Addition Of Phosphine Research Articles

Hydrophosphination of Unactivated Alkenes and Alkynes Using Iron(II): Catalysis and Mechanistic Insight

The catalytic addition of phosphines to alkenes and alkynes is a very attractive process that offers access to phosphines in a 100% atom-economic reaction using readily available and inexpensive materials. The products are potentially useful ligands and organocatalysts. Herein, we report the first example of intramolecular hydrophosphination of a series of nonactivated phosphinoalkenes and phosphinoalkynes with a simple iron β-diketiminate complex. Kinetic studies suggest that this transformation is first-order with respect to both the phosphine and the catalyst. A mechanistic interpretation of the iron-catalyzed hydrophosphination is presented, supported by the experimental evidence collected.

ChemInform Abstract: One‐Pot Synthesis of Tetraphene and Construction of Expanded Conjugated Aromatics.

AbstractThe method comprises a multi‐step sequence consisting of a propargyl‐allenyl isomerization, phosphine addition, Wittig and Diels‐Alder reactions in an operationally simple one‐pot manner.

Noncatalytic addition of secondary phosphines to vinyl selenides

Noncatalytic addition of secondary phosphines to vinyl selenides

Mechanistic insights into phospha–Michael reaction of tertiary phosphines with electron-deficient alkenes

ABSTRACTThe Michael-type addition of tertiary phosphines to electron-deficient alkenes is a convenient way to generate reactive phosphonium zwitterionic intermediates, which participate readily in many synthetically useful transformations. Although the synthetic usefulness of the phospha–Michael addition has been largely demonstrated, knowledge on the kinetics and mechanism of this reaction is sparse. This paper briefly summarizes the contribution of our research group to find out the mechanism of this reaction.

Engaging Allene‐Derived Zwitterions in an Unprecedented Mode of Asymmetric [3+2]‐Annulation Reaction

AbstractCatalytic addition of chiral phosphine, that is, (R)‐ or (S)‐SITCP, to an α‐substituted allene ester generated a zwitterionic dipole. Under optimized reaction conditions, this dipole could engage isatine‐derived N‐Boc‐ketimines in a novel mode of [3+2] annulation reaction. Pyrrolinyl spirooxindoles are thus afforded in high yields and with excellent enantioselectivities. The unprecedented annulation reaction successfully facilitated the construction of sp3‐rich and highly substituted 3,2′‐pyrrolidinyl spirooxindoles supporting many chiral centers.

Engaging Allene-Derived Zwitterions in an Unprecedented Mode of Asymmetric [3+2]-Annulation Reaction.

Catalytic addition of chiral phosphine, that is, (R)- or (S)-SITCP, to an α-substituted allene ester generated a zwitterionic dipole. Under optimized reaction conditions, this dipole could engage isatine-derived N-Boc-ketimines in a novel mode of [3+2] annulation reaction. Pyrrolinyl spirooxindoles are thus afforded in high yields and with excellent enantioselectivities. The unprecedented annulation reaction successfully facilitated the construction of sp(3) -rich and highly substituted 3,2'-pyrrolidinyl spirooxindoles supporting many chiral centers.

One-Pot Synthesis of Tetraphene and Construction of Expanded Conjugated Aromatics.

Acene derivatives as a class of polycyclic aromatic hydrocarbons have attracted considerable interest because of their outstanding semiconductor properties. We developed a one-pot synthesis for fully conjugated tetraphene via a sequence of propargyl-allenyl isomerization, phosphine addition, intramolecular Wittig reactions, and Diels-Alder cyclization reactions. The derivative-conjugated aromatic compounds including carbazole or triphenylamine have been constructed via Pd-catalyzed coupling reaction with dibromotetraphene. These compounds show superior photophysical and electrochemical properties, which make them possible candidates for optoelectronic conjugated materials.

Palladium-catalyzed enantioselective hydrophosphination of enones for the synthesis of chiral P,N-compounds

We developed a method that involved an asymmetric conjugate addition of secondary phosphines to α,β-unsaturated enones bearing β-2-pyridyl substituents catalyzed by a PCP pincer–Pd complex. The technique was established for the preparation of chiral P,N-compounds in excellent enantioselectivity (up to 99% ee) under mild conditions.

