C60-fullerenides of ytterbium and lutetium

Cp^#₂Yb (Cp^#=C₅H₄(CH₂)₂NMe₂) has been obtained by reaction of YbI₂(THF)₂ with 2 equiv. of C₅H₄(CH₂CH₂NMe₂)K in THF. The X-ray structure analysis shows a bent structure with intramolecular coordination of both nitrogen atoms to ytterbium. The reaction of C₆₀-fullerene with Cp^#₂Yb leads to the formation of the fullerenide derivative [Cp^#₂Yb]₂C₆₀, which shows an ESR signal in the solid state and in THF solution at room temperature (solid: ΔH = 50 G, G = 1.9992; solution: ΔH = 10 G, G = 2.0001) and a magnetic moment of 3.6 BM. The lutetium fullerenides CpLu(C₆₀)(DME) (3) and Cp^*Lu(C₆₀)(DME)(C₆H₅CH₃) (4), (Cp = η⁵−C₅H₅, Cp^* = η⁵−C₅Me₅), were obtained by reaction of C₆₀ with CpLu(C₁₀H₈) (DME) and Cp^*Lu(C₁₀H₈) (DME) in toluene. Both complexes are paramagnetic (μ_eff = 1.4 and 0.9 BM) and exhibit temperature-dependent ESR signals (293 K: g = 1.992 and 2.0002 respectively).     

Heats of reaction of HMo(CO)3(C5R5) (R = H, CH3) with diphenyldisulfide and of formation of the clusters [PhSMo(CO)x(C5H5)]2, X = 1,2. Thermodynamic study of molybdenum-sulfur bond strengths

The enthalpies of reaction of HMo(CO)₃C₅R₅ (R = H, CH₃) with diphenyldisulfide producing PhSMo(CO)₃C₅R₅ and PhSH have been measured in toluene and THF solution (R = H, ΔH= −8.5 ± 0.5 kcal mol⁻¹ (tol), −10.8 ± 0.7 kcal mol⁻¹ (THF); R = CH₃, ΔH = −11.3±0.3 kcal mol⁻¹ (tol), −13.2±0.7 kcal mol⁻¹ (THF)). These data are used to estimate the Mo---SPh bond strength to be on the order of 38–41 kcal mol⁻¹ for these complexes. The increased exothermicity of oxidative addition of disulfide in THF versus toluene is attributed to hydrogen bonding between thiophenol produced in the reaction and THF. This was confirmed by measurement of the heat of solution of thiophenol in toluene and THF. Differential scanning calorimetry as well as high temperature calorimetry have been performed on the dimerization and subsequent decarbonylation reactions of PhSMo(CO)₃Cp yielding [PhSMo(CO)₂Cp]₂ and [PhSMo(CO)Cp]₂. The enthalpies of reaction of PhSMo(CO)₃Cp and [PhSMo(CO)₂Cp]₂ with PPh₃, PPh₂Me and P(OMe)₃ have also been measured. The disproportionation reaction: 2[PhSMo(CO)₂Cp]₂ → 2PhSMo(CO)₃Cp + [PhSMP(CO)Cp]₂ is reported and its enthalpy has also been measured. These data allow determination of the enthalpy of formation of the metal-sulfur clusters [PhSMo(CO)_nC₅H₅]₂, N = 1,2.     

The migratory insertion of carbon monoxide in pentamethylcyclopentadienyliridium (III) complexes. Structural effects on reactivity and mechanism for rhodium and iridium systems

