Rosenthal's reagent

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Structure of Rosenthal's reagent with titanium and zirconium. Rosenthal reagent general structure.svg
Structure of Rosenthal's reagent with titanium and zirconium.
Molecular structure of Titanocene-bis(trimethylsilyl)acetylene Titanocene bis(trimethylsilyl)acetylene.png
Molecular structure of Titanocene-bis(trimethylsilyl)acetylene

Rosenthal's reagent is a metallocene bis(trimethylsilyl)acetylene complex with zirconium (Cp2Zr) or titanium (Cp2Ti) used as central atom of the metallocene fragment Cp2M. Additional ligands such as pyridine or THF are commonly used as well. With zirconium as central atom and pyridine as ligand, a dark purple to black solid with a melting point of 125–126 °C is obtained. Synthesizing Rosenthal's reagent of a titanocene source yields golden-yellow crystals of the titanocene bis(trimethylsilyl)acetylene complex with a melting point of 81–82 °C. [1] [2] This reagent enables the generation of the themselves unstable titanocene and zirconocene under mild conditions. [3]

Contents

The reagent is named after the German chemist Uwe Rosenthal  [ de ] (born 1950) and was first synthesized by him and his co-workers in 1995. [4]

Synthesis

Rosenthal's reagent can be prepared by reduction of titanocene or zirconocene dichloride with magnesium in the presence of bis(trimethylsilyl)acetylene in THF. The illustrated product for a titanocene complex can be represented by the resonance structures A and B. If zirconium is used as central atom, additional ligands (e.g. pyridine) are necessary for stabilization. [5]

Synthesis of rosenthal reagent with titanocene.svg

Application and reactions

The main area of application is the synthesis of synthetically challenging organic structures such as macrocycles and heterometallacycles. Rosenthal's reagent allows the selective preparation of these compounds with high yields. [6] [7]

Currently, Rosenthal's reagent is often used instead of Negishi's reagent (1-butene)zirconocene to generate zirconocene fragments as it offers a number of compelling advantages. Unlike Negishi's reagent, Rosenthal's reagent is stable at room temperature and can be stored indefinitely under an inert atmosphere. A much more precise control over the stoichiometry of reactions is possible, especially because the instable (1-butene)zirconocene cannot be formed quantitatively. [7] Stoichiometric and catalytic reactions can be performed and influenced by the use of different ligands, metals and substrate substituents. While for titanium complexes, a dissociative reaction mechanism has been observed, zirconium complexes favor an associative pathway. [6] The combination of these organometallic complexes with different suitable substrates (e.g. carbonyl compounds, acetylenes, imines, azoles, etc.) often leads to novel bond types and reactivities. [3] [8] A particularly interesting aspect is the novel C–C coupling reaction of nitriles to form precursors for the realization of so far unknown heterometallacycles. [6] As main side products of coupling reactions with Rosenthal's reagent, pyridine and bis(trimethylsilyl)acetylene are obtained. These compounds are soluble and volatile, and therefore easy to remove from the product mixture. [7]

Related Research Articles

<span class="mw-page-title-main">Metallocene</span>

A metallocene is a compound typically consisting of two cyclopentadienyl anions (C
5
H
5
, abbreviated Cp) bound to a metal center (M) in the oxidation state II, with the resulting general formula (C5H5)2M. Closely related to the metallocenes are the metallocene derivatives, e.g. titanocene dichloride or vanadocene dichloride. Certain metallocenes and their derivatives exhibit catalytic properties, although metallocenes are rarely used industrially. Cationic group 4 metallocene derivatives related to [Cp2ZrCH3]+ catalyze olefin polymerization.

A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes (alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility:

The Sonogashira reaction is a cross-coupling reaction used in organic synthesis to form carbon–carbon bonds. It employs a palladium catalyst as well as copper co-catalyst to form a carbon–carbon bond between a terminal alkyne and an aryl or vinyl halide.

An alkyne trimerisation is a [2+2+2] cycloaddition reaction in which three alkyne units react to form a benzene ring. The reaction requires a metal catalyst. The process is of historic interest as well as being applicable to organic synthesis. Being a cycloaddition reaction, it has high atom economy. Many variations have been developed, including cyclisation of mixtures of alkynes and alkenes as well as alkynes and nitriles.

<span class="mw-page-title-main">Titanocene dichloride</span> Chemical compound

Titanocene dichloride is the organotitanium compound with the formula (η5-C5H5)2TiCl2, commonly abbreviated as Cp2TiCl2. This metallocene is a common reagent in organometallic and organic synthesis. It exists as a bright red solid that slowly hydrolyzes in air. It shows antitumour activity and was the first non-platinum complex to undergo clinical trials as a chemotherapy drug.

