Novel Synthesis of Macrocylic Systems Containing Phosphorus and Sulfur

Abstract

Macrocyclic systems containing phosphine. phosphoryl or thiophosphoryl functions in the ring demonstrate high ability to complex metal ions Complexed structures of this type show interesting Fatalytic properties and can be used in homogenous and heterogenous catalysis^[1,2] Macrocyclic compounds containg phosphorus are also useful as complexing agents for ammonlum salts. anions. etc [3,4] Generally three types of reactions are used to synthesize phosphorus containing macrocyclic compounds the cyclocondensation, the ring opening reaction and the reaction with metal as a matrix^[5]. We have devoloped a new procedure for the synthesis of the title systems of different sizes and of different P and S contents It is based on a double conjugate addition of dithiolates to divlnyl phosphine oxides and sulfides and makes use of the so-called “cesium effect”.     

The Pyrolysis of Azides in the Gas Phase

The chemistry of the non-metallic elements has in recent years passed through a period of rapid development, often referred to as its “renaissance”. To emphasize just one of the key facets: numerous short-lived molecules containing multiple bonds to elements of the third and higher periods have been discovered, often accompanied by the planned synthesis of derivatives which are sterically shielded by bulky groups and thus kinetically stabilized. Thus today molecules such as silabenzenes H₆C_6?nSi_n and silaethenes H₂Si?CH₂ or R₂Si?CR₂, disilenes R₂Si?SiR₂ and diphosphenes RP?PR, silaphenylisonitrile H₅C₆? N?Si, or methylidyne-phosphanes R? C?P, are all well-known species. Sandwich compounds with P₆ rings or silicon centers demonstrate that there are now hardly any barriers to impede the imagination of the non-metal chemist. In sharp contrast is our lack of knowledge regarding the “microscopic” pathways of chemical reactions: thus apart from information provided for example by molecular beam experiments, or from exact numerical calculations involving species consisting of only a few atoms, it remains largely unknown from which directions medium-sized molecules must approach each other to successfully collide and form a “reaction complex”, in which way their structures are changed in such a process or which role is played by molecular dynamics in the energy transfer.–The pyrolysis of azides X? N₃, i.e. compounds which tend to explode violently when ignited in the condensed phase but can be heated in low-pressure gas flow systems without much risk, illustrates that studies of reactive intermediates are of interest not only because novel molecules may be discovered and isolated, and thereby possibilities for synthesis expanded. Moreover, some aspects of the “microscopic” pathways of these azide pyrolyses can be described satisfactorily on the basis of calculated energy hypersurfaces, and the influence of molecular dynamics becomes experimentally visible in the “chemical activation” of intermediates which leads to their “thermal explosion”.     

Principles of Phosphorus Chemistry: Molecular States of Phosphorus Compounds - A Report on Gasphase Investigations 1-3

Abstract

An up-to-date concept of bonding in phosphorus compounds has to be based on the reality of molecular states. Molecules, which change their structure with energy, at present are best rationalized in terms of topology and symmetry, effective nuclear potentials and charge distribution. To reduce the complexity of the resulting manifold, comparison of equivalent states of chemically related molecules, based advantageously on quantum chemical calculations, is strongly recommended. Adding the time-scale, molecular dynamics within the numerous degrees of freedom become important, also as a basis to gain some understanding of the rather complex microscopic reaction pathways of medium-sized molecules. Examples are presented to illustrate the use of spectroscopic ‘fingerprints’ for the analysis and optimization of gasphase reactions as well as the benefit of inherent information on molecular states for the preparative phosphorus chemist. The catalytic dehydrochlorination of alkyldichlorophosphanes RH₂C-PCl₂ → RHC = PCI → R-C ≡ P and their dechlorination on magnesium metal surface are discussed in some detail as well as the generation of other unsaturated phosphorus molecules like Cl-P = O, Cl-P = S, Cl-P(= O)₂, Cl-P(= S)₂ or H₃C-P =CH₂. Approximate energy hypersurface calculations for the gasphase equilibrium P₄ ? 2 P₂ or for the unexpected dehydration (H₃C)₂HP=O → H₂O + H₃C-P = CH₂, which includes chemical activation, provide some insight into microscopic reaction pathways of phosphorus compounds.     

Phosphorus isocyanates

Compounds containing the PNCO grouping can be obtained e.g. from phosphorus halides and silver cyanate or esters of N-chloroiminocarbonic acid and by thermal decomposition of alkoxycarbonylimino-phosphoranes. The phosphorus (V) isocyanates resemble the “carbon” isocyanates in their chemical properties, whereas the phosphorus (III) isocyanates resemble the phosphorus (III) chlorides. Some of the compounds discussed have insecticidal or cytostatic actions.     

