Unimolecular reactions of ionized methyl acetate and its hydrogen-rearranged isomers

The proposed formation of [CH₃C(OH)OCH₂]⁺˙ (b) as the intermediate in the isomerization [CH₂?C(OH)OCH₃]⁺˙ (c)?b?[CH₃COOCH₃]⁺˙ (c has been confirmed by preparation of b from CH₃COOCH₂OCH₃. For the three isomers a–c the dominant metastable ion (MI) dissociation, CH₃O˙ loss, involves identical kinetic energy release values. The kinetic barriers for a?b and b?c must be nearly as high as that for CH₃O˙ loss from c, as shown by the insensitivity of the mass spectra from collisionally activated dissociation (CAD) of a–c to ionizing electron energy. The H/D scrambling of metastable [CH₂?C(OD)OCH₃]⁺˙ and c–D₃ ions confirm this, indicating that the barrier for a?b is slightly below that for b?c. Minor low-energy dissociations include losses of CH₄ and CH₃OH from a and losses of ˙CHO and CH₂O from b. Comparison of MI and CAD spectra of a–c with those from [CH₃(OH)CH₂O]⁺˙ (d) and [CH₃COCH₂OH]⁺˙ (e) give no evidence for skeletal rearrangement of a–c to d or e.     

Does the dieckmann condensation occur in the gas phase?

Burinsky and Cooks¹ have reported that deprotonated dimethyl adipate eliminates methanol via a gas-phase Dieckmann condensation. This is in contrast to the behaviour of simple methyl ester enolates which lose MeOH by a different mechanism, e.g. MeOCOC?HCH₂R → [MeO (OCCHCH₂R)] → O?C?CHC?HR + MeOH. Evidence is presented which supports the Dieckmann mechanism for adipates. For example, MeOCOC?(Me)CH₂CH₂CD(Me)CO₂Me should eliminate MeOD in a Dieckmann condensation, but MeOH by the alternative mechanism outlined above. Experimentally, MeOD is lost exclusively. Similarly, MeOCOC?DCH₂CH₂C(Me)₂CO₂Me also loses MeOD, consistent with a Dieckmann process.     

Structure and formation of gaseous [C4H6O]+˙ ions: 1—The enolic ions [CH2C(OH)?CHCH2]+˙ and [CH2CH?CHCH(OH)]+˙ and their relationship with their keto counterparts

The [C₄H₆O]^+˙ ion of structure [CH₂?CHCH?CHOH]^+˙ (a) is generated by loss of C₄H₈ from ionized 6,6-dimethyl-2-cyclohexen-1-ol. The heat of formation ΔH_f of [CH₂?CHCH?CHOH]^+˙ was estimated to be 736 kJ mol^?1. The isomeric ion [CH₂?C(OH)CH?CH₂]^+˙ (b) was shown to have ΔH_f, ? 761 kJ mol^?1, 54 kJ mol^?1 less than that of its keto analogue [CH₃COCH?CH₂]^+˙. Ion [CH₂?C(OH)CH?CH₂]^+˙ may be generated by loss of C₂H₄ from ionized hex-1-en-3-one or by loss of C₄H₈ from ionized 4,4-dimethyl-2-cyclohexen-1-ol. The [C₄H₆O]^+˙ ion generated by loss of C₂H₄ from ionized 2-cyclohexen-1-ol was shown to consist of a mixture of the above enol ions by comparing the metastable ion and collisional activation mass spectra of [CH₂?CHCH?CHOH]^+˙ and [CH₂?C(OH)CH?CH₂]^+˙ ions with that of the above daughter ion. It is further concluded that prior to their major fragmentations by loss of CH₃˙ and CO, [CH₂?CHCH?CHOH]⁺˙ and [CH₂?C(OH)CH?CH₂]^+˙ do not rearrange to their keto counterparts. The metastable ion and collisional activation characteristics of the isomeric allenic [C₄H₆O]^+˙ ion [CH₂?C?CHCH₂OH]^+˙ are also reported.     

