Nucleophilic Substitution at Phosphorus Centers (SN2@P)

We have studied the characteristics of archetypal model systems for bimolecular nucleophilic substitution at phosphorus (S_N2@P) and, for comparison, at carbon (S_N2@C) and silicon (S_N2@Si) centers. In our studies, we applied the generalized gradient approximation (GGA) of density functional theory (DFT) at the OLYP/TZ2P level. Our model systems cover nucleophilic substitution at carbon in X^?+CH₃Y (S_N2@C), at silicon in X^?+SiH₃Y (S_N2@Si), at tricoordinate phosphorus in X^?+PH₂Y (S_N2@P3), and at tetracoordinate phosphorus in X^?+POH₂Y (S_N2@P4). The main feature of going from S_N2@C to S_N2@P is the loss of the characteristic double‐well potential energy surface (PES) involving a transition state [X? CH₃? Y]^? and the occurrence of a single‐well PES with a stable transition complex, namely, [X? PH₂? Y]^? or [X? POH₂? Y]^?. The differences between S_N2@P3 and S_N2@P4 are relatively small. We explored both the symmetric and asymmetric (i.e. X, Y=Cl, OH) S_N2 reactions in our model systems, the competition between backside and frontside pathways, and the dependence of the reactions on the conformation of the reactants. Furthermore, we studied the effect, on the symmetric and asymmetric S_N2@P3 and S_N2@P4 reactions, of replacing hydrogen substituents at the phosphorus centers by chlorine and fluorine in the model systems X^?+PR₂Y and X^?+POR₂Y, with R=Cl, F. An interesting phenomenon is the occurrence of a triple‐well PES not only in the symmetric, but also in the asymmetric S_N2@P4 reactions of X^?+POCl₂? Y.     

Density functional theory study on the reactions of X− with CH3SY (X,Y = F,Cl, Br,I)

Gas‐phase anionic reactions X^? + CH₃SY (X, Y = F, Cl, Br, I) have been investigated at the level of B3LYP/6‐311+G (2df,p). Results show that the potential energy surface (PES) of gas‐phase reactions X^? + CH₃SY (X, Y = Cl, Br, I) has a quadruple‐well structure, indicating an addition–elimination (A–E) pathway. The fluorine behaves differently in many respects from the other halogens and the reactions F^? + CH₃SY (Y = F, Cl, Br, I) correspond to deprotonation instead of substitution. The gas‐phase reactions X^? + CH₃SF (X = Cl, Br, I), however, follow an A–E pathway other than the last two out going steps (COM2 and PR) that proceeds via a deprotonation. The polarizable continuum model (PCM) has been used to evaluate the solvent effects on the energetics of the reactions X^? + CH₃SY (X, Y = Cl, Br, I). The PES is predicted to be unimodal in the solvents of high polarity. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Kinetics and mechanism of some fast anation reactions of a series of substituted dien complexes of palladium(II). Temperature and pressure dependencies in weakly acidic aqueous solution1

Anation reactions of the type [Pd(L)(H₂O)]²⁺ + X^? »[Pd(L)X]⁺ + H₂O with L = 1, 4, 7-Et₃dien, 1, 1, 7, 7-Me₄dien and 1, 1, 4, 7, 7-Me₅dien and X^? = Cl^?, Br^?, I^? and N₃? have been studied kinetically as a function of [X?], temperature and pressure (up to 1 kbar). Second-order anation rate constants decrease with an increase in the size of L, and are accompanied by an increase in ΔH≠. For a given L the sequence Cl^? < Br^? < I^? < N₃^? holds, and the values of ΔS≠ and ΔV≠ are consistent with an associative mechanism. The results are discussed with reference to similar anation reactions previously investigated.     