The reactions of complex (C₅Me₅)Ir(Cl) (CO) (Me) (1a) with cyclohexylisocyanide and phosphines (L=CyNC, PHPh₂, PMePh₂, PMe₂Ph) give the products of alkyl migratory insertion (C₅Me₅Ir(Cl) (COMe) (L), in toluence or tetrahydrofuran at 323 K or higher temperature. The phenyl analogue (C₅Me₅)Ir(Cl)(CO)(Ph) or the iodide complexes (C₅Me₅)Ir(I) (CO) (R) (R=Me, Ph_are not reactive under the same conditions. The reaction of (C₅Me₅)Ir(Cl)(CO)(Me) with PMePh₂ and PMe₂Ph in acetonitrile yields the chloride substitution product [(C₅Me₅)Ir(CO)(L)(Me)]⁺Cl⁻. Kinetic measurements for the reactions of (C₅Me₅)Ir(Cl)(CO)(Me) in toluene are first order in the iridium complex and exhibit a saturation dependence on the incoming donors L. Analysis of the data suggests a two-step process involving (i) rapid formation of a molecular complex [(C₅Me₅)Ir(Cl)(CO)(Me), (L)], in which the structure of 1a is unperturbed within the limits of spectroscopic analysis, and (ii) rate determining methyl migration. The reaction parameters are K for the pre-equilibrium step (K = 1.5 (CyNC), 7.3 (PHPh₂), 7.1 (PMePh₂) dm³ mol⁻¹ at 323 K) and k₂ for the slow carbon---carbon bond formation (k₂ (10⁵) = 6.9 (CyNC), 1.2 (PHPh₂), 1.0 (PMePh₂) s⁻¹ at 323 K). The activation parameters for the methyl migration step in the reaction with PMePh₂ obtained between 308 and 338 K, are ΔH^≠ = 106±16 kJ mol⁻¹ and ΔS^≠ = − 14±5 J K⁻¹ mol⁻¹. The reaction of 1a with PMePh₂ proceeds at similar rates in tetrahydrofuran (K = 3.7 dm³ mol⁻¹, k₂ (10⁵) = 1.2 s⁻¹, 323 K). The crystal structure of (C₅Me₅)Ir(Cl)(COMe) (PMe₂Ph) has been determined by X-ray diffraction. C₂₀H₂₉ClOPIr: M_r = 544.1, monoclinic, P2₁/n, A = 8.084 (2), B = 9.030(2), C = 28.715 (3) Å, β = 91.41 (3)°, Z = 4, D_c = 1.71 g cm⁻³, V = 2095.5 ų, room temperatyre, Mo K, γ = 0.71069, μ = 65.55 cm⁻¹, F(000) = 1044, R = 0.037 for 2453 independent observed reflections. The complex shows a deformed tetrahedral coordination assuming the η⁵-C₅Me₅ molecular fragment as a single coordination site. The iridium-chlorine bond is staggered with respect to two adjacent C(ring)-methyl bonds, while the Ir---P and the Ir---COMe bonds are eclipsed with respect to C(ring)-methyl bonds.     

Synthesis of symmetric and unsymmetric 1,4-bis(p-R-phenylethynyl)benzenes via palladium/copper catalyzed cross-coupling and comments on the coupling of aryl halides with terminal alkynes

A series of symmetric 1, 4-bis(p-R-phenylethynyl)benzenes (6a-h) have been prepared via Pd¹¹/Cu¹ catalyzed cross- coupling of 1, 4-diiodobenzene (5) and p-substituted phenylethynes (4a-h). Similarly, the unsymmetric analogues (9a-c) were obtained from 1-iodo-4-(p-nitrophenylethynyl)benzene (8) and p-substituted phenylethynes (4c, 4d, 4g). Quantitative analysis of 1,4-(trimethylsilyl)butadiyne (10), produced in the catalytic coupling of ethynyltri- methylsilane with aryl halides using PdCl₂(PPh₃)₂/CuI in an amine solvent, confirmed that catalyst initiation proceeds via reduction of Pd¹¹ to Pd⁰ with concomitant oxidative homo-coupling of two ethynyltrimethylsilane molecules producing exactly one equivalent of 10 based on Pd¹¹. If air is present, the PdCl₂(PPh₃)₂/CuI/amine mixture provides a very effective system for catalytic oxidative homo-coupling of terminal alkynes to diynes and thus air must be rigorously excluded from the cross-coupling reactions. Hydrodehalogenation can compete effectively with the cross-coupling reaction for highly fluorinated aryl halides. Under certain conditions, the fluorinated aryl bromide or iodide can serve as the oxidant for the alkyne to diyne oxidative homo-coupling reaction. This can be avoided by appropriate choice of reaction conditions and reagents. These competing pathways have significant implications for the cross-coupling of aryl halides with terminal alkynes and are discussed herein.     

