Tricoordinate Phosphorus Research Articles

Metal-Ligand Role Reversal: Hydride-Transfer Catalysis by a Functional Phosphorus Ligand with a Spectator Metal.

Hydride transfer catalysis is shown to be enabled by the nonspectator reactivity of a transition metal-bound low-symmetry tricoordinate phosphorus ligand. Complex 1·[Ru]+, comprising a nontrigonal phosphorus chelate (1, P(N(o-N(2-pyridyl)C6H4)2) and an inert metal fragment ([Ru] = (Me5C5)Ru), reacts with NaBH4 to give a metallohydridophosphorane (1H·[Ru]) by P-H bond formation. Complex 1H·[Ru] is revealed to be a potent hydride donor (ΔG°H-,exp < 41 kcal/mol, ΔG°H-,calc = 38 ± 2 kcal/mol in MeCN). Taken together, the reactivity of the 1·[Ru]+/1H·[Ru] pair comprises a catalytic couple, enabling catalytic hydrodechlorination in which phosphorus is the sole reactive site of hydride transfer.

Two-Site O-H Addition to an Iridium Complex Featuring a Nonspectator Tricoordinate Phosphorus Ligand.

The synthesis and reactivity of an ambiphilic iridium complex IrCl(PPh3)(L1) (1; L1 = P(N(o-N(2-pyridyl)C6H4)2)) featuring a chelating nontrigonal phosphorus triamide ligand is reported. The tandem Lewis basic Ir and Lewis acidic P of 1 achieve a two-site oxidative addition of phenol giving the iridaphenoxyphosphorane species IrHCl(PPh3)(L1OPh) (3'). In contrast, reactions of 1 with benzenethiol and benzeneselenol do not engage L1 and instead proceed via metal-centered oxidative addition of the chalcogen-hydrogen bond. These findings establish metal-ligand cooperation involving nonspectator reactivity of tricoordinate phosphorus ligands.

Enthalpy-Controlled Insertion of a "Nonspectator" Tricoordinate Phosphorus Ligand into Group 10 Transition Metal-Carbon Bonds.

Insertion of a tricoordinate phosphorus ligand into late metal-carbon bonds is reported. Metalation of a P^P-chelating ligand (L1), composed of a nontrigonal phosphorous (i.e., P(III)) triamide moiety, P(N(o-N(Ar)C6H4)2, tethered by a phenylene linker to a -PiPr2 anchor, with group 10 complexes L2M(Me)Cl (M = Ni, Pd) results in insertion of the nontrigonal phosphorus site into the metal-methyl bond. The stable methylmetallophosphorane compounds thus formed are characterized spectroscopically and crystallographically. Metalation of L1 with (cod)PtII(Me)(Cl) does not lead to a metallophosphorane but rather to the standard bisphosphine chelate (κ2-L1)Pt(Me)(Cl). These divergent reactivities within group 10 are rationalized by reference to periodic variation in M-C bond enthalpies.

Addition reactions of a phosphorus triamide to nitrosoarenes and acylpyridines

Tricoordinate phosphorus compounds react with a wide variety of double bonds through addition reactions. The dipolar and cyclic products formed are important intermediates in organophosphorus chemistry. We investigated the reactivity between phosphorus triamide 1 and nitrosoarenes and 2-acylpyridines. For sterically congested substrates, the formation of σ5,λ5-phosphorus products is observed. DFT calculations indicate this product is formed through a concerted [4 + 1] mechanism. For less sterically congested substrates, products are observed arising from cleavage of the N = O or C = O bond with formation of a terminal P = O bond and aryl nitrene or carbene migration into a P–N bond of the phosphorus triamide core. DFT calculations are consistent with an initial [2 + 1] addition to phosphorus followed by formal carbene/nitrene migration in these cases.

