Secondary Phosphine Boranes Research Articles

Nickel-Catalyzed Enantioselective Alkylation of Primary Phosphines.

Functional molecules derived from stereogenic phosphorus centers have important applications in the discovery of drugs and agrochemicals. They are also widely utilized as chiral ligands or organocatalysts for diverse asymmetric transformations. However, access to P-stereogenic motifs has always been regarded as a highly challenging yet desirable goal in organic synthesis. The development of general and practical methods for the stereoselective construction of synthetically versatile P(III)-stereogenic phosphines is particularly appealing but remains elusive. Herein, we describe a nickel-catalyzed asymmetric alkylation of primary phosphines with alkyl halides for the synthesis of P-stereogenic secondary phosphine-boranes with high enantioselectivity and broad substrate scope. The resulting optically active secondary phosphine-boranes allow for further stereospecific transformations, thereby establishing a modular and efficient platform for the diversity-oriented construction of P-stereogenic phosphine compounds.

Photoinduced Copper-Catalyzed C(sp3)-P Bond Formation by Coupling of Secondary Phosphines with N-(Acyloxy)phthalimides and N-Fluorocarboxamides.

A photoinduced copper-catalyzed C(sp3)-P bond formation has been developed by using N-(acyloxy)phthalimides as radical precursors and secondary phosphine boranes as coupling partners. A variety of alkyl carboxylic acid derivatives can be readily transformed into the corresponding phosphines with high reaction efficiency and structural diversity. Besides, utilizing the 1,5-HAT of the N-centered radical process, the δ C(sp3)-H bond can be coupled with secondary phosphines, which provides a novel method for the regioselective formation of C(sp3)-P bonds.

Asymmetric Synthesis of P-Stereogenic Secondary Phosphine-Boranes by an Unsymmetric Bisphosphine Pincer-Nickel Complex

The first highly enantioselective catalytic synthesis of P-stereogenic secondary phosphine-boranes was realized by the asymmetric addition of primary phosphine to electron-deficient alkenes with a newly developed unsymmetric bisphosphine (PCP') pincer-nickel complex. Various P-stereogenic secondary phosphine-boranes were obtained in 57-92% yields with up to 99% ee and >20:1 dr. The follow-up alkylation upon P-C bond formation with alkyl halides provided a practical way to access P-chiral compounds with diverse functional groups.

Direct conversion of sec-phosphine oxides to sec-phosphine-boranes using BH3

An effective and mild synthetic method for secondary phosphine-boranes from secondary phosphine oxides was developed. The slow addition of borane-tetrahydrofuran to a solution of secondary phosphine oxides at ambient temperature gave secondary phosphine-boranes with high yield. The use of air-sensitive secondary phosphines, which are common substrates for secondary phosphine-borane syntheses, is avoided in this mild process. Moreover, generation of by-products, such as secondary hydroxy-phosphine-boranes, is also minimized.

60]Fullerene l-Amino Acids and Peptides: Synthesis under Phase-Transfer Catalysis Using a Phosphine-Borane Linker. Electrochemical Behavior.

A new method to link amino acid and peptide derivatives to [60]fullerene is described. It uses hydrophosphination with a secondary phosphine borane. First, the stereoselective synthesis of secondary phosphine borane amino acid derivatives was achieved by alkylation of phenylphosphine borane with γ-iodo-α-amino ester reagents under phase-transfer catalysis (PTC). Second, a sec-phosphine borane amino ester was saponified and coupled with α,γ-diamino esters to afford the corresponding dipeptide derivatives in good yields. Finally, the hydrophosphination reaction of [60]fullerene by the sec-phosphine borane compounds was performed under PTC to obtain C60-amino acid or dipeptide derivatives in yields up to 80% by P-C bond formation. This addition reaction which proceeds in mild and moderate dilute conditions (0.03 M) leads to [60]fullerene derivatives as epimeric mixtures (∼1:1) due to the P-chirogenic center but without racemization of the amino acid or peptide moiety. In addition, the electrochemical behavior of a C60-phosphine borane amino ester was investigated by cyclic voltammetry and spectroelectrochemistry after controlled-potential electrolysis. It showed evidence for the retro-hydrophosphination reaction into free [60]fullerene and sec-phosphine borane amino ester compound. Consequently, the synthesis of sec-phosphine borane amino acids followed by their use in hydrophosphination reactions of [60]fullerene under phase-transfer catalysis has demonstrated a great utility for the preparation of C60-derivatives. Indeed, the hydrophosphination and the retro-hydrophosphination reactions of [60]fullerene/phosphine borane compounds offer a promising new strategy for the reversible immobilization of amino acid or peptide derivatives on carbon nanomaterials such as [60]fullerene.

ChemInform Abstract: Recent Advances in Synthesis of P‐BH3 Compounds

AbstractReview: 141 refs.

