Characterization of the selenotrisulfide formed by reaction of selenite with end-capped phytochelatin-2

The phytochelatins are a family of peptides synthesized by plants in response to exposure to heavy metals and metalloids, including selenium in the form of selenite. The amino acid sequence of the phytochelatin (PC) peptides is (-Glu-Cys) _n -Gly, where n typically ranges from 2 to 5. In this paper, the products of the reaction of selenite with an end-capped analogue of PC₂, Ac-(-Glu-Cys)₂-Gly-NH₂, are characterized. Selenite reacts with Ac-(-Glu-Cys)₂-Gly-NH₂ (Ac-PC2-NH₂) to form a compound that contains an intramolecular selenotrisulfide (-SSeS-)-linkage (Se[Ac-PC2-NH₂]) and oxidized Ac-PC2-NH₂. Both Se[Ac-PC2-NH₂] and oxidized Ac-PC2-NH₂ were isolated by HPLC and were characterized by MALDI–TOF mass spectrometry, by two-dimensional ¹H and ¹³C NMR and, in the case of Se[Ac-PC2-NH₂], by ⁷⁷Se NMR. Using dihedral angles determined from vicinal ¹H–¹H coupling constants as constraints for the conformations around the Cys_CH–Cys_CH bonds, structures were predicted for the most abundant form of both compounds by Monte Carlo molecular mechanics simulations.     

Synthesis and structures of new 1,3,6,2-dioxazaborocanes containing substituents in the ocane fragment

New 1,3,6,2-dioxazaborocanes R¹N(CHR³CR⁴R²O)(CHR⁶CHR⁵O)BX (1–11, X = Ph, 4-MeC₆H₄, Me; R¹ = Me, PhCH₂; R², R³, R⁴, R⁵, R⁶ = H, Ph) were synthesized by the reactions of aryl- or methylboronic acids with dialkanolamines. The treatment of (Me₂NCH₂CH₂O)₃B (15) with MeN(CH₂CH₂OH)(CH₂CPh₂OH) afforded 2-[2-(dime-thylamino)ethoxy]-1,3,6,2-dioxazaborocane (12). 2-Fluoro-1,3,6,2-dioxazaborocanes R¹N(CHR³CHR²O)(CH₂CH₂O)BF (13: R¹ = PhCH₂, R² = R³ = H; 14: R¹ = Me, R² = R³ = Ph, threo) were synthesized by the reaction of bis(trimethylsilyl) ethers of the corresponding dialkanolamines with BF₃·Et₂O. The new borocanes can be used for the synthesis of the corre-sponding germanium derivatives PhCH₂N(CH₂CH₂O)₂GeX₂ (16, X = OEt; 17, X = Cl), as exemplified by the reaction of compound 6. The structures of erythro-MeN(CH₂CH₂O)(CHPhCHPhO)BPh (3), threo-MeN(CH₂CH₂O)(CHPhCHPhO)BPh (4), erythro-MeN(CH₂CH₂O)(CHPhCHPhO)B(4-MeC₆H₄) (8), and PhCH₂N(CH₂CH₂O)₂BF (13) were established by X-ray diffraction. The coordination polyhedra of the boron atoms in these complexes can be described as distorted tetrahedra. The boron-nitrogen distances (1.705(7)–1.723(3) Å) provide unambiguous evidence for the presence of the B←N transannular interaction in these compounds. The structures of the resulting borocanes containing phenyl substituents at the carbon atoms of the ocane skeleton were studied by NMR spectroscopy and quantum chemical density functional theory calculations.     

New divalent samarocenes for butadiene polymerisation: influence of the steric effect and the electron density on the catalytic activity

Two new divalent samarocenes, Cp^*′₂Sm(THF) (1) and (Cp^Ph3)₂Sm(THF) (2) (Cp^*′=C₅Me₄ⁿPr, Cp^Ph3=H₂C₅Ph₃-1,2,4), were synthesized and characterized by ¹H NMR and elemental analysis. The activity of 1 and 2 as butadiene polymerisation catalysts was studied, in the presence of MAO and MMAO, and compared to this of Cp^*₂Sm(THF)₂ (3) and (Cp⁴ⁱ)₂Sm (4) (Cp^*=C₅Me₅, Cp⁴ⁱ=C₅HⁱPr₄), in the same conditions. The 1/MAO system presents the highest activity. The less active 2/MAO system leads to a high cis-1,4 regular structure up to 97%. The MMAO cocatalyst is found very sensitive to the steric hindrance of the samarocenes: the activity decreases from 1/MAO to 1/MMAO, and no activity is observed in the case of complexes 2 and 4, associated to MMAO. Complexes 1 and 2 can be both oxidized with AlMe₃ to give the corresponding Sm/Al bimetallics and , respectively.     