Theoretical investigation on identical anionic halide‐exchange SN2 reaction processes on N‐haloammonium cation NH3X+ (X = F,Cl, Br,and I)

CCSD(T) calculations have been used for identically nucleophilic substitution reactions on N‐haloammonium cation, X^? + NH₃X⁺ (X = F, Cl, Br, and I), with comparison of classic anionic S_N2 reactions, X^? + CH₃X. The described S_N2 reactions are characterized to a double curve potential, and separated charged reactants proceed to form transition state through a stronger complexation and a charge neutralization process. For title reactions X^? + NH₃X⁺, charge distributions, geometries, energy barriers, and their correlations have been investigated. Central barriers ΔE for X^? + NH₃X⁺ are found to be lower and lie within a relatively narrow range, decreasing in the following order: Cl (21.1 kJ/mol) > F (19.7 kJ/mol) > Br (10.9 kJ/mol) > I (9.1 kJ/mol). The overall barriers ΔE relative to the reactants are negative for all halogens: ?626.0 kJ/mol (F), ?494.1 kJ/mol (Cl), ?484.9 kJ/mol (Br), and ?458.5 kJ/mol (I). Stability energies of the ion–ion complexes ΔE_comp decrease in the order F (645.6 kJ/mol) > Cl (515.2 kJ/mol) > Br (495.8 kJ/mol) > I (467.6 kJ/mol), and are found to correlate well with halogen Mulliken electronegativities (R² = 0.972) and proton affinity of halogen anions X^? (R² = 0.996). Based on polarizable continuum model, solvent effects have investigated, which indicates solvents, especially polar and protic solvents lower the complexation energy dramatically, due to dually solvated reactant ions, and even character of double well potential in reactions X^? + CH₃X has disappeared. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

The anomeric effect: Ab-initio studies on molecules of the type X?CH2?O?CH3

The anomeric effect of the functional groups X = C?N, C?CH, COOH, COO^?, O? CH₃, NH₂, and NH⁺₃ has been studied with ab initio techniques. Geometry effects upon rotation around the central C? O bond in X? CH₂? O? CH₃ have been compared in the various compounds. The energy differences between the conformers with a gauche and trans (X? C? O? C) arrangement were calculated at the 6-31G* level in the fully optimized 4-21G geometries. Energy differences calculated at the 4-21G level appeared not to be reliable, especially for the groups X that contain non-sp³ hybridized atoms. The 6-31G* energy differences indicate a normal anomeric effect for X = COO^?, O? CH₃, and NH₂(g⁺) (ca. 13 kJ/mol) and a small anomeric effect for X = COOH, C?N, and C?CH (ca. 6 kJ/mol). For X = NH₂(t) and NH⁺₃ a reverse anomeric effect occurs. These observations are in line with experimental results and evidence is given for a competition among various stereoelectronic interactions that occur at the same anomeric center. Geometry variations can be understood in terms of simple rules associated with anomeric orbital interactions. Trends followed when the group X is varied cannot be related in a straightforward way to the energy differences between the trans and the gauche forms in these compounds. Only the variation in the gauche torsion angle X? C? O? C follows roughly the same trend.     

Fluoridolyse von N-Phosphorylphosphazenen

Fluoridolysis of N-Phosphoryl Phosphazenes In the reaction of the N-phosphoryl phosphazenes X₃P?N? P(Y)X₂ (X = Cl, PhO, Et₂N, CF₃CH₂O, PrS, Ph; Y = O, S) ( 1 – 18 ) with Et₃N · nHF (n ≈? 3 or 0.6) fluoro derivatives of N-phosphoryl phosphazenes (see table 2) as well as N-phosphorylated imiddotetrafluorophosphates, [F₄P?N? P(Y)Cl₂]^? (Y = O, S), and imidopentafluorophosphates, [F₅P? N? P(Y)X₂]^2? or [F₅P? NH? P(O)X₂]^? (see table 3), are formed. t-BuNHPCl₂?N? POCl₂ reacts in acetonitrile with Et₃N or i-Pr₂EtN to form a product, representing probably the diazadiphosphetine ( 5 b ).     

