Nucleophilic Addition-Oxidation Reactions of σ3,λ3 Dialkyl(Silylamino)Phosphines with Mono and Disubstituted Acetylenes

Abstract:

Dialkyl(silylamino)phosphines R₂PNT₂ undergo a nucleophilic addition-oxidation reaction with either mono- or di-substituted acetylenes which is followed by a silyl migration to form phosphoranimines with unsaturated substituents. The reaction route depends on the substituent on the acetylenic carbon atom. Reactions of the acetylenes with dialkyl(silylamino)phosphines show high chemo and regio selectivity for addition to the triple bond in the formation of the alkene phosphoranimines. The reaction of (silylamino)-phosphines with α,β-acetylenic carbonyl compounds is more complicated; the reaction route depends critically on the substituents at both the carbonyl and the β-acetylenic carbon atoms.     

Reactions of P-donor ligands with N-silyl(halogeno)organophosphoranimines: formation of cations with P-P coordination bonds and poly(alkyl/aryl)phosphazenes at ambient temperature

A series of phosphine donor-stabilized N-silylphosphoranimine salts [R'3P.PR2=NSiMe3]+Br- were prepared from the direct reaction between the phosphoranimines BrR2P=NSiMe3 (R = Me, OCH2CF3) and the tertiary phosphines nBu3P and Me3P. The 1JPP values of these salts exhibit an unusual dependence on the substituents at the phosphoranimine acceptor and appear to reflect an electronic push-pull mechanism. Employment of phosphites as the phosphorus donor results in the generation of high molecular weight poly(alkyl/aryl)phosphazenes at ambient temperature. This preparative route is potentially advantageous over the conventional thermal polycondensation route.     

Silylated Phosphines and Phosphoranimines

Abstract

The N-silyl phosphoranimines [e.g., Me₃SiN=P(OCH₂CF₃)Me₂] undergo a variety of reactions including deprotonation/substitution of the P-Me groups, transilylation, and condensation with reactive phosphines. Some new 1,2-addition and oxidation reactions of the P=C systems, R₂NP=CHR, R₂NP(=NR)=CHR, and R₂NP=CR-CH=CHR (R = SiMe₃) are also reported.     

The Usefulness of Trivalent Phosphorus for the Synthesis of Dendrimers

Dendrimers are hyperbranched macromolecules, which are synthesized step-by-step by the repetition of a series of reactions. While many different types of dendrimers are known, this review focusses on the use of trivalent phosphorus derivatives (essentially phosphines and phosphoramidites) for the synthesis of dendrimers. The first part presents dendrimers constituted of phosphines at each branching point. The other parts display the use of trivalent phosphorus derivatives during the synthesis of dendrimers. Different types of reactions have been applied to phosphines. The very first examples of phosphorus-containing dendrimers were obtained by the alkylation of phosphines. Then, several families of dendrimers were elaborated by reaction of phosphoramidites. Such a type of reaction is the base of the solid phase synthesis of oligonucleotides; it has been applied in particular for the synthesis of dendrimers constituted of oligonucleotides. Finally, the Staudinger reaction between phosphines and azides afforded different families of dendrimers, and was at the origin of accelerated methods of synthesis of dendrimers. Besides, the reactivity of the P=N-P=S linkages created by this reaction led to very original dendritic structures.     

Polymeric materials based on main group elements: the recent development of ambient temperature and controlled routes to polyphosphazenes

This Perspective discusses the development of new routes to polyphosphazenes, [R(2)P[double bond, length as m-dash]N](n), that occur at ambient temperature and, in some cases, allow molecular weight control and access to narrow molecular weight distributions and block copolymers. For example, the room temperature silyl-carborane initiated ring-opening polymerisation of (NPCl(2))(3) is described together with chain growth condensation polymerisations of phosphoranimines Cl(3)P[double bond, length as m-dash]NSiMe(3) and BrMePhP[double bond, length as m-dash]NSiMe(3). Recent works on donor-stabilised cationic phosphoranimines are also discussed.     

Scavenging and reclaiming phosphines associated with group 10 metal-mediated couplings

[reaction: see text] Exposure of any of several mono- or bidentate phosphines to CuCl leads to quick removal of unwanted ligands from solution. Most phosphines, if desired, can be easily recovered.     

α‐Radical Phosphines: Synthesis,Structure, and Reactivity

A series of phosphines featuring a persistent radical were synthesized in two steps by condensation of dialkyl‐/diarylchlorophosphines with stable cyclic (alkyl)(amino)carbenes (cAACs) followed by one‐electron reduction of the corresponding cationic intermediates. Structural, spectroscopic, and computational data indicate that the spin density in these phosphines is mainly localized on the original carbene carbon from the cAAC fragment; thus, it remains in the α‐position with respect to the central phosphorus atom. The potential of these α‐radical phosphines to serve as spin‐labeled ligands is demonstrated through the preparation of several Au^I derivatives, which were also structurally characterized by single‐crystal X‐ray diffraction.     

