Carboxyl derivatives of phosphazenes

The review describes the modern methods of synthesis and chemical modification of carboxylcontaining phosphazenes. The possibility of their use in the synthesis of polyamides, epoxy resins, star-shaped and structured polymers, hydrogels, and metal complexes is considered. Carboxyl-containing phosphazenes and their derivatives are of great interest for medicine, electronics, photonics, and design of multipurpose hightech composite materials, offering wide opportunities for further research and application.     

Reaction of acetylenic esters and N-functionalized phosphazenes. 1,2-versus 1,4-addition of N-vinylic phosphazenes

Reaction of phosphazenes derived from aminophosphonates with acetylenic esters leads to conjugated phosphorus ylides. The formation of these stabilized ylides is explained through a [2 + 2] cycloaddition reaction of the P = N linkage of the phosphazene (1,2-addition) and the triple bond of the acetylenic ester followed by ring opening of the azaphosphete intermediate. However, in the case of N-vinylic phosphazenes, the phosphazenes derived from triphenyl- and trimethyl-phosphine react as enamines (1,4-addition) with diacetylenic esters, whereas in phosphazenes derived from trimethylphosphine a 1,2-addition of ethyl propiolate to the P = N linkage of the phosphazene is produced.     

Synthesis and structure of nongeminally substituted cyclic phosphazenes with haloalkyl and thioester functional groups

Nongeminally substituted cyclic phosphazenes with various haloalkyl substituents were prepared using deprotonation-substitution reactions at the methyl groups of the cis isomers of nongeminally substituted cis-[Me(Ph)P=N]3, 2. Treatment of 2 with n-BuLi followed by reaction with organic halogenated reagents (RX=C2Cl6, BrC(O)CMe2Br, and ICH2COOEt) at low temperature afforded the various cyclic derivatives cis-[(XCH2)(Ph)PN]3 (3, X=Cl, 4, Br, and 5, I). The mono- and dibromoalkyl derivatives, cis-[Ph3(BrCH2)Me2P3N3], 6, and [Ph3(BrCH2)2MeP3N3], 7, were also isolated along with 4 when the electrophile was dibromoethane. Reaction of cis-[Ph(BrCH2)PN]3, 4, with KSC(O)Me gave cis-[Ph(MeC(O)SCH2)PN]3, 8. The structures of all the cis cyclic phosphazenes were determined by NMR spectroscopy and X-ray diffraction. All retained the basketlike shape with the hydrophobic phenyl groups opposite the haloalkyl groups on the P3N3 ring. Thermal analysis of the new cyclic trimers indicates that ring-opening polymerization does not occur. The melting points and the thermal stabilities of haloalkyl cyclophosphazenes were higher than those of the parent compound 2.     

Tuning the electronic structure of diboradiferrocenes

A series of diboradiferrocenes with different aryl substituents was prepared through reaction of B,B-dichlorodiboradiferrocene with arylcopper and Grignard reagents. The mesityl and pentafluorophenyl derivatives, - and -, were fully characterized by multinuclear NMR, MALDI-TOF mass spectrometry and X-ray crystallography, and their electronic structure was examined by UV-visible spectroscopy and cyclic voltammetry. A comparison of the data for - and - with those of the parent compound - revealed the importance of electronic and steric effects of the substituents on the electronic structure of the compounds and ultimately the degree of electronic interaction between the two ferrocene moieties. An unusually large redox splitting of DeltaE = 703 mV was determined from the cyclic voltammogram of -.     

Experimental gas-phase basicity scale of superbasic phosphazenes

Seventeen superbasic phosphazenes and two Verkade's bases were used to supplement and extend the experimental gas-phase basicity scale in the superbasic region. For 19 strong bases the gas-phase basicity values (GB) were determined for the first time. Among them are such well-known bases as BEMP (1071.2 kJ/mol), Verkade's Me-substituted base (1083.8 kJ/mol), Et-N=P(NMe2)2-N=P(NMe2)3 (Et-P2 phosphazene, 1106.9 kJ/mol), and t-Bu-N=P(NMe2)3 (t-Bu-P1 phosphazene, 1058.0 kJ/mol). For the first time experimental GB values were determined for P2 phosphazenes. Together with our previous results self-consistent experimental gas-phase basicity scale between 1020 and 1107 kJ/mol is now established. This way an important region of the gas-phase basicity scale, which was earlier dominated by metal hydroxide bases, is now covered also with organic bases making it more accessible for further studies. The GB values for several superbases were calculated using density functional theory at the B3LYP/6-311+G** level. For the phosphazene family the standard deviation of the correlation between the experimental and theoretical values was 6.5 kJ/mol.     

Linear, cyclic and polymeric phosphazenes

An assessment of the diversity of phosphazene chemistry is presented with an emphasis on recent developments and their significance. Fundamental properties of phosphazenes are examined such as structure, nomenclature and bonding, and the various synthetic procedures are catagorized. In addition, the more important reactivity patterns are detailed and analysed. The review compares all systems containing the phosphazene bond, and makes extensive reference to previous reviews on specific types of phosphazene.     

The electronic structure of the silyl halides

Calculations have been performed on the silyl and methyl halides, using the CNDO method and the photoelectron spectra of the silyl halides are interpreted from the results. Inclusion of d orbitals on silicon is found to be necessary so that the calculated ionisation potentials of silyl bromide and chloride are greater than the corresponding methyl compounds, in agreement with observation.One of us (J.J.) thanks the Scottish Education Department for a Maintenance Grant.     

