Why are SiX5(-) and GeX5(-) (X = F, Cl) stable but not CF5(-) and CCl5(-)?

The possible existence of the CF(5)(-), CCl(5)(-), SiF(5)(-), SiCl(5)(-), GeF(5)(-), and GeCl(5)(-) anions has been investigated using ab initio methods. The species containing Si and Ge as central atoms were found to adopt the D(3h)-symmetry trigonal bipyramidal equilibrium structures whose thermodynamic stabilities were confirmed by examining the most probable fragmentation channels. The ab initio re-examination of the electronic stabilities of the SiF(5)(-), SiCl(5)(-), GeF(5)(-), and GeCl(5)(-) anions [using the OVGF(full) method with the 6-311+G(3df) basis set] led to the very large vertical electron detachment (VDE) energies of 9.316 eV (SiF(5)(-)) and 9.742 eV (GeF(5)(-)), whereas smaller VDEs of 6.196 and 6.452 eV were predicted for the SiCl(5)(-) and GeCl(5)(-) species, respectively. By contrast, the high-symmetry and structurally compact anionic CF(5)(-) and CCl(5)(-) systems cannot exist due to the strongly repulsive potential predicted for the X(-) (F(-) or Cl(-)) approaching the CX(4) (CF(4) or CCl(4)). The formation of weakly bound CX(4)···X(-) (CF(4)···F(-) and CCl(4)···Cl(-)) anionic complexes (consisting of pseudotetrahedral neutral CX(4) with the weakly tethered X(-)) might be expected at low temperatures (approaching 0 K), whereas neither CX(5)(-) (CF(5)(-), CCl(5)(-)) systems nor CX(4)···X(-) (CF(4)···F(-) and CCl(4)···Cl(-)) complexes can exist in the elevated temperatures (above 0K) due to their susceptibility to the fragmentation (leading to the X(-) loss).     

Detection of σ-alkane complexes of manganese by NMR and IR spectroscopy in solution: (η5-C5H5)Mn(CO)2(ethane) and (η5-C5H5)Mn(CO)2(isopentane)

Irradiation of CpMn(CO)₃ in liquid ethane at 135 K at 355 nm yields a photoproduct that exhibits ν(CO) bands in the IR spectrum shifted to low wavenumber with respect to CpMn(CO)₃ that are indicative of a Mn(i) dicarbonyl. Parallel experiments employing in situ irradiation within an NMR probe (133 K, 355 nm photolysis) reveal the ¹H NMR signals of this product and confirm its formulation as the σ-ethane complex CpMn(CO)₂(η²-C1–H-ethane). The resonance of its coordinated C–H group is observed at δ –5.84 and decays with lifetime of ca. 360 s. Analogous photolysis experiments in isopentane solution with IR detection produce CpMn(CO)₂(η²-C–H-isopentane) with similar IR bands to those of CpMn(CO)₂(η²-C–H-ethane). ¹H NMR spectra of the same species were obtained by irradiation of CpMn(CO)₃ in a 60 : 40 mixture of propane and isopentane; three isomers of CpMn(CO)₂(η²-C–H-isopentane) were detected with coordination of manganese at the two inequivalent methyl positions and at the methylene group, respectively. The lifetimes of these isomers are ca. 380 ± 20 s at 135 K and do not vary significantly from each other. These σ-complexes of manganese are far more reactive than those of related CpRe(CO)₂(alkane) complexes which are stable in solution at 170–180 K. The room temperature lifetimes of CpMn(CO)₂(η²-C–H-ethane) and CpMn(CO)₂(η²-C–H-isopentane), as determined by TRIR spectroscopy, are 2.0 ± 0.1 and 28 ± 1 μs, respectively.     

Syntheses and Anti-inflammatory Action of (η-C_5H_5)_2Ti(Cin)_2 and (η-C_5H_5)_2Ti(Tzea)_2

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Syntheses and Characterizations of Cd(Ⅱ) and Pr(Ⅲ) Complexes Based on 5-(Tetrazol-5-yl) Isophthalic Acid

