Hei and heii spectra of 3-halopyridines

The ultraviolet photoelectron spectra (UPS) of 3-fluoro-, 3- chloro-, 3-bromo- and 3- iodopyridine were recorded and interpreted using a composite-molecule model. The sequence of the four lowest ionization energies for 3-fluoro- and 3-chloropyridine is: π₃ (1a₂) < n_N (11a₁)ππ₂ (2b₁)π∼_pyr (7b₂), whereas for 3-bromo- and 3-iodopyridine the assignment is: π₃ (1a₂) - π_xπn_N (11a₁)πσ_x π₂ (2b₁) (where X represents a bromine or iodine lone-pair). Comparison of the HeI and HeII band intensities and correlations with the UPS assignment of the 2-halopyridines confirm this sequence. However, ab initio calculations using the STO-3G*//STO-3G* and 6–31G**//STO-3G* models do not agree with either the composite-molecule model, simple UPS correlations and HeI/HeII cross-section ratios. For 3-fluoropyridine, the HAM/3 model was in agreement with the proposed assignment.     

Photoelectron Spectra of Unsaturated Oxides. I. 1,4-Dioxin and related systems

The He (Iα) photoelectron spectra of the four unsaturated oxides 3,4-dihydropyran ( 6 ), γ-pyran ( 7 ), 2, 3-dihydro-1, 4-dioxin ( 9 ) and 1, 4-dioxin ( 10 ) are reported and analysed. Band assignments are based on ab-initio calculations, using the STO-3G basis set. The proposed orbital sequences (with reference to the coordinate systems given in Table 1) are, for the top three orbitals: 6 , π, nσ, nπ; 7 , 3b₁(π), 1a₂(π), 11a₁(σ); 9 , 11b(π), 12a(σ), 11a(π); 10 , 2b_3u(π), 1b_1g(π), 6a_g(σ). Finally the (almost) localized π-orbitals have been computed by the Foster-Boys localization procedure.     

The He(Iα) Photoelectron Spectra of Substituted 1,2-Dithietes

The He(Iα) photoelectron (PE.) spectra of a series of substituted 1,2-dithietes have been recorded and assigned with respect to the orbital sequence derived from an STO-3G model calculation and by correlation with the PE. spectra of related compounds. The results provide additional support for the presence of a closed, four-membered ring moiety in all the 1,2-dithietes investigated. In all cases the two highest occupied molecular orbitals are b₂(π)= HOMO, a₂(π), with exception of 3,4-bis(trifluoromethyl)-1,2-dithiete where the sequence b₂(π), a₂(π) or a₂(π), b₂(π) is uncertain.     

He(I) and He(II) photoelectron spectra of some mixed sandwich compounds of titanium,zirconium and hafnium

The He(I) and He(II) photoelectron spectra are reported for two series of transition metal mixed sandwich complexes of general formula L_aML_b (M = Ti, L_a = η⁵-C₅H₅, η⁵-CH₃C₅H₄, η⁵-C₅(CH₃)₅; M = Zr, Hf, L_a = η⁵-C₅(CH₃)₅; L_b = η⁷-C₇H₇ (series I); M = Ti, L_a = η⁵-CH₃C₅H₄, η⁵-C₅(CH₃)₅; M = Zr, L_a = η⁵-C₅(CH₃)₅; L_b = η⁸-C₈H₈ (series II)). Assignments were made of the metal d, cyclopentadienyl and carbocyclic π orbitals on the basis of He(I)/He(II) intensity ratios and shift effects and by comparison with UP data for related compounds. For series I no influence of the central metal upon the IEs of the highest occupied molecular orbital e₂ was observed. The IE of the non-bonding metal d_z2 orbital of Ti or Zr (5.28 and 4.70 eV, respectively) in the complexes of series II (L_a = η⁵-C₅(CH₃)₅) is very low.     

