Synthesis and structure of BIS(Trifluoromethyl)BIS(Tri-methylsilyl)Amino dichloroarsorane, (CF3)2AsCl2N(SiMe3)2

The synthesis of (CF₃)₂AsCl₂N(SiMe₃)₂ is reported. This compound has been characterized on the basis of an X-ray analysis. It has a trigonal bipyramidal geometry with axial chlorine atoms. Variable temperature ¹H- and ¹⁹F-NMR data show no observable changes. In comparison to pentacoordinated phosphorus compounds the tendency to form tetracoordinated derivatives is strongly diminished in the case of arsenic compounds.     

Does a sterically bulky group occupy the equatorial site in trigonal bipyramidal phosphorus?

[structure: see text] The sterically bulky tert-butyl group occupies an apical position in trigonal bipyramidal phosphorus in the compound [CH2(6-t-Bu-4-Me-C6H2O)2]P(t-Bu)(1,2-O2C6Cl4) in contrast to the occupation of an equatorial position by the small methyl group in [CH2(6-t-Bu-4-Me-C6H2O)2]P(Me)(1,2-O2C6Cl4); this observation contradicts the familiar "apicophilicity rules" for trigonal bipyramidal phosphorus. Low-temperature solution 31P NMR spectra of [CH2(6-t-Bu-4-Me-C6H2O)2]P(R)(1,2-O2C6Cl4) (R = Me, Et, and n-Bu) show the presence of more than two isomers.     

Reactivity of fused 1,3-benzothiaphospholes: Formation of pentacoordinated derivatives

Fused 1,3-benzothiaphospholes 2 (cis-2,6,10-trimethyl-[1, 3]benzothiaphospholo[2,3-b][1, 3]benzothiaphosphole) reacts with H₂O₂ and S₈, giving the corresponding oxide and sulfide, respectively. The reactions of 2 with diethyl azodicarboxylate (DEAD)/catechol or DEAD/o-aminophenol, o-azidophenol, and tetrachloro-o-benzoquinone (TOB) give the first examples of spiro pentacoordinated phosphorus derivatives of this heterocyclic system. The X-ray structural analysis of spiro compound 3 showed a trigonal bipyramidal configuration at phosphorus in which the three rings assume axial-equatorial positions.     

Transition Metal Complexes with Bidentate Ligands Spanning trans-Positions. VII. The preparation of the five-coordinate complexes [M(CO)3(1)] (M = Fe,Ru; (1) = 2,11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene)

The five-coordinate mononuclear complexes [M(CO)₃( 1 )] (M = Fe, Ru; ( 1 ) = 2,11-bis(diphenylphosphinomethyl)benzo[c]phenanthrene) have been prepared and assigned trigonal bipyramidal structures with apical phosphorus atoms from IR. and NMR. data.     

Pentacoordinate Phosphorus in a High‐Pressure Polymorph of Phosphorus Nitride Imide P4N6(NH)

Coordination numbers higher than usual are often associated with superior mechanical properties. In this contribution we report on the synthesis of the high‐pressure polymorph of highly condensed phosphorus nitride imide P₄N₆(NH) representing a new framework topology. This is the first example of phosphorus in trigonal‐bipyramidal coordination being observed in an inorganic network structure. We were able to obtain single crystals and bulk samples of the compound employing the multi‐anvil technique. γ‐P₄N₆(NH) has been thoroughly characterized using X‐ray diffraction, solid‐state NMR and FTIR spectroscopy. The synthesis of γ‐P₄N₆(NH) gives new insights into the coordination chemistry of phosphorus at high pressures. The synthesis of further high‐pressure phases with higher coordination numbers exhibiting intriguing physical properties seems within reach.     

A Fast Catalytic Process of Transfer of a Phosphorus Atom: How Folding of the Reagent is Related to its Catalytic Activity. A Possible Correlation with Rna Behavior

Abstract

A simple and very fast process of transfer of a phosphorus atom, performed by a simple molecule acting as catalyst in an almost infinite catalytic cycle is described. The catalyst donates a P atom to a mixture of two different Grignard reagents giving, in a very fast and in a highly selective manner, only one phosphorus-containing compound with an enormous rate enhancement with respect to the corresponding no-catalyzed reaction which gives a final cluttered mixture of many organophosphorus products. The focal factor to explain this highly selective process of P transport lies in the folded structure of the reagent with particular angles around the phosphorus atom which can facilitate the formation of cyclic trigonal bipyramidal pentacoordinated species and then its catalytic activity. In a similar manner, RNA can adopt, in a precise position, a particular three-dimensional structure that might facilitate the formation of pentacoordinated species leading to the catalytic function.     