Lewis Base Free Oxophosphonium Ions: Tunable, Trigonal‐Planar Lewis Acids

Oxophosphonium ions (R2 P=O)+ are fascinating chemical intermediates related to the well-known acylium cations (RC=O)+ , and comprise a tricoordinate phosphorus(V) center with a phosphorus-oxygen double bond. Here, we report the synthesis of two oxophosphonium ions stabilized by bulky imidazolin-2-imine and imidazolin-2-olefin substituents attached to phosphorus. The novel species were characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis, and the bonding situation was probed by DFT calculations. Determination of the acceptor number and the fluoride ion affinity revealed that the choice of the substituents has a strong influence on the electrophilicity of the phosphorus center. Additionally, the formation of Lewis base adducts with pyridine derivatives and the reactivity with isopropyl alcohol was explored.

Biphilic Organophosphorus-Catalyzed Intramolecular Csp2-H Amination: Evidence for a Nitrenoid in Catalytic Cadogan Cyclizations.

A small-ring phosphacycloalkane (1,2,2,3,4,4-hexamethylphosphetane, 3) catalyzes intramolecular C-N bond forming heterocyclization of o-nitrobiaryl and -styrenyl derivatives in the presence of a hydrosilane terminal reductant. The method provides scalable access to diverse carbazole and indole compounds under operationally trivial homogeneous organocatalytic conditions, as demonstrated by 17 examples conducted on 1 g scale. In situ NMR reaction monitoring studies support a mechanism involving catalytic PIII/PV═O cycling, where tricoordinate phosphorus compound 3 represents the catalytic resting state. For the catalytic conversion of o-nitrobiphenyl to carbazole, the kinetic reaction order was determined for phosphetane catalyst 3 (first order), substrate (first order), and phenylsilane (zeroth order). For differentially 5-substituted 2-nitrobiphenyls, the transformation is accelerated by electron-withdrawing substituents (Hammett factor ρ = +1.5), consistent with the accrual of negative charge on the nitro substrate in the rate-determining step. DFT modeling of the turnover-limiting deoxygenation event implicates a rate-determining (3 + 1) cheletropic addition between the phosphetane catalyst 3 and 2-nitrobiphenyl substrate to form an unobserved pentacoordinate spiro-bicyclic dioxazaphosphetane, which decomposes via (2 + 2) cycloreversion giving 1 equiv of phosphetane P-oxide 3·[O] and 2-nitrosobiphenyl. Experimental and computational investigations into the C-N bond forming event suggest the involvement of an oxazaphosphirane (2 + 1) adduct between 3 and 2-nitrosobiphenyl, which evolves through loss of phosphetane P-oxide 3·[O] to give the observed carbazole product via C-H insertion in a nitrene-like fashion.

Preparation and crystal structure of 1,1-tetramethylethylenedioxy-3,4-diphenyl-6-trichloromethyl-2,5,7,1-trioxaphosphabicyclo[2.2.11,4]heptane and 2-(1-hydroxy-2,2,2-trichloroethoxy)-4,4,5,5-tetramethyl- 2-oxo-1,3,2-dioxaphospholane

The state of the art of chloral applications in the chemistry of tricoordinate phosphorus derivatives has been analyzed. The highly stereoselective reaction of 4,4,5,5-tetramethyl-2-(2-oxo-1,2-diphenylethoxy)-1,3,2-dioxaphospholane with chloral has been shown to afford a caged phosphorane with the phosphorus–carbon bond, 1,1-tetramethylethylenedioxy-3,4-diphenyl-6-trichloromethyl-2,5,7,1-trioxaphosphabicyclo- [2.2.11,4]heptane. Structure of the phosphorane and its hydrolysis product, 2-(1-hydroxy-2,2,2-trichloroethoxy)- 4,4,5,5-tetramethyl-2-oxo-1,3,2-dioxaphospholane, has been elucidated by X-ray diffraction analysis.

P(NMe2)3-Mediated Umpolung Alkylation and Nonylidic Olefination of α-Keto Esters.

A commercial phosphorus-based reagent (P(NMe2)3) mediates umpolung alkylation of methyl aroylformates with benzylic and allylic bromides, leading to either Barbier-type addition or ylide-free olefination products upon workup. The reaction sequence is initiated by a two-electron redox addition of the tricoordinate phosphorus reagent with an α-keto ester compound (Kukhtin-Ramirez addition). A mechanistic rationale is offered for the chemoselectivity upon which the success of this nonmetal mediated C-C bond forming strategy is based.

