Alkylidynephosphines - Syntheses and Reactivity

Abstract

In the past, different methods have been utilized for the preparation of alkylidynephosphines. Whereas, however, small amounts of thermally instable derivatives might be obtained from reactions in the gas phase, the synthesis of phosphines which are stable under an inert atmosphere, as for instance those with a tert-butyl or a 1-adamantyl substituent at the carbon atom of the PEC group, is best started with tris (trimethylsilyl) phosphine itself or with the more reactive lithium bis (trimethylsilyl) phosphide.2 tetrahydrofuran complex. Treatment of either compound with acyl halides results in the formation of acylbis (trimethylsilyl) phosphines which, at room temperature, rearrange to the corresponding trimethylsilyl [1-(trimethylsiloxy) alkylidene] isomers. As traces of hydrogen halide accelerate the conversion of tris (trimethylsilyl) phosphine to the triacyl derivatives, the use of the lithium phosphide is strongly recommended in all cases where impure acyl halides are used. In the presence of small amounts of solid sodium hydroxide suspended in an etherial solvent, the thus prepared trimethyl[1-(trimethylsiloxy)-alkylidene]phosphines eliminate hexamethyldisiloxane to yield the required alkylidyne compounds. Running the decomposition without a solvent at a higher temperature, Regitz and coworkers were able to improve this method further.     

1,2- and 1,3-diphosphetanes from alkylidenephosphines

Abstract

Alkyl- or arylbis(trimethylsilyl)phosphines as well as tris(trimethylsilyl)phosphine and the corresponding arsines react with acyl chlorides to give [1-(trimethylsiloxy)alkylidene]phosphines 1 and -arsines 2; most of their 2,2-dimethylpropylidene derivatives are thermally stable at room temperature. With the same class of phosphines as starting compounds and carbon disulfide [bis(trimethylsilylsulfano)methylidene]phosphines 3 are formed, whereas [(dialkylamino)methylidene]-4 and [diarylmethylidene]phosphines 5 or the corresponding arsines 6 and 7 can be obtained from acyl amides or ketones.¹     

Effective Control of the Electron-donating Ability of Phosphines by using Phosphazenyl and Phosphoniumylidyl Substituents

Phosphoniumylidyl and phosphazenyl groups are effective substituents to increase the electron-donating ability of tertiary phosphines. However, the influence of structural variations among those substituents on the electronic properties of the phosphines is little explored. Herein, we show that protonation of the ylidic carbon atom of phosphoniumylidyl phosphines increases the Tolman electronic parameter (TEP) by ΔTEP = 16.0–18.8 cm^–1. Furthermore, phosphazenyl phosphines were synthesized with isopropyl groups (NP{iPr}₃) and tetramethylguanidino groups (NP{tmg}₃) at the phosphonium center. Determination of their TEP values reveals a remarkable low substituent parameter of χ = –18.5 cm^–1 for the NP(tmg)₃ group. In addition, we prepared the corresponding gold(I) complexes and determined their solid-state structures using single-crystal X-ray diffraction studies to analyze the steric profile of the new phosphine ligands.     

SQSQh: 1H‐detected SQ–SQ experiment for determination of signed silicon–carbon coupling constants

A new variant of SQ–SQ pulse sequence (SQSQh) for relative sign determination and detection of small silicon–carbon couplings over more than one bond is presented. In the SQSQh sequence, proton detection replaces carbon detection used in the original SQ–SQ pulse sequence (SQSQc). The theoretical gain in sensitivity was experimentally tested on two samples (trimethylsiloxyethane, 1, and 1,2,4‐tris(trimethylsiloxy)benzene, 2), the experimentally found gain provided by the SQSQh over the SQSQc method varied between 6 and 8. The method can be applied to linear spin systems, i.e. to systems where the silicon is coupled to the carbon in question and to any hydrogen not necessarily bonded to the carbon. Copyright © 2010 John Wiley & Sons, Ltd.     