Selective radical cyclisation of propargyl bromoethers to tetrahydrofuran derivatives via electrogenerated nickel(I) tetramethylcyclam

The controlled-potential reduction of [1-bromo-2-methoxy-2-(prop-2′-ynyloxy)ethyl]benzene (1a), 1-[2-bromo-2-phenyl-1-(prop-2′-ynyloxy)ethyl]-4-methoxybenzene (1b) and 2-bromo-3-(3′,4′-dimethoxyphenyl)-3-propargyloxypropanamide (1c) catalysed by (1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane)nickel(I), [Ni(tmc)]⁺, at a vitreous carbon cathode in DMF/Et₄NBF₄ leads to 2-methoxy-4-methylene-3-phenyl-tetrahydrofuran (2a), 2-(4′-methoxyphenyl)-4-methylene-3-phenyl-tetrahydrofuran (2b) and 2-(3′,4′-dimethoxyphenyl)-3-carbamoyl-4-methylenetetrahydrofuran (2c), respectively, in very high yields.     

The Electronic Structure of Cubane (C8H8) as Revealed by Photoelectron Spectroscopy

High resolution He (Iα) and He (IIα) photoelectron spectra of cubane are reported. The assignments of the bands to different states of the cubane radical cation are made on the basis of ab initio STO-3G and MINDO/3 calculations, using geometries optimized within each treatment. The vibrational fine-structure observed supports the proposed assignment. An open shell MINDO/3 model for ground state cubane radical cation suggests that the Jahn-Teller distorted system fluctuates between twelve equivalent structures of C_2v-symmetry. Localized molecular orbitals derived from the STO-3G model of cubane indicate that the major feature which discriminates this molecule with respect to other hydrocarbons is the large interaction matrix element between the opposed CC-σ-orbitals of each face.     

UV photoelectron spectra of some transition metal(II) acetylacetonates

The He(I) photoelectron spectra of acetylacetone (HAA) and its metallo complexes, M(II)(AA)₂ (M(II) = Mn, Co, Ni, Cu and Zn), have been measured. These spectra show characteristic metal-dependence, from which the assignment is made. The order of the orbital energy level, d > π₃ > n_? > n₊, holds for all the complexes reported here. The splitting of these orbitals is found to depend on the central metal ion specifically.     

Improved syntheses of thieno[2,3-b]- and [3,2-b]-fused naphthyridines

The preparation of eight isomeric thieno[2,3-b]- and [3,2-b]-fused naphthyridines [1] was improved through the Pd(0) catalyzed cross-coupling of 3-formyl-4-iodopyridine, 2-formyl-3-iodopyridine, 3-bromo-4-formylpyridine and 2-bromo-3-formylpyridine with t-butyl N-(2-trimethylstannyl-3-thienyl)car-bamate and t-butyl N-(3-trimethylstanny-2-thienyl)carbamate.     

Preparation of β-fluoro- and β,β-difluoro-histidinols

Nucleophilic attack of azide on 2-bromo-3-fluoro-3-(1-trityl-1H-imidazol-4-yl)-propan-1-ol (1a) in aprotic solvent occurs on the 2-position to give the 2-azido derivative (2a). Reduction of azide and removal of the trityl group produces β-fluorohistidinol (6a). Elimination of HBr from 1a followed by “FBr” addition to the resulting double bond gives 2-bromo-3,3-difluoro-3-(1-trityl-1H-imidazol-4-yl)-propan-1-ol (1b). Nucleophilic attack of azide followed by reduction and removal of the trityl group, as for the preparation of 6a, gives β,β-difluorohistidinol (6b). Initial attempts, under a variety of conditions, to oxidize the fluorinated histidinol precursors to carboxylic acids have not been successful.     