The electronic structure of the boron hydrides

The expansion of topological basis functions for tetrahedral and octahedral boron cage molecules in terms of an explicit atomic orbital basis is considered. A maximum localisation criteria is used to define mixing coefficients. The overlap between face basis functions in the two geometries is 0.79 and only a very crude parameter transferability exists. However, some aspects of the relative molecular orbital energy levels generated with a topological basis appear to be an improvement on those using an atomic orbital basis.

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Zusammenfassung Die Entwicklung topologischer Basisfunktionen nach einer expliziten Basis von Atomorbitalen für käfigförmige, tetraedrische und oktaedrische Moleküle, die Boratome enthalten, wird untersucht. Ein Kriterium maximaler Lokalisierung wird zur Bestimmung der Mischungskoeffizienten verwendet. Die Überlappung zwischen den Basisfunktionen, die zu den Seiten der beiden Geometrien gehören, beträgt 0,79, und es existiert nur eine ungefähre Übertragbarkeit der Parameter. Einige Aspekte der relativen MO-Energiewerte, die mit einer topologischen Basis gewonnen wurden, stellen eine Verbesserung gegenüber der Verwendung einer Atomorbitalbasis dar.

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Résumé Développement des fonctions de base topologiques en termes d'une base explicite d'orbitales atomiques pour des molécules cages de bore tétraédrique et octaédrique. Un critère de localisation maximum est utilisé pour définir les coefficients de mélange. Le recouvrement entre les fonctions de base faciales dans les deux geometries est de 0.79 et la transférabilité des paramètres n'est que très grossière. Cependant, certains aspects relatifs des niveaux d'énergie des orbitales moléculaires engendrées avec une base topologique apparaissent plus satisfaisants que ceux obtenus avec une base d'orbitales atomiques.

     

The electronic structure of the disilavinylidene anion

The electronic structure of the disilavinylidene (H₂Si = Si)⁻ anion is investigated with the MC SCF CI and CEPA methods. In addition to the doublet ground state (²B₂) with an electron affinity of 1.65 eV, an excited state (⁴A'') is found which is still stable by about 0.6 eV.     

Relativistic electronic structure theory

The theoretical and technical foundations are presented for the efficient relativistic electronic structure theories to treat heavy-atomic molecular systems. This review contains two surveys of four-component and two-component quasi-relativistic approaches. First, we review our highly efficient computational scheme for four-component relativistic ab initio molecular orbital (MO) methods over generally contracted spherical harmonic Gaussian-type spinors (GTSs). Illustrative calculations, which are performed with a new four-component relativistic ab initio molecular orbital program package REL4D, clearly show the efficiency of our computational scheme by the Dirac-Hartree-Fock (DHF) and Dirac-Hartree-Fock (DKS) methods. Next, in the two-component quasi-relativistic framework, two relativistic Hamiltonians, RESC and higher order Douglas-Kroll (DK) Hamiltonians, are introduced, and several illustrative calculations are shown. Numerical results for several systems show that good accuracy can be obtained with our third-order DK (DK3) Hamiltonian.     

The electronic spectrum and electronic structure of 1,5 dinitronaphthialene

The electronic absorption spectra of the n-heptane and ethanol solutions and the polarized absorption spectrum of the single crystal were measured with 1,5-dinitronaphthalene. 1,5-Dinitronaphthalene shows three absorption bands at 198.7, 230 and 323 m. The 230 m and 323 m. bands are polarized almost parallel with the long and short axes of the naphthalene ring respectively. The assignment of the bands has been made by combining the observed results with the theoretical consideration.

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Zusammenfassung Das UV-Absorptionsspektrum von 1,5-Dinitronaphthalin in Lösung von n-Heptan und Äthanol und das Polarisationsabsorptionsspektrum des Einkristalls wurde aufgenommen. Es zeigt drei Banden bei 198,7, 230 und 323 m, wobei die Polarisationsrichtungen der beiden letzteren nahezu parallel zur langen und kurzen Achse des Naphthalinringes liegen. Die Zuordnung der Banden wurde auf Grund einer Kombination experimenteller und theoretischer Gegebenheiten vorgenommen.

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Résumé Le spectre électronique d'absorption du 1,5-dinitronaphthalène a été mesuré dans l'éthanol, le n-heptane et dans le monocristal. Des bandes à 198,7, 230 et 323 m la deuxième (troisième) est polarisée presque parallèle à l'axe longue (courte) du noyau naphthalénique. La comparison aux résultats théoriques permet l'interprétation des bandes.

     

On the electronic structure of the hydrogenase H-cluster

X-ray absorption spectroscopic measurements and density functional calculations suggest that the hydrogenase H-cluster is best described as an electronically inseparable 6Fe-cluster due to extensive delocalization of frontier molecular orbitals of the iron centres, sulfide and the non-innocent dithiolate ligands.     

The electronic structure of dibenzotetrathiafulvalene

The electronic polarization spectrum in stretched polyethylene film and the photoelectron spectrum of dibenzotetrathiafulvalene are reported. The spectra are compared with those of tetrathiafulvalene, and discussed in terms of semi-empirical calculations.