Conformational Transmission in DNA

Abstract

This poster presents our recent results on DNA dimers in which a stable trigonal bipyramidal pentacoordinated phosphorus (P^v) structure forms the internucleoside linkage. Conformational analysis of the systems 1-4 with 300 and 500 ¹H NMR has shown that the P^v structure results in a distorted conformation of the backbone structuE (1).     

Pentacoordinate phosphoranes with reversed apicophilicity as stable intermediates in a mitsunobu-type reaction

Diisopropyl azodicarboxylate (DIAD) undergoes a cycloaddition reaction with the cyclic phosphites CH(2)(6-t-Bu-4-Me-C(6)H(2)O)(2)PX (1) [X = NCS (a), N(3) (b), Cl (c), NHMe (d) and Ph (e)] to afford the novel pentacoordinate phosphoranes 2a-e as crystalline solids. This result is different from the reaction of PPh(3) with DIAD used in the well-known Mitsunobu reaction. X-ray crystallography of 2a, 2b, and 2d reveals that the nitrogen, rather than the oxygen, occupies an apical position of the trigonal bipyramidal phosphorus. This is in violation of the commonly accepted preferences for substituents in trigonal bipyramidal phosphorus. In 2e, although the oxygen of the five-membered ring occupies the expected apical position, the phenyl group also occupies (the other) apical position, forcing the more electronegative oxygen atoms of the eight-membered ring to span equatorial-equatorial positions. In contrast to the above, the isocyanato compound CH(2)(6-t-Bu-4-Me-C(6)H(2)O)(2)PNCO (1f), upon treatment with DIAD, affords compound 3 to which a tetracoordinate structure is assigned.     

Synthesis and <Emphasis Type="Italic">in vitro</Emphasis> Fungicidal Study of Organotin(IV) Complexes of Monomethyl Glutarate

The synthesis and study of new coordination compounds of some organotin(IV) chlorides with monomethyl glutarate are reported. The ligand molecule appears to be bound to the tin atom through the carboxylic oxygen. The results obtained from ¹H, ¹³C, and ¹¹⁹Sn NMR, FT-IR and ¹¹⁹Sn Mossbauer spectra show that the complexes are pentacoordinated with the trigonal bipyramidal structure. Biological screening of organotin(IV) derivatives shows promising activity, especially for the triphenyltin complex exhibiting higher antifungal activity. In addition, the rest of the compounds also prove to be active against various fungi used.     

Trichlorostannato(diphosphine)rhodium(I) complexes. Crystal structure of [Rh(SnCl3)(1,5-cyclooctadiene)(dppp)]

The molecular structure of [Rh(SnCl₃)(1,5-cyclooctadiene)(dppp)] [dppp = 1,3-bis(diphenylphosphino)propane] has been determined to R_F = 3.6% single-crystal X-ray techniques. The crystal contains two discrete molecules 1 and 2 per asymmetric unit. Molecule 1 is best described as distorted trigonal bipyramidal with the diolefin and the diphosphine occupying both apical and equatorial positions and the SnCl₃ group on an equatorial position, and molecule 2 as distorted square pyramidal with the equatorial positions occupied by the diolefin and the diphosphine, respectively, and the SnCl₃ fragment in the apical position. In solution at room temperature, complexes [Rh(SnCl₃)(COD)(diphosphine)] exhibit tin dissociation and various intramolecular rearrangements.     