New Acyclic Neutral Phosphorus Sulfides and Sulfide Oxides

A great number of binary neutral phosphorus sulfides was discovered and investigated. However all stable representatives of this family of compounds adopt a polycyclic structure in contrast to their lighter homologues, the nitrogen oxides. Acyclic representatives can be stabilized by adduct formation with a nitrogen base. The bis(pyridine) adduct py₂P₂S₅ of the unstable acyclic phosphorus sulfide P₂S₅ is readily obtained stirring P₄S₁₀ in pyridine at ambient temperature. X‐ray diffraction studies on single crystals of py₂P₂S₅ · 0.5 py ( 1b ) show a N₂O₅ like structure for the P₂S₅ framework. The long P–N distances of 1.86 Å indicate only weak coordination of the pyridine molecules to phosphorus. Single crystal X‐ray diffraction studies on py₂P₂S_4.34O_0.66 ( 2 ) reveal the presence of py₂P₂S₄O ( 3 ) together with py₂P₂S₅ in the crystal. Compound 3 contains the mixed phosphorus oxide sulfide molecule P₂S₄O stabilized as bis(pyridine) adduct. It is readily obtained from pyP₂S₅ by oxidation with KMnO₄ in pyridine. The oxygen atom occupies the bridging position between the two phosphorus atoms. Quantum chemical calculations at the MPW1PW91 level of theory as well as DTA/TG thermal analyses confirm the weak coordination of the pyridine molecules in py₂P₂S₅, py₂P₂S₄O, and py₂P₂S₇ to phosphorus.     

Ab initio MRD-CI calculations for breaking a chemical bond in a molecule in a crystal or other solid environment. III. Me2N?NO2 decomposition of dimethylnitramine in a large crystalline environment

Recently we extended our strategy for MRD-CI (multireference double excitation-configuration interaction) calculations, based on localized/local orbitals and an “effective” CI Hamiltonian, for molecular decompositions of large molecules to breaking a chemical bond in a molecule in a crystalline or other solid environment. Our technique begins with an explicit quantum chemical SCF calculation for a reference molecule surrounded by a number of other molecules in the multipole environment of more distant neighbors. The resulting canonical molecular orbitals are then localized, and the localized occupied and virtual orbitals in the region of interest are included explicitly in the MRD-CI with the remainder of the occupied localized orbitals being folded into an “effective” CI Hamiltonian. The MRD-CI calculations are then carried out for breaking a bond in the reference molecule. This method is completely general in that the space treated explicitly, as well as the surrounding space, may contain voids, defects, deformations, dislocations, impurities, dopants, edges and surfaces, boundaries, etc. Dimethylnitramine is the smallest prototype of the energetic R₂N—NO₂ nitramines, such as the 6-member ring RDX or the 8-member ring HMX. Decomposition of energetic compounds is initiated in the solid by a breaking of the target bond. Thus, it is crucial to know the difference in energy between breaking a bond in an isolated energetic molecule versus in the molecule in a solid. In the present study, we have carried out MRD-CI calculations for the Me₂N—NO₂ dissociation of dimethylnitramine in a dimethylnitramine crystal. The cases we investigated were one dimethylnitramine molecule (surrounded by 53 and 685 neighboring dimethylnitramine molecules represented by multipoles), three dimethylnitramine molecules, and three dimethylnitramine molecules (surrounded by 683 neighbors). All multipoles were cumulative atomic multipoles up through quadrupoles. The MRD-CI calculations on dimethylnitramine required large numbers of reference configurations from which were allowed all single and double excitations.     

Correlation of the von Braun,Ritter, Bischler-Napieralski,Beckmann and Schmidt reactions via nitrilium salt intermediates

The Bischler-Napieralski dihydroisoquinoline synthesis from N-arylethyl-amides a formerly “one-pot” process was proven to occur via the imidoyl chlorides and the corresponding nitrilium salt. This led to the recognition of using other leaving groups better than chloride (e.g. trifluoroacetate, trifluoromethanesulfonate) and electrophiles better than phosphoryl chloride-POCl₄^? being an unfavorable counterion for the nitrilium ion. Previous facts about better yields with phosphorus pentoxide than phosphorus oxychloride were interpreted in the same light. The two-step process requires much milder conditions, 20–70° vs 110–205°. The “anomaly”, that is, the failure of 1,2-diaryl-ethylbenzamides to undergo cyclization as reported in literature was now rationalized in terms of fragmentation of the nitrilium salts into stilbenes, with formation of the conjugated π-system being the driving force for this product-controlled reaction. This, in fact, was now recognized as a reversal of the Ritter reaction which itself had been used in the synthesis of isoquinolines. The intermediate carbonium ion, from the nitrilium salt can, alternatively, undergo nucleophilic attack by an ionic halogen yielding products, expected from a von Braun reaction.Thus, correlation of the formerly unrelated Ritter, von Braun, Bischler-Napieralski, Beckmann and the Schmidt reactions has been established (Scheme 18) and a few other aspects of nitrilium salt chemistry such as elaboration of a modified Vilsmeier-Haack aldehyde synthesis via nitrilium salt intermediates and an attempt to synthesize compounds with the nitrilium group in a ring are discussed.     

