Spiro[1,2]oxaphosphetanes of Nonstabilized and Semistabilized Phosphorus Ylide Derivatives: Synthesis and Kinetic and Computational Study of Their Thermolysis.

A series of tri- and tetrasubstituted spiro-oxaphosphetanes stabilized by ortho-benzamide (oBA) and N-methyl ortho-benzamide (MoBA) ligands have been synthesized by the reaction of Cα,Cortho-dilithiated phosphazenes with aldehydes and ketones. They include enantiopure products and the first example of an isolated oxaphosphetane having a phenyl substituent at C3 of the ring. Kinetic studies of their thermal decomposition showed that the process takes place irreversibly through a polar transition state (ρ = -0.22) under the influence of electronic, [1,2], [1,3] steric, and solvent effects, with C3/P-[1,2] interactions as the largest contribution to ΔG⧧ of olefination. Inversion of the phosphorus configuration through stereomutation has been observed in a number of cases. DFT calculations showed that oBA derivatives olefinated through the isolated (N, O)(Ph, C6H4, C) oxaphosphetanes (Channel A), whereas MoBA compounds decomposed faster via the isomer (C6H4, O)(C, N, Ph) formed by P-stereomutation involving a MB2 permutational mechanism (Channel B). The energy barrier of P-isomerization is lower than that of olefination. Fragmentation takes place in a concerted asynchronous reaction. The thermal stability of oxaphosphetanes is determined by strong C3/P-[1,2] interactions destabilizing the transition state of olefination. The effect of charge distribution and C3/C4-[1,2] and C4/P-[1,3] steric and solvent interactions on ΔG⧧ was also evaluated.

Influence of Mn²âº concentration on Mn²âº-doped ZnS quantum dot synthesis: evaluation of the structural and photoluminescent properties.

The intentional introduction of transition metal impurities into semiconductor nanocrystals is an attractive approach for tuning quantum dot photoluminescence emission. Particularly, doping of ZnS quantum dots with Mn(2+) (Mn:ZnS QDs) results in a phosphorescence-type emission, attributed to the incorporation of manganese ions into the nanocrystal structure, so that delayed radiational deactivation of the energy of nanoparticles, excited through the energy levels of the metal, is enabled. However, the development of effective doping strategies can be challenging, especially if a highly efficient photoluminescent emission within a known crystalline core structure, is required (e.g. for analytical phosphorescence applications). The spectroscopic properties and the crystal structure of Mn(2+)-doped ZnS QDs are studied here to provide a better understanding on how the luminescence emission and the crystalline composition are influenced by the presence of Mn(2+) and its concentration used during the synthesis. In order to further control and optimize the synthesis of doped QDs for future bioanalytical applications, different complementary techniques including photoluminescence and X-ray powder diffraction have been employed. The information obtained has allowed standardization of the synthesis conditions of these doped QDs and the identification and quantification of the crystal phases obtained under different synthesis conditions.

Directed ortho-lithiation of aminophosphazenes: an efficient route to the stereoselective synthesis of P-chiral compounds.

Ortho-directed lithiation of P,P-diphenylaminophosphazenes followed by electrophilic quench is described as an efficient process for synthesizing P-chiral ortho-functionalized derivatives in high yields and diastereoselectivities. The method allows the tunable preparation of structurally diverse enantiopure P-chiral compounds including phosphinic and phosphinothioic amides, phosphinic esters, phosphine oxides, and o-aminophosphines.

Mechanisms of stereomutation and thermolysis of spiro-1,2-oxaphosphetanes: new insights into the second step of the Wittig reaction.

The experimentally observed stereomutation of spiro-1,2-oxaphosphetanes is shown by DFT calculations to proceed through successive M(B2) or M(B4) and M(B3) mechanisms involving two, four, and three Berry pseudorotations at phosphorus, respectively. Oxaphosphetane decomposition takes place in a single step via a polar transition state. The calculated activation parameters for this reaction are in good agreement with those determined experimentally.

Transformations of diphenylphosphinothioic acid tertiary amides mediated by directed ortho metallation.

ortho-Lithiation of N,N-diisopropyl-P,P-diphenylphosphinothioic amide using n-BuLi in the presence of TMEDA in diethyl ether followed by electrophilic trapping is described as an efficient method for the synthesis of ortho-functionalised derivatives in high yields. The structural modification of the phosphinothioic amide includes C-X (X = P, S, Si, Sn, I) and C-C bond forming reactions with a large variety of electrophiles. Additional applications based on functional group transformations are also reported. They include imine formation, desulfurization and Suzuki cross-coupling reactions on selected compounds.

Synthesis and structure of tridentate bis(phosphinic amide)-phosphine oxide complexes of yttrium nitrate. Applications of 31P,89Y NMR methods in structural elucidation in solution.