Syntheses and Reactions of Dimolybdenum Alkyne Compounds Containing Functionally Substituted Ligands. The Crystal Structure of [Co2Mo2(μ4-CHCH)(μ-CO)4(CO)4-(η5-C5H4C(O)Me)2]

Abstract

Three dimolybdenum alkyne complexes containing functionally substituted ligands [Mo₂(μ-CHCH)(CO)₄(η⁵?C₅H₄C(O)R)₂] [R ? OEt, (1a); R ? Me, (1b); R ? Ph, (1c)] were synthesized by reactions of acetylene with in situ generated metal-metal triply bonded complexes [Mo(CO)₂(η⁵?C₅H₄C(O)R)]₂ (R ? OEt, Me, Ph). Further reaction of (1a), (1b) or (1c) with Co₂(CO)₈ in refluxing toluene gave another three new butterfly compounds [Co₂Mo₂-(μ₄-CHCH)(μ-CO)₄(CO)₄(η⁵-C₅H₄C(O)R)₂] [R ? OEt, (2a); R ? Me, (2b); R ? Ph, (2c)]. The resulting compounds were characterized by elemental analyses, IR, ¹H NMR and MS. The crystal structure of (2b) was determined by single-crystal X-ray analysis. The results indicate that the existence of functional groups on the cyclopentadienyl ring has an influence on the reactivity of this type of complex.     

The energy surface for isomeric [C2H3O]+ ions: Further experimental evidence

Mass spectra from collisionally activated dissociation (CAD) of [C₂H₃O]⁺ ions, including isotopically labeled analogs, provide further information on the isomers [CH₃C?O⁺] (a), [CH₂?C?O⁺H] (b), [⁺CH₂CH?O] (c) and (d). Our data generally support the recent conclusions from theory by Radom and coworkers and from experiment by Terlouw, Holmes and coworkers. Most acetyl-containing molecular ions form a ions in high purity only at low energies, consistent with isomerization of higher energy molecular ions to form the more stable enol which dissociates to b. Isomer d, prepared from (CICH₂)₂CHOH, undergoes facile hydrogen scrambling, presumably through a degenerate 1,2-hydrogen shift. Theory suggests that c undergoes spontaneous isomerization to a and d; although [C₂H₃O]⁺ ions from BrCH₂CHO appear to consist of a and ～15% d, the latter are formed without substantial hydrogen scrambling.     

Chemistry of Fischer-type rhenacyclobutadiene complexes. II. Reactions with alkynes and sulfonium ylides, and rearrangements induced by nitriles and pyridine