Substituent group effects on the self-assembly of oxovanadium(V) complexes with hydrazone ligands bearing benzoic acid (1-methyl-3-oxobutylidene)hydrazide backbones

An oxo-bridged dinuclear oxovanadium(V) complex, [V₂O₂(μ-O)(L¹)₂] (1) [H₂L¹ = 3-nitrobenzoic acid (1-methyl-3-oxobutylidene)hydrazide], and a mononuclear oxovanadium(V) complex, [VO(OMe)(L²)] (2) [H₂L² = 3-hydroxynaphthalene-2-carboxylic acid (1-methyl-3-oxobutylidene)hydrazide], were prepared by the reactions of [VO(acac)₂] with H₂L¹ and H₂L², respectively, in methanol. Both complexes were characterized by elemental analysis, IR spectra, and single crystal X-ray crystallography. The crystal of 1 crystallizes in the monoclinic space group P2/n, with a = 13.116(3) Å, b = 7.597(2) Å, c = 13.927(2) Å, β = 104.851(2)°, V = 1341.4(5) ų, Z = 2. The crystal of 2 crystallizes in the triclinic space group \(P\overline 1 \), with a = 7.897(2) Å, b = 9.690(2) Å, c = 11.576(3) Å, α = 86.405(2)°, β = 70.597(2)°, γ = 85.991(2)°, V = = 832.7(3) ų, Z = 2. The V atoms in the complexes have square pyramidal environment. The substituent groups attached to the aromatic rings can influence the self-assembly of the complexes.     

Regiospecific and sequential P-C bond activation/cluster transformations in the reaction of PhCCo2MoCp(CO)8 with the diphosphine ligands 2,3-bis(diphenylphosphino)maleic anhydride (bma) and 3,4-bis(diphenylphosphino)-5-methoxy-2(5H)-furanone (bmf)

Thermolysis of the mixed-metal cluster PhCCo₂MoCp(CO)₈ (1) with the diphosphine ligand 2,3-bis(diphenylphosphino)maleic anhydride (bma) in CH₂Cl₂ leads to the sequential formation of the phosphido-bridged cluster Co₂MoCp(CO)₅[μ₂,η²,η¹-C(Ph)CC(PPh₂)C(O)OC(O)](μ-PPh₂) (3) and the bis(phosphido)-bridged cluster Co₂MoCp(CO)₄[η³,η¹,η¹-C(Ph)CCC(O)OC(O)](μ-PPh₂)₂ (4). 3 and 4 have been isolated and characterized in solution by IR and NMR (¹H, ¹³C, and ³¹P) spectroscopies, and the solid-state structures have been established by X-ray diffraction analyses. Both clusters contain 48e- and exhibit triangular Co₂Mo cores. The structure of 3 reveals the presence of a phosphido moiety that bridges the Co-Co vector and a six-electron μ₂,η²,η¹-C(Ph)CC(PPh₂)C(O)OC(O) ligand that caps one of the Co₂Mo faces. The X-ray structure of 4 confirms that the five-electron η³,η¹,η¹- C(Ph)CCC(O)OC(O) ligand is σ-bound to the two cobalt centers in an η¹ fashion and π-coordinated to the molybdenum center through a traditional η³-allylic interaction. The reaction between PhCCo₂MoCp(CO)₈ and the chiral diphosphine ligand 3,4-bis(diphenylphosphino)-5-methoxy-2(5H)-furanone (bmf) proceeds similarly, furnishing the phosphido-bridged cluster Co₂MoCp(CO)₅ [μ₂,η²,η¹-C(Ph)CC(PPh₂)C(O)OCH(OMe)](μ-PPh₂) (6), followed by conversion to Co₂MoCp(CO)₄[η³,η¹,η¹-C(Ph)CCC(O)OCH(OMe)](μ-PPh₂)₂ (7). The identities of clusters 6 and 7 have been ascertained by solution spectroscopic methods and X-ray crystallography. The overall molecular structure of cluster 6 is similar to that of cluster 3, except that the P-C(furanone ring) bond cleavage occurs with high regioselectivity and high diastereoselectivity. The cleavage of the remaining P-C(furanone ring) bond in cluster 6 gives rise to the bis(phosphido)-bridged cluster 7, whose structure is discussed relative to its bma-derived analogue 4. The diastereoselectivity that accompanies the formation of 6 and 7 is discussed relative to steric effects within the Co₂Mo polyhedron. The cyclic voltammetric properties of cluster 3 have been examined, with three well-defined one-electron processes for the 0/+1, 0/−1, −1/−2 redox couples found. The composition of the HOMO and LUMO in 3 was established by extended Hückel MO calculations, with the data discussed relative to the parent tetrahedrane cluster 1.     