Hydrothermal reactions of 5-(tetrazol-5-yl) isophthalic acid with cadmium nitrate/praseodymium nitrate led to two complexes of [Cd_3(TZI)_2(H2_O)_(11)]_n(1) and [Pr(TZI)(H_2O)_5]_n(2). Their structures and properties were determined by X-ray diffraction, IR spectroscopy, fluorescence spectrum, thermal gravimetric analyses and elemental analysis. Complex 1 belongs to monoclinic system, I2/c space group, with a = 12.8688(3), b = 18.0925(3), c = 14.5190(3) ?, β = 116.054(3)°, V =3036.92(13) ?~3, Z = 4; complex 2 crystallizes in triclinic, space group P 1, with a = 7.9690(5), b =9.7665(8), c = 10.4353(9) ?, α = 116.709(9), β = 107.461(6), γ = 95.671(6)°, V = 665.54(9) ?3 and Z =2. Complex 1 is a 3D planar structure. Complex 2 is a one-dimensional double chain configuration and extends into a 3D network by hydrogen bonds and π-π interactions.     

Indole derivatives. 138. Synthesis of α-(5-indolyl)ethylamine and 5-(2-aminoethoxy)- and 5-(aminoethylthio)tryptamines

The reaction of 5-acetylindole with hydroxylamine with subsequent reduction of the resulting oxime gave -(5-indolyl)ethylamine. Coupling of 4-(2-phthalimidoethoxy)- and 4-(2-phthalimidoethylthio)phenyldiazonium chlorides with ethyl -acetyl--phthalimidovalerate, subsequent cyclization of the resulting hydrazones, hydrolysis, decarboxylation, and removal of the phthalyl protecting group led to the formation of 5-(2-aminoethoxy)- and 5-(2-aminoethylthio)tryptamines, respectively.For Communication 137, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 46–48, January, 1992.     

Substitution and insertion reactions of (η5-C5H5)Cr(CO)3C2H5

The complex (η⁵-C₅H₅)Cr(CO)₃Cp42 H₅ has been made and its reactions with σ donor ligands L (L = (MeO)₃P and (EtO)₃P) and with SO₂ studied. The alkyl phosphites give compounds of the composition (η⁵-C₅H₅)Cr(CO)₂LC₂H₅, and sulfur dioxide gives the corresponding S-sulfinato (η⁵-C₅H₅)Cr(CO)₃SO₂C₂H₅.     

Trans hexaco-ordinate complexes of copper(II) and nickel(II) with 4(5)-hydroxymethyl-5(4)-methylimidazole—crystal structure and physico-chemical properties

Trans complexes of Cu(II) and Ni(II) with 4-hydroxymethyl-5-methylimidazole (L), of the general formula [ML₄](NO₃)₂ have been obtained. The complexes were characterized by single X-ray diffraction, elemental analysis, EPR spectroscopy, IR, FIR and Vis–NIR spectra. In these co-ordination compounds, the azole ligand has a dual nature. Two of these molecules are monodentate, co-ordinated through the ‘3’ ‘pyridynic’ nitrogen atom of the imidazole ring, while the remaining two are bidentate ligands, the oxygen atom of the CH₂OH group being another electron donor (giving CuN₄O₂ and NiN₄O₂ chromophores). The structure of both chromophores is described by a slightly distorted tetragonal bipyramid. The stability constants and structures of the Cu(II) and Ni(II) complexes with the studied ligand (4-CH₂OH5-CH₃im) in aqueous solution have been determined by potentiometric and spectrophotometric methods. The stability of the transition metal complexes of 4-CH₂OH5-CH₃im depends on the presence of the hydroxymethyl group, the oxygen atom of which interacts with the metal-ion.     

The Syntheses and crystal structures of trans-dichlorobis (10-thiabenzo-15-crown-5)-palladium(Ⅱ)and trans-dichlorobis-(10-selenabenzo-15-crown-5)palladium(Ⅱ)

The preparation and X-ray crystal structures of the adducts of 10-thiabenzo-15-crown-5 and 10-selenabenzo-15-crown-5 with PdCl2 are reported. [PdCl2(C14H20O4S)2] (1): or-thorhombic, space group Pbca with cell dimensions of a=17.285(5), 6=8.354(3), c=21.689(4) A, K=3131.9 A3, Z=4;R=0.0330 for 2301 reflections with I > 3o(I), [PdCl2(C14H2oO4Se)2] (2): monoclinic, space group P21/n with cell dimensions of a=18.928(4), b=8.912(3), c=9.813(2) A, β=96.90(2)0, V=1643.4 A3, Z=2; R=0.0289 for 2617 reflections with I> 3σ(I), Both complexes are monomeric, square-planar palladiurn(Ⅱ) compounds with the Pd(Ⅱ) ion situating on a crystal-lographic inversion centre, and the crown ligands all adopt the axial coordination with the Pd-S bond of 2.3233(7) A and the Pd-Se bond of 2.4357(3) A. Their complexing characteristics are discussed in brief.     

