Tributylphosphine 

【English name】Tri-n-Butylphosphine

 [Molecular formula] C12H27P 

【Molecular weight】202.32 

【CA registration number】998-40-3

 [Physical properties] bp 240 °C, mp 30~35°C, d 0.834 g/cm3 (20 °C). Soluble in most organic solvents, slightly soluble in acetonitrile and water. 31PNMR can be used to detect the purity of the reagent. 

[Preparation and merchandise] Available for sale from major international reagent companies. 

[Note] It is flammable and smelly, and can be kept at room temperature under the protection of inert gas. When in contact with air, a free radical chain reaction may occur and be oxidized, producing tributylphosphine oxide and dibutylbutylphosphonite. Therefore, purification by vacuum distillation is usually required before use.

Unlike most commonly used three-coordinate phosphorus reagents, tributylphosphine is a nucleophile. It is a relatively weak base (pKa = 8.70 in MeNO3, pKa = 5.60 in methanol). The solvent does not need to be strictly deoxygenated during use, but it needs to be protected with inert gas. If exposed to air, a violent oxidation reaction will occur, producing tributylphosphine oxide and butyl dibutylphosphonite. 

Synthesis of thioethers and thioesters: The reaction of tributylphosphine with disulfide and alcohol can produce the corresponding thioether and Bu3PO, and the reaction with disulfide and carboxyl group can produce thioester. Catalyze the addition reaction of carbonyl groups and alkenes. Since tributylphosphine is nucleophilic, attacking the double bond will cause the electron cloud to shift, causing the addition reaction to occur. For example: tributylphosphine can promote the cyclization reaction of benzaldehyde and allene. Catalyzing nucleophilic substitution reactions Tributylphosphine can also be used as a catalyst for nucleophilic substitution reactions. For example: it can catalyze the substitution reaction of phthalamide and alkoxy groups.

Catalyzing 1,4-addition reaction Tributylphosphine is also the most commonly used catalyst for 1,4-addition reaction. Because tributylphosphine is nucleophilic and weakly basic, it is more suitable for catalyzing this type of reaction than other three-coordinated phosphorus catalysts (such as triphenylphosphine, etc.). Therefore, tributylphosphine is one of the important catalysts for ring-forming reactions. Catalyze the formation of C-X bonds Tributylphosphine can also activate azide compounds to form carbon-nitrogen double bonds. This type of reaction is often used in synthetic routes such as ring closure. In addition, tributylphosphine can also be used in the alkylation reaction of phosphine azide. Formation of C-C bonds Tributylphosphine can catalyze the coupling reaction of unsaturated hydrocarbons and aromatic compounds, as well as the coupling reaction of alkenes with a leaving group at the α-position. Among them, the latter is often used as a ring-closing reaction. As a ligand for metal catalysts, tributylphosphine can be used with some metal catalysts to catalyze different types of reactions. For example: the complex formed with Ni can catalyze the alkylation reaction of phosphite.

Triphenylphosphine 

【English name】Triphenylphine

 [Molecular formula] C18H15P 

【Molecular weight】262.29 

【CA registration number】603-35-0

 [Physical properties] White crystal, bp337°C/1.0 mmHg (133.322 Pa), mp 79-81°C, d 1.18g/cm3, soluble in most organic solvents, easily soluble in ethanol, benzene, and chloroform. Very soluble in ether, but insoluble in water. 

【Preparation and Products】Sold by domestic and foreign reagent companies. It can be recrystallized from n-hexane, methanol or 95% ethanol and dried with CaSO4 or P2O5 at 65°C/1.0 mmHg (133.322 Pa) to obtain a pure solid. 

[Caution] It will irritate the human body under severe exposure to the sun, and it will be neurotoxic if exposed for a long time. The reactivity of arylphosphine with oxygen is lower than that of benzyl and alkylphosphine, but the oxidation of triphenylphosphine by air is very obvious, forming triphenylphosphine oxide. Triphenylphosphine is not prone to fire and explosion, but it will generate toxic phosphine and POx fumes when heated and decomposed.

Triphenylphosphine is a quite commonly used reducing agent. In most cases, the reaction is driven by the formation of triphenylphosphine oxide, a thermodynamically favorable reaction. In addition, triphenylphosphine is widely used as a ligand for metal catalysts. Deoxygenation reaction Triphenylphosphine is widely used in the reduction reaction of hydrogen peroxide or peroxide to produce alcohols, carbonyl compounds or epoxides. The main driving force for this type of reaction is the ability of triphenylphosphine to form strong P=O bonds with relatively weak O-O bonds (188-209 kJ/mol). For example, triphenylphosphine can be used to reduce and decompose ozonides and selectively prepare ketones and aldehydes. Reaction with Azides Triphenylphosphine reacts with organic azide compounds to form iminophosphine. Iminophosphine is a relatively active nucleophile and easily reacts with electrophiles. For example: react with aldehydes and ketones to form imines and triphenylphosphine oxides. This reaction is similar to the Wittig reaction and is called the aza-Wittig reaction. The driving force of this reaction is also due to the formation of triphenylphosphine oxide. Reactions with organosulfides Triphenylphosphine can convert episulfides into alkenes at room temperature.