Synthesis,crystal structure,and kinetics of thermal decomposition of the Zn(II) complex with vanillin

A complex [Zn(C₈H₇O₃)₂(H₂O)₂] (C₈H₈O₃ is vanillin) has been synthesized and characterized by IR, elemental analysis, and X-ray diffraction single-crystal analysis. The crystals are monoclinic, space group C2/c, a = 22.236(8) Å, b = 10.594(2) Å, c = 7.8190(16) Å, α = 89.90(3)°, β = 106.87(4)°, γ = 89.99(3)°, V = 1762.6(8) ų, Z = 4, F(000) = 832, S = 1.079, ρ _c = 1.521g cm^?3, R = 0.0221, R _w = 0.0604, μ = 1.433 mm^?1. The Zn²⁺ ion is six-coordinated with a distorted octahedron geometry. The complex forms a three-dimensional network through intermolecular hydrogen bonds. The thermal decomposition kinetics of the complex for the second stage was studied under non-isothermal conditions by the TG and DTG methods. The kinetic equation can be expressed as dα/dt = Ae^?E/RT 2(1 ? α)[1 ? ln(1 ? α)]^1/2. The kinetic parameters (E, A), activation entropy ΔS ^≠, and activation free-energy ΔG ^≠ were also gained.     

The 3,5-dimethyl-4-nitropyrazole ligand in the construction of supramolecular networks of silver(I) complexes

Three new ionic silver complexes based on the 3,5-dimethyl-4-nitropyrazole ligand (Hpz^NO₂) and 1:2 or 1:3 (Ag:Hpz^NO₂) stoichiometries, [Ag(Hpz^NO₂)₂][BF₄], [Ag(Hpz^NO₂)₃][SbF₆] and [Ag(Hpz^NO₂)₃][PO₂F₂]·Hpz^NO₂ have been prepared and structurally characterised. The linear or trigonal metallic coordination environment, the NO₂ groups on the pyrazole ligand as well as the presence of counteranions of the type as , or (the latter one evolving to ) were strategically selected to produce molecular assemblies established on the basis of hydrogen-bonds (N-H?X) and π?π or coordinative interactions involving the NO₂ group. The complex [Ag(Hpz^NO₂)₂][BF₄] exhibited polymeric N-H?F hydrogen-bonded chains which were assembled in a 3D network by weaker coordinative Ag?O(NO₂) and π(NO₂)?π(NO₂) interactions. In the complex [Ag(Hpz^NO₂)₃][SbF₆], consistent with the three-coordinated molecular environment, the interactions were extended to give rise an open 3D cationic sub-network in which the counteranions were encapsulated. By contrast, in the related complex [Ag(Hpz^NO₂)₃][PO₂F₂]·Hpz^NO₂ the presence of a fourth non-coordinated pyrazole Hpz^NO₂ avoided the formation of a 3D network giving rise to a double-chained 1D structure.     

Occurrence of the Unusual 2C5 (1C4) Chair Conformation in Two Carbohydrates and the Reverse Anomeric Effect. X-Ray Structures of 3,4,5,7-Tetra-O-Acetyl-2,6-Anhydro-D-Glycero-D-Ido-Heptonamide (1) and 3,4,5,7-Tetra-O-Acetyl-2,6-Anhydro-D-Glycero-L-Gluco-Heptonamide (2)