A Tertiary Carbon–Iron Bond as an FeICl Synthon and the Reductive Alkylation of Diphosphine-Supported Iron(II) Chloride Complexes to Low-Valent Iron

Ligand-induced reduction of ferrous alkyl complexes via homolytic cleavage of the alkyl fragment was explored with simple chelating diphosphines. The reactivities of the sodium salts of diphenylmethane, phenyl(trimethylsilyl)methane, or diphenyl(trimethylsilyl)methane were explored in their reactivity with (py)4FeCl2. A series of monoalkylated salts of the type (py)2FeRCl were prepared and characterized from the addition of 1 equiv of the corresponding alkyl sodium species. These complexes are isostructural and have similar magnetic properties. The double alkylation of (py)4FeCl2 resulted in the formation of tetrahedral high-spin iron complexes with the sodium salts of diphenylmethane and phenyl(trimethylsilyl)methane that readily decomposed. A bis(cyclohexadienyl) sandwich complex was formed with the addition of 2 equiv of the tertiary alkyl species sodium diphenyl(trimethylsilyl)methane. The addition of chelating phosphines to (py)2FeRCl resulted in the overall transfer of Fe(I) chloride concurrent with...

Zirconium-Catalyzed Imine Hydrogenation via a Frustrated Lewis Pair Mechanism

Zirconium-based frustrated Lewis pairs (FLPs) are active imine hydrogenation catalysts under mild conditions. Complexes of the type [CpR2ZrOMes][B(C6F5)4] utilize the imine substrate itself as the Lewis base component of the FLP. Catalyst performance is a function of ligand structure; in general more bulky, more electron rich cyclopentadienyl derivatives give the best results. However, Cp* derivatives are not catalytically active, being stable after initial heterolytic cleavage of H2; this allows experimental verification of the competence of the zirconocene–imine pair in FLP-type heterolytic H2 cleavage. Enamines and protected nitriles are also hydrogenated if an additional internal phosphine base is used.

Reagent-Controlled Tandem Reactions of Vinyl Epoxides: Access to Functionalized γ-Butenolides.

A new approach to functionalized γ-butenolides based on reagent-controlled tandem reaction sequences of Morita-Baylis-Hillman-type vinyl epoxides is described. The nucleophilic addition of a tertiary phosphine to the electron-deficient alkene led to ring-opening of the epoxide followed by lactonization to produce phosphonium ylides, which could undergo Wittig olefination with aryl trifluoromethyl ketones and aryl aldehydes to give 3-alkenyl γ-butenolides in moderate to good yields and high E/Z selectivity. Tertiary amine promoted the Michael-type addition of carbon- and nitrogen-based nucleophiles to the vinyl epoxides followed by lactonization to provide diverse 3-substituted γ-butenolides.

Factors That Control C-C Cleavage versus C-H Bond Hydroxylation in Copper-Catalyzed Oxidations of Ketones with O2.

The Cu-catalyzed oxidation of ketones with O2 has recently been extensively utilized to cleave the α-C-C bond. This report examines the selective aerobic hydroxylation of tertiary α-C-H bonds in ketones without C-C cleavage. We set out to understand the underlying mechanisms of these two possible reactivity modes. Using experimental, in situ IR spectroscopic, and computational studies, we investigated several mechanisms. Our data suggest that both C-C cleavage and C-H hydroxylation pathways proceed via a common key intermediate, i.e., an α-peroxo ketone. The fate of this peroxide dictates the ultimate product selectivity. Specifically, we uncovered the role of hppH [=1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine] to act not only as a base in the transformation but also as a reductant of the peroxide to the corresponding α-hydroxy ketone. This reduction may also be accomplished through exogenous phosphine additives, therefore allowing the tuning of reduction efficiency toward higher driving forces, if required (e.g., for more-activated substrates). The likely competitive pathway is the cleavage of peroxide to the α-oxy radical (likely catalyzed by Cu), which is computationally predicted to spontaneously trigger C-C bond cleavage. Increasing the susceptibility of this deperoxidation step via (i) the removal of reductant (use of different base, e.g., DBU) or the modulation of (ii) the substitution pattern toward greater activation (substrate control) and (iii) the nature of Cu catalyst (counterion and solvent dependence) will favor the C-C cleavage product.