Photochemical loss of dinitrogen from cyclopentadienylcobalt 1,4-diaryltetraazadienes

Irradiation of the thermally stable metallotetraazadiene complexes [(η⁵-C₅H₅)Co(RN₄R)] (R = C₆H₅, C₆F₅) with visible or low-energy UV light, produces an unusual transformation to the diimine complexes [(η⁵-C₅H₅)Co(HNC₆X₄NC₆X₅)] X = H (IVa), F (IVb). Disappearance quantum yields for both reactions are wavelength-dependent (IIIa → IVa: Φ₃₆₆ = 2.4 × 10^?4; Φ₃₁₃ = 26 × 10^?4; IIIb → IVb: Φ₃₆₆ = 9.8 × 10^?4; Φ₃₁₃ = 45 × 10^?4). Crossover experiments are consistent with an intramolecular rearrangement.     

15N- und 19F-NMR-spektroskopischer Nachweis und Xa-Austauschreaktionen der Clusteranionen [(Mo6Cl)(15NCS) X]2−, Xa = F,Cl, Br,I; n = 1–6

¹⁵N and ¹⁹F NMR Spectra and X^a-Exchange Reactions of the Cluster Anions [(Mo₆Clⁱ₈)(¹⁵NCS)^a_nX^a_6?n]^2?, X^a = F, Cl, Br, I; n = 1–6 By intermolecular ligand exchange reaction of the new compound [(Mo₆Clⁱ₈)(¹⁵NCS)^a₆] ^2? with [(Mo₆Clⁱ₆)X^a₆]^2?, X^a = F, Cl, Br, I, in acetone, the outersphere mixed cluster ions [(Mo₆Clⁱ₈)(¹⁵NCS)^a₆X^a_6?n]^2?, n = 1–6, are formed and characterized by their distinct ¹⁵N nmr chemical shifts. The ambident SCN^? is exclusively N-bonded, indicated by ¹⁵N nmr and vibrational spectra. The mixed cluster ions containing X^a = F are identified in acetonitrile by ¹⁹F nmr measurement as well. The kinetic analysis reveals equilibration at room temperature within 10 hours to statistical distribution of all compounds, inclusive the ratios for the geometric isomers for each system at any time with n = 2,4 cis:trans = 4 : 1 and n = 3 fac:mer = 2 : 3, indicating the equivalence of all X^a positions with respect to exchange reactions. For [(Mo₆Clⁱ₈)X^a₆]^2? the reaction rates increase in the series X^a = Cl < Br < I < SCN < F. The ¹⁵N nmr chemical shifts are depending on the electronegativity and the number of the X^a ligands. Furthermore an antipodal influence working on ¹⁵N trans-positioned to X^a effects an additional highfield shift for X^a = F and an additional downfield shift for X^a = Cl, Br, I.     

Kinetics of the reactions Br + NO2 + M and I + NO2+ M

The reactions Br + NO₂ + M → BrNO₂ + M (1) and I + NO₂ + M → INO₂ + M (2) have been studied at low pressure (0.6-2.2 torr) at room temperature and with helium as the third body by the discharge-flow technique with EPR and mass spectrometric analysis of the species. The following third order rate constants were found k₁₍₀₎ = (3.7 ± 0.7) × 10^?31 and k₂₍₀₎ = (0.95 ± 0.35) × 10^?31 (units are cm⁶ molecule^?2 s^?1). The secondary reactions X + XNO₂ → X₂ + NO₂ (X = Br, I) have been studied by mass spectrometry and their rate constants have been estimated from product analysis and computer modeling.     

An electrical conductivity (EC) study of the thermal dissociation of [Co(NH3)6]X3 and [Co(en)3]X3 complexes

The thermal dissociation of the [Co(NH₃)₆]X₃ (X = Cl^?, Br^?, I^?, and NO^?₃), [Co(en)₃]X₃ (X = Cl^?, Br^?, I^?, NO^?₃, HSO^?₄ and $\text{1}\text{2}$ C₂O^2?₄), cis- [Co(en)₂Cl₂]Cl, and trans-[Co(en)₂ClBr]NO₃ complexes was investigated by an electrical conductivity (EC) technique. During the thermal dissociation reactions, liquid or semi-liquid phases are formed which cause large increases in the EC of the compound. The effect of concentration of the complex in a matrix medium as well as the composition of the matrix material on the EC curves were also determined.     