Further investigations into the chemistry of the rhenacyclobutadiene complexes (CO)₄Re(η²-C(R)C(CO₂Me)C(X)) (1: R=Me, X=OEt (1a), O(CH₂)₃CCH (1b), NEt₂ (1c); R=CHEt₂, X=OEt (1d); R=Ph, X=OEt (1e)) are reported. Reactions of 1 with alkynes at reflux temperature of toluene and at ambient temperature either under photochemical conditions or in the presence of PdO yield ring-substituted η⁵-cyclopentadienylrhenium tricarbonyl complexes, 2. The symmetrical alkynes R^′CCR^′ (R^′=Ph, Me, CO₂Me) afford the pentasubstituted complexes (η⁵-C₅(Me)(CO₂Me)(OEt)(Ph)(Ph))Re(CO)₃ (2d), (η⁵-C₅(Me)(CO₂Me)(OEt)(Me)(Me))Re(CO)₃ (2e), (η⁵-C₅(Me)(CO₂Me)(OEt)(CO₂Me)(CO₂Me))Re(CO)₃ (2f), and (η⁵-C₅(Me)(CO₂Me)(NEt₂)(CO₂Me)(CO₂Me))Re(CO)₃ (2i) on reaction with the appropriate 1, whereas the unsymmetrical alkynes R^′CCR″ (R^′=Ph; R″=H, Me) give either only one, (η⁵-C₅(Me)(CO₂Me)(OEt)(Ph)H)Re(CO)₃ (2a)), or both, (η⁵-C₅(Me)(CO₂Me) (OEt)(Ph)(Me))Re(CO)₃ (2b) and (η⁵-C₅(Me)(CO₂Me)(OEt)(Me)(Ph))Re(CO)₃ (2c), (η⁵-C₅(Ph)(CO₂Me)(OEt)(Ph)H)Re(CO)₃ (2g) and (η⁵-C₅(Ph)(CO₂Me)(OEt)(H)(Ph))Re(CO)₃ (2h), of the possible products of [3 + 2] cycloaddition of alkyne to η²-C(R)C(CO₂Me)C(X). Thermolysis of (CO)₄Re(η²-C(Me)C(CO₂Me)C(O(CH₂)₃CCH)) (1b) containing a pendant alkynyl group proceeds to (η⁵-C₅(Me)(CO₂Me)(O(CH₂)₃)H)Re(CO)₃ (2j), a η⁵-cyclopentadienyl-dihydropyran fused-ring product. Competition experiments showed that each of PhCCH and MeO₂CCCCO₂Me reacts faster than PhCCPh with 1a. The results with unsymmetrical alkynes are rationalized by steric properties of substituents at the CC and ReC bonds and by a preference of ReC(Me) over ReC(OEt) to undergo alkyne insertion. A mechanism is proposed that involves substitution of a trans CO by alkyne in 1, insertion of alkyne into ReC bond to give a rhenabenzene intermediate, and collapse of the latter to 2. Complexes 1a and 1d undergo rearrangement in MeCN at reflux temperature to give rhenafuran-like products, (CO)₄Re(κ²-OC(OMe)C(CHCR₂)C(OEt)) (R=H (3a) or Et (3b)). The reaction of 1d also proceeds in EtCN, PhCN, and t-BuCN at comparable temperature, but is slower (especially in t-BuCN) than in MeCN. In pyridine at reflux temperature, 1a undergoes a similar rearrangement, with CO substitution, to give (CO)₃(py)Re(κ²-OC(OMe)C(CHCEt₂)C(OEt)) (4). A mechanism is proposed for these reactions. The sulfonium ylides Me₂SCHC(O)Ph and Me₂SC(CN)₂ (Me₂SCRR^′) react with 1a in acetonitrile at reflux temperature by nucleophilic addition of the ylide to the ReC(Me) carbon, loss of Me₂S, and rearrangement to a rhenafuran-type structure to yield (CO)₄Re(κ²-OC(OMe)C(C(Me)CRR^′)C(OEt)) (R=H, R^′=C(O)Ph (5a); R=R^′CN (5b)). All new compounds were characterized by a combination of elemental analysis, mass spectrometry, and IR and NMR spectroscopy.     

Chemistry of Fischer-type rhenacyclobutadiene complexes. I. Deprotonation, addition/substitution of nucleophilic reagents at α-carbon, and insertion of heteroatoms into rhenium-carbon bonds