Hydroformylation of alkenes and alkynes using a heterobinuclear Rh---W catalyst

Hydroformylation reactions of a series of alkenes and alkynes have been carried out using the heteronuclear Rh---W catalyst, (CO)₄ hH(CO)(PPh₃) (1). The results of these reactions have been compared with corresponding reactions using [Rh(OAc)₂]₂ as catalyst. Catalysis of a reaction of styrene using 1 gave a very high yield of the branched chain aldehyde containing only a trace of the straight chain isomer. Reactions of the phosphinoalkene, Ph₂P(CH₂)₃CH=CH₂ (7) and the corresponding alkyne, Ph₂P(CH₂)₃CCH (11) gave similar products using either catalyst system with the alkryne reaction being significantly slower. Reaction of the alkenyl dithiane, H---CH₂CH=CH₂ (2), using the Rh---W catalyst (1) gave a higher ratio of linear to branched aldehydes (47 linear:53 branched) than the corresponding reaction using [Rh(OAc)₂]₂ (25 linear:75 branched). Reactions of vinyl acetate using 1 as catalyst gave a significant amount of linear aldehyde in contrast to reactions using [Rh(OAc)₂]₂ but reactions of allyl acetate gave similar products for both catalyst systems.     

Preparation of trimethylsilyl alkyne complexes of bis(pentamethylcyclopentadienyl)zirconium, (η-C5Me5)2Zr(RC≡CSiMe3), and their regioselective reactions with nitrous oxide

Benzene solutions of Cp^*₂ZrCl₂ (1) (Cp^* = η⁵-C₅Me₅) react with the alkynes Me₃SiC≡CPh, Me₃SiC≡C(c-C₅H₉) and Me₃SiC≡CCMe₃ in the presence of Na/Hg amalgam to afford high yields of the respective alkyne complexes Cp^*₂Zr(Me₃SiC≡CPh) (2), Cp^*₂Zr{Me₃SiC≡C(c-C₅H₉)} (3) and Cp^*₂Zr(Me₃SiC≡CCMe₃) (4) as crystalline compounds. Complex 2 crystallizes in the triclinic space group with a = 9.791(6), b = 10.466(6), c = 15.756(12) Å, = 86.09 (5), β = 72.09(5), γ = 72.06(4)° and Z = 2. The least-squares refinement converged to R(F) = 0.0604 and R(wF) = 0.0628 for the 3655 unique data with F_o > 4σ (F_o). Salient metrical parameters of the bound alkyne include the following: C(30)-C(31) = 1.340(9) Å; Zr-C(30) = 2.178(6) Å; Zr-C(31) = 2.219(5) Å; C(30)-C(31)-Si = 141.0(5)°; C(31)-C(30)-C(26) = 135.5(5)°. Nitrous oxide reacts with 2 or 3 to afford ((5) R = Ph; (6) R = c-C₅H₉) and 1 equiv. of N₂ via an intermediate, , which is unstable with respect to loss of dinitrogen to give the oxametallacyclobutene derivatives 5 and 6. The oxygen-atom insertion is regiospecific for the Zr-C bond that is attached to the carbyl (Ph or c-C₅H₉) substituent. Under similar conditions, complex 4, in which the alkyne is particularly labile, gives a myriad of products in its reaction with N₂O.     