New N-heterocyclic carbene silver(I) and mercury(II) 2-D supramolecular layers by the π-π stacking interactions

The precursor 1-(9-anthracenylmethyl)-3-alkylbenzimidazolium chlorides (1a, alkyl = C₄H₉, 1b, alkyl = C₆H₁₃) and their three new NHC silver(I) and mercury(II) complexes {[1-(9-anthracylmethyl)-3-alkylbimy]MCl}₂ (2a, alkyl = C₄H₉, M = Ag; 2b, alkyl = C₆H₁₃, M = Ag; 3a, alkyl = C₄H₉, M = Hg; bimy = benzimidazol-2-ylidene) have been prepared and characterized. The crystal structures of 2a, 2b and 3a showed that 2-D supramolecular layers are formed by both benzimidazole ring head to tail π-π stacking interactions and anthracene ring face-to-face π-π stacking interactions.     

Ultraviolet photoelectron spectra of some resorcinols and dithioresorcinols

The photoelectron spectra of resorcinol, dithioresorcinol, 4,6-dichlororesorcinol 1, 4,6-dichlorodithioresorcinol 3 and their methyl derivatives were recorded by using He(I) and HE(II) excitations. The assignment of the photoelectron bands was mainly based on relative band intensity variations and on the results of ab initio STO-3G calculations. The results show clear evidence of the presence of intramolecular OH … Cl hydrogen bonding interactions in 1, while no effects of such a bonding was observed in the corresponding dithiocompound 3. These findings are confirmed by the STO-3G calculations. The photoelectron spectra of both 1,3-dithiomethoxybenzene and 1,3-dithiomethoxy-4,6-dichlorobenzene give evidence of rotational isomerism of the SCH₃ group.     

Spectres photoélectroniques He(I) et He(II) du benzo[b]sélénophène et du benzo[b]tellurophène

He(I) and He(II) photoelectron spectra of benzo[b]selenophene and benzo[b]tellurophene The photoelectron spectra of benzo[b]selenophene ( 2 ) and benzo[b]tellurophene ( 1 ) have been recorded with He(I) and He(II) radiation and been compared to those of benzo[b]thiophene ( 3 ), benzo[b]furan ( 4 ), indole ( 5 ) and indene ( 6 ). The first four bands are correlated with π-orbitals, of which the highest occupied one is strongly localized on the heteroatom in the case of 1 . The results are in agreement with semi-empirical PPP-calculations.     

An efficient synthesis of (7S,10R)-2-bromo-5,6,7,8,9,10-hexahydro-7,10-epiminocyclohepta[b]indole: application in the preparation and structural confirmation of a potent 5-HT6 antagonist

(7S,10R)-5-Methyl-2-((3-(trifluoromethyl)phenyl)sulfonyl)-5,6,7,8,9,10-hexahydro-7,10-epiminocyclohepta[b]indole 1a is a potent 5-HT₆ antagonist (h5-HT₆ K_i = 1.5 nM) which is derived from an epiminocyclohept[b]indole scaffold. In order to synthesize 1a on a multi-gram scale to support advanced biological testing, an efficient chiral resolution of the intermediate tert-butyl 2-bromo-5,6,7,8,9,10-hexahydro-7,10-epiminocyclohepta[b]indole-11-carboxylate 2 was developed. After derivatizing 2 with (1R)-(?)-menthyl chloroformate it was found that a single diastereomer 7a could be isolated by selective precipitation from n-hexane. The absolute stereochemistry of 7a was determined by X-ray crystallography and the structure was confirmed as (7S,10R)-tert-butyl 2-bromo-5,6,7,8,9,10-hexahydro-7,10-epiminocyclohepta[b]indole-11-carboxylate. Removal of the chiral auxiliary under basic conditions afforded intermediate 2a in >99% enantiomeric purity and with 80% yield based on recovery from the racemic compound 2. Intermediate 2a was used successfully to synthesize 5-HT₆ antagonist 1a on a multi-gram scale.     