Neutral Hexacoordinate Phosphorus: Substituted Carbodiimide Phosphoranes and Other Chelated Substituted 2-Pyridine Derivatives

Abstract

A series of neutral hexacoordinate λ⁶ phosphorus compounds of the general formula X_4-n(CF₃)_nPN(R)C(C1)N(R) (n = 0, 1, 2, 3; R = cyclohexyl, isopropyl) has been prepared. The parent compounds are obtained by “insertion” of carbodiimide into the P-C1 bond of λ⁵-chlorophosphorane. Substituted pyridines also react readily with λ⁵ chloro and fluoro phosphoranes to form 2-methylamino, thio and oxopyridine chelates of the form X₄P(Epy) (E = 0, NMe and S; X = F, Cl) in which the phosphorus achieves six coordination through acceptance of the pyridine nitrogen. Selected reactions and the fluxional behavior of the λ⁶ systems are discussed.     

Encapsulation and Polymerization of White Phosphorus Inside Single-Wall Carbon Nanotubes

Elemental phosphorus displays an impressive number of allotropes with highly diverse chemical and physical properties. White phosphorus has now been filled into single-wall carbon nanotubes (SWCNTs) from the liquid and thereby stabilized against the highly exothermic reaction with atmospheric oxygen. The encapsulated tetraphosphorus molecules were visualized with transmission electron microscopy, but found to convert readily into chain structures inside the SWCNT “nanoreactors”. The energies of the possible chain structures were determined computationally, highlighting a delicate balance between the extent of polymerization and the SWCNT diameter. Experimentally, a single-stranded zig-zag chain of phosphorus atoms was observed, which is the lowest energy structure at small confinement diameters. These one-dimensional chains provide a glimpse into the very first steps of the transformation from white to red phosphorus.     

Zur Chemie und Strukturchemie der Phosphide und Polyphosphide. 29. Die molaren Volumina von Metall-Phosphiden,ein Beitrag zur Raumchemie der festen Stoffe

Chemistry and Structural Chemistry of Phosphides and Polyphosphides. 29. Molar Volumes of Metal-Phosphides, a Contribution to the “Raumchemie” of Solids After a short introduction into the “Raumchemie” of solids, developed in 1934 by W. Biltz, the behaviour of the molecular volumes of phosphorus in metal phosphides is discussed. In the case of salt-like phosphides the volume increment of phosphorus, V_P, which is obtained after removal of the cation increment, increases with increasing negative charge z_P of the phosphide ions P^z (?0.07 ≥ z ≥ ?3) and on the other hand decreases with increasing cation charge z_M. The relations are shown by the interpolation equation V_P(z_P, z_M) = exp (αz_Pz_M + βz_P + γz_M + δ) with α = 0.046, β = ?0.368, γ = ?0.066, δ = 2.630. There is no observable difference between compounds with A and B metals. Special conditions due to crystal structure and chemical bonding are discussed. Semimetallic phosphides are appropriately discussed on the basis of the volumes of the metals and of increments of semimetallic phosphorus. Here the V_P values lie between 10 and 6 cm³ · mol^?1. They become smaller as the ratio M/P increases. Some examples are given to show that in special cases the volume can be used to judge the type of bonding. The statement of tho theorem of optima1 volumes is explained for a group of salt-like phosphides. Our study shows, that the “Raumchemie” of BILTZ reliable on the field of metal phosphides.     