Steric control in the formation of Co2(CO)6-alkyne complexes from Group 14 tetraalkynes and their reactions with acid

A series of tetrakis(trimethylsilylethyne) derivatives of Group 14 metals (2–4) was prepared. Co₂(CO)₆ complexes 5–10 were synthesised by the reaction of 2–4 with Co₂(CO)₈. From the silyl and germyl based compounds 2 and 3, either one or two alkynes could be complexed with Co₂(CO)₆. In contrast, the tin derived compound 4 could accommodate up to four Co₂(CO)₆ complexes. The longest wavelength UV-Vis absorbances of the silicon and germanium-based complexes were consistent with multiple, non-conjugated Co₂(CO)₆ chromophores. The tetrakis Co₂(CO)₆ complex 10, however, absorbs at a much longer wavelength suggesting conjugation of Co₂(CO)₆ complexes through the tin. The reactivity towards protonolysis of the uncomplexed alkynes 2–4 is a consequence of the hyperconjugative stabilisation of the intermediate β-vinyl cation (the β-effect): Sn(CCSiMe₃)₃>SnOTf(CCSiMe₃)₂>SiMe₃>Ge(CCSiMe₃)₃. The reactivity of the Co₂(CO)₆ complexes, however, was quite different from the reactions of 2–4 and from analogous all-carbon systems. Treatment of 5–10 with strong acid led neither to protiodemetallation of the complexed or non-complexed alkynes but to decomplexation of the cobalt. Similarly, ligand metathesis reactions between 10 and Ph₂SiCl₂ were not observed. The normal reactivity of silylalkynes towards electrophiles, which was expected to be enhanced by the presence of the cobalt complex, was diminished by the particular steric environment of the molecules under examination (5–10). As a result, the favoured reaction under these conditions was decomplexation of the cobalt.     

On the mechanism of silylformylation catalyzed by Rh-Co mixed metal complexes

Possible mechanisms for the silylformylation of 1-alkynes catalyzed by Rh₂Co₂(CO)₁₂ are investigated. Novel Rh-Co mixed metal complexes, (PhMe₂Si)₂Rh(CO)nCo(CO)₄ (n = 2 or 3) (3) and RhCo(HC≡CBuⁿ)(CO)₅ (5), are found to play important roles in this catalysis. The reaction of 3 with 1-hexyne and HSiMe₂Ph at ambient temperature and pressure of CO gives n-BuC(CHO)=CHSiMe₂Ph (1a, Z/E = 95/5), (PhMe₂Si)₂Rh(CO)₃Co(CO)₄ (3-B) and an Rh-Co mixed metal butterfly complex, h₂Co₂(HC≡CBuⁿ)(CO)₁₀ (4). The reaction of 5 with 1-hexyne and HSiMe₂Ph under the same ambient conditions affords 1a (100% Z) very cleanly as the sole reaction product. The crossover experiments u sing RhCo(DC≡CBuⁿ)(CO)₅(5-d), 1-hexyne-1d and DSiMe₂Ph strongly support the mixed metal bimetallic catalysis and involvement of bis(alkyne)-Rh-Co species. The most plausible catalytic cycle of silylformylation which can accommodate all the observed results is proposed.     

Oxidation of 1,4-alkanediols into γ-lactones via γ-lactols using Rhodococcus erythropolis as biocatalyst

Whole cells of Rhodococcus erythropolis DSM 44534 grown on ethanol, (R)- and (S)-1,2-propanediol were used for biotransformation of racemic 1,4-alkanediols into γ-lactones. The cells oxidized 1,4-decanediol (1a) and 1,4-nonanediol (2a) into the corresponding γ-lactones 5-hexyl-dihydro-2(3H)-furanone (γ-decalactone, 1c) and 5-pentyl-dihydro-2(3H)-furanone (γ-nonalactone, 2c), respectively, with an EE(R) of 40–75%. The transient formation of the γ-lactols 5-hexyl-tetrahydro-2-furanol (γ-decalactol, 1b) and 5-pentyl-tetrahydro-2-furanol (γ-nonalactol, 2b) as intermediates was observed by GC–MS. 1,4-Pentanediol (3a) was transformed into 5-methyl-dihydro-2(3H)-furanone (γ-valerolactone, 3c) whereas (R)- and (S)-2-methyl-1,4-butanediol (4a) was converted to the methyl-substituted γ-butyrolactones 4-methyl-dihydro-2(3H)-furanone (4c₁) and 3-methyl-dihydro-2(3H)-furanone (4c₂) in a ratio of 80:20 with a yield of 55%. Also cis-2-buten-1,4-diol (5a) was transformed resulting in the formation of 2(5H)-furanone (γ-crotonolactone, 5c). At the higher pH values of 8.8 the yield of lactone formed was improved; however, the enatiomeric excesses were slightly higher at the lower pH of 5.2.     

