The structures of 1:1 and 1:2 adducts of phosphanetricarbonitrile with 1,4-diazabicyclo[2.2.2]octane

In the structures of 1:1 and 1:2 adducts of phosphanetricarbonitrile (C3N3P) with 1,4-diazabicyclo[2.2.2]octane (C6H12N2), the 1:1 adduct crystallizes in the orthorhombic space group, Pbcm, with four formula units in the unit cell (Z′ = 0.5). The P(CN)3 unit lies on a crystallographic mirror plane while the C6H12N2 unit lies on a crystallographic twofold axis passing through one of the C—C bonds. The P(CN)3 moiety has close to C 3v symmetry and is stabilized by forming adducts with two symmetry-related C6H12N2 units. The phosphorus atom is in a five-coordinate environment. As a result of the symmetry, the two trans angles are equal so τ5 = 0.00 and thus the geometrical description could be considered to be square pyramidal. However, the electronic geometry is distorted octahedral with the lone pair on the phosphorous occupying the sixth position. As would be expected from VSEPR considerations, the repulsion of the lone-pair electrons with the equatorial bonding electrons means that the trans angles for the latter are considerably reduced from 180° to 162.01 (4)°, so the best description of the overall geometry for phosphorus is distorted square pyramidal. The 1:2 adduct crystallizes in the monoclinic space group, P21/m with two formula units in the asymmetric unit (i.e. Z' = 1/2). The P(CN)3 moiety lies on a mirror plane and one of the two C6H12N2 (dabco) molecules also lies on a mirror plane. The symmetry of the P(CN)3 unit is close to C 3v. There are three P...N interactions and consequently the molecular geometry of the phosphorus atom is distorted octahedral. This must mean that the lone pair of electrons on the phosphorus atom is not sterically active. For the 1:1 adduct, there are weak associations between the phosphorus atom and one of the terminal nitrogen atoms from the C[triple-bond] N moiety, forming chains in the a-axis direction. In addition there are weak C—H...N interactions between a terminal nitrogen atoms from the C[triple-bond]N moiety and the C6H12N2 molecules, which form sheets perpendicular to the a axis.

Primary Phosphines and Phosphine Oxides with a Stereogenic Carbon Center Adjacent to the Phosphorus Atom: Synthesis and Anti-Markovnikov Radical Addition to Alkenes

Organophosphorus compounds with stereogenic phosphorus and carbon atoms have received increasing attention. In this regards, primary phosphines with a stereogenic carbon atom adjacent to the phosphorus atom were synthesized by the reduction in phosphonates and phosphonoselenoates with a binaphthyl group. Their oxidized products, i.e., phosphine oxides with a stereogenic tetrasubstituted carbon atom, were found to undergo BEt3-mediated radical addition to cyclohexene to give P-stereogenic secondary phosphine oxides with a diastereoselectivity of 91:9. The products were characterized by ordinary analytical methods, such as Fourier transform infrared spectroscopy; 1H, 13C, and 31P NMR spectroscopies; and mass spectroscopy. Computational studies on the phosphorus-centered radical species and the obtained product implied that the thermodynamically stable radical and the adduct may be formed as a major diastereomer. The radical addition to a range of alkenes took place in an anti-Markovnikov fashion to give P-stereogenic secondary phosphine oxides. A variety of functional groups in the alkenes were tolerated under the reaction conditions to afford secondary phosphine oxides in moderate yields. Primary phosphines with an alkenyl group, which were generated in situ, underwent intramolecular cyclization to give five- and six-membered cyclic phosphines in high yields after protection by BH3.

Computer simulation of the interaction of the surface of an aluminosilicate filler and an organoelement modifier

Geometry optimization and molecular dynamics modeling are performed in the quantum-classical approximation for a phosphorus-boron-containing oligomer and aluminosilicate microspheres. By modeling the phosphorusboron-containing oligomer with the numbers of units of 3—5, the possibility of the appearance of internal cycles in oligomers with the number of chain units more than 3 as a result of the formation of bonds of boron atoms with the oxygen of the phosphorus atom was established. The interaction of the surface of the aluminosilicate filler and the phosphorus-boron-containing oligomer modifier is due to hydrogen bonds between the hydroxyl groups of the silicon atoms of the aluminosilicate filler and the oxygen and hydrogen atoms of the oligomer. Keywords: phosphorus-boron-containing oligomer, aluminosilicate microspheres, computer simulation. [email protected]

AB INITIO CALCULATION OF ADSORPTION POSITION EFFECT ON MAGNETIZATION REDISTRIBUTION IN P-DOPED SILICENE

The behavior (substitution and adsorption) of a phosphorus atom on the surface of silicene is studied using quantum mechanical calculations. The most favorable positions, binding energy and activation of the phosphorus diffusion barrier have been established. The change in the local magnetic moment of the phosphorus atom is described depending on its position and the position of the surrounding silicon elements.