Symmetrical Bis‐Phosphorus Compounds and Macrocycles with two 1,3,2‐Benzodiazaphosphorinone Units – Oxidation and X‐Ray Structure Analysis of Selected Compounds

The hydrolysis of 1,2‐bis(5,6‐benzo‐1‐methyl‐2‐chloro‐1,3,2‐diazaphosphorin‐4‐on‐3‐yl)ethane ( 1 ) and its 1,3‐propane derivative ( 2 ) with excess water led, without decomposition, to the formation of the bis‐phosphoryl compounds 3 and 4 . Reaction of 1 and 2 with bis(trimethylsiloxy)ethane formed the symmetrical macrocycles 5 and 6 , which could readily be oxidized by (H₂N)₂C(:O) · H₂O₂ or elemental sulfur, leading to the formation of the phosphoryl compounds 7 and 10 , and the thiophosphoryl derivatives 9 and 11 , respectively. The influence of the ring size on the reaction rate of the oxidation was investigated. For the sulfurization of 6 , the stepwise addition of sulfur to phosphorus was proved by NMR spectroscopy. All compounds exist as single conformers in common organic solvents such as toluene, diethyl ether, dichloromethane or chloroform. For compounds 7 (dichloromethane solvate) and 9 , single crystal X‐ray structure analyses were conducted; both diastereomeric molecules were shown to display RR/SS configuration. In both structures one short non‐classical hydrogen bond was observed.     

Reactions of Azides of Sugars with Derivatives of Tri-Valent Phosphorus Leading to N-Phosphorylated Sugars

Abstract

This communication deals with a simple method for preparation of X-phosphorylated sugars by the reaction of trivalent phosphorus derivatives with 1-α,β-azides of 2,3,4,5-tetraacetylated and 2,3,4,6-tetra(trimethyl)silylated glycose. It has been established that ohosphimine derivatives, obtained as a result of the Staudinger reaction, can be easily hydrolyzed to give derivatives of acetylated glucosaminphosphoric acids. It has been discovered that susceptibility to hydrolysis depends on the phosphorus suhstituents. When using esters of trivalent phosphorus the rate of hydrolysis for compounds with alkyl substituents decreases in order

C₃H₇ > C₂H⁵O >> CH₃O

This can probably be explained by the electronic and steric influence of the alkyl groups.     

Organophosphorus Synthesis Without Phosphorus Trichloride: The Case for the Hypophosphorous Pathway

Abstract

The vast majority of organophosphorus compounds is currently synthesized from phosphorus trichloride (PCl₃), even though the final consumer products do not contain reactive phosphorus–chlorine bonds. In order to bypass phosphorus trichloride, significant interest has been devoted to functionalizing elemental phosphorus (P₄, the precursor to PCl₃), red phosphorus (P_red), or phosphine (PH₃). Yet, other industrial-scale precursors are hypophosphorous derivatives (H₃PO₂ and its alkali salts), but their use as phosphorus trichloride replacements has been completely overlooked. Here, the case is made for an alternative approach to the industrial synthesis of organophosphorus compounds based on hypophosphites.     

Encapsulation and Polymerization of White Phosphorus Inside Single‐Wall Carbon Nanotubes

Elemental phosphorus displays an impressive number of allotropes with highly diverse chemical and physical properties. White phosphorus has now been filled into single‐wall carbon nanotubes (SWCNTs) from the liquid and thereby stabilized against the highly exothermic reaction with atmospheric oxygen. The encapsulated tetraphosphorus molecules were visualized with transmission electron microscopy, but found to convert readily into chain structures inside the SWCNT “nanoreactors”. The energies of the possible chain structures were determined computationally, highlighting a delicate balance between the extent of polymerization and the SWCNT diameter. Experimentally, a single‐stranded zig‐zag chain of phosphorus atoms was observed, which is the lowest energy structure at small confinement diameters. These one‐dimensional chains provide a glimpse into the very first steps of the transformation from white to red phosphorus.     

The crystal and molecular structure of acetylcyclopentadienyl-manganese and -rhenium tricarbonyls

The X-ray investigation of the title compounds has shown that in CH₃COC₅H₄Mn(CO)₃ the orientation of CO groups with respect to the cyclopentadienyl ring is almost the same as in the unsubstituted manganese compound whereas in CH₃COC₅H₄Re(CO)₃ the orientation is different to that in C₅H₅Re(CO)₃, so that the molecule as a whole becomes less symmetrical. Unsubstituted cyclopentadienyl-manganese and -rhenium tricarbonyls are isostructural and entirely analogous; that the two acetyl derivatives are not isostructural is possibly caused by conformational differences. Both molecules have the “piano stool” configuration with the CH₃CO group almost coplanar with the cyclopentadienyl ring plane. Interatomic distances and bond angles in these molecules are typical for this type of compound.     