Crystal structure of Zn(trz)Cl (trz = 11,2,4,-triazolato); a layered compound with triply bridging triazolato groups

ZnCl₂ reacts with 1,2,4-1H-triazole to afford Zn(trz)Cl. A spontaneous deprotonation of Htrz occurs. The crystal structure of Zn(trz)Cl has been solved. The compound crystallizes in the space group P2₁/n. The lattice parameters are a = 8.863(4), B = 9.762(4), C = 6.146(3) Å, β = 99.56(10)°, with Z = 4. The 1,2,4-triazolato bridges three zinc atoms through its three nitrogen atoms, affording a layered structure. The zinc atom is in an N₃Cl tetrahedral coordination. The layers are not planar, but rather corrugated. The chlorine atoms point to either side of the layers, and play the role of spacers. The shortest interlayer ZnZn separation is 5.701 Å.     

Synthesis, characterization, and anticonvulsant activity of enaminones. Part 5: Investigations on 3-carboalkoxy-2-methyl-2,3-dihydro-1H-phenothiazin-4[10H]-one derivatives

A new series of anticonvulsant 3-carboalkoxy-2-methyl-2,3-dihydro-1H-phenothiazin-4[10H]-ones is herein reported. 2-Aminothiophenols underwent cyclocondensation with 4-carboalkoxy-5-methylcyclohexane-1,3-diones in refluxing dimethylsulfoxide (DMSO) to yield 3-carboalkoxy-2-methyl-2,3-dihydro-1H-phenothiazin-4[10H]-ones, 4a–k. In the case of the carbo-tert-butoxy derivatives (4c and 4k) prolonged reaction times led to the isolation of the respective 3-unsubstituted-2-methyl-2,3-dihydro-1H-phenothiazin-4[10H]-ones (4l and 4m) instead. Significant anticonvulsant activity was displayed by these analogues, most particularly 4k, which was active at 30 mg/kg intraperitoneally (ip) in mice in the maximal electroshock seizure (MES) evaluation, with no toxicity noted at dosages up to 300 mg/kg. Oral (po) rat evaluation of 4k in the MES evaluation provided an ED₅₀ of 17.60 mg/kg, with no toxicity noted at dosages up to 500 mg/kg, providing a protective index (PI = TD₅₀/ED₅₀) > 28.40. These compounds represent the first reported series of phenothiazines which possess anticonvulsant activity.     

Hydride complexes of platinum(II) containing unsymmetrical di(phosphine) ligands: synthesis, characterization and evidence for pairwise addition of hydrogen based on parahydrogen induced polarization

Unsymmetrical di(phosphine) ligands (dpp)₂Rop (1a, b = bis(diphenylphosphino)-2-alkyl-3-oxapropane (alkyl = methyl and ethyl)) and (dpp)₂oCy (1c = trans-2-diphenylphosphinocyclohexyl diphenylphosphinite) and their Pt(II) dichloride complexes, PtCl₂((dpp)₂mop) (2a), PtCl₂((dpp)₂eop) (2b) and PtCl₂((dpp)₂oCy) (2c), have been synthesized and characterized by NMR spectroscopy. The crystal structures of 2b and 2c show that the geometry about the platinum centers is square planar. In 2b, the metal and di(phosphine) ligand chelate ring are in a chair conformation, whereas in 2c, the chelate ring conformation is a skewed boat. Initial reaction of sodium borohydride with 2a, b, c yields the monohydride monochloride complexes PtHCl((dpp)₂mop) (5a), PtHCl((dpp)₂eop) (5b) and PtHCl((dpp)₂oCy) (5c). At longer reaction times, fluxional dimeric species are obtained, [PtH((dpp)₂mop)]₂ (4a), [PtH((dpp)₂eop)]₂ (4b) and [PtH((dpp)₂oCy)]₂ (4c),and in the case of 4c two different isomers exist. The dihydride complexes PtH₂((dpp)₂mop) (3a), PtH₂((dpp)₂eop) (3b) and PtH₂((dpp)₂oCy) (3c), are prepared by further reaction of NaBH₄ and 2. Hydrogen cycling is facile in the dihydride complexes 3a, b, c, and oxidative addition of H₂ proceeds in a pairwise manner as determined by the observation of parahydrogen induced polarization (PHIP) in the ¹H NMR spectra. The reductive elimination of H₂ is also shown to be concerted by reaction of dihydride complexes with D₂. Crystal data: 2b (C₃₀H₃₂Cl₆OP₂Pt), monoclinic, space group P2₁/c (No. 14), a = 13.7040(1), b = 11.3430(7), c = 21.3880(9) Å, β = 97.923(9)°, V = 3292.9(2) ų and Z = 4; 2c (C₃₀H₃₀Cl₂OP₂Pt), monoclinic, space group P2₁ (No. 4), a = 11.7360(2), b = 8.4311(2), c = 14.2789(2) Å, β = 101.290(1)°, V = 1385.52(4) ų and Z = 2.     