New N-heterocyclic carbene mercury(II) and silver(I) complexes

The complexes [1-(9-anthracenylmethyl)-3-octylimy]₂Hg[HgCl₄] (2a) (imy = imidazol-2-ylidene) and [1-(9-anthracenylmethyl)-3-butylbimy]₂AgPF₆ (2b) (bimy = benzimidazol-2-ylidene) have been prepared and characterized. Crystal packing of complex 2a revealed that 1D polymeric chains are formed by [1-(9-anthracenylmethyl)-3-octylimy]Hg and [HgCl₄]²⁻ through weak Hg…Cl bonds. The packing diagram of 2b showed that 1D supramolecular chains are formed by both benzimidazole ring head to tail π–π stacking interactions and anthracene ring face-to-face π–π stacking interactions.     

A new type of chiral porphyrin: Organopalladium porphyrins with chiral chelating diphosphine ligands

Peripherally palladated Ni(II) porphyrins have been prepared using enantiopure chiral chelating diphosphines as supporting ligands on the attached Pd(II) fragment. Both enantiomers of the following complexes have been obtained in good yields, using oxidative addition of the bromoporphyrin starting material 5-bromo-10,20-diphenylporphyrinatonickel(II) (NiDPPBr (1)) to the [Pd⁰L] complex generated in situ from Pd₂dba₃ and the chiral ligand L: [PdBr(NiDPP)(CHIRAPHOS)] (2a,b) [CHIRAPHOS = 2,3-bis(diphenylphosphino)butane], [PdBr(NiDPP)(Tol-BINAP)] (3a,b) [Tol-BINAP) = 2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl] and [PdBr(NiDPP)(diphos)] [diphos = 1,2-bis(methylphenylphosphino)benzene] (4a,b). The induced asymmetry in the porphyrin was readily detected by ¹H NMR and CD spectroscopy. The porphyrin chiroptical properties are strongly dependent upon the structure of the chiral ligand, such that a monosignate CD signal, and symmetric and asymmetric exciton couplets were observed for 4a, 2b, and 3a,b, respectively.     

The synthesis of γ-fluoroisoleucine

Condensation of 3-fluoro-2-butanone ($\text{2}$) with alkyl diethylphosphonoacetates ($\text{4a–d}$) gave alkyl 4-fluoro-3-methyl-2-pentenoates ($\text{5a–d}$). Addition of bromine yielded alkyl-2,3-dibromo-4-fluoro-3-methylpentanoates ($\text{6a,b}$) which were dehydrobrominated to alkyl 2-bromo-4-fluoro-3-methyl-2- pentenoates ($\text{7a,b}$). Since these compounds could not be hydrogenated to the desired alkyl 2-bromo-4-fluoro-3-methylpentanoates ($\text{8a,b}$), another route was taken. The esters $\text{5a–d}$ were hydrogenated to alkyl 4-fluoro-3- methylpentanoates ($\text{11a–c}$) which were converted to their carbanions. Treatment with bromine gave esters $\text{8a–c}$, and iodine gave alkyl 4-fluoro-2-iodo- 3-methylpentanoates ($\text{12a,b}$). Esters $\text{8a–c}$ and $\text{12a,b}$ were converted to alkyl 2-azido-4-fluoro-3-methylpentanoates ($\text{13a–c}$) whose hydrogenation gave alkyl 2-amino-4-fluoro-3-methylpentanoates ($\text{14a–c}$). Hydrolysis afforded γ-fluoroisoleucine ($\text{1}$).     

The structures and stability of pentacoordinate germylenoid PhCH<Subscript>2</Subscript>(OH)CH<Subscript>3</Subscript>GeLiF

The structures and stability of pentacoordinate germylenoid PhCH₂(OH)CH₃GeLiF were first theoretically studied by density functional theory. Two equilibrium structures, the three-membered ring (1a) and the p-complex (1b) structures, were located. Their energy are in the order of 1b > 1a. The Ge-O coordination energies at the B3LYP/6-311+G(d, p) level are 13.6 and 0.2 kJ/mol in 1a and 1b, respectively. The insertion reactions with CH₃F indicate that germylenoid PhCH₂(OH)CH₃GeLiF is more stable than germylene PhCH₂(OH)CH₃Ge. The insertion barrier of 1a with CH₃F is only 3.1 kJ/mol higher than that of PhCH₃CH₃GeLiF, indicating that the oxygen coordination PhCH₂(OH)CH₃GeLiF has the same stability as PhCH₃CH₃GeLiF.     