Highly Enantioselective Pd-Catalyzed Synthesis of P-Stereogenic Supramolecular Phosphines, Self-Assembly, and Implication

Metal-catalyzed asymmetric addition of a secondary phosphine to an aryl halide is one of the most efficient and reliable approaches for the construction of enantiopure carbon–phosphorus bonds. An isolated Pd(II) complex (5) catalyzes the carbon–phosphorus coupling reaction between tolylphenylphosphine (1a) and 3-iodophenylurea (2b), which proceeds with an unprecedented enantiomeric excess (ee) of 97%. The generality of the strategy has been demonstrated by preparing a small library of a new class of P-stereogenic phosphines with an in-built hydrogen bonding motif for the first time. The P-stereogenic phosphines self-assemble on a metal template via deliberately installed hydrogen-bonding motifs and mimic the bidentate ligand coordination. Interestingly, when it was employed in asymmetric hydrogenation, the supramolecular phosphine {1-(3-(phenyl(o-tolyl)phosphanyl)phenyl)urea} (6b) produced the corresponding hydrogenated product with the highest enantiomeric excess of 99% along with excellent conversion, d...

Capable Cross-links: Polymersomes Reinforced with Catalytically Active Metal–Ligand Bonds

Polymersomes, hollow spherical nano-to-microscale polymer assemblies, have increasingly become important constructs in the development of biomimetic materials that expand the library of functional and robust analogs to lipid-based vesicles. As compared to liposomes, polymersomes possess superior physical properties and the nearly unlimited potential for synthetic fine-tuning. Herein we improve on the physical properties of these polymer vesicles by introducing platinum-based metal–ligand cross-links into the hydrophobic core, which gave the vesicles demonstrated resistance to destabilization by surfactants over un-cross-linked polymersomes. The formation of cross-links was capable of being selectively reversed by the addition of phosphines. In addition, the Pt(0) cross-links retained their catalytic activity for the hydrosilylation of alkenes.

Synthesis of Poly(3-hexylthiophene), Poly(3-hexylselenophene), and Poly(3-hexylselenophene-alt-3-hexylthiophene) by Direct C–H Arylation Polymerization via N-Heterocyclic Carbene Palladium Catalysts

Direct C–H arylation polymerization of 2-bromo-3-hexylselenophene and 2-bromo-3-hexylthiophene catalyzed by N-heterocyclic carbene (NHC) palladium-based and Pd(OAc)2-based systems has been carried out and investigated. Under the optimized conditions, high molecular weight poly(3-hexylthiohphene) (P3HT) (Mn = 26.9K g/mol) with high head-to-tail regioregularity (94%) can be obtained by using [1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene]chloro[3-phenylallyl]palladium(II) (Pd-IPr) as the catalyst. Pd-IPr exhibits a wide range of working temperatures from 70 to 140 °C and good catalytic reproducibility as a result of its high thermal stability. It was found that the presence of additional phosphine ligand, such as tris(o-methoxyphenyl)phosphine, can increase the polymerization efficiency in the Pd(OAc)2 system. This improvement is linked to the stability enhancement for the active species during the course of catalysis. For the first time, poly(3-hexylselenophene) (P3HS) was also obtained by direct-arylation polymerization in this research. The modest molecular weight is attributed to the poor solubility of P3HS in the used solvents. Density-functional-theory (DFT) calculations were performed to investigate the postulated reaction mechanisms for our catalytic systems. The experimental observations can thus be elucidated by the help of computation. Most significantly, a main-chain alternating and side-chain regioregular (RR = 94%) poly(3-hexylselenophene-alt-3-hexylthiophene) (Alt-P3HST) with high molecular weight (20.0K g/mol) was successfully synthesized via the Pd-IPr-catalyzed direct-arylation polymerization of a well-designed 2-bromo-3-hexyl-5-(3-hexylselenophen-2-yl)thiophene monomer. The molecular properties of the Alt-P3HST were characterized to compare with those of P3HT and P3HS. This research demonstrates in-depth investigation on the NHC-based palladium catalysts for the synthesis of conjugated polymers via direct C–H bond polymerization.