Chemie der Phosphorfluoride. XXXIX. Synthese und Untersuchung der Temperaturabhängigkeit der kernmagnetischen Resonanzspektren von Hexafluorisopropylideniminofluorphosphoranen und Fluorphosphin-Bis(Trifluormethyl)hexafluorisopropylideniminomethylimiden

Chemistry of Phosphorus Fluorides. XXXIX. Synthesis and Investigation of the Dependence of Temperature of the NMR Spectra of Hexafluoroisopropylidence Iminofluorophoranes and Fluorophosphin-Bis(Trifluormethy)hexafluroisopropylidene Imnomethylimides. The title compounds were obtained by the reaction of the lithium salt of hexafluoroisopropylimine with fluorophosphoranes, R_nPF_5?n (n = 0, 1; R = hydrocarbon group). ¹⁹F variable temperature n.m.r. spectra show intermediate rate of intramolecular exchange at phosphorus but apparent fast “isomerisation” at nitrogen. The fluorophosphine imides, on the other hand, show intermediate rates of “isomerisation” at nitrogen in the hexafluoroisopropylidene moiety.     

Synthesis and Redox and Photophysical Properties of Benzodifuran–Spiropyran Ensembles

Two benzodifuran (BDF)‐coupled spiropyran (SP) systems and their BDF reference compounds were obtained in good yields through Huisgen–Meldal–Sharpless “click” chemistry and then subjected to investigation of their electrochemical and photophysical properties. In both SP and merocyanine (MC) forms of the coupled molecules, the BDF‐based emission is quenched to around 1 % of the quantum yield of emission from the BDF reference compounds. Based on electrochemical data, this quenching is attributed to oxidative electron‐transfer quenching. Irradiation at 366 nm results in ring opening to the MC forms of the BDF‐coupled SP compounds and the SP reference compound with a quantum efficiency of about 50 %. The rate constants for the thermal ring closing are approximately 3.4×10^?3 s^?1. However, in the photostationary states the MC fractions of the coupled molecules are substantially lower than that of the reference SP compound, attributed to the observed acceleration of the ring‐closing reaction upon irradiation. As irradiation at 366 nm invariably also excites higher‐energy transitions of the BDF units in the coupled compounds, the ring‐opening reaction is accelerated relative to the SP reference, which results in lower MC fractions in the photostationary state. Reversible photochromism of these BDF‐coupled SP compounds renders them promising in the field of molecular switches.     

Vitamin B12: Experiments Concerning the Origin of Its Molecular Structure

Following the chemical synthesis of vitamin B₁₂, a search was begun for a potentially biomimetic “dark” variant of the photochemical A/D-secocorrin → corrin cycloisomerization, the central ring-closure step in one of the two cobyric acid syntheses. Significantly, not just one but a whole family of such variants was discovered. According to what is currently known, one of these variants can indeed be regarded as a chemical model for the reaction path followed by Nature in the biosynthetic construction of the corrin ring. These chemical studies of vitamin B₁₂ biosynthesis had revealed that the A/D-ring junction, regarded as the main obstacle to a chemical vitamin B₁₂ synthesis at the outset, is in fact a structural element that is formed readily and in a variety of ways from structurally appropriate precursors. More recent investigations have shown that the same holds for other specific structural elements of the vitamin B₁₂ molecule, including the characteristic arrangement of double bonds in the corrin chromophore, the special dimension of the macrocyclic ring of the corrin ligand, the specific attachment of the nucleotide loop to the propionic acid side chain of ring D, and the characteristic constitutional arrangement of the side chains around the ligand periphery (which vitamin B₁₂ shares with all uroporphinoid cofactors). All these outwardly complex structural elements are found to “self-assemble” with surprising ease under structurally appropriate preconditions; the amount of “external instruction” required for their formation turns out to be surprisingly small in view of the complexity and specificity of these structural elements. We view these findings as steps on the way toward a chemical rationalization of the vitamin B₁₂ structure. The goal is to arrive experimentally at a perception of the biomolecule's intrinsic potential for structural self-assembly. This potential, together with the specific type of reactivity related to the biological function, is considered to be responsible for the biomolecule having been chosen by natural selection. The chemical rationalization of the structure of biomolecules is an objective of organic natural product chemistry. The field of natural product synthesis provides appropriate conceptual and methodological tools to approach this objective experimentally.     

NMR study of the properties of Si-H bonds in monoorganosilanes

A comparative study has been carried out of the relation of the¹H chemical shifts of the SiH₃ and CH₃ groups in phenyl- and butylsilanes and in toluene on the value of the field at infinite dilution in 17 solvents with different volume permeabilities, in order to obtain reliable information on the properties of the Si-H bond in “isolated” molecules of monoorganosilanes. It is shown that the shielding constants for the hydrogens in the SiH₃ group are more sensitive to field changes than are those of the CH₃ group. There was no ring current effect on the chemical shift of the hydrogens of the SiH₃ group in phenylsilane, and this is connected with π-d conjugation of the aromatic ring with the silicon atom.