<span class="mw-page-title-main">Schwartz's reagent</span> Chemical compound

Schwartz's reagent is the common name for the organozirconium compound with the formula (C5H5)2ZrHCl, sometimes called zirconocene hydrochloride or zirconocene chloride hydride, and is named after Jeffrey Schwartz, a chemistry professor at Princeton University. This metallocene is used in organic synthesis for various transformations of alkenes and alkynes.

<span class="mw-page-title-main">Organotitanium chemistry</span>

Organotitanium chemistry is the science of organotitanium compounds describing their physical properties, synthesis, and reactions. Organotitanium compounds in organometallic chemistry contain carbon-titanium chemical bonds. They are reagents in organic chemistry and are involved in major industrial processes.

A carbometallation is any reaction where a carbon-metal bond reacts with a carbon-carbon π-bond to produce a new carbon-carbon σ-bond and a carbon-metal σ-bond. The resulting carbon-metal bond can undergo further carbometallation reactions or it can be reacted with a variety of electrophiles including halogenating reagents, carbonyls, oxygen, and inorganic salts to produce different organometallic reagents. Carbometallations can be performed on alkynes and alkenes to form products with high geometric purity or enantioselectivity, respectively. Some metals prefer to give the anti-addition product with high selectivity and some yield the syn-addition product. The outcome of syn and anti- addition products is determined by the mechanism of the carbometallation.

<span class="mw-page-title-main">Organonickel chemistry</span> Branch of organometallic chemistry

Organonickel chemistry is a branch of organometallic chemistry that deals with organic compounds featuring nickel-carbon bonds. They are used as a catalyst, as a building block in organic chemistry and in chemical vapor deposition. Organonickel compounds are also short-lived intermediates in organic reactions. The first organonickel compound was nickel tetracarbonyl Ni(CO)4, reported in 1890 and quickly applied in the Mond process for nickel purification. Organonickel complexes are prominent in numerous industrial processes including carbonylations, hydrocyanation, and the Shell higher olefin process.

<span class="mw-page-title-main">Organozirconium and organohafnium chemistry</span>

Organozirconium chemistry is the science of exploring the properties, structure, and reactivity of organozirconium compounds, which are organometallic compounds containing chemical bonds between carbon and zirconium. Organozirconium compounds have been widely studied, in part because they are useful catalysts in Ziegler-Natta polymerization.

<span class="mw-page-title-main">Metallacycle</span>

In organometallic chemistry, a metallacycle is a derivative of a carbocyclic compound wherein a metal has replaced at least one carbon center; this is to some extent similar to heterocycles. Metallacycles appear frequently as reactive intermediates in catalysis, e.g. olefin metathesis and alkyne trimerization. In organic synthesis, directed ortho metalation is widely used for the functionalization of arene rings via C-H activation. One main effect that metallic atom substitution on a cyclic carbon compound is distorting the geometry due to the large size of typical metals.

Zirconocene dichloride is an organozirconium compound composed of a zirconium central atom, with two cyclopentadienyl and two chloro ligands. It is a colourless diamagnetic solid that is somewhat stable in air.

In organometallic chemistry, bent metallocenes are a subset of metallocenes. In bent metallocenes, the ring systems coordinated to the metal are not parallel, but are tilted at an angle. A common example of a bent metallocene is Cp2TiCl2. Several reagents and much research is based on bent metallocenes.

<span class="mw-page-title-main">Bis(trimethylsilyl)acetylene</span> Chemical compound

Bis(trimethylsilyl)acetylene (BTMSA) is an organosilicon compound with the formula Me3SiC≡CSiMe3 (Me = methyl). It is a colorless liquid that is soluble in organic solvents. This compound is used as a surrogate for acetylene.

In organometallic chemistry, a transition metal alkyne complex is a coordination compound containing one or more alkyne ligands. Such compounds are intermediates in many catalytic reactions that convert alkynes to other organic products, e.g. hydrogenation and trimerization.

<span class="mw-page-title-main">Zirconocene</span> Chemical compound

Zirconocene is a hypothetical compound with 14 valence electrons, which has not been observed or isolated. It is an organometallic compound consisting of two cyclopentadienyl rings bound on a central zirconium atom. A crucial question in research is what kind of ligands can be used to stabilize the Cp2ZrII metallocene fragment to make it available for further reactions in organic synthesis.

<span class="mw-page-title-main">Decamethyltitanocene dichloride</span> Chemical compound

Decamethyltitanocene dichloride is an organotitanium compound with the formula Cp*2TiCl2 (where Cp* is C5(CH3)5, derived from pentamethylcyclopentadiene). It is a red solid that is soluble in nonpolar organic solvents. The complex has been the subject of extensive research. It is a precursor to many organotitanium complexes. The complex is related to titanocene dichloride, which lacks the methyl groups.