α-Radical Phosphines: Synthesis,Structure, and Reactivity

A series of phosphines featuring a persistent radical were synthesized in two steps by condensation of dialkyl-/diarylchlorophosphines with stable cyclic (alkyl)(amino)carbenes (cAACs) followed by one-electron reduction of the corresponding cationic intermediates. Structural, spectroscopic, and computational data indicate that the spin density in these phosphines is mainly localized on the original carbene carbon from the cAAC fragment; thus, it remains in the α-position with respect to the central phosphorus atom. The potential of these α-radical phosphines to serve as spin-labeled ligands is demonstrated through the preparation of several Au^I derivatives, which were also structurally characterized by single-crystal X-ray diffraction.     

Controlled Synthesis of Polyphosphazenes with Chain-Capping Agents

N-alkyl phosphoranimines were synthesized via the Staudinger reaction of four different alkyl azides with tris(2,2,2-trifluoroethyl) phosphite. N-adamantyl, N-benzyl, N-t-butyl, and N-trityl phosphoranimines were thoroughly characterized and evaluated as chain-capping compounds in the anionic polymerization of P-tris(2,2,2-trifluoroethoxy)-N-trimethylsilyl phosphoranimine monomer. All four compounds reacted with the active chain ends in a bulk polymerization, and the alkyl end groups were identified by ¹H-NMR spectroscopy. These compounds effectively controlled the molecular weight of the resulting polyphosphazenes. The chain transfer constants for the monomer and N-benzyl phosphoranimine were determined using Mayo equation.     

Iron catalysis for the synthesis of ligands: Exploring the products of hydrophosphination as ligands in cross-coupling

Catalytic hydrophosphination is a useful technique for the synthesis of phosphines, however, the phosphine products have been little exploited as ligands in catalysis. We have selected three phosphines prepared by iron catalyzed hydrophosphination and used them as ligands in a series of cross-coupling reactions: Heck, Suzuki-Miyaura and Buchwald-Hartwig. Rather than limit the chemistry to simple cross-coupling partners which are almost guaranteed to perform well in these transformations, industrially relevant substrates which are challenging from and electronic and/or steric perspective, along with substrates which contain several heteroatoms, were explored in order to gauge the true potential of these phosphine ligands.     

Lewis base catalyzed addition of trimethylsilyl cyanide to aldehydes

A variety of achiral Lewis bases were found to catalyze the addition of TMSCN to the aldehydes. Among them, phosphines and amines were the most efficient catalysts. In addition, several chiral amines and phosphines were examined in a catalytic, asymmetric addition of TMSCN to benzaldehyde albeit with low enantioselectivity. A mechanistic study revealed that the reaction was first order in aldehyde, first order in Lewis base, and zeroth order in TMSCN, suggesting the complex formation of TMSCN and Lewis base formation of complex i. However, there are at least two possible scenarios for this catalytic process, and in view of the low selectivities observed, it is not clear which mechanism is operative.     

Reaction between Dichlorophosphines and Azoalkenes: A General Synthesis of 3,4-Dihydro-2H-1,2,3-diazaphosphole Derivatives

The reaction between dichlorophosphines and azoalkenes provides a smooth method for the preparation of 3,4-dihydro-2H-1,2,3-diazaphosphole-3-oxides. When R¹ ≠ H, the cis: trans ratio is strongly dependent on the nature of the R⁴ substituent. Compounds arising from phenylazoalkenes are stable for several months, whereas compounds arising from methylazoalkenes undergo modifications during silica gel chromatography. Trichlorosilane reduction of these oxides gives the corresponding phosphines with retention of configuration. In some cases, this process competes with stereomutation of the starting phosphine oxide. Aryl-substituted phosphines are much more stable than the corresponding alkyl-substituted phosphines.     

HYDROGEN BONDING BETWEEN TERTIARY PHOSPHINES AND ALCOHOLS

Abstract

The hydrogen bond between several alcohols, in particular benzyl alcohol and isopropanol, as donors, and a number of tertiary phosphines, as well as a smaller number of tertiary arsines, as acceptors was investigated by means of ir spectroscopy in the temperature range +40° to -20°C. Toluene was used as a solvent. The equilibrium constant K, the hydrogen bond enthalpy -ΔH and the entropy -ΔS were determined. The equilibrium constants as well as the -ΔH values are essentially dependent on the basicity of the phosphines. There is no evidence of any steric influence. In the systems with aliphatic phosphines, the highest equilibrium constants are about 20, the lowest values are near unity. Aromatic phosphines possess a lower affinity of interaction with the alcohols. -ΔH varies for the different systems between 1.2 and 3.5 kcalμmole^?1. Investigating the acceptor power of arsines we found both K and -ΔH one order of magnitude lower than in the case of phosphines.     