Ni(II) and Cu(II) complexes of phenoxy-ketimine ligands: Synthesis,structures and their utility in bulk ring-opening polymerization (ROP) of l-lactide

Synthetic, structural and catalysis studies of Ni(II) and Cu(II) complexes of a series of phenoxy-ketimine ligands with controlled variations of sterics, namely 2-[1-(2,6-diethylphenylimino)ethyl]phenol (1a), 2-[1-(2,6-dimethylphenylimino)ethyl]phenol (1b) and 2-[1-(2-methylphenylimino)ethyl]phenol (1c), are reported. Specifically, the ligands 1a, 1b and 1c were synthesized by the TiCl₄ mediated condensation reactions of the respective anilines with o-hydroxyacetophenone in 21–23% yield. The nickel complexes, {2-[1-(2,6-diethylphenylimino)ethyl]phenoxy}₂Ni(II) (2a) and {2-[1-(2,6-dimethylphenylimino)ethyl]phenoxy}₂Ni(II) (2b), were synthesized by the reaction of the respective ligands 1a and 1b with Ni(OAc)₂ · 4H₂O in the presence of NEt₃ as a base in 71–75% yield. The copper complexes, {2-[1-(2,6-diethylphenylimino)ethyl]phenoxy}₂Cu(II) (3a), {2-[1-(2,6-dimethylphenylimino)ethyl]phenoxy}₂Cu(II) (3b) and {2-[1-(2-methylphenylimino)ethyl]phenoxy}₂Cu(II) (3c) were synthesized analogously by the reactions of the ligands 1a, 1b and 1c with Cu(OAc)₂ · H₂O in 70–87% yield. The molecular structures of the nickel and copper complexes 2a, 2b, 3a, 3b and 3c have been determined by X-ray diffraction studies. Structural comparisons revealed that the nickel centers in 2a and 2b are in square planar geometries while the geometry around the copper varied from being square planar in 3a and 3c to distorted square planar in 3b. The catalysis studies revealed that while the copper complexes 3a, 3b and 3c efficiently catalyze ring-opening polymerization (ROP) of l-lactide at elevated temperatures under solvent-free melt conditions, producing polylactide polymers of moderate molecular weights with narrow molecular weight distributions, the nickel counterparts 2a and 2b failed to yield the polylactide polymer.     

The energy optimized configurations of Be18 and Be20 clusters and the effect of He atom in these clusters

The optimized configurations of Be₁₈ (D_3d) and Be₂₀ (D_3h) clusters which are considered as the smallest subunits of Be crystal are calculated by the ab initio STO-3G SCF energy gradient method. The characteristics of these optimized geometries are discussed. The impurity effect caused by a He atom in the center of these clusters is also discussed.     

Photochemical cyclodehydrogenation of Lewis acid-conjugates of azobenzenes

Irradiation of the conjugate acids of azobenzene (1a) with Lewis acids like anhydrous AlCl₃, anhydrous SnCl₄ and anhydrous FeCl₃ in 1,2-dichloroethane results in cyclodehydrogenation to benzo[c]cinnoline (2a). The formation of benzidine (3a) along with 2a suggests that the reaction is a photochemical disproportionation. The absorption spectra of the conjugate acids in 1,2-dichloroethane reveal that inversion of the n → π* and π → π* singlet state energies occurs on complexation of the azo nitrogen with the Lewis acid. Irradiation of the Lewis acid-conjugates of 2-methylazobenzene (1b), 2,2′-dimethylazobenzene (1c), 4,4′-dimethylazobenzene (1d) and 4-chloroazobenzene (1e) also results in cyclodehydrogenation.