Organotin(IV) derivatives of mercaptosuccinic and thiodiacetic acids

Di- and tri-organotin(IV) complexes of general formula R₂SnAH, (R₃Sn)₂AH, R₂SnB, (R₃Sn)₂B (A=dianion of mercaptosuccinic acid; B=dianion of thiodiacetic acid; R=Me, Et, nPr, nBu, nOct in R₂Sn and nBu in R₃Sn) have been synthesized and characterized by elemental analysis, IR and ¹H and ¹³C NMR spectroscopy. These data support the preferential binding of sulphur over carboxylate by tin(IV) in R₂SnAH and (R₃Sn)₂AH. R₂SnAH complexes are assigned pentacoordinated bridged polymeric trigonal bipyramidal geometry whereas (R₃Sn)₂AH complexes are monomeric with trigonal bipyramidal geometry at tin arising from a bidentate carboxylate group at one tin atom and from weak bonding via Sn←O?C at the other tin atom. In R₂SnB and (R₃Sn)₂B, tin(IV) binds to two carboxylate groups in a unidentate and a bidentate manner respectively, resulting in tetracoordinated and pentacoordinated structures. Potential uses of these compounds are discussed.     

APICOPHILICITY AND RING-STRAIN IN FIVE-COORDINATE PHOSPHORANES

Abstract

In order to dicuss mechanism in organophosphorus chemistry a number of assumptions have to be made. Among them are: (a) that substitutions at tetrahedral phosphorus proceed via five-coordinate intermediates; (b) these intermediates are trigonal bipyramidal; (c) they are formed by apical attack and decompose by apical loss; and (d) if sufficiently long-lived, they may undergo permutational isomerization, that is the ligands may alter their relative dispositions round the phosphorus, before going on to products or back to reactants.

Assuming that the course of a given substitution is dictated primarily by thermodynamic considerations, in order to understand the course of that substitution one needs to know how to assess the relative stabilities of the four isomeric tbps (trigonal bipyramids) that can be formed initially and of the others that could be formed by subsequent isomerization, the barriers to those isomerizations, and the relative rates of the various product-forming steps. We have concentrated on the first of these factors and this lecture describes our attempts to provide the necessary data.

The energy difference between two isomeric tbps can be analyzed in terms of changes in the relative apicophilicities¹ of the groups occupying apical positions, changes in ring-strain as small rings move between apical-equatorial and diequatorial positions, and changes in steric strain. I shall consider each of these in turn. Ligand subset symmetry may also have to be taken into account.^1,2     

Hyperconjugation as it affects conformational analysis

A primer for the qualitative identification and quantitative analysis of hyperconjugative delocalization is presented. The particular focus is upon the influence of hyperconjugation as it affects conformational analysis. Computational methodologies are illustrated within the context of several diverse molecular systems: anomeric and reverse anomeric effects in 2-tetrahydropyranosylammonium, generalized anomeric effects in phosphorus-stabilized carbanions, and hyperconjugative effects in phosphorus- and silicon-based trigonal bipyramids. Hyperconjugation is shown to compete with apicophilicity in the final examples. Although the latter influence has long been accounted for in traditional conformational analysis of trigonal bipyramidal systems, the former has been less appreciated.     

Synthesis and crystal structure of 1-(4-fluorophenyl)-and 1-(4-dimethylamino)phenylgermatranes

The X-ray crystal structure of 1-(4-fluorophenyl)-and 1-(4-dimethylaminophenyl)germatranes reveals that the germanium atom is pentacoordinated and adopts a trigonal bipyramidal geometry. The fluorophenyl and dimethylaminophenyl groups and the nitrogen atom each occupy an apical position with the transannular N→Ge bond of 2.192(3) and 2.249(3) Å; the deviation of the Ge atom from the O(2)-O(8)-O(9) plane is 0.2306(4) and 0.2693(3) Å, correspondingly. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 776–781, May, 2008.     

[62]Tetradecaphyrin and Its Mono‐ and Bis‐ZnII Complexes

A coiled structure of meso‐pentafluorophenyl‐substituted [62]tetradecaphyrin 1 was revealed by X‐ray structural analysis. Synthetic protocols were devised to form mono‐ and bis‐Zn^II complexes, 1 Zn and 1 Zn₂ , selectively. The former displayed a trigonal‐bipyramidal pentacoordinated Zn^II ion as a rare case and a cyclic voltammogram exhibiting eleven reversible redox waves. The latter showed a Ci‐symmetric structure with modest Hückel aromaticity owing to a 62 π‐electronic circuit as the largest aromatic molecule to date.     