Mechanistic aspects of the stereospecific reduction of chiral hydroxyalkyl phosphinates and phosphine oxides

Abstract We present recent advances in the understanding of the reduction of optically pure hydroxyalkylphosphinates and phosphine oxides, which represent key intermediates for the preparation of P-stereogenic ligands. Their reduction leads to P-chiral phosphinites and phosphines, respectively, and occurs stereospecifically with inversion of configuration using BH3·THF, which plays three roles: activating, reducing and protecting agent. The formation of by-products as hydroxyalkyl secondary phosphine–boranes has also been studied.

Dehydrocoupling of phosphine-boranes using the [RhCp*Me(PMe3)(CH2Cl2)][BArF4] precatalyst: stoichiometric and catalytic studies.

We report a detailed, combined experimental and computational study on the fundamental B-H and P-H bond activation steps involved in the dehydrocoupling/dehydropolymerization of primary and secondary phosphine-boranes, H3B·PPhR'H (R = Ph, H), using [RhCp*(PMe3)Me(ClCH2Cl)][BArF4], to either form polyphosphino-boranes [H2B·PPhH] n (Mn ∼ 15 000 g mol-1, PDI = 2.2) or the linear diboraphosphine H3B·PPh2BH2·PPh2H. A likely polymer-growth pathway of reversible chain transfer step-growth is suggested for H3B·PPhH2. Using secondary phosphine-boranes as model substrates a combined synthesis, structural (X-ray crystallography), labelling and computational approach reveals: initial bond activation pathways (B-H activation precedes P-H activation); key intermediates (phosphido-boranes, α-B-agostic base-stabilized boryls); and a catalytic route to the primary diboraphosphine (H3B·PPhHBH2·PPhH2). It is also shown that by changing the substituent at phosphorus (Ph or Cy versust Bu) different final products result (phosphido-borane or base stabilized phosphino-borane respectively). These studies provide detailed insight into the pathways that are operating during dehydropolymerization.

The Hydroxyalkyl Moiety As a Protecting Group for the Stereospecific Alkylation of Masked Secondary Phosphine-Boranes.

The synthesis of functionalized tertiary phosphine-boranes has been developed via a chemodivergent approach from readily accessible (hydroxymethyl) phosphine-boranes under mild conditions. O-Alkylation or decarbonylative P-alkylation product could be exclusively obtained. The P-alkylation reaction was found to proceed in moderate to very good yields and very high enantiospecificity (es >95%) using a variety of alkyl halides as electrophiles. The configurational stability of the sodium phosphido-borane intermediate was also investigated and allowed a deeper understanding of the reaction mechanism, furnishing secondary phosphine-boranes in moderate yield and enantiopurity.

Utilization of optically active secondary phosphine–boranes: synthesis of P-chiral diphosphines and their enantioinduction ability in rhodium-catalyzed asymmetric hydrogenation

Both enantiomers of tert-butylmethylphosphine–borane have been used for the synthesis of P-chiral diphosphines and/or their borane complexes. The enantiopure borane complex of 1,2-bis(tert-butylmethylphosphino)ethane (t-Bu-BisP∗) was prepared in high yield from the secondary phosphine–borane and 1,2-dichloroethane. A mono-chelated Rh-complex of t-Bu-MiniPHOS was prepared and its catalytic activity was examined in the asymmetric hydrogenation of some representative functionalized alkenes. Synthesis of three new P-chiral phosphine ligands with quinoline or quinoxaline backbone is also described together with their enantioinduction ability.

Synthesis of phosphaguanidines by hydrophosphination of carbodiimides with phosphine boranes.

The direct addition of anionic secondary phosphine boranes to carbodiimides yields both chiral and achiral phosphaguanidine boranes under ambient temperature conditions. An analogous preparation of menthol-derived phosphinite boranes is also described. These products can be deborinated to give the corresponding phosphines, and subsequently oxidized to give phosphine oxides. The robustness of this method was further demonstrated in the synthesis of structurally novel cyclic phosphaguanidines.

Recent advances in synthesis of P-BH3 compounds.

This chapter is dedicated to the main achievements since 2007 regarding the synthesis of BH3-phosphorus complexes. Among this class of compounds, phosphine-boranes are the most studied derivatives, mainly as valuable surrogates of phosphines, enabling easy handling and purification. In contrast, metal phosphido-boranes have so far only been considered as in situ intermediates in the P-functionalization of secondary phosphine-boranes. Thorough investigations of their structures as well as their chemical properties have recently been reported. Besides phosphine-boranes and their phosphides, new families of phosphorus-BH3 complexes, have emerged as useful precursors of new structures in the asymmetric series. New routes toward optically active phosphinous-acid boranes and their esters were developed and applied to the synthesis of enantiopure P-stereogenic secondary and tertiary phosphine-boranes. The stereoselective synthesis of P-stereogenic aminophosphine-boranes, precursors of a new class of chiral ligands, has been reported. Studies dealing with the synthesis and reactivity of phosphonite-boranes were successfully applied to the development of efficient syntheses of functionalized H-phosphinates, compounds difficult to access by other routes.