Thermochromie der organischen Lösungen des Nickel-komplexes von N,N′-Bis[3-Aminopropyl] Piperazin

Thermochromism of Organic Solutions of N,N′-Bis-(3-Aminopropyl)Piperazine Nickel Complexes The orange-red planar nickel complex of N,N′-bis-(3-aminopropyl)piperazine (bapp) is thermochromic in solutions of acetonitril and DMF, and becomes blue at low temperature. This change is caused by the formation of the 6-coordinated species [NibappL₂]²⁺ (L = solvent molecule). If Cl^? or Br^? ions coexist, other kinds of thermochromism involving the formation of the 5-coordinated species [NibappX]⁺ (X^? = Cl^? or Br^?) are observed. Spectral data on these phenomena are given, together with those observed in nitromethane, and discussed in terms of the coordination abilities of L and X^?.     

Kinetics of the reactions of O(3P) and Cl(2P) with HBr and Br2

A laser flash photolysis-resonance fluorescence technique has been employed to study the kinetics of reactions (1)–(4) as a function of temperature. In all cases, the concentration of the excess reagent, i.e., HBr or Br₂, was measured in situ in the slow flow system by UV-visible photometry. Heterogeneous dark reactions between XBr (X = H or Br) and the photolytic precursors for Cl(²P) and O(³P) (Cl₂ and O₃, respectively) were avoided by injecting minimal amounts of precursor into the reaction mixture immediately upstream from the reaction zone. The following Arrhenius expressions summarize our results (errors are 2σ and represent precision only, units are cm³ molecule^?1 s^?1): ??₁ = (1.76 ± 0.80) × 10^?11 exp[(40 ± 100)/T]; ??₂ = (2.40 ± 1.25) × 10^?10 exp[?(144 ± 176)/T]; ??₃ = (5.11 ± 2.82) × 10^?12 exp[?(1450 ± 160)/T]; ??₄ = (2.25 ± 0.56) × 10^?11 exp[?(400 ± 80)/T]. The consistency (or lack thereof) of our results with those reported in previous kinetics and dynamics studies of reactions (1)–(4) is discussed.     

The solid state reaction between hexaamminechromium(III) complexes and L-α-alanine

The solid reaction between [Cr(NH₃)₆]X₃(X^? = Cl, I, SCN and NO₃) and L-α-alanine was studied under continuous rise in temperature and isothermal heating. Under continuous rise in temperature, the main products were [Cr(NCS)₃-(NH₃)₃] (X^? = NCS) and [Cr(L-ala)₃] (X^? = NO₃), when [Cr(NH₃)₆]Cl₃ and [Cr(NH₃)₆]I₃ as starting complexes were used; in both cases only the decomposition proceeds. Under isothermal heating at 150°C the main products were [CrCl(NH₃)₅]-Cl₂ (X^? = Cl), [Cr(NH₃)₆]I₂ (X^? = I), [Cr(NCS)₃(NH₃)₃] (X^? = SCN) and [Cr(L-ala)₃] (X^? = NO₃). In those matrix reactions, the ease of anion coordination was: SCN^? > Cl^? > I^? > alanine. For the synthesis of tris(alaninato)chromium(III) complex the most desirable starting complex was [Cr(NH₃)₆](NO₃)₃.The solid state reaction between [Cr(en)₃]X₃ type complexes and NH₄X (X^? = F, Cl, Br, I and SCN), KX (X^? = Cl, Br and I), and NaSCN have been reported by Wendlandt and Stembridge¹. They reported that the reaction product in most cases, was cis-[Cr(en)₂Y₂]X, where Y and X are the same or different anions, depending upon the matrix material employed and the thermal matrix method appears to be a useful new route for the synthesis of bis(ethylendiamine(chromium(III) complexes.In the previous paper², the solid state reaction between [Cr(NH₃)₆](NO₃)₃ and L-amino acids has been utilized in the preparation of tris(amino acidato)chromium(III) complexes. The preparation of [Cr(L-ala)₃] by the solid state reaction between [Cr(NH₃)₆](NO₃)₃ and L-alanine have been reported. No studies on the effect of the counter-ion have been reported.In this paper, various hexaamminechromium(III) complexes, [Cr(NH₃)₆]X₃ (X^? = Cl, I, SCN and NO₃), were heated with L-α-alanine under continuous rise in temperature and under isothermal heating at 150°C for studies on the ease of anion coordination. It will seen that the anion which replaces the ammonia in the hexaamminechromium(III) complex comes from either the alanine or counter-ion.     