Abstract

The title compounds 1 and 2 (both C₁₅O₁₅NH₂₁) crystallized in the monoclinic space group P2₁ (Z = 2) with a=8.864(1), b=8.346(1), c =13.569(1)Å, β =114.12(1), V=918.1(2)A3, D(calc) = 1.358 g/cc for compound 1, and a=15–045(1), b=8.106(1), c=7.491(1)Å, β =97.23(1)°, V=906.4(3)Å3 D(calc)= 1.375 g/cc, for compound 2. The structures were solved by direct methods and refined by the full-matrix least squares technique to R indices of 0.010 and 0.046, respectively. Both compounds are in the α ? D configuration and adopt the unusual ²C₅, (¹C₄) chair conformation with the carbamoyl groups on the anomeric carbon atoms equatorially oriented. In this conformation the orientations of the substituents are 2e, 3a, 4a, 5a and 6a in 1 and 2e, 3a, 4a, 5e and 6a in 2 which leads to unfavorable 1,3-diaxial interactions. The “reverse anomeric effect” which induces the ²c₅ chair conformation in these compounds, may have its origin in the unfavorable steric interactions found in the ⁵c₂ (⁴C₁) conformation where the carbamoyl group is axially oriented. Furthermore, the ²C₅ conformation is stabilized by the N-H … O intramolecular hydrogen bond between the carbamoyl nitrogen atom and the pyranosyl ring oxygen atom. Semi-empirical energy calculations reveal that the rotational freedom of the carbamoyl group is greater for the equatorial orientation (²C₅) than for the axial orientation (⁵C₂).     

Synthesis,characterization, and thermal behavior of palladium(II) complexes containing 4-iodopyrazole

The mononuclear pyrazolyl complexes [PdCl₂(HIPz)₂] (1), [PdBr₂(HIPz)₂] (2), [PdI₂(HIPz)₂] (3), [Pd(SCN)₂(HIPz)₂] (4), and [Pd(NHCOIPz)₂] (5) have been prepared. Compound 1 was obtained from the displacement of acetonitrile from [PdCl₂(CH₃CN)₂] precursor by the 4-iodopyrazole (HIPz) ligand, whereas 2–5 were synthesized by substitution of the chlorido in 1 by the respective anionic group. The compounds were characterized by elemental analysis, infrared spectroscopy, and ¹H NMR spectroscopy. The thermal behavior of 1–5 has been studied by TG and DTA. The thermal stability of [PdX₂(HIPz)₂] compounds varies according to the trends X = Cl^? < I^? ? SCN^?< Br^?. No stable intermediates were isolated during the thermal decompositions due to the overlap of the degradation processes. The final products of the thermal decompositions were characterized as metallic palladium by X-ray powder diffraction.     

MCSCF reaction-path energetics and thermal rate-constants for the reaction of3NH with H2

Summary The intrinsic reaction-path, reactants, transition state and products for the reaction of NH (^3–)+H₂ (¹ _g ⁺ ) NH₂ (²B₁)+H (²S) involving the lowest triplet electronic state of NH₃ were calculated using multi-configuration (MC) SCF methods. The calculated change of internal energy for the reaction of 11.0 kcal mol^–1 agrees with the experimental value within 2 kcal mol^–1. The barrier to reaction is 23.4 kcal mol^–1 high. The harmonic MCSCF reaction-path potential was calculated and canonical variational transition state theory calculations of the rate constants performed over a temperature range from 400 to 2500 K. The computed rate constants are generally two orders of magnitude smaller than those of the comparable reaction of OH with H₂, whereas those of the reverse reaction are by a factor of 20 larger than those of OH₂ with H.     

Determination of the mechanism of the oxidation of the trichloromethyl radical by the photolysis of chloral in the presence of oxygen

The photooxidation of chloral was studied by infrared spectroscopy under steady-state conditions with irradiation of a blackblue fluorescent lamp (300 nm < λ < 400 nm, λ_max = 360 nm) at 296 ± 2 K. The products were hydrogen chloride, carbon monoxide, carbon dioxide, and phosgen. The kinetic results reveal that the reaction proceeds via chain reaction of the Cl atom: The results lead to the conclusion that mechanism (B) is confirmed to be more likely than mechanism (A), which was favored at one time by Heicklen for the mechanism of the oxidation of trichloromethyl radicals by oxygen molecules: The ratio of the initial rates of CO and CO₂ formation gave k₇/k₆ = 4.23M^?1, and the lower limit of reaction (5) was found to be 3.7 × 10⁸M^?1 sec^?1.     