Acyl- und Alkylidenphosphane. XII [1]. Synthese und Eigenschaften des 2,2-Dimethylpropionylphosphans und einiger Derivate

Acyl and alkylidene phosphines. XII. Syntheses and properties of 2,2-dimethylpropionylphosphine and of some derivatives At ?25°C bis(trimethylsilyl)phosphine 1b and 2,2-dimethylpropionyl chloride form (2,2-dimethylpropionyl)trimethylsilylphosphine 2b . As this compound is thermally more stable than similar acyltrimethylsilylphosphines, it might be treated at ?55°C with methyllithium to form the correspondig lithium phosphide 2d ; after the addition of chlorotrimethylsilane [2,2-dimethyl-1-(trimethylsiloxy)propylidene]-trimethylsilylphosphine 3c is obtained. At +20°C 2b rearranges to the E and Z isomer of [2,2-dimethyl-1-(trimethylsiloxy)propylidene]phosphine 3b . The NMR data of E- 3b and Z- 3b differ mostly in the coupling constants. Kept in the diffuse daylight for several days 3b dimerizes to form 2,4-di(tert.butyl)-2,4-bis(trimethylsiloxy)-1,3-diphosphetane 10 . In solution 10 is unstable and decomposes again to a mixture of the E und Z isomer of 3b . Reacting 3b or 3c with alcoholes all trimethylsilyl groups are replaced by hydrogen atoms and unstable 2,2-dimethylpropionylphosphane 4b is formed. Lithium(2,2-dimethylpropionyl)phosphide 4d , synthesized at ?60°C from 4b and methyllithium, crystallizes with one molecule 1,2-dimethoxyethane per formula unit and is dimeric in benzene. As shown by the NMR data 4d has the structure of an alkylidene-phosphine with the lithium atom bound to oxygen. At ?50°C 4d and chlorotrimethylsilane react to form 3b .     

Acyl- und Alkylidenphosphane. XVII. Triacetylphosphan aus Tris(trimethylsilyl)phosphan

Acyl- and Alkylidenephosphines. XVII. Triacetylphosphine from Tris(trimethylsilyl)-phosphine Tris(trimethylsilyl)phosphine reacts at 0°C with excess acetyl chloride in cyclopentane to form chlorotrimethylsilane and triacetylphosphine 3a . In contrast to the corresponding 2,2-dimethylpropionyl derivate (Z)- 5b the intermediate compounds (E)- and (Z)-acetyl-[1-(trimethylsiloxy)ethylidene]phosphine 5a are thermally instable. They could not be isolated in a pure state, but were characterized by NMR spectroscopic methods only. The isomers differ scarcely in their chemical shift values, but very much in their coupling constants. If the solution is cooled unsufficiently diacetyl-[1-(trimethylsiloxy)vinyl]phosphine 7 and the keto-enol-tautomers of diacetylphosphine K-/E- 2a are formed to a greater extend. ¹H-{³¹P}-INDOR experiments allowed the correlation between ¹H- and ³¹P-NMR resonances and hence the correct identification of the phosphines formed. Within days the compounds 2a and 7 also react at +20°C with an excess of acyl halide to give triacetylphosphine 3a .     

First 1-phospha-1,3-dienes unsubstituted in the carbon chain by pyrolysis of diallylphosphines: A novel route to the phosphorus—carbon double bond

Allylic phosphine systems were studied as phosphorus–carbon double bond precursors. 1-Phenyl and 1-butyl-1-phospha-1,3-dienes were generated by pyrolysis at 350–460°C of the corresponding diallyl phosphines in a stirred-flow reactor. The unsubstituted phosphadienes generated in this manner dimerized; the formation of [4 + 2] cycloaddition products was confirmed by NMR and mass spectroscopic analysis. ³¹P NMR data of the 1-phospha-1,3-dienes were obtained.     

29Si NMR spectra of trimethylsilylated cyclic acyloins and ketones. 29Si chemical shifts as a measure of ring size

²⁹Si chemical shifts are reported for nine 1,2-bis(trimethylsiloxy)cycloalkenes and four 1-trimethylsiloxycycloalkenes, (Me₃SiO)_xC_nH_2n–2–x (x=1, 2). For cycloalkene derivatives with n?8 the silicon shift exhibits a strong dependence on the ring size, although the silicon is exocyclic and is separated by two bonds from the olefinic carbon atom. The dependence can be exploited for ring size determination of cyclic ketones after trimethylsilylation.     