The rhenacyclobutadienes (CO)₄Re(η²- C(R)C(CO₂Me)C(OR^′)) (2) undergo a number of reactions that mirror those of Fischer alkoxycarbene complexes. Thus, (CO)₄Re(η²-C(Me)C(CO₂Me)C(OEt)) (2a) can be deprotonated by LDA, Na[OBu-t], or Na[CH(CO₂Me)₂] to give the ylide-like conjugate base [(CO)₄Re(η²-C(CH₂)C(CO₂Me)C(OEt)]⁻ (3), which was isolated as PPN(3). Li(3) undergoes deuteriation with DCl/D₂O and alkylation with Et₃OPF₆ at ReCCH₂, with the latter reaction affording (CO)₄Re(η²-C(CH₂Et)C(CO₂Me)C(OEt)) (4). Repetition of the sequence deprotonation-ethylation on 4 generates (CO)₄Re(η²-C(CHEt₂)C(CO₂Me)C(OEt)) (5). The nature of the alkoxy substituent in 2 can be varied by use of the rhenacyclobutenones Na[(CO)₄Re(η²-C(R)C(CO₂Me)C(O))] (Na(1)) in conjunction with AcCl and R^′OH to produce a series of new complexes (R=Ph, R^′=Et (2b); R=Me, R^′=CH₂CHCH₂ (2c), (CH₂)₃CCH (2d), Me (2e)). Aminolysis of 2a with the primary and secondary amines PhNH₂, HO(CH₂)₂NH, p-TolNH₂, and Et₂NH yields the aminorhenacyclobutadiene complexes (CO)₄Re(η²-C(Me)C(CO₂Me)C(NHR^′ or NR^′₂)) (R₂^′=Et₂ (6a); R^′=Ph (6b), (CH₂)₂OH (6c), p-Tol (6d)). These complexes display lesser carbene-like character than their alkoxy counterparts 2, as evidenced by ¹H and ¹³C NMR spectroscopic properties and lack of reactivity toward LDA by 6a. Reactions of each 2a and 6a with PPhMe₂ at low temperature afford (CO)₄Re(η²-C(Me)(PPhMe₂)C(CO₂Me)C(OEt)) (7) and (CO)₃(PPhMe₂)Re(η²-C(Me)C(CO₂Me)C(NEt₂)) (9), respectively, further in agreement with the more carbenoid nature of 2a than 6a. 7 undergoes conversion to (CO)₃(PPhMe₂)Re(η²-C(Me)C(CO₂Me)C(OEt)) (8) upon heating. 2a reacts with each of (NH₄)₂[Ce(NO₃)₆], DMSO, EtNO₂/Et₃N, and Me₃NO under various conditions to afford one or both of the oxygen atom insertion products into the ReC bonds, (CO)₄Re(κ²-OC(Me)C(CO₂Me)C(OEt)) (10) and (CO)₄Re(κ²-C(Me)C(CO₂Me)C(OEt)O) (11). In contrast, no reaction occurred between 2a and S₈ on heating. However, 6a was converted to the NH insertion product (CO)₄Re(κ²-NHC(Me)C(CO₂Me)C(NEt₂)) (12) by the action of H₂NNH₂ · H₂O at 0 °C. All new compounds were characterized by a combination of elemental analysis, mass spectrometry, and IR and NMR spectroscopy.     

Structures and stabilities of [C3H3O]+ ions in the gas phase: A molecular orbital study

The relative energies of 11 [C₃H₃O]⁺ ions are calculated by different molecular orbital methods (MINDO/3, MNDO, ab initio with 3-21G and 4-31G* basis set and configuration interaction). The four most stable structures are: a ([CH₂?CH? CO]⁺), b c ([CH?C? CHOH]⁺) and d ([CH₂?C?COH]⁺); their relative energies at the CI/4-31G*//3-21G level are 0, 117, 171 and 218 kJ mol^?1, respectively. The isomerizations c→[CH?CH? CHO]⁺→[CH₂?C? CHO]⁺→ a and dissociations into [C₂H₃]⁺+CO and [HCO]⁺+C₂H₂ are explored. The calculated potential energy profile reveals that the energy-determining step is the 1,3-H migration c→[CH?CH? CHO]⁺. This explains the value of unity of the branching ratio and the spread of kinetic energy released for the two dissociation channels.     