Dehalogenation reaction α-bromoketone reacts with triphenylphosphine to form ketone. Reaction with organic epoxides Triphenylphosphine can convert epoxy compounds into cyclic amine compounds with the participation of sodium azide under reflux in water and acetone solvents. Preparation of substituted pyrrole: Aniline, furandione react with triphenylphosphine to form 1-phenyl-2,5-pyrroledione. Used as a ligand for metal catalysts Triphenylphosphine can be used as a ligand to form metal catalysts with many transition metals. For example: Pd(PPh3)4 is an important catalyst, often used to catalyze coupling reactions. These coupling reactions are important methods for building carbon-carbon bonds and are characterized by mild catalytic conditions. Another example: under the combined action of Pd(PPh3)4 and Ag2O, phenylboronic acid reacts directly with aromatic halogenated hydrocarbons to form biphenyl compounds. The yield of this reaction can reach 90% (Formula 8). In addition to phenylboronic acid and halogenated compounds, magnesium reagents, zinc reagents, tin reagents, silicon compounds, etc. can be used as substrates for coupling reactions.

Tri-tert-butylphosphine 

【English name】Tri-tert-Butylphosphine

 [Molecular formula] C12H27P 

【Molecular weight】202.32 

【CA registration number】13716-12-6 

[Physical properties] Low melting point solid, mp 30-35 °C, bp 102-103 °C/13 mmHg (1733.2 Pa), d 0.83~0.84 g/cm 3. 

[Preparation and commodities] It is sold by large international reagent companies. Commercial reagents are usually 10% n-hexane and 1,4-dioxane solutions. It can also be prepared by reacting tert-butylmagnesium chloride with phosphorus trichloride in diethyl ether and then treating it with tert-butyllithium. 

[Note] It is very sensitive to air and must be stored in isolation from air at low temperatures. Must be operated in a glove box or under inert gas protection.

P(t-Bu)3 is an electron-rich ligand. The complex formed with palladium can catalyze the cross-coupling between metal organic compounds (M=B, Sn, Zn, Si, Mg) and aryl halides. linked reaction. This type of reaction is an important and efficient way to form C-C bonds. Traditional catalyst systems can easily achieve the insertion reaction of palladium into aryl C-Br bonds or C-I bonds, but it is very difficult to activate the cheaper and inert aryl C-Cl bonds. The study found that adding the electrorich P(t-Bu)3 ligand can effectively realize the insertion reaction of metal palladium into aryl C-Cl bonds, which undoubtedly injects new vitality into the C-C bond formation reaction. In addition to P(t-Bu)3 ligands, organic ligands that can activate C-Cl bonds include the large-volume, electron-rich chelated bisphosphine ligand proposed by Milstein, and the large-volume, electron-rich chelated bisphosphine ligand proposed by Buchwald. Strong phosphine ligands, N-heterocyclic carbene ligands proposed by Herrmann, and phosphite ligands proposed by Beller. In the presence of P(t-Bu)3 ligand, the palladium reagent-catalyzed amination reaction of halogenated arenes with aniline substrates can be extended to chlorinated arenes (Equation 2). At the same time, P(t-Bu)3 can also promote the cross-coupling reaction between aryl metal reagents (such as: B, Zn, Sn, Si) and halogenated aromatics or arylsulfonyl chlorides.

The Sonogashira reaction between terminal alkynes and brominated aromatics catalyzed by traditional palladium reagents is completed at high temperature and with the addition of cocatalyst Cul. After adding the electron-rich ligand P(t-Bu)3, not only can the reaction be carried out at room temperature, but also the use of Cul can be avoided. At the same time, the reaction of chlorinated aromatics and terminal alkynes can also be realized at high temperature. In the presence of P(t-Bu)3 ligand, Heck-Mizoroki cross-coupling reaction of chlorinated aromatics and mono- or disubstituted alkenes can also occur. In the presence of P(t-Bu)3 ligands, 1-aryltriazenes as electrophiles can also undergo cross-coupling reactions with aryl metal reagents (such as aryl boron, aryl silicon).

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