Steric effects in 29Si and 13C n.m.r. spectra of trimethylsiloxy-substituted benzenes

²⁹Si and ¹³C NMR spectra of trimethylphenoxysilane and three bis(trimethylsiloxy)benzenes have been investigated. Crowding in the ortho derivative leads to a small but observable deshielding of both silicon and carbon nuclei of the trimethylsiloxy group. In comparison to analogous effects observed in trimethylsilyl-substituted benzenes the oxygen link appears to increase the susceptibility of silicon to this steric effect but to decrease that of the methyl carbons. It is suggested that the operative steric interaction might not be that between the terminal methyl groups but involves the oxygen atom.     

Synthesis of New Benzoxaphosphole Derivatives from the Reaction of Dialkylphosphonates and Trisdialkylaminophosphines with 2,6-Bis(benzylidene)cyclohexanones

The reaction of 2,6-bis(benzylidene)cyclohexanones with dialkylphosphonates and tris(dialkylamino)phosphines afforded the new benzoxaphosphole derivatives (5a–5d) and (9a–9f). The biological activity of the newly synthesized compounds was also examined. Possible reaction mechanisms are considered, and the structural assignments are based on analytical and spectroscopic results. The structure of the new benzoxaphosphole 5a was confirmed by a single crystal X-ray determination.     

Ylide‐Functionalized Phosphines: Strong Donor Ligands for Homogeneous Catalysis

Phosphines are important ligands in homogenous catalysis and have been crucial for many advances, such as in cross‐coupling, hydrofunctionalization, or hydrogenation reactions. Herein we report the synthesis and application of a novel class of phosphines bearing ylide substituents. These phosphines are easily accessible via different synthetic routes from commercially available starting materials. Owing to the extra donation from the ylide group to the phosphorus center the ligands are unusually electron‐rich and can thus function as strong electron donors. The donor capacity surpasses that of commonly used phosphines and carbenes and can easily be tuned by changing the substitution pattern at the ylidic carbon atom. The huge potential of ylide‐functionalized phosphines in catalysis is demonstrated by their use in gold catalysis. Excellent performance at low catalyst loadings under mild reaction conditions is thus seen in different types of transformations.     

RhI‐Catalyzed PIII‐Directed C−H Bond Alkylation: Design of Multifunctional Phosphines for Carboxylation of Aryl Bromides with Carbon Dioxide

We report the C?H alkylation of biarylphosphines at the ortho′ position(s) with alkenes by using rhodium(I) catalysis, which provides straightforward access to a large library of multifunctionalized phosphines. Some of these modified ligands outperformed commercially available phosphines in the Pd‐catalyzed carboxylation of aryl bromides with carbon dioxide in the presence of a photoredox catalyst.     

Synthesis of Mixed Arylalkyl Tertiary Phosphines via the Grignard Approach

Trialkyl and triaryl phosphines are important classes of ligands in the field of catalysis and materials research. The wide usability of these low-valent phosphines has led to the design and development of new synthesis routes for a variety of phosphines. In the present work, we report the synthesis and characterization of some mixed arylalkyl tertiary phosphines via the Grignard approach. A new asymmetric phosphine is characterized extensively by multi-spectroscopic techniques. IR and UV–Vis spectra of some selected compounds are also compared and discussed. Density functional theory (DFT)-calculated results support the formation of the new compounds.     

Copolymerization of propylene oxide and carbon disulfide with diethylzinc–electron-donor catalyst

Copolymerization of propylene oxide with carbon disulfide was studied by using a catalyst consisting of diethylzinc (ZnEt₂) and various electron donors. Tertiary amines, tertiary phosphines, and hexamethylphosphoric triamide were the effective donors for the copolymerization, but ZnEt₂–water, alcohol, and primary or secondary amines having high activities for the homopolymerization of propylene oxide were not effective for the copolymerization of propylene oxide and carbon disulfide. The copolymers obtained were of low molecular weight and had a monomer unit ratio (CS₂/PO) of 0.5–0.7. In addition, a considerable amount of 1,3-oxathioran-4-methyl-2-thion was isolated as a by-product.     