Synthesis of Pentacoordinated Spiro[4,4]phosphoranes by Reaction of Cyclic Phosphazenyl Anions with Epoxides. Study of their P-Remote Functionalization and Hydrolysis

The synthesis of a new family of pentacoordinated spiro[4,4]phosphoranes stabilized by the ortho-benzamide bidentate ligand (oBA,-C6H4-2-C(O)NH-) through reaction of Cα -Cortho-dilithiated phosphazenes with oxiranes is reported. Mixtures of epimers that differ in configuration at the phosphorus atom were obtained with moderate to high yields and diastereoselectivities. C3-disubstituted derivatives could be separated, which provided access to enantiopure products arising from the reaction with (R)-2-phenyloxirane. Stereomutation was observed by heating the spirophosphoranes at 100 ºC. Directed ortho lithiation of spirophoshoranes followed by electrophilic quench reactions including carbon-based and heteroatom-based electrophiles afforded derivatives functionalized in remote position with respect to the phosphorus atom. Benzoic acid catalyzed hydrolysis of spirophosphoranes furnished ortho-(hydroxyalkylphosphoryl)benzamides by cleavage of the P‒O and P‒N bonds with retention of the phosphorus configuration. In contrast, alkaline hydrolysis led to the formation of γ-hydroxyphosphinic acids and benzamide.

Access to cationic polyhedral carboranes via dynamic cage surgery with N-heterocyclic carbenes

Polyhedral boranes and heteroboranes appear almost exclusively as neutral or anionic species, while the cationic ones are protonated at exoskeletal heteroatoms or they are instable. Here we report the reactivity of 10-vertex closo-dicarbadecaboranes with one or two equivalents of N-heterocyclic carbene to 10-vertex nido mono- and/or bis-carbene adducts, respectively. These complexes easily undergo a reaction with HCl to give cages of stable and water soluble 10-vertex nido-type cations with protonation in the form of a BHB bridge or 10-vertex closo-type cations containing one carbene ligand when originating from closo-1,10-dicarbadecaborane. The reaction of a 10-vertex nido mono-carbene adduct with phosphorus trichloride gives nido-11-vertex 2-phospha-7,8-dicarbaundecaborane, which undergoes an oxidation of the phosphorus atom to P = O, while the product of a bis-carbene adduct reaction is best described as a distorted C2B6H8 fragment bridged by the (BH)2PCl2+ moiety.

α-Cationic Phosphines: from Curiosities to Powerful Ancillary Ligands

The distinguishing feature of α-cationic phosphines is the presence of at least one substituent, normally (hetero)cyclic and positively charged, which is directly attached to the phosphorus atom. As result from this unique substitution pattern, the thus designed ligands depict significantly diminished donor properties if compared with their neutral counterparts. Thus, if in a hypothetical catalytic cycle, the step that determines the rate is facilitated by an increase of the electrophilicity at the metal center; then, the use of α-cationic ancillary phosphines can be highly beneficial. This fact, combined with their easy syntheses and stability, which allows an easy handling, make α-cationic phosphines a useful tool for the synthetic practitioner. Our research on the topic demonstrates that generally a remarkable ligand acceleration effect is observed when α-cationic phosphines are employed in Au(I)- and Pt(II)-promoted cycloisomerizations; moreover, in some cases even otherwise not operative transformations can be promoted. This Account describes how we entered into the topic, our efforts, and those of others to understand the coordination behavior of α-cationic phosphines and further develop their range of applications in catalysis; but it also identifies the drawbacks associated with their use, which limit their range of application.1 Introduction2 Polycationic Phosphines: Stronger Acceptors than Phosphites3 Inconveniences Derived from the Use of (Poly)cationic phosphines4 A Second Generation of Cationic Ligands: α-Pyridiniophosphines5 Chiral α-Cationic Phosphines6 α-Radical Phosphines and (Poly)cationic Phosphine Oxides7 Conclusions and Outlook

[(1,2,5,6-η)-Cycloocta-1,5-diene](1-ethyl-3-isopropyl-1,3-imidazol-2-ylidene)(triphenylphosphane)rhodium(I) tetrafluoridoborate

A new N-heterocyclic cationic rhodium(I) complex with a tetrafluoridoborate counter-anion, [Rh(C8H14N2)(C8H12)(C18H15P)]BF4, has been prepared and structurally characterized. The cationic complex exhibits a distorted square-planar environment around the rhodium(I) ion. Two connections are made from rhodium(I) to the carbon atom of an N-heterocylic carbene ligand and to the phosphorus atom of a triphenylphosphane ligand. The remaining two coordination sites are made via a bidentate interaction from the two olefinic bonds of cyclooctadiene to the rhodium(I) ion. The compound includes an out-sphere tetrafluoridoborate counter-anion. Within the crystal of the compound exist several weak intermolecular C—H...F interactions.