Hydrophosphination of Propargylic Alcohols and Amines with Phosphine Boranes

The first uncatalyzed hydrophosphinations of propargylic amines and alcohols with phosphine- borane complexes are described. The reactions proceed at ambient temperature or below without the use of protecting groups or the need to handle pyrophoric secondary phosphines, furnishing air-stable phosphineborane-amines and alcohols in good yields. Utilization of chiral propargylic substrates and unsymmetrical secondary phosphineboranes leads to diastereomeric P-chiral products that can be separated by fractional crystallization or chromatography. Initial applications of these new P-X species to asymmetric catalysis are detailed.

An ESR and DFT revisitation of phosphonitroxides prompted by an ineffective ESR approach to the hydrophosphination of alkynes

An ESR investigation of the thermal hydrophosphination of 1-hexyne by five different secondary phosphines and phosphine-boranes did not lead to the observation of any radical, but in the presence of the spin trap MNP (2-methyl-2-nitrosopropane) several phosphonitroxides were detected. The unusually low phosphorus splitting exhibited by some of these species could be accounted for on the basis of DFT calculations. Although two phospho-substituted vinyl nitroxides were identified in the course of the hydrophosphination reaction, they could not be considered as evidence of the direct involvement of phosphorus-centred radicals.

ChemInform Abstract: Stereoselective Synthesis of o‐Bromo (or Iodo)aryl P‐Chirogenic Phosphines Based on Aryne Chemistry.

AbstractThe method is based on the reaction of a secondary phosphine borane with the aryne species formed in situ from 1,2‐dibromo‐ or 1,2‐diiodobenzene by treatment with BuLi.

Stereoselective Synthesis of o-Bromo (or Iodo)aryl P-Chirogenic Phosphines Based on Aryne Chemistry

The efficient synthesis of chiral or achiral tertiary phosphines bearing an o-bromo (or iodo)aryl substituent is described. The key step of this synthesis is based on the reaction of a secondary phosphine borane with the 1,2-dibromo (or diiodo)arene, owing to the formation in situ of an aryne species in the presence of n-butyllithium. When P-chirogenic secondary phosphine boranes were used, the corresponding o-halogeno-arylphosphine boranes were obtained without racemization in moderate to good yields and with ee up to 99%. The stereochemistry of the reaction, with complete retention of the configuration at the P atom, has been established by X-ray structures of P-chirogenic o-halogenophenyl phosphine borane complexes. The decomplexation of the borane was easily achieved without racemization using DABCO to obtain the free o-halogeno-arylphosphines in high yields.

Bulky, Optically Active P-Stereogenic Phosphine–Boranes from Pure H-Menthylphosphinates

The transformation of readily available pure-H-menthylphosphinates into chiral phosphinous acid-boranes permits the elaboration of bulky P-stereogenic secondary phosphine-boranes. Taking advantage of the synthetic potential of these compounds, a broad range of hindered P-chiral tertiary phosphine-boranes has been prepared with excellent enantiomeric excesses. The utility of bulky o-tolylphosphines was illustrated by the synthesis of a rare enantiopure phosphapalladacycle (S(P),S(P))-12.

ChemInform Abstract: Copper‐Catalyzed Synthesis of Alkynylphosphine Derivatives: Unprecedented Use of Nucleophilic Phosphorus Compounds.

AbstractA new and efficient access to various alkynylphosphine derivatives is developed using Cu‐catalyzed cross‐coupling reactions of secondary phosphine boranes with alkynyl bromides.

Copper-catalyzed synthesis of alkynylphosphine derivatives: unprecedented use of nucleophilic phosphorus compounds

A new and smooth approach towards alkynylphosphine derivatives is described. It relies on the unprecedented catalytic coupling of secondary phosphine boranes with alkynyl bromides using the CuI/1,10-phenanthroline couple.

First study on the enantioselective palladium-catalyzed C-P cross-coupling reaction between an alkenyltriflate and a phosphine-borane

In this article, we report the first example of a palladium-catalyzed asymmetric C-P cross-coupling reaction between a racemic secondary phosphine-borane, methylphenylphosphine-borane 1, and an achiral triflate. The influence of various parameters such as the structure of the chiral ligand, the temperature and the nature of the solvent on the activity and the selectivity of the reaction is reported. Enantiomeric ratios up to 78:22 were obtained using (S,S)-Me-DUPHOSPdCl2 as catalyst. A kinetic resolution process is proposed to account for this selectivity. Dans cet article, nous décrivons le premier exemple de couplage C-P asymétrique catalysé au palladium entre une phosphine-borane secondaire racémique, la méthylphénylphosphine-borane 1 et un triflate achiral. L’influence de différents paramètres tels que la structure du ligand chiral, la température, la nature du solvant et de la base, sur l’activité et la sélectivité de la réaction a été étudiée. Un rapport énantiomérique de 78:22 a été obtenu lorsque le catalyseur (S,S)-Me-DUPHOSPdCl2 est utilisé. Un processus de dédoublement cinétique est proposé pour justifier cette sélectivité.