THE PHENOMENON OF CONGLOMERATE CRYSTALLIZATION. PART 54. THE CRYSTALLIZATION MODES OF FIVE NEW COMPLEXES [TRANS-(3,2,3-TET)Co(III)X 2]Y,X=NO− 2, CN−, NCS−

Abstract

A few complexes of formula [trans-Co(N₄)X ₂]Y, where X = a monodentate ligand, N₄ = a tetraamine ligand and Y = a halide or oxy anion have been found to crystallize as conglomerates; however, the majority crystallize as racemates. The complexes are of such variety of composition and packing characteristics that it is difficult to ascertain why they crystallize in one form or the other. We decided to investigate a series of [trans-Co(N₄)X ₂]Y compounds in which the amine was kept constant in order to limit the variables that affect the outcome.

Five different compounds of composition [trans-Co(3,2,3-tet)X ₂]Y (3,2,3-tet = 1,10-diamino-4,7-diaza-decane, X = NO^? ₂, CN^?, SCN^?, and Y = BF^? ₄, Cl^?, Br^?, I^?) were prepared and their crystallization behavior examined by determining their crystal structures. In all cases, when crystallized from deionized water at 21°C, these substances are racemates. Suggestions regarding this crystallization mode are offered in the discussion.     

Extraction of Perchlorate and Iodide by Ion-Pair Formation with the Iron(II)-di(2-Pyridyl)N,N-DI[(8-quinolyl)amino]methane Complex

Abstract

Di(2-pyridyl)N, N-di[(8-quinolyl)amino]methane (DPQAM) was used for the substoichiometric extraction and photometric determination of perchlorate and iodide in the ranges 10–1000 and 50–1000 ppm, respectively, by extraction of the Fe(DPQAM)₂X₂ (X = C1O₄ ^? or I^?) into chloroform. The determination ranges were found to be dependent on the Fe(II) concentration used.     

Kinetics and mechanism of the reaction of para‐chlorophenyl aryl chlorophosphates with anilines in acetonitrile

The kinetics and mechanism of the nucleophilic substitution reactions of p‐chlorophenyl aryl chlorophosphates ( 2 ) with anilines are investigated in acetonitrile at 55°C. Relatively large magnitudes of ρ_X and β_X values are indicative of a large degree of bond making in the TS. Smaller magnitudes of ρ_X (0.20 for X = H) and ρ_XY (?0.30) than those for the corresponding reactions with phenyl aryl chlorophosphates ( 1 ) (ρ_X = 0.54 for X = H and ρ_XY = ?1.31) are interpreted to indicate partial electron loss, or shunt, towards the electron acceptor equatorial ligand (p‐ClC₆H₄O‐) in the bipyramidal pentacoordinated transition state. The inverse secondary kinetic isotope effects (k_H/k_D = 0.64–0.87) involving deuterated aniline (ND₂C₆H₄X) nucleophiles, and small ΔH^? and large negative ΔS^? are obtained. These results are consistent with a concerted nucleophilic substitution mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 632–637, 2002     