Synthesis,characterization and cytotoxic activity of diorganotin complexes with Schiff base derived from salicylaldehyde and l-tyrosine

Seven diorganotin complexes with the Schiff bases derived from salicylaldehyde and l-tyrosine, R₂Sn[2-O-5-XC₆H₃CH?=?NCH(CH₂C₆ H₄OH-4)COO] (X?=?H (1), Br (2); R?=?Me (a), Et (b), Bu (c), Cy (cyclohexyl) (d)), were synthesized and characterized by elemental analysis, IR, ¹H and ¹³C NMR spectra, and the single-crystal X-ray diffraction. In methanol, the racemization of chiral center of l-tyrosinate fragment occurred and the racemic products were obtained. X-ray analyses of 1c, 1d, and 2a–2c showed that the tin atoms of the complexes exhibit distorted trigonal-bipyramidal geometries. In 1c, 1d, and 2c, the intermolecular O–H???O hydrogen bonds connected the molecules into 1-D supramolecular chain or a R₂²(20) macrocyclic dimer, and 2a and 2b formed the 2-D supramolecular network by the intermolecular Sn???O and O–H???O interactions. Bioassay results indicated that 1a, 1c, and 1d had moderate antibacterial activity against Escherichia coli and 1c, 1d, and 2c belonged to the efficient cytostatic agents against two human tumor cell lines (A549 and HeLa) and the activity tends to follow the order Cy > Bu?>?Et?>?Me for the R group attached to tin.     

Ruthenium(II) carbonyl complexes of P,P and P,O donor diphosphine ligands,Ph2P(CH2)nPPh2 and Ph2P(CH2)nP(O)Ph2, n = 2, 3 and their activities in catalytic transfer hydrogenation reactions

The polymeric precursor [RuCl₂(CO)₂]_n reacts with the ligands, P∩P (a, b) and P∩O (c, d), in 1:1 M ratio to generate six-coordinate complexes [RuCl₂(CO)₂(?²-P∩P)] (1a, 1b) and [RuCl₂(CO)₂(?²-P∩O)] (1c, 1d), where P∩P: Ph₂P(CH₂)_nPPh₂, n = 2(a), 3(b); P∩O: Ph₂P(CH₂)_nP(O)Ph₂, n = 2(c), 3(d). The complexes are characterized by elemental analyses, mass spectrometry, thermal studies, IR, and NMR spectroscopy. 1a–1d are active in catalyzed transfer hydrogenation of acetophenone and its derivatives to corresponding alcohols with turnover frequency (TOF) of 75–290 h^?1. The complexes exhibit higher yield of hydrogenation products than catalyzed by RuCl₃ itself. Among 1a–1d, the Ru(II) complexes of bidentate phosphine (1a, 1b) show higher efficiency than their monoxide analogs (1c, 1d). However, the recycling experiments with the catalysts for hydrogenation of 4-nitroacetophenone exhibit a different trend in which the catalytic activities of 1a, 1b, and 1d decrease considerably, while 1c shows similar activity during the second run.     

STUDIES ON THE BACTERIAL ACTIVITY OF COBALT(III) COMPLEXES. PART III. COBALT(III) CARBOXYLATE COMPLEXES

Abstract

Cobalt(III) complexes of the type [Co(en)₂(chel)]X.nH₂O where en = ethylenediamine, chel = phthalato = C₆H₄CO₂)^2? ₂, maleato = (O₂CCH = CHCO₂)^2?, succinato = (O₂CCH₂CH₂CO₂)^2?, homophthalato = (O₂CC₆H₄(CH₂)CO₂)^2?, citraconato = (O₂CC(CH₃) = CHCO₂)^2?, itaconato = (CH₂ = C(CO₂)CH₂CO₂)^2?, X = NO^? ₃, Br^?, (O₂CC₆H₄CO₂H)^?, (O₂CHC = CHCO₂H)^?, (O₂C(CH₂)₂CO₂H)^?, (O₂CC₆H₄(CH₂)CO₂H)^?, (O₂CHC = C(CH₂)-CO₂H)^?, and (O₂C-CH₂?C(= CH₂)-CO₂H)^?, [Co(en)₂(malonato)]X.2H₂O (where malonato = (O₂CCH₂CO₂)^2?, X = Cl^?, Br^?, and NO^? ₃) and [Co(en)₂CO₃]Cl.2H₂O have been investigated for their bacterial activity against Escherichia coli B growing on EMB agar and in minimal glucose media both in lag and log phases. Among the most active are where chel = phthalato and homophthalato. The effects are distinct from those known for compounds of Pt, e.g., cis?[Pt(NH₃)₂Cl₂] and rhodium, e.g., trans?[Rh(C₅H₅N)₄,Cl₂].6H₂O. Antagonisms are reported.     