Multicomponent Reactions of Phosphines, Enynedioates and Cinnamaldimines Give γ‐Lactams with a 1,3,5‐Hexatriene Moiety for Facile 6π Electrocyclization: Access to Oxindoles, Isatins and Isoxazolinones

AbstractMulticomponent reactions of phosphines, enynedioates and cinnamaldimines generated 3‐phosphorus ylide γ‐lactams having a 1,3,5‐hexatriene moiety with low activation energy barrier for 6π electrocyclization, through initial formation of 1,3‐dipoles from the α(δ′)‐Michael addition of phosphines to enynedioates. The reactive 1,3‐dipoles underwent addition to cinnamaldimines, lactamization, 6π electrocyclization and oxidation to give 3‐phosphorus ylide oxindoles as platform molecules toward isatins and isoxazolinones. The key step, 6π electrocyclization, was further examined by a kinetic and a computational study.magnified image

ChemInform Abstract: Multicomponent Reactions of Phosphines, Diynedioates, and Aryl Aldehydes Generated Furans Appending Reactive Phosphorus Ylides Through Cumulated Trienoates as Key Intermediates: A Phosphine α‐Addition‐δ‐Evolvement of an Anion Pathway.

AbstractThe title synthesis of furans involves an initial novel α(δ′)‐addition of phosphines to diynedioates followed by addition reaction of the resulting trienoates to aldehydes and subsequent 5‐endo‐dig cyclization.

ChemInform Abstract: Biphenyl‐Derived Phosphepines as Chiral Nucleophilic Catalysts: Enantioselective [4 + 1] Annulations to Form Functionalized Cyclopentenes.

Because of the frequent occurrence of cyclopentane subunits in bioactive compounds, the development of efficient catalytic asymmetric methods for their synthesis is an important objective. Introduced herein is a new family of chiral nucleophilic catalysts, biphenyl-derived phosphepines, and we apply them to an enantioselective variant of a useful [4+1] annulation. A range of one-carbon coupling partners can be employed, thereby generating cyclopentenes which bear a fully substituted stereocenter [either all-carbon or heteroatom-substituted (sulfur and phosphorus)]. Stereocenters at the other four positions of the cyclopentane ring can also be introduced with good stereoselectivity. An initial mechanistic study indicates that phosphine addition to the electrophilic four-carbon coupling partner is not the turnover-limiting step of the catalytic cycle.

Phosphine addition to the σ,π–thienyl complex [Fe2(CO)6(μ-Th)(μ-PTh2)] (Th = C4H3S): Carbonyl substitution and migratory carbonyl insertion to give the thienyl–acyl complexes [Fe2(CO)4(diphosphine)(μ-O[dbnd]C-Th)(μ-PTh2)

The reactivity of the σ,π–thienyl complex [Fe2(CO)6(μ-Th)(μ-PTh2)] (1) towards a range of phosphines has been studied. With PR3 (R=Ph, Th) carbonyl substitution affords [Fe2(CO)5(PR3)(μ-Th)(μ-PTh2)] (2a–b) as the major product, with smaller amounts of the thienyl–acyl complexes [Fe2(CO)5(PR3)(μ-OC-Th)(μ-PTh2)] (3a–b) resulting from a migratory carbonyl insertion into the thienyl ligand. With diphosphines, thienyl–acyl complexes are the major products in all cases. With dppm, [Fe2(CO)4(μ-dppm)(μ-OC-Th)(μ-PTh2)] (4) results in which the diphosphine bridges the iron–iron bond, while with other diphosphines the chelate complexes [Fe2(CO)4(κ2-diphosphine)(μ-OC-Th)(μ-PTh2)] (5–9) are isolated, as established through crystallographic studies on [Fe2(CO)4(κ2-dppe)(μ-OC-Th)(μ-PTh2)] (5) and [Fe2(CO)4(κ2-dppb)(μ-OC-Th)(μ-PTh2)] (9), both of which show that the diphosphine binds selectively to the oxygen-bound metal centre with phosphorus atoms lying trans to the metal–metal bond and μ-PTh2 bridge. With 1,2-bis(diphenylphosphino)benzene (dppb), [Fe2(CO)5{μ,κ2-C6H4PPh(C6H4)PPh2}(μ-PTh2)] (10) is isolated in low yields and results from cyclometalation of a phenyl ring and putative elimination of thiophene. In a separate experiment, it has been shown that heating 9 results in the slow formation of 10.

Atom-economic synthesis of highly branched functional ‘tripod-like’ triphosphine sulfides

The tertiary polyfunctional triphosphine sulfides with amino and (or) ether groups have been synthesized in excellent yields by the exhaustive regioselective (in anti-Markovnikov manner) addition of secondary phosphines sulfides to trivinyl ethers of aminotriols and triols under free-radical conditions (UV-irradiation, 1.5–5 h).