NH(A3Π → X3Σ−) Chemiluminescence from the CH(X2 Π) + NO reaction

NH(A³Π → X³Σ^?) and OH(A²Σ⁺ → X²Π) chemiluminescences from the reaction of CH(X²Π) with NO and O₂, respectively, have been observed at room temperature. From the decay of such emissions we have measured the rate constants for these two reactions: k_NO = (2.5 ± 0.5) × 10^?10 and k_O2 = (8 ± 3) × 10^?11 cm³ molecule ^?1 s^?1, which are in agreement with previously reported rates determined by direct CH(X) detection using, laser-induced fluorescence. This indicates that a four-centered mechanism generating these excited species is operative in both reactions. The CH generation from 266 nm photolysis of CHBr₃ has also been investigated via analysis of CH* emissions.     

Thermal decompositions of N-methylpyridinium,quinolinium, isoquinolinium and phenanthridinium salts in a mass spectrometer. Evidence for a specific HI elimination and for an oxidation to amides

The mass spectra of some N-methylpyridinium, quinolinium, isoquinolinium and phenanthridinium salts (R⁺X^?)

1 The salt will be represented by R⁺X^? or RX, R⁺ being the organic moiety, with its associated mass and X- the inorganic anion.

are analyzed (X^? = I^? or ClO₄^?). For X^? = I^?, thermal decomposition gives rise mainly to the superimposed spectra of CH₃I and the free base. Hence, iodide salts cannot be determined specifically by their mass spectra. When an α-methyl group is present, e.g. 2-methylpyridinium methiodide, elimination of HI becomes an important thermal process. For X^? = ClO₄^?, the same pattern is observed, but in addition a generally important peak at [R + 15] is present. This peak is due to the oxidation, mainly α to the nitrogen of the organic moiety by the ClO₄^? ion, giving rise to the corresponding amide. In some cases, chlorination of the organic moiety has been observed as well as double oxidation. The thermal processes for the perchlorate salts are characteristic and are useful in the elucidation of the quaternary structure.     

Kraftkonstanten von Verbindungen des Typs (CH3)3ElCl+X− (El = N,P, As,Sb; X− = SbCl6−)

Force Constants of Compounds of the Type (CH₃)₃ElCl⁺X^?(El = N, P, As, Sb; X^? = SbCl₆^?) For the cations (CH₃)₃NCl⁺ ( 1 ), (CH₃)₃PCl⁺ ( 2 ), (CH₃)₃AsCl⁺ ( 3 ), and (CH₃)₃SbCl⁺ ( 4 ) a normal coordinate analysis using a general valence force field is performed by the method of Fadini. The force constants are discussed. Calculations of the potential energy distribution show, that the skeletal vibrations in 4 are all characteristic vibrations, but there is a strong coupling of vibrations in 1 .     

Theoretical study on a chemosensor for fluoride anion‐based on a urea derivative

The sensing mechanism of the N‐Phenyl‐N′‐(3‐quinolinyl)urea (PQU) chemosensor for fluoride anion has been investigated by density functional theory/time‐dependent density function theory. The double intermolecular hydrogen bonds are formed between the three anions (X^??F^?, AcO^?, Cl^?) and the urea fragment of PQU. In the S₀ states, the H_b? X^? hydrogen bonds are slightly stronger than the H_a? X^? hydrogen bonds and the fluoride‐induced deprotonation occurs at the N? H_b position rather than at the N? H_a position. Consequently, the absorption peaks, including an intramolecular charge transfer transition and a ππ* transition, are significantly red‐shifted. Thermodynamic calculations confirm that the deprotonation in the ground state is favorable in energy only when excess fluoride anion exists. Along with the S₀ → S₁ transition, the H_a? X^? hydrogen bonds strengthen and the H_b? X^? hydrogen bonds weaken. However, the emission spectra of [PQU‐H_b]^?, instead of [PQU‐H_a]^?, are observed upon addition of fluoride anion. © 2013 Wiley Periodicals, Inc.