Aktivierungsenergie und Mechanismus der intramolekularen Wasserstoff-Wanderung bei Radikal-Kationen von Keto/Enol-Tautomeren in der Gasphase

The collisional activation mass spectra prove that non-decomposing ionized methyl acetate [CH₃COOCH₃]⁺? and its enolic isomer [CH₂?C(OH)OCH₃]⁺? exist as stable species in potential wells. It is shown, however, that prior to CH₃O? loss the decomposing [CH₂?C(OH)OCH₃]⁺? ion isomerizes via a rate determining symmetry forbidden [1.3] hydrogen rearrangement to ionized methyl acetate. The alternative mode of two consecutive formally symmetry allowed [1.2] hydrogen migrations can be certainly excluded for this isomerization. The activation energy of such hydrogen rearrangements is of the order of 41–83 kcal · mol^?1 depending on the electronic nature of the cations (“open” or “closed” shell systems).     

Synthesis and Characterization of a Gold Vinylidene Complex Lacking π‐Conjugated Heteroatoms

Hydride abstraction from the gold (disilyl)ethylacetylide complex [( P )Au{η¹‐C?CSi(Me)₂CH₂CH₂SiMe₂H}] ( P =P(tBu)₂o‐biphenyl) with triphenylcarbenium tetrakis(pentafluorophenyl)borate at ?20 °C formed the cationic gold (β,β‐disilyl)vinylidene complex [( P )Au?C?CSi(Me)₂CH₂CH₂Si (Me)₂]⁺B(C₆F₅)₄^? with ≥90 % selectivity. ²⁹Si NMR analysis of this complex pointed to delocalization of positive charge onto both the β‐silyl groups and the ( P )Au fragment. The C1 and C2 carbon atoms of the vinylidene complex underwent facile interconversion (ΔG^≠=9.7 kcal mol^?1), presumably via the gold π‐disilacyclohexyne intermediate [( P )Au{η²‐C?CSi(Me)₂CH₂CH₂Si (Me)₂}]⁺B(C₆F₅)₄^?.     

NMR of enaminones. Part 7 1H-, 13C-, and 17O-NMR and X-ray structure determinations of 1,2-disubstituted conjugated 3-[(tert-Butyl)amino]enones

¹H-, ¹³C-, and ¹⁷O-NMR spectra for the 2-substituted enaminones MeC(O)C(Me)?CHNH(t-Bu) ( 1 ), EtC(O)C(Me)?CHNH(t-Bu) ( 2 ), PhC(O)C(Me)?CHNH(t-Bu) ( 3 ), and MeC(O)C(Me)?CHNH(t-Bu) ( 4 ) are reported. These data show that 3 exists mainly in the (E)-form, 4 in (Z)-form, and 1 and 2 as mixtures of both forms. Polar solvents favour the (E)-form. The (Z)- and (E)-forms exist in the 1,2-syn,3,N-anti and 1,2-anti,1,N-anti conformations A and B , respectively. The structures of the (E)- and (Z)-form are confirmed by X-ray crystal-structure determinations of 3 and 4. The shielding of the carbonyl O-atom in the ¹⁷O-NMR spectrum by intramolecular H-bonding (Δλ_HB) ranging from ?28 to ?41 ppm, depends on the substituents at C(l) and C(2). Crystals of 3 at 90 K are monoclinic. with a = 9.618(2) Å, b = 15.792(3) Å, c = 16.705(3) Å, and β = 94.44(3)°, and the space group is P2₁/c with Z = 8 (refinement to R = 0.0701 on 3387 independent reflections). Crystals of 4 at 101 K are monoclinic, with a = 16.625(8) Å, b = 8.637(6) Å, c = 11.024(7) Å, and β = 101.60(5)°, and the space group is Cc with Z = 4 (refinement to R = 0.0595 on 2106 independent reflections).     