Total synthesis of (±)-cycloclavine and (±)-5-epi-cycloclavine

Novel routes to the naturally occurring indole alkaloid cycloclavine and its unnatural C(5)-epimer are described. Key features include the rapid construction of the heterocyclic core segments by two Diels-Alder reactions. An indole annulation was accomplished by a late-stage intramolecular Diels-Alder furan cycloaddition, and a methylenecyclopropane dienophile was used for a stereoselective intramolecular [4 + 2] cycloaddition to give the cyclopropa[c]indoline building block present in cycloclavine.     

2-Polyfluoroalkylchromones. 11. Synthesis and structures of 5-hydroxy-3-(2-hydroxyaryl)-5-polyfluoroalkyl-Δ2-pyrazolines and 3(5)-(2-hydroxyaryl)-5(3)-polyfluoroalkylpyrazoles

The reaction of 2-hydroxy-2-polyfluoroalkylchroman-4-ones with hydrazine affords 5-hydroxy-3-(2-hydroxyaryl)-5-polyfluoroalkyl-²-pyrazolines, whereas 2-polyfluoroalkylchromones under similar conditions produce 3(5)-(2-hydroxyaryl)-5(3)-polyfluoroalkylpyrazoles. 5-(2-Hydroxyaryl)-1-methyl-3-polyfluoroalkylpyrazoles were synthesized in the reaction with methylhydrazine, and the reaction with phenylhydrazine afforded regioisomeric 3(5)-(2-hydroxyphenyl)-1-phenyl-5(3)-polyfluoroalkylpyrazoles.     

Aurated tungsten-triosmium cluster compounds. Synthesis and characterization ofLWOs3(CO)12(AuPPh3) and related hydrogenation productsLWOs3(CO)11(μ-H)2(AuPPh3),L = C5 H5 and C5 Me5

Two heterometallic compoundsLWOs₃(CO)₁₂(AuPPh₃),L = Cp (6);L = Cp* (7), were prepared byin-situ generation of clusters [LWOs₃(CO)₁₂][PPh₄] from Os₃(CO)₁₀(NCMe)₂ and [LW(CO)₃][PPh₄], followed by addition of Ph₃ PAuCl. These derivatives possess a tetrahedral Os₃W core in which the AuPPh₃ unit bridges an Os-Os edge and the unique bridging CO ligand spans the opposite Os-W edge. Crystal data for6: space group P;a = 9.328(3),b = 13.745(3),c = 16.231(3) Á, = 115.00(2), = 97.27(2), = 90.17(2)°,Z = 2; finalR _F = 0 045,R _W = 0.044 for 4049 reflections withI > 2(I). Crystal data for7: space group P2₁/n;a = 9.775(2),b = 17.106(4),c = 25.074(3) Á, = 91.10(1)°,Z = 4; finalR _F = 0 035,R _W = 0.028 for 4196 reflections with I > 2(I). Hydrogenation of6 and7 afforded the respective dihydride complexesLWOs₃(CO)₁₁(-H)₂(AuPPh₃), (8)L = Cp; (9),L = Cp* in moderate yields. Their dynamic processes in solution were also established by¹H,¹³C and,³¹P NMR spectroscopies.     

Heats of formation of C(6)H(5)(•), C(6)H(5)(+), and C(6)H(5)NO by threshold photoelectron photoion coincidence and active thermochemical tables analysis

Threshold photoelectron photoion coincidence has been used to prepare selected internal energy distributions of nitrosobenzene ions [C(6)H(5)NO(+)]. Dissociation to C(6)H(5)(+) + NO products was measured over a range of internal energies and rate constants from 10(3) to 10(7) s(-1) and fitted with the statistical theory of unimolecular decay. A 0 K dissociative photoionization onset energy of 10.607 ± 0.020 eV was derived by using the simplified statistical adiabatic channel model. The thermochemical network of Active Thermochemical Tables (ATcT) was expanded to include phenyl and phenylium, as well as nitrosobenzene. The current ATcT heats of formation of these three species at 0 K (298.15 K) are 350.6 (337.3) ± 0.6, 1148.7 (1136.8) ± 1.0, and 215.6 (198.6) ± 1.5 kJ mol(-1), respectively. The resulting adiabatic ionization energy of phenyl is 8.272 ± 0.010 eV. The new ATcT thermochemistry for phenyl entails a 0 K (298.15 K) C-H bond dissociation enthalpy of benzene of 465.9 (472.1) ± 0.6 kJ mol(-1). Several related thermochemical quantities from ATcT, including the current enthalpies of formation of benzene, monohalobenzenes, and their ions, as well as interim ATcT values for the constituent atoms, are also given.     