Solvent extraction of divalent palladium and platinum from aqueous solutions of their chloro complexes using an N,N-dimethyldithiocarbamoylethoxy substituted calix[4]arene

The compound 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra-(2-bromoethoxy)calix[4]arene has been prepared by first converting 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra-(2-hydroxyethoxy)calix[4]arene into the tosylate, and then to the product by reaction with LiBr. The compound crystallizes in the trigonal space group P3₂21 with A = 13.160(2), C = 25.595(6) Å, A = 90.00(2), β = 90.00(1), γ = 120.000(9)⁰, Z = 3, _calc = 1.40 g cm⁻³. The final R value for 2391 unique reflections was 0.061. The compound reacts with excess sodium N,N-dimethyldithiocarbamate to give 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetra-(2-N,N-dimethyldithiocarbamoylethoxy)calix[4]arene. This compound is an effective extractant for transferring palladium(II) from an aqueous to a chloroform phase. No extraction of PtCl₄²⁻ is observed under thermal conditions. Under photochemical conditions using a mixture of PtCl₄²⁻ and PtCl₆²⁻, extraction of platinum into the chloroform layer is observed. An explanation for this observation is given.     

Hetero-polynuclear complexes containing bridging diphenylphosphino-alkenes and -alkynes. The crystal structure of an Rh2{μ−ν:ν−P(Ph2) (CH2)3C≡CR}Co2 complex

The phosphinoalkenes Ph₂P(CH₂)_nCH=CH₂ (n= 1, 2, 3) and phosphinoalkynes Ph₂P(CH₂)_n C≡CR (R = H, N = 2, 3; R = CH₃, N = 1) have been prepared and reacted with the dirhodium complex (η−C₅H₅)₂Rh₂(μ−CO) (μ−η²−CF₃C₂CF₃). Six new complexes of the type (ν−C₅H₅)₂(Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃)L, where L is a P-coordinated phosphinoalkene, or phosphinoalkyne have been isolated and fully characterized; the carbonyl and phosphine ligands are predominantly trans on the Rh---Rh bond, but there is spectroscopic evidence that a small amount of the cis-isomer is formed also. Treatment of the dirhodium-phosphinoalkene complexes with (η−CH₃C₅H₄)Mn(CO)₂thf resulted in coordination of the manganese to the alkene function. The Rh₂---Mn complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂P(CH₂)₃CH=CH₂} (η−CH₃C₅H₄)Mn(CO)₂] was fully characterized. Simi treatment of the dirhodium-phosphinoalkyne complexes with Co₂(CO)₈ resulted in the coordination of Co₂(CO)₆ to the alkyne function. The Rh₂---Co₂ complex [(η−C₅H₅)₂Rh₂(CO) (μ−η¹:η¹−CF₃C₂CF₃) {Ph₂PCH₂C≡CCH₃}Co₂(CO)₂], C₃₇H₂₅Co₂F₆O₇PRh₂, was fully characteriz spectroscopically, and the molecular structure of this complex was determined by a single crystal X-ray diffraction study. It is triclinic, space group (C_i¹, No. 2) with a = 18.454(6), B = 11.418(3), C = 10.124(3) Å, = 112.16(2), β = 102.34(3), γ = 91.62(3)°, Z = 2. Conventional R on |F| was 0.052 fo observed (I > 3σ(I)) reflections. The Rh₂ and Co₂ parts of the molecule are distinct, the carbonyl and phosphine are mutually trans on the Rh---Rh bond, and the orientations of the alkynes are parallel for Rh₂ and perpendicular for Co₂. Attempts to induce Rh₂Co₂ cluster formation were unsuccessful.     