Synthesis,spectral and antimicrobial studies of chlorodiorganotin(IV)[3(2′-hydroxyphenyl)-5-(4-substitutedphenyl) pyrazolinates]

Chlorodiorganotin(IV)pyrazolinates of the type R₂SnCl(C₁₅H₁₂N₂O?·?X) [where C₁₅H₁₂N₂O?·?X?=?3(2′-Hydroxyphenyl)-5(4-X-phenyl)pyrazoline {where X?=?H (a); CH₃ (b); OCH₃ (c); Cl (d) and R?=?Me, Pr ⁿ and Ph}] have been synthesized by reaction of R₂SnCl₂ with the sodium salt of pyrazolines in 1?:?1 molar ratio, in anhydrous benzene. These newly synthesized derivatives have been characterized by elemental analysis (C, H, N, Cl and Sn), molecular weight measurement and spectral studies [IR and multinuclear NMR (¹H, ¹³C and ¹¹⁹Sn)]. The bidentate behavior of the ligands was confirmed by IR, ¹H and ¹³C NMR spectral data. Trigonal bipyramidal structure around tin(IV) for R₂SnCl(C₁₅H₁₂N₂O?·?X) is suggested. The free pyrazoline and some chlorodiorganotin(IV) pyrazolinates have been screened for their antibacterial and antifungal activities. Some chlorodiorganotin(IV) pyrazolinates exhibit higher antibacterial and antifungal effect than free pyrazoline and some antibiotics.     

Trichloro- and methyldichlorogermyl monochelates and dibromo- and dichlorogermyl bischelates derived from N,N-disubstituted amides of 2-hydroxycarboxylic acids

The reactions of GeCl₄, GeBr₄, and MeGeCl₃ with O-trimethylsilyl derivatives of N,N-disubstituted amides of 2-hydroxycarboxylic acids afforded pentacoordinate and hexacoordinate neutral (O,O)-mono- and (O,O)-bischelates. The reactions of glycolic acid derivatives with GeX₄ produced bischelates X₂Ge[OCH₂C(O)NR²R³]₂ 7a,c,d (X = Cl, R² = R³ = Me (a), (CH₂)₅ (c), (CH₂CH₂)₂O (d)) and 8a (X = Br). By contrast, the reactions of lactic and mandelic acid derivatives with GeCl₄ and MeGeCl₃ gave monochelates Cl₃Ge[OCH(R¹)C(O)NR²R³] (S)-9a–c (R¹ = Me) and Cl₂MeGe[OCH(R¹)C(O)NR²R³] 10a (R¹ = H), (S)-11a,b (R¹ = Me), and (S)-12a (R¹ = Ph) (R²R³ = (CH₂)₄ (b)), respectively. According to the X-ray diffraction data, the Ge atom in bischelates 7c,d and 8a has a coordination number 6, and its coordination polyhedron can be described as a slightly distorted octahedron. In monochelates (S)-9a-c, 10a, (S)-11a,b, and (S)-12a, the Ge atom has a coordination number 5, and its coordination polyhedron can be described as a trigonal bipyramid with two halogen atoms or one halogen atom and one ethereal oxygen atom in equatorial positions and the halogen atom and the amide oxygen atom in the axial positions. The bonds in the axial positions are somewhat longer than the corresponding bonds in tetracoordinate Ge compounds.     