The formation,crystal and molecular structures of bis(η5-indenyl)dicarbonyltitanium and bis(η5-indenyl)dicarbonylzirconium

Bis(η⁵-indenyl)dicarbonyltitanium has been produced in 47% yield by reduction of bis(η⁵-indenyl)dichlorotitanium with activated aluminum in THF solution under a carbon monoxide atmosphere. Bis(η⁵-indenyl)dicarbonylzirconium can similarly be prepared in 45% yield by the reductive carbonylation of bis(η⁵-indenyl)dichlorozirconium using activated magnesium turnings. IR spectral evidence has been obtained for the corresponding hafnium analog, although it could not be isolated. Detailed syntheses for the precursors (η⁵-indenyl)₂MCl₂ (M = Ti, Zr, Hf) have been developed. Bis(η⁵-indenyl)dicarbonyltitanium crystallizes in the monoclinic space group C2/c with unit cell parameters a 30.435(8), b 7.357(5), c 28.279(8) Å and β 90.93(5)°. Refinement of 3530 observed reflections lead to final agreement indices of R = 0.052 and R_w = 0.049. Bis(η⁵-indenyl)dicarbonylzirconium crystallizes in the monoclinic space group P2₁/n with unit cel parameters of a 7.288(5), b 14.398(8), c 15.273(7) Å and β 89.84(5)°. Refinement of 2253 observed reflections lead to final agreement indices of R = 0.049 and R₂ = 0.055.     

Syntheses and characterization of η 5-pentamethylcyclopentadienyl rhodium(III) and iridium(III) complexes containing polypyridyls

Reaction of [(η ⁵-C₅Me₅)M(μ-Cl)Cl]₂ {M?=?Rh (1), Ir (2)} and [(η ⁵-C₅Me₅)MCl₂(DBT)] (DBT?=?dibenzothiophene) {M?=?Rh (3), Ir (4)} with polypyridyl ligands 2,3-bis(2-pyridyl)pyrazine (bpp), 2,3-bis(2-pyridyl)quinoxaline (bpq), 1,3,5-tris(2-pyridyl)-2,4,6-triazine (tptz), 2,3,5,6-tetrakis(2-pyridyl)pyrazine (tppz) and 4′-pyridyl-2,2′:6′,2′′-terpyridine (py-terpy) results in the formation of mononuclear cationic complexes, [(η ⁵-C₅Me₅)MCl(poly-py)]⁺ (poly-py?=?polypyridyl ligand). The complexes were isolated as hexafluorophosphate salts and characterized by IR and NMR spectroscopy.     

Synthesis of (3S,5R)-cis- and (3S,5S)-trans-3,5-Dimethylvalerolactones and Their Conversion to Biotransformation Products of (S)-5-Ethyl-5-(2′-pentyl)barbituric Acid

(R,S)-5-Ethyl-5-(2′-pentyl)barbituric acid (I)^1,2 is metabolized in vivo to give all four possible optical isomers of 5-ethyl-5-(3′-hydroxy-1′-methylbutyl)barbituric acid (II). ^3,4 From metabolism studies of pure (1′S)- I and (1′3)-I, Palmer and co-workers^4,5 were able to determine the relative amounts of each of the four isomers formed. These studies showed that (1′S)-I gave mainly one enantiomer of (1′S)-II, whereas (1′R)-I gave approximately equal amounts of both (1′R)-II enantiomers.     