Possible singlet oxygen generation from the photolysis of indigo dyes in methanol, DMSO, water, and ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate

We suggest that singlet molecular oxygen [¹O₂ (¹Δ_g)] is formed upon irradiation of indigo 1 [in air or O₂-saturated DMSO and DMSO (0.5% H₂SO₄)] and indigo carmine 2 [in air or O₂-saturated CH₃OH, D₂O, and 1-butyl-3-methylimidazolium tetrafluoroborate (BmIm-BF₄)]. The quantum yield for production of ¹O₂ is estimated to be 0.6 for 1 and 0.3-0.5 for 2. The rates of reaction of ¹O₂ with 1 and 2 were determined by monitoring the emission of ¹O₂ at 1270 nm over time. Low molar absorptivities (at 532 nm) and rapid physical quenching caused by 1 and 2 limit their utility as ¹O₂ photosensitizers in solution. Compounds 1 and 2 degrade slowly during the photolysis due to a self-sensitized (type I or II) photooxidation reaction. Oxidative cleavage of 1 by singlet oxygen and superoxide, and 2 by superoxide has been noted before (Kuramoto, N.; Kitao, T. J. Soc. Dyers Color. 1979, 95, 257-261; Kettle, A. J.; Clark, B. M.; Winterbourn, C. C. J. Biol. Chem. 2004, 279, 18521-18525).     

The kinetics of the chlorate-bisulfite and chlorate-sulfite/bisulfite reaction systems

The kinetics of the reactions of ClO₃ ⁻ with HSO₃ ⁻ and H₂SO₃ was studied by measuring the concentration of [Cl⁻] and [H⁺] both in chlorate-bisulfite and chlorate-sulfite/bisulfite solutions. A reaction mechanism was applied for simulation of the experimental observations. Rate constants k₁ = (1±0.5)·10⁻⁴ M⁻¹ s⁻¹ and k₂ = (0.23±0.01) M⁻¹ s⁻¹ were determined for the following reactions:

Relationships between Fe NMR, Mössbauer parameters, electrochemical properties and the structures of ferrocenylketimines

A comparative study of the electrochemical properties, ⁵⁷Fe NMR and Mössbauer spectroscopic data of compounds [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-C(R¹)N-R²}] {R¹ = H, R² = CH₂-CH₂OH (1a), CH(Me)-CH₂OH (1b), CH₂C₆H₅ (1c), C₆H₄-2Me (1d), C₆H₄-2SMe (1e) or C₆H₄-2OH (1f) and R¹ = C₆H₅, R² = C₆H₄-2Me (2d)} is reported. The X-ray crystal structure of [(η⁵-C₅H₅)Fe{(η⁵-C₅H₄)-CHN-C₆H₄-2OH}] (1f) is also described. Density functional theoretical (DFT) studies of these systems have allowed us to examine the effects induced by the substituents of the “-C(R¹)N-R²” moiety or the aryl rings (in 1d-1f) upon the electronic environment of the iron(II) centre.     

Unusual condensation of propargylamine. Generation of the 1,3-di(propargylimino)propane anion coordinated to the cobalt(iii) atom

The reaction of propargylamine with the hexanuclear complex Co^II ₆(₃-OH)₂(OOCCMe₃)₁₀(HOOCCMe₃)₄ or the polymer [Co(OH)_n(OOCCMe₃)_2–n]_x under an argon atmosphere afforded the unstable paramagnetic tetramine complex Co^II(OOCCMe₃)₂(H₂NCH₂CCH)₄ (1). In air, if an excess of propargylamine is present, the latter complex is transformed into the complex Co^III(OOCCMe₃)₂(NH₂CH₂CCH)₂[²-N,N"-(HCCCH₂N=CHCHCH=N—CH₂CCH)] (2) containing a new ligand, viz., the 1,3-di(propargylimino)propane anion, which is a formal analog of the acetylacetonate anion. In contrast to propargylamine, 1,3-diaminopropane reacted with the Co^II trimethylacetate clusters in air to produce the cationic complex [Co^III{1,3-(NH₂)₂(CH₂)₃}₂(OOCCMe₃)₂]⁺OOCCMe₃ ^– (3) without entering into condensation reactions. The structures of the resulting complexes were determined by X-ray diffraction analysis.     