<span class="mw-page-title-main">Transition metal phosphinimide complexes</span>

Transition metal phosphinimide complexes are metal complexes that contain phosphinimide ligands of the general formula NPR3 (R = organic substituent). Several coordination modes have been observed, including terminal and various bridging geometries. In the terminal bonding mode the M-N=P core is usually linear but some are quite bent. The preferred coordination type varies with the oxidation state and coligands on the metal and the steric and electronic properties of the R groups on phosphorus. Many transition metal phosphinimide complexes have been well-developed and, more recently, main group phosphinimide complexes have been synthesized.

Titanocene bis(trimethylsilyl)acetylene is a formally titanium(II) organometallic compound with the formula Ti(C5H5)2C2(Si(CH3)3)2. This complex and it's zirconium analogue are often referred to as Rosenthal's reagent, after the first chemist to synthesize it, Uwe Rosenthal. This article will discuss it's history, synthesis, structure, reactivity, and applications.

<span class="mw-page-title-main">Zirconocene bis(trimethylsilyl)acetylene pyridine</span>

Zirconocene bis(trimethylsilyl)acetylene pyridine is an organozirconium metallocene compound that appears as a dark purple solid with a melting point of 125-126°C. Also referred to as Rosenthal’s reagent, this complex features two cyclopentadienyl ligands, a bis(trimethylsilyl)acetylene ligand and a coordinating pyridine molecule. Named after the work of Uwe Rosenthal, this compound with various coordinating solvents replacing the pyridine and the solvent free titanium analogue all share the title of Rosenthal’s reagent. The general reactivity for this version of Rosenthal’s reagent differs from its titanium counterpart and is most often reacted with alkynes to replace the zirconocyclopropene with a larger zirconacyclopentadiene rings.

References

  1. Linshoeft, Julian (2014-09-26). "Rosenthal's Zirconocene". Synlett. 25 (18): 2671–2672. doi: 10.1055/s-0034-1379317 . ISSN   0936-5214.
  2. Rosenthal, Uwe; Burlakov, Vladimir V. (2002), Titanium and Zirconium in Organic Synthesis, Wiley-VCH Verlag GmbH & Co. KGaA, pp. 355–389, doi:10.1002/3527600671.ch10, ISBN   978-3527304288
  3. 1 2 Ohff, A.; Pulst, S.; Lefeber, C.; Peulecke, N.; Arndt, P.; Burkalov, V. V.; Rosenthal, U. (February 1996). "Unusual Reactions of Titanocene- and Zirconocene-Generating Complexes". Synlett. 1996 (2): 111–118. doi:10.1055/s-1996-5338. ISSN   0936-5214.
  4. Rosenthal, Uwe; Ohff, Andreas; Baumann, Wolfgang; Tillack, Annegret; Görls, Helmar; Burlakov, Vladimir V.; Shur, Vladimir. B. (January 1995). "Struktur, Eigenschaften und NMR-spektroskopische Charakterisierung von Cp2Zr(Pyridin)(Me3SiC≡CSiMe3)". Zeitschrift für Anorganische und Allgemeine Chemie (in German). 621 (1): 77–83. doi:10.1002/zaac.19956210114. ISSN   0044-2313.
  5. Rosenthal, Uwe; Burlakov, Vladimir V.; Arndt, Perdita; Baumann, Wolfgang; Spannenberg, Anke (March 2003). "The Titanocene Complex of Bis(trimethylsilyl)acetylene: Synthesis, Structure, and Chemistry†". Organometallics. 22 (5): 884–900. doi:10.1021/om0208570. ISSN   0276-7333.
  6. 1 2 3 Rosenthal, Uwe (2018-08-23). "Reactions of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes with Nitriles and Isonitriles". Angewandte Chemie International Edition. 57 (45): 14718–14735. doi:10.1002/anie.201805157. ISSN   1433-7851. PMID   29888436.
  7. 1 2 3 Nitschke, Jonathan R.; Zürcher, Stefan; Tilley, T. Don (October 2000). "New Zirconocene-Coupling Route to Large, Functionalized Macrocycles". Journal of the American Chemical Society. 122 (42): 10345–10352. doi:10.1021/ja0020310. ISSN   0002-7863.
  8. Rosenthal, Uwe; Pellny, Paul-Michael; Kirchbauer, Frank G.; Burlakov, Vladimir V. (February 2000). "What Do Titano- and Zirconocenes Do with Diynes and Polyynes?". Accounts of Chemical Research. 33 (2): 119–129. doi:10.1021/ar9900109. ISSN   0001-4842.