In Situ Generation of Ruthenium Carbonyl Phosphine Complexes as a Versatile Method for the Development of Enantioselective C−O Bond Arylation

We report here a method for in situ generation of various ruthenium carbonyl phosphine catalysts for arylation via cleavage of inert aromatic carbon–oxygen bonds. The use of catalyst systems consisting of [RuCl₂(CO)(p-cymene)], CsF, styrene, and phosphines enabled facile screening of phosphine ligands. Asymmetric C–O arylation was also achieved for atropo-enantioselective biaryl synthesis using a chiral monodentate phosphine ligand.     

Methylsiloxane Oligomers with Oxyalkyl Fragments in the Side Chain

The dehydrocondensation reactions of α,ω–bis(trimethylsiloxy)methylhydridesiloxane with saturated primary n-alcohols in the presence of anhydrous powder-like potassium hydroxide or platinum on the carbon (Pt/C-5%) at 1:30 ratio of initial compounds, at various temperature (40–60 °C) was carried out, and methylsiloxane oligomers with n-alkyloxy substituted groups in the side chain were obtained. It was shown that completely dehydrocondensation of all active Si H groups do not take place. Dehydrocondensation reaction order, activation energy and rate constants were found. The synthesized oligomers were characterized by ¹H, ¹³C NMR, Cosy and FTIR spectra data. Gel-permeation chromatography, differential scanning calorimetric, thermogravimetric and wide-angle X-ray investigations of synthesized oligomers were carried out.     

Enantioselective synthesis of spirocyclic cyclopentenes: asymmetric [3+2] annulation of 2-arylideneindane-1,3-diones with MBH carbonates derivatives catalyzed by multifunctional thiourea–phosphines

The [3+2] annulation reactions of 2-arylideneindane-1,3-diones with Morita–Baylis–Hillman (MBH) carbonates proceeded smoothly in the presence of multifunctional thiourea–phosphines to produce the corresponding quaternary carbon centered spirocyclic cyclopentenes in moderate yields, with high diastereoselectivities and enantioselectivities under mild conditions. The plausible reaction has been also discussed on the basis of previous literature.     

SYNTHESIS AND 31P NMR STUDY OF DIHYDRONAPHTHALENO- AND NAPHTHALENO-DERIVATIVES OF PHOSPHOLENE OXIDES

Abstract

Naphthalenophospholenes (dihydrobenzo[e] and [g]-phosphindoles) represent a new heterocyclic type that forms in 65-80% yield on dehydrogenation with Pd–C of the corresponding dihydronaphthaleno derivatives. The latter are readily accessible from hydrolysis of cycloadducts of certain vinyldihydronaphthalenes with P(III) chlorides. Six members of this family, as well as some derived phosphines and phosphonium salts, have been prepared. A phenanthrenophospholene oxide, also a new system, was synthesized similarly. ³¹P nmr chemical shifts were appreciably (5-10 ppm) upfield in aromatized phosphine oxides relative to the dihydro forms. It is proposed that this shift results more from a change in the steric environment about phosphorus, as the carbon beta- to it in the adjacent ring changes from tetrahedral to planar geometry, rather than from a change in the degree of interaction of a carbon p-orbital with phosphorus. The upfield shift was even more pronounced (13 ppm) for a phosphine. Most of the new compounds were characterized also by ¹³C nmr spectroscopy.     

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.     

Flash vacuum pyrolysis of 1-methoxy-1,3-bis(trimethylsiloxy)-1,3-dienes: synthesis of α-allenic acids.

Flash vacuum pyrolysis at 680–700°C of 2- and 4- substituted 1-methoxy-1,3-bis (trimethylsiloxy)-1,3-butadienes yields α-allenic silyl esters which, upon hydrolysis, provide a direct route to α-allenic acids with good overall yield.