非离子水溶性膦配体的合成及其应用进展

按非离子水溶性膦配体的发展特点,就羟基取代膦配体、天然碳水化合物为母体的膦配体、聚醚基取代的膦配体、具手性中心的膦配体、高分子负载型膦配体、温控相转移膦配体、环糊精改性的膦配体等类型的非离子水溶性膦配体的合成及其在两相催化中的应用作一综述。     

CsOH-promoted P-alkylation: a convenient and highly efficient synthesis of tertiary phosphines

A mild and efficient method for the synthesis of tertiary phosphines and ditertiary phosphines has been developed. In the presence of cesium hydroxide, molecular sieves and DMF at room temperature, various secondary phosphines and alkyl bromides were examined, and the results have demonstrated that this methodology offers a general synthetic procedure to produce tertiary phosphines in moderate to high yields. Optically active tertiary phosphine synthesis is also described.     

Zn(II) Robson macrocycles as templates for chelating diphosphines

Chelating diphosphines were constructed using dinuclear Zn(II) complexes of Robson macrocycles (Zn-RMCs) as templates. The assembly process is driven by the interaction between the metal centers (Lewis acids) with anionic and neutral Lewis base-functionalized monophosphines. The stability of the final structure depends on the geometry and the affinity of the functional groups of the ditopic phosphines and on the structure of the RMC. In the free ligand the ditopic phosphines coordinate at opposite faces of the pseudo-planar macrocycle as is shown in the molecular structure of several of the assemblies, according to X-ray diffraction. Pre-organization of the system by coordinating the phosphorus atoms to a transition metal center enforced coordination of the functional groups at the same face of the RMC. For several templated diphosphines cis-PtCl(2) complexes were identified by NMR. The in situ assembled diphosphines showed a chelating effect in the rhodium catalyzed hydroformylation of 1-octene. Combination of Zn-RMC 3 and phosphine A gave the highest l/b ratio (13) in acetonitrile.     

First-principle predictions of basicity of organic amines and phosphines in acetonitrile

Amines and phosphines are widely utilized as bases and basic organocatalysts in organic chemistry. Thus it is highly valuable to develop a coherent theoretical method that can accurately predict the basicity of structurally unrelated amines and phosphines in organic solvents from the first principles. Herein we developed the first ab initio protocol that could predict the pK_a value of any protonated amine or phosphine in acetonitrile through systematic benchmarking. By comparing to a variety of available experimental data (total number=98), it was determined that the precision of the optimized method in basicity prediction was as low as 1.1 pK_a unit. With the powerful new method in hand, we subsequently conducted some systematic studies about the basicity of organic amines and in particular phosphines, for which very few experimental data were available. It was found that the solvent exerted profound effects on the basicity of amines and phosphines. Accordingly we concluded that it was not valid to use gas-phase data to interpret the solution-phase basicity of amines and phosphines. Next we reported the basicity of a number of synthetically important aliphatic and aromatic amines and phosphines in acetonitrile. We also compared, for the first time, the α-substituent effects on the basicity of aliphatic amines and phosphines and the remote substituent effects on the basicity of aromatic amines and phosphines. Finally, we studied for the first time the basicity of cyclic amines and phosphines. It was found that the ring strain exerted some interesting effects on the basicity of amines and phosphines.     

Palladacycle-catalyzed asymmetric hydrophosphination of enones for synthesis of C*- and P*-chiral tertiary phosphines

A highly reactive and stereoselective hydrophosphination of enones catalyzed by palladacycles for the synthesis of C*- and P*-chiral tertiary phosphines has been developed. When Ph(2)PH was employed as the hydrophosphinating reagent, a series of C*-chiral tertiary phosphines were synthesized (C*-P bond formation) in high yields with excellent enantioselectivities, and a single recrystallization provides access to their enantiomerically pure forms. When racemic secondary phosphines rac-R(3)(R(4))PH were utilized, a series of tertiary phosphines containing both C*- and P*-chiral centers were generated (C*-P* bond formation) in high yields with good diastereo- and enantioselectivities. The stereoelectronic factors involved in the catalytic cycle have been revealed.     

手性膦配体的设计及不对称催化氢化反应

本文综述了手性膦配体及其碳碳双键的不对称催化氢化反应研究和最新进展,并对手性膦配体的设计做了分析和总结。     

Ionophilic phosphines: versatile ligands for ionic liquid biphasic catalysis

Phosphine ligands bearing an imidazolium fragment were easily prepared by one-step radical chain addition of secondary phosphines to allyl or vinyl imidazolium salts. These ligands were used to prepare new ionophilic second generation Grubbs-type catalysts. The catalyst immobilized in 1-butyl-3-methyl imidazolium ILs shows good catalytic activity in RCM reactions of several substrates and, depending on the media employed, is stable up to eight cycles.