A novel one-pot three-component reaction: synthesis of triheterocyclic 4H-pyrimido[2,1-b]benzazoles ring systems

A novel one-pot three-component condensation reaction of an aldehyde, β-ketoester and 2-aminobenzimidazole or 2-aminobenzothiazole in 1,1,3,3-N,N,N′,N′-tetramethylguanidinium trifluoroacetate as an ionic liquid is described. During the course of this reaction 4H-pyrimido[2,1-b]benzimidazoles or 4H-pyrimido[2,1-b]benzothiazoles are formed in high yields at 100 °C. The ionic liquid can be recovered conveniently and reused efficiently.     

Synthesis and antimicrobial activity of 5-hydroxymethyl- 8-methyl-2-(N-arylimino)-pyrano[2,3-c]pyridine-3-(N-aryl)-carboxamides

Several novel 2-imino-5-hydroxymethyl-8-methyl-2H-pyrano[2,3-c]pyridine-3-(N-aryl) carboxamides were prepared by reaction of pyridoxal hydrochloride with various N-arylcyanoacetamides. Reaction of these compounds with aromatic amines furnished a wide series of 2-(N-R-phenyl) imino-5-hydroxymethyl-8-methyl-2H-pyrano[2,3-c]pyridine-3-carboxamides. Antibacterial and antifungal activities of the synthesized compounds were studied. Most of the obtained compounds demonstrated significant activity against bacterial or fungal strains (MIC in the range of 12.5–25 μg/mL), displaying comparable or even better efficacy than the standard drugs.     

Regioselective enzymatic aminoacylation of lobucavir to give an intermediate for lobucavir prodrug

Synthesis of lobucavir prodrug, L-valine, [(1S,2R,3R)-3-(2-amino-1,6-dihydro-6-oxo-9H-purin-9-yl)-2-(hydroxymethyl)cyclobutyl]methyl ester monohydrochloride (BMS 233866), requires regioselective coupling of one of the two hydroxyl groups of lobucavir (BMS 180194) with valine. Either hydroxyl group of lobucavir could be selectively aminoacylated with valine by using enzymatic reactions. N-[(Phenylmethoxy)carbonyl]-L-valine, [(1R,2R,4S)-2-(2-amino-6-oxo-1H-purin-9-yl)-4-(hydroxymethyl)cyclobutyl]methyl ester (3, 82.5% yield), was obtained by selective hydrolysis of N,N′-bis[(phenylmethoxy)carbonyl]bis[L-valine], O,O′-[(1S,2R,3R)-3-(2-amino-6-oxo-1H-purin-9-yl)cyclobuta-1,2-diyl]methyl ester (1) with lipase M, and L-valine, [(1R,2R,4S)-2-(2-amino-1,6-dihydro-6-oxo-9H-purin-9-yl)-4-(hydroxymethyl)cyclobutyl]methyl ester monohydrochloride (4, 87% yield) was obtained by hydrolysis of bis[L-valine], O,O′-[(1S,2R,3R)-3-(2-amino-6-oxo-1H-purin-9-yl)cyclobuta-1,2-diyl]methyl ester, dihydrochloride (2), with lipase from Candida cylindracea. The final intermediate for lobucavir prodrug, N-[(phenylmethoxy)carbonyl]-L-