The synthesis and characterisation of a tridentate ligand containing two diphenylphosphinic amide side-arms connected through the ortho position to a phenylphosphine oxide moiety and the 1:1 and 2:1 complexes formed with yttrium nitrate are reported for the first time. The free ligand (R(P1)*,S(P3)*)-11 is obtained diastereoselectively by reaction of ortho-lithiated N,N-diisopropyl-P,P-diphenylphosphinic amide with phenylphosphonic dichloride. Complexes [Y((R(P1)*,S(P3)*)-11)(NO(3))(3)] and [Y((R(P1)*,S(P3)*)-11)(2)(NO(3))](NO(3))(2) were isolated by mixing ligand 11 with Y(NO(3))(3)·6H(2)O in acetonitrile at room temperature in a ligand to metal molar ratio of 1:1 and 2:1, respectively. The 1:1 derivative is the product of thermodynamic control when a molar ratio of ligand to yttrium salt of 1:1 is used. The new compounds have been characterised both as the solid (X-ray diffraction) and in solution (multinuclear magnetic resonance). In both yttrium complexes the ligand acts as a tridentate chelate. The arrangement of the two ligands in the 2:1 complex affords a pseudo-meso structure. Tridentate chelation of yttrium(III) in both complexes is retained in solution as evidenced by (89)Y NMR data obtained via(31)P,(89)Y-HMQC, and (89)Y,(31)P-DEPT experiments. The investigation of the solution behaviour of the Y(III) complexes through PGSE NMR diffusion measurements showed that average structures in agreement with the 1:1 and 1:2 stoichiometries are retained in acetonitrile.

Metal organic frameworks assembled from Y(III), Na(I), and chiral flexible-achiral rigid dicarboxylates.

New chiral metal organic frameworks, assembled from Y(III), Na(I), and chiral flexible-achiral rigid dicarboxylate ligands, formulated as [NaY(Tart)(BDC)(H(2)O)(2)] (1) and [NaY(Tart)(biBDC)(H(2)O)(2)] (2) (H(2)Tart = Tartaric acid; H(2)BDC = Terephthalic acid; H(2)biBDC = Biphenyl-4,4'-dicarboxylic acid), were obtained as single phases under hydrothermal conditions. Their structures were solved by single-crystal X-ray diffraction (XRD), and characterized by (13)C CPMAS NMR, thermal analyses (thermogravimetry-mass spectrometry (TG-MS) and differential scanning calorimetry (DSC)), and X-ray thermodiffractometry. Both compounds crystallize in the orthorhombic chiral space group C222(1) with a = 6.8854(2) A, b = 30.3859(7) A, c = 7.4741(2) A for 1, and a = 6.8531(2) A, b = 39.0426(8) A, c = 7.4976(2) A for 2. 1 and 2 are layered structures whose three-dimensional stability is ensured by strong hydrogen bond interactions. The dehydration of both compounds is accompanied by phase transformation, while the spontaneous rehydration process is characterized by different kinetics, fast in the case of 1 and slow for 2.

Synthesis and characterization of a coupled binuclear Cu(I)/Cu(III) complex.

The synthesis through reaction of a C(alpha),C(ortho) dilithiated phosphazene with CuBr and structural characterization of the first example of a binuclear mixed valence [Cu(I)(N(2))/Cu(III)(C(4))] complex showing a metal-metal bond, as well as its applications in cyclopropanation and oxidation reactions, are described.

Enantioselective desymmetrization of diphenylphosphinamides via (-)-sparteine-mediated ortho-lithiation. Synthesis of P-chiral ligands.

Asymmetric ortho-lithiation of N-dialkyl-P,P-diphenylphosphinamides using [n-BuLi.(-)-sparteine] is described as an efficient method for the synthesis of P-chiral ortho-functionalized derivatives in high yields and ee's from 45 to >99%. The method allows access to new enantiomerically pure P-chiral phosphine and diimine ligands.

Asymmetric deprotonation-substitution of N-Pop-benzylamines using [RLi/(-)-sparteine]. Enantioselective sequential reactions and synthesis of N-heterocycles.

Pop-directed asymmetric deprotonation of benzylic amines using [n-BuLi/(-)-sparteine] provides an efficient method for the synthesis of chiral NC alpha and NC alpha,alpha' derivatives with total selectivity with respect to competing allylic and ortho lithiation. The method described herein offers a straightforward route of accessing chiral N-Pop-protected nitrogen heterocycles.

Crystallization and preliminary X-ray diffraction analysis of vaccinia virus H1L phosphatase.

The cysteine-based protein phosphatase H1L was the first reported dual-specificity protein phosphatase. H1L is encapsidated within the vaccinia virus and is required for successful host infection and for the production of viable vaccinia progeny. H1L has therefore been proposed as a target candidate for antiviral compounds. Recombinant H1L has been expressed in a catalytically inactive form using an Escherichia coli host, leading to purification and crystallization by the microbatch method. The crystals diffract to 2.1 A resolution using synchrotron radiation. These crystals belong to space group P422, with unit-cell parameters a = b = 98.31, c = 169.15 A, and are likely to contain four molecules in the asymmetric unit. A sulfur SAD data set was collected to 2.8 A resolution on beamline BM14 at the ESRF to facilitate structure determination. Attempts to derivatize these crystals with xenon gas changed the space group to I422, with unit-cell parameters a = b = 63.28, c = 169.68 A and a single molecule in the asymmetric unit. The relationship between these two crystal forms is discussed.