Energy dependence of the fragmentation of ester enolate ions

The energy dependence of the fragmentation of a selection of ester enolate ions has been studied by variable, low-energy collision-induced dissociation experiments in the quadrupole collision cell of a hybrid BEQQ mass spectrometer. The dominant fragmentation reactions observed are where ΔH₁ ? ΔH₂=PA([RCCO]^?) ? PA([?O]^?) (PA=proton affinity). The anion of lowest proton affinity is formed preferentially at low internal energies with the yield of the anion of higher proton affinity increasing with increasing internal energy. The [CH₃OCOCOCH₂]^? anion derived from methyl pyruvate forms [CH₃OCO]^? by reaction (2); this anion readily fragments to [CH₃G]^?+ CO consistent with a structure represented by a dipole-stabilized cluster of [CH₃O]^? and CO. Comparison of the 8-keV with the 50-eV collision-induced dissociation mass spectra indicated that the average internal energy of the fragmenting ions is considerably lower in the high-energy collisional experiments than it is in the low-energy collisional experiments.     

The variability of hydrogen-bonded supramolecular assemblies in crystalline picrates prepared from ferrocenyl-substituted β-aminoalcohols

Ferrocene-based β-aminoalcohols FcCH₂NHCR₂CH₂OH (R = H, 1a; R = Me, 1b) and (S)-FcCH₂NHCH(CHMe₂)CH₂OH (1c; Fc = ferrocenyl) react with 2,4,6-trinitrophenol (Hpic) under proton transfer to afford the corresponding ammonium picrates 2a-c. In the crystal, these picrates associate predominantly via N-H?O and O-H?O bifurcated hydrogen bonds between the NH₂⁺ and OH groups in the aminoalcohol chain as the donors and the phenoxide and NO₂ oxygen atoms of the picrate anion as the acceptors. Compounds 2a and 2b form closed dimeric assemblies [1nH]₂[pic]₂ (n = a, b) around the crystallographic inversion centres. By contrast, their chiral analogue 2c gives rise to monomeric units [1cH][pic] (albeit through similar interactions), that further aggregate into infinite linear chains via N-H?O hydrogen bonds. The formed assemblies are interconnected by the soft C-H?O hydrogen bonds and via π?π stacking interactions of the picrate ions.     

含卤素端基的单取代对-叔丁基杯[6]芳烃的合成与表征

用THF作为反应溶剂, K₂CO₃作碱, 对-叔丁基杯[6]芳烃与二溴丁烷、二溴己烷和1,4-二氯丁炔-2反应以中等产率选择性地合成了含有卤素端基的单取代对-叔丁基杯[6]芳烃2a～2c. 2a和2b可与对甲苯磺酸甲酯(MeOTs)反应高产率地得到全甲基化产物3a和3b. 通过核磁共振谱(¹H NMR)和质谱(FAB-MS)表征, 发现所有化合物都具有预期结构, 2a～2c和3b在室温下是锥式构象, 而3a没有固定构象.     

Hydrothermal synthesis,crystal structure and thermal stability of a new 2D layered metal(II) phosphonate: [NH3CH2CH2NH3][Fe2(O3PCH(OH)CO2)2(H2O)2]·2H2O

In the presence of ethylenediamine template agents, a metal(II) phosphonate, [NH₃CH₂CH₂NH₃][Fe₂(O₃PCH(OH)CO₂)₂(H₂O)₂]?·?2H₂O (1) has been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction as well as infrared spectroscopy, elemental analysis and thermogravimetric analysis. The compound crystallines in the monoclinic space group P2₁/n: Crystal data for 1: a?=?8.4523(8)?Å, b?=?9.8196(9)?Å, c?=?10.9217(10)?Å, β?=?105.9500(10)°, V?=?871.58(14)?Å, Z?=?2, D _c?=?2.103?g?cm^?3, R ₁?=?0.0290, wR ₂?=?0.0811. The Fe (II) cation is octahedrally coordinated by six oxygen atoms from the three ligands and one coordinated water molecule to form a 2D layered structure with a one-dimensional channel system in the a-axis direction.