acid, now encompassing metal ions and main-group compounds. Here, we compare the 31P NMR of the Lewis acid-base adduct Ph3P-BH3 to free triphenylphosphine.

Lewis Acid-Base Interaction in Ph3P-BH3

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University&#160;
One of the goals of chemistry is to use models that account for trends ...

Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of Phosphorus(I)

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