Triphospha-Ferrocenes as Ligands. Crystal Structures of [Fe(η5-C5Me5)(η5-C2 TBu2P3)M(CO)5)], (M= Cr,MO, W) and the Novel ruthenium and Nickel Complexes [Fe(η5-C5Me5) (η5-C2 TBu2P3)Ru3(CO)9] and [Fe(η5-C5Me5)(η5-C2 tBu2P3)Ni(Co)2]2

Abstract

Syntheses and structures of penta- and hexaphosphorus analogues of ferrocene have been described recently¹. Unlike their simple ferrocene analogues, these complexes have further ligating potential towards other transition metal centres by virtue of the availability of the ring phosphorus lone-pair electrons that are not involved in the η⁵-coordination. We now describe the first examples of coordination compounds of the triphospha-ferrocene [Fe(η⁵-C₅Me₅) (η⁵-C₂ ^tBu₂P₃]. In the ruthenium complex [Fe(η⁵-C₅Me₅)(η⁵-C₂ ^tBu₂P₃) Ru₃(CO)₉] ² two adjacent phosphorus atoms of the η⁵-C₂ ^tBu₂P₃ ring are interlinked by a ruthenium carbonyl cluster in which all three ruthenium atoms interact with the phosphorus atoms. The tetrametallic nickel complex [Fe(η⁵-C₅Me₅)(η⁵-C₂ ^tBu₂P₃)Ni(CO)₂]₂ ³ represents the first example of intermolecular interlinkage of two phospha-ferrocene systems by two metal centres.     

Homogeneous catalytic hydrogenation and isomerization of linear and cyclic monoenes and dienes in the presence of the heterometallic cluster (η5-C5H5)NiRu3(μ-H)3(CO)9

The complex (η⁵-C₅H₅)NiRu₃(μ-H)₃(CO)₉ catalyses the selective hydrogenation of the terminal double bond of conjugated linear dienes in homogeneous conditions; isomerization of non-conjugated to conjugated dienes and of pent-1-ene to pent-2-enes also occurs. Selective hydrogenation and isomerization of cyclic hexenes and hexadienes takes place without opening of the ring; a reaction scheme is proposed, and the activity of the cluster itself relative to that of its decomposition products is discussed. Its behaviour is compared with the analogous complex (η⁵-C₅H₅)NiOs₃(μ-H)₃(CO)₉.     

Synthesis of (E)‐ and (Z)‐5‐(Bromomethylene)furan‐2(5H)‐one by Bromodecarboxylation of (E)‐2‐(5‐Oxofuran‐2(5H)‐ylidene)acetic Acid

(E)‐ and (Z)‐5‐(bromomethylene)furan‐2(5H)‐one have been prepared starting from the commercially available adduct between furan and maleic anhydride. A bromodecarboxylation reaction is a key step in the synthesis. The reaction gives the (E)‐ or (Z)‐5‐(bromomethylene)furan‐2(5H)‐one as the major product, dependent on the method used in the bromodecarboxylation.     

Synthesis of ( )-5α-Hydroxy-β-selinene and (-)-5β-Hydroxy-β-selinene

Eudesmanederivativeshavebeendrawingconsiderableattentionduetotheirwidespectrumofbiologicalproperties,particularlyantifeedant,cellgroWthinhibitoryandplantgroWthregulatingactivitiesl'2.Recently,twoepimericeudesmanederivatives( )-5a-hydroxy-6-selinene1and(-)-56-hydroxy-6-selinene2wereisolated3fromtheaerialpartsofCSubtraPicaFMell.,andtheirstructuresweredeterminedbyspectroscopicmethods.Herein,wereportafacilesynthesisofbothtwodiastereomers1and2from( )-dihydrocarvone3infivesteps,usingtheregioselect…     

5-Bromouracil and 5-bromouracil–histidine complexes with metal(III) ions and their antitumour activity

Complexes of the [AILCl₂], [ML(OH)Cl] and [MLL(H₂O)Cl] type, where HL = 5-bromouracil; HL = histidine; M = Cr^III or Fe^III and M = Al^III, Cr^III or Fe^III were synthesized and characterized. The complexes are polymers with high temperature decomposition points and are insoluble in H₂O and common organic solvents. 5-Bromouracil is coordinated to the metal ion through the O atom of C₍₄₎=O and the N atom of N₍₁₎, while histidine coordinates through the O atom of —CO₂ ^– and the N atom of the —NH₂ groups. The _eff values, electronic spectral bands and e.s.r. spectra suggest a polymeric six-coordinate spin-free octahedral stereochemistry for the Cr^III and Fe^III complexes. The in vivo antitumour effect of 5-bromouracil and its complexes was examined on C₃H/He mice versus P815 murine mastocytoma. As is evident from their T/C values Cr^III and Fe^III complexes display significant and higher antitumour activity compared to 5-bromouracil while the Al^III complexes show lower activity. The in vitro results of the complexes on the same cells indicate that Cr^III and Fe^III complexes show higher inhibition on ³H-thymidine and ³H-uridine incorporation in DNA and RNA replication, respectively.