Spectroscopic characterization and biological activity of L‐methionyl‐L histidinato complexes of R2Sn(IV) ions (R = Me,nBu, Ph) and X‐ray structure of Me2SnMetHis ˙ 0.5MeOH

Complexes of L ‐methionyl‐L ‐histidine (H₂MetHis) with R₂Sn(IV) ions (R = Me, nBu, Ph) have been synthesized. The crystal and molecular structures of Me₂SnMetHis·0.5MeOH have been determined by X‐ray diffraction. The title compound contains two crystallographically independent molecular units possessing the same trigonal‐bipyramidal geometry at tin, each dimethyltin(IV) moiety being coordinated by the terminal amino nitrogen, deprotonated peptide nitrogen and terminal carboxylate group, neither the imidazole nor thioether groups being involved in bonding. IR spectroscopy was used to probe the structure of the complexes in the solid state, and the structure in solution (CD₃OD) was assessed by ¹H and ¹³C NMR. Me₂Sn(IV)dipeptide complexes appear to be undissociated and to retain a pentacoordinated structure. Rotamer population of C‐terminal histidine was determined by analysis of vicinal coupling constants and side‐chain orientations have been interpreted with a view to potential applications of the compounds as recognition agents. Biological activity was tested on Ascidian embryos of Ciona intestinalis at different stages of development. Copyright © 2000 John Wiley & Sons, Ltd.     

The bonding in hexagonal Ba2/3Pt3B2 and CeCo3B2 type ternary metal borides

Tight-binding calculations with an extended Hückel Hamiltonian were performed on Ba_2/3Pt₃B₂ and LuOs₃B₂. Hypothetical linear metal boride chains present in these materials are analyzed with a three-dimensional model that contains a trigonal bipyramidal T₃B₂ (T = transition metal) building unit for the compounds. The geometrical structure for the T₃B₂ trigonal bipyramids depends on the number of electrons. For systems that have greater than 36 electrons in its trigonal bipyramidal building unit, a structural distortion is expected. Electron back donation from the electron-rich M₃ fragment to the empty e′ set on B₂ creates boron–boron interaction along the z-axis. Boron–boron pairing then participates as an electron sink and causes a trigonal distortion of the platinum Kagome net. On the other hand, a system with <35 electrons should have an undistorted, CeCo₃B₂ type structure. The electronic factors that create the breathing motion are discussed and analyzed with the aid of molecular and solid-state models. The metal–metal bonding associated with the structural properties also has been examined.     

Synthesis,structural characterization and in vitro antitumour properties of triorganoantimony(V) disalicylates: Crystal and molecular structures of [5-Y-2-(ho)-C6H3COO]2SbMe3 (YH,Me, MeO)

Triorganoantimony(V) salicylates, [5-Y-2-(HO)-C₆H₃COO]₂SbR₃ (R=Me, Ph; Y=H, Me, MeO), were obtained by reacting R₃SbCl₂ with the appropriate sodium salt. The compounds have been characterized by IR, MS, ¹H and ¹³C NMR spectroscopy. The molecular structure of the three substituted trimethylantimony(V) disalicylates has been determined by X-ray diffraction. The salicylate ligands are mono-coordinated to antimony through an oxygen atom of each carboxylate, leading to a trigonal bipyramidal geometry, with the antimony-methyl groups in equatorial positions and the oxygen atoms in axial positions. The trimethylantimony compounds tested in vitro against a series of human tumour cell lines were found to be inactive.     

Pentacoordinate silicon derivatives: relative apicophilicity of functional groups attached to a silicon atom

For bifunctional organosilanes o-(Me₂$\text{NCH}{}_2\text{)C}{}_6\text{H}{}_4\text{Si}$XFR the relative order of apicophilicity of substituent X versus the apicophilicity of F is determined as H, OR, NR₂ < F < Cl, OCOC₆H₅X. The results show that the major trigonal bipyramidal conformer is not influenced by the electronegativity of the F atom.     

Chemical and stereochemical behaviour of bifunctional enantiomeric silicon compounds : I. Study of α-naphthylferrocenyl-fluorosilane and -chlorofluorosilane

The synthesis of the first bifunctional enantiomeric silicon compounds is described. A high selectivity between the two functional groups is observed in substitution reactions with organolithium compounds and Grignard reagents, the more polarizable group being specifically replaced. The stereochemistry of the reactions has been determined by chemical correlations. The stability of the pentacoordinated intermediate (discussed in terms of apicophilicity of the various groups) does not suffice to explain the results. Inversion of the configuration comes from an axial attack of the reactant and retention of configuration is explained by an equatorial attack.