Extending framework based on the linear coordination polymers: Alternative chains containing lanthanum ion and acrylic acid ligand

One-dimensional alternative chains of two lanthanum complexes: [La(L¹)₃(CH₃OH)(H₂O)₂]·5H₂O (L¹=anion of α-cyano-4-hydroxycinnamic acid ) 1 and [La(L²)₃(H₂O)₂]·3H₂O (L²=anion of trans-3-(4-methyl-benzoyl)-acrylic acid) 2 were synthesized and structurally characterized by single-crystal X-ray diffraction, element analysis, IR and thermogravimetric analysis. The crystal structure data are as follows for 1: C₃₁H₃₆LaN₃O₁₇, triclinic, P-1, , , , α=72.7960(10)°, β=83.3820(10)°, γ=67.1650(10)º, Z=2, R₁=0.0377, wR₂=0.0746; for 2: C₃₃H₃₇LaO₁₄, triclinic, P-1, , , , α=81.145(2)°, β=87.591(2)°, γ=67.345(5)°, Z=2, R₁=0.0869, wR₂=0.220. 1 is a rare example of the alternative chain constructed by syn-syn and anti-syn coordination mode of carboxylato ligand arranged along the chain alternatively. La(III) ions in 2 are linked by two η³-O bridges and four bridges (two η²-O and two η³-O) alternatively. Both of the linear coordination polymers grow into two- and three-dimensional networks by packing through extending hydrogen-bond network directed by ligands.     

Palladium acetate complexes in the gas phase

New palladium acetate complexes, Pd₂(OOCMe) ₄ ⁺ , Pd₂(OOCMe) ₃ ⁺ , Pd₂(OOCMe) ₂ ⁺ , and Pd₂(OOCMe)⁺ were detected in the thermal decomposition products of trans-Pd(Py)₂(OOCMe)₂ by mass spectrometry with direct ion source. The geometric and electronic structures of the Pd₂(μ-OOCMe) ₄ ⁺ cation and the Pd₂(OOCMe)₄ molecule were established by quantum chemical calculations (DFT with the PBE1PBE hybrid exchange correlation potential in the 6-31G*/SDD basis set) and natural orbital analysis.     

The transannular interaction germanium-nitrogen in germocanes: The influence of substituents

The reaction of RN(CH₂CH₂OH)CHR¹CR²R³OH (1-8) with a stoichiometric amount of tetrachloro(bromo)germane leads to the corresponding RN(CH₂CH₂O)(CHR¹CR²R³O)GeHal₂ (9-21). Difluorenylgermocane 22 was prepared by treatment of diethoxydifluorenylgermane with N-methyldiethanolamine. Different dialkanolamines were found to be successive precursors of dimethylgermocanes, RN(CH₂CH₂O)(CHR¹CR²R³O)GeMe₂ (23-26). The chemical properties of simple and easy to access germocanes RN(CH₂CH₂O)₂GeX₂ [X = OH, Br (28), Cl (29)] were studied and the difluoro (27), haloalkoxy (30-32), and dialkoxy (33, 34) derivatives were prepared. The structures of the compounds 16, 20-22, and 26 were confirmed by X-ray diffraction and the structural features in solution of 23 and 26 were studied by NMR spectroscopy (NOEs). The relationship between the nature of substituents at different positions of the germocane skeleton and the strength of the intramolecular Ge ← N bond is discussed.     

Potential energy profiles of the geometric isomerization and the thermal decomposition of diphosphene HP=PH in the ground and excited electronic states

Summary The geometric isomerization and the dehydrogenation of HP=PH in the ground and some low-lying excited states are investigated by theoretical calculations. The reaction paths are traced by either the CASSCF or UHF-SCF calculations using the 6-31G(d,p) basis functions, and the accompanying energy changes are calculated by the MRD-CI method employing the [5s3p1d]/[2s1p] basis functions. The barrier heights for the trans-to-cis isomerization, by the planar inversion and the nonplanar twisting, in the ground state are calculated to be 265 and 144 kJ/mol (with the vibrational zero-point energy corrections), respectively. The latter barrier is noticeably lower than the H-P and the P-P bond dissociation energies oftrans-HP=PH (¹A_g), which are 304 and 271 kJ/mol, respectively. The ground-state HP₂ radical (²A'), which is to be formed by the dehydrogenation of HP=PH, should suffer further decomposition into P₂ (¹ _g ⁺ ) and H with an activation energy of 139 kJ/mol. The lowest excited state of HP₂ is found to be a hydrogen-bridged 3-electron system (²A₂) having an isosceles triangle structure. It has proved to be formed by the dehydrogenation of the lowest excited singlet state (¹B) of HP=PH via a transition state which lies 194 kJ/mol above the¹B state. The excited HP₂ (²A₂) is state-correlated with P₂ (³_u)+H.