Reversible intermolecular E-H oxidative addition to a geometrically deformed and structurally dynamic phosphorous triamide.

The synthesis and reactivity of geometrically constrained tricoordinate phosphorus (σ(3)-P) compounds supported by tridentate triamide chelates (N[o-NR-C6H4]2(3-); R = Me or (i)Pr) are reported. Studies indicate that 2 (P{N[o-NMe-C6H4]2}) adopts a Cs-symmetric structure in the solid state. Variable-temperature NMR studies demonstrate a low-energy inversion at phosphorus in solution (ΔG(‡)(exptl)(298) = 10.7(5) kcal/mol), for which DFT calculations implicate an edge-inversion mechanism via a metastable C2-symmetric intermediate. In terms of reactivity, compound 2 exhibits poor nucleophilicity, but undergoes oxidative addition at ambient temperature of diverse O-H- and N-H-containing compounds (including alcohols, phenols, carboxylic acids, amines, and anilines). The resulting pentacoordinate adducts 2·[H][OR] and 2·[H][NHR] are characterized by multinuclear NMR spectroscopy and X-ray crystallography, and their structures (which span the pseudorotation coordinate between trigonal bipyramidal and square planar) are evaluated in terms of negative hyperconjugation. At elevated temperatures, the oxidative addition is shown to be reversible for volatile alcohols and amines.

ChemInform Abstract: Applications of Tricoordinated Phosphorus Compounds in Organocatalysis

AbstractReview: 142 refs.

ChemInform Abstract: Applications of Tricoordinated Phosphorus Compounds in Homogeneous Catalysis

AbstractReview: 320 refs.

ChemInform Abstract: Reactions of Phosphorus-Containing Compounds with Diazo Compounds and Carbenes

The reactions of various phosphorus-containing systems with diazo-compounds and carbenes are presented for the first time in a general form and a systematic account is given of literature data on the reactivities of phosphorus-containing acids, salts, esters, amides, sulphenamides, phosphorus acid sulphenyl halides, phosphorus halides, and derivatives of mono-, di-, and tri-coordinate phosphorus in reactions with diazo-compounds and carbenes. The differences between the reactivities of diazo-compounds and carbenes in relation to the above groups of organophosphorus compounds are demonstrated. The bibliography includes 244 references.

ChemInform Abstract: Tricoordinate Phosphorus Compounds as Catalysts for the Isomerization of (Z)- to (E)-Azobenzene.

ChemInform Abstract: Tricoordinate Phosphorus Compounds as Catalysts for the Isomerization of (Z)- to (E)-Azobenzene.

Phosphorylation of polyesterpolyoles Boltorn-H20 and -H40 with pyrocatechol chlorophosphite

Hyperbranched aliphatic polyester of the grade Boltorn-H20 were obtained by polycondensation of 2,2bis(hydroxymethyl)propionic acid with polyhydric alcohols [1, 2]. They were phosphorylated with 2,4-bis(3,5-di-tert-butyl-4-hydroxyphenyl)-1,3,2,4-dithiadiphosphethane 2,4-disulfide [3] and 2-(N,N-diethylamido)1,3,2-dioxaphosphorinane [4]. In these reactions insertion products formed of a monomer fragment ArPS2 from 1,3,2,4dithiadiphosphethane-2,4-disulfide into the O–H bonds and substitution products arising from the cleavage of P–Cl bond resulting in the formation of fragments C– O–P(III). The organic compounds with a tricoordinate phosphorus atom are commonly synthesized by reacting hydroxy compounds with acid chlorides of the trivalent phosphorus acids or with chlorophosphines [5]. In extension of the synthetic potential of the modification with phosphorus of hyperbranched polymers we report here on the results of the investigation of the reactions between the polyesterpolyols of the brands Boltorn-H20 (Ia) and -H40 (Ib) with pyrocatechol chlorophosphite (II). In the presence of triethylamine in the medium of chloroform–benzene, 1:1, the reactions proceed under mild conditions at all hydroxy groups affording 2-(O-1,3,2dioxapyrocatecholphosphorinano)polyesters Boltorn-H20 (IIIa) and -H40 (IIIb) whose 31P NMR spectra contain singlet signals in the region characteristic of phosphites [6], at δ 128.4 and 128.1 ppm respectively, unlike the signal of initial chlorophosphite II at δ 173.2 ppm [6]. 2-(O-1,3,2-Dioxapyrocatecholphosphorinano)polyester Boltorn-H20 (IIIa). To a solution of 6.0 g (2.9 mmol) polyesterpolyol Ia and 4.6 g (45.5 mmol) of triethylamine in the mixture of 15 ml of anhydrous benzene and 15 ml of chloroform at 20°C in a flow of dry argon under stirring was added dropwise 8.0 g (45.5 mmol) of chlorophosphite II. The mixture was stirred for 2 h at 20°C and kept for 12 h at 20°C. The precipitate was filtered off and washed with anhydrous benzene. The solvent was evaporated from the filtrate at a reduced pressure (0.5 ppm) for 1 h at 40°C and in a vacuum (0.02 ppm) for 1 h at 40°C. We obtained as a residue 4.1

Aminophosphines: their chemistry and role as ligands and synthons

AbstractIn recent years, research in organophosphorus chemistry has mainly focused in designing newer and better phosphorus ligands for synthesizing novel metal complexes with improved catalytic activities. Aminophosphines [tricoordinate phosphorus(III)–nitrogen systems] are considered as versatile compounds owing to the presence of nitrogen centres which, in principle, can influence additional reactivity features. They are quite sensitive to air and moisture due to the presence of polar PN bond(s). In spite of this, research in aminophosphine chemistry is gaining momentum day‐by‐day and this is due mainly to one reason: their rich behaviour as ligands in metal complex chemistry and subsequently in catalysis. Their role as synthons in inorganic heterocyclic chemistry has also helped produce new types of heterocycles. In this paper, the chemistry of simple acyclic aminophosphines (synthesis, characterization, reactivity and applications) is covered and particular focus is given to their ability to form chalcogenides along with their role played as ligands in coordination chemistry and as synthons in inorganic heterocyclic chemistry. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Studies on the Efficient Generation of PhosphorusCarbon Bonds via a Rearrangement of PIII Esters Catalysed by Trimethylhalosilanes

Halotrimethylsilanes Me(3)SiX (X = Br, I) catalyse rearrangements of tricoordinate phosphorus esters R'R''P-OR into the corresponding phosphoryl systems R'R''P(O)R. This provides a simple and efficient route to a variety of structures containing phosphorus-carbon bonds, under mild conditions and with good yields. The reaction mechanism was investigated in detail by (31)P NMR spectroscopy and independent synthesis of the reaction intermediates. It has been demonstrated that the primary products of this catalytic reaction are halogeno P(III) structures R'R''PX and silyl ethers ROSiMe(3) and that they subsequently react to give the corresponding phosphorus silyl esters-Me(3)SiOPR'R''-and alkyl halides RX. At higher temperatures these intermediates then react to form R'R''P(O)R compounds. This paper also features the surprising observation that when esters Ph(2)POR and halotrimethylsilanes Me(3)SiX (X = Br, I) are used in 2:1 ratio, phosphonium salts Ph(2)R(2)P(+)X(-) and trimethylsilyl diphenylphosphinate--Ph(2)P(O)OSiMe(3)--are formed as the major products. Experimental evidence indicates that the mechanisms of both reactions are fundamentally different from that of the Michaelis-Arbuzov reaction. Me(3)SiCl is not reactive and this paper explains why.

PYRAMIDALITY AND AROMATICITY IN POLYPHOSPHAPHOSPHOLES

Ab initio calculations show that, for the P n( CH )4-n PH with n = 0 - 4, the fully optimized structures have decreasing pyramidality at the tri-coordinated phosphorus atom with n. The interaction between the tri-coordinated phosphorus [Formula: see text] and the carbons–phosphorus π-system [Formula: see text] with different n, the differences of the structure, electron properties and energy among the phospholes indicate that the ring strain and the delocalization of the lone pair electron of tri-coordinated phosphorus should be responsible for this phenomena. Various aromatic criteria such as geometry, magnetism, and energy show that these molecules are aromatic, and their aromaticities increase with the number of phosphorus atoms in the nonplanar pentagons. The electron circulation in the aromatic molecules can promote the delocalization of the lone pair. In contrast to the B3LYP prediction, we draw some similar conclusions, but the planarity and aromaticity of molecules increase largely at the MP2 lever due to the consideration of electron correlation.

Nucleophilic Substitution at C, Si and P: How Solvation Affects the Shape of Reaction Profiles (Eur. J. Org. Chem. 4/2008)

AbstractThe cover picture shows that solvation smoothes reaction profiles not only for SN2 reactions at carbon but also for SN2 reactions at silicon, tricoordinate phosphorus and tetracoordinate phosphorus. Thus, the characteristic double‐well, single‐well and triple‐well structures on the gas‐phase potential energy surfaces (PES) disappear, which results, in all cases, in a unimodal reaction profile in solution. Details are discussed in the article by M. A. van Bochove and F. M. Bickelhaupt on p. 649 ff. We thank Dr. Marcello Luppi for the design of the cover picture.

Nucleophilic Substitution at C, Si and P: How Solvation Affects the Shape of Reaction Profiles

AbstractWe have studied how solvation affects the shape of potential energy surfaces (PES) of archetypal nucleophilic substitution reactions at carbon (SN2@C), silicon (SN2@Si) and phosphorus (SN2@P), using the generalized gradient approximation (GGA) of density functional theory (DFT) at OLYP/TZ2P. Our model systems cover nucleophilic substitution, in water and in the gas phase, at carbon in X– + CH3Y (SN2@C), at silicon in X– + SiH3Y (SN2@Si), at tricoordinate phosphorus in X– + PR2Y (SN2@P3), and at tetracoordinate phosphorus in X– + POR2Y (SN2@P4) with substituents R = H, F, Cl, CH3, OCH3. In the gas phase, particular types of SN2 reactions are characterized by different shapes of reaction profiles, such assingle‐, double‐ and triple‐well PESs. The main effect of solvation is to turn the PESs of the SN2@C but also of SN2@Si and SN2@P into unimodal reaction profiles which lead from the reactants via one single barrier to the products. The results are discussed in terms of differential solvation of reactants and transition states. We also address the question how the relative heights of reaction barriers are affected by solvation. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2008)

Nucleophilic Substitution at Phosphorus Centers (SN2@P)

We have studied the characteristics of archetypal model systems for bimolecular nucleophilic substitution at phosphorus (SN2@P) and, for comparison, at carbon (SN2@C) and silicon (SN2@Si) centers. In our studies, we applied the generalized gradient approximation (GGA) of density functional theory (DFT) at the OLYP/TZ2P level. Our model systems cover nucleophilic substitution at carbon in X(-)+CH3Y (SN2@C), at silicon in X(-)+SiH3Y (SN2@Si), at tricoordinate phosphorus in X(-)+PH2Y (SN2@P3), and at tetracoordinate phosphorus in X(-)+POH2Y (SN2@P4). The main feature of going from SN2@C to SN2@P is the loss of the characteristic double-well potential energy surface (PES) involving a transition state [X--CH3--Y]- and the occurrence of a single-well PES with a stable transition complex, namely, [X--PH2--Y]- or [X--POH2--Y](-). The differences between SN2@P3 and SN2@P4 are relatively small. We explored both the symmetric and asymmetric (i.e. X, Y=Cl, OH) SN2 reactions in our model systems, the competition between backside and frontside pathways, and the dependence of the reactions on the conformation of the reactants. Furthermore, we studied the effect, on the symmetric and asymmetric SN2@P3 and S(N)2@P4 reactions, of replacing hydrogen substituents at the phosphorus centers by chlorine and fluorine in the model systems X(-)+PR2Y and X(-)+POR2Y, with R=Cl, F. An interesting phenomenon is the occurrence of a triple-well PES not only in the symmetric, but also in the asymmetric SN2@P4 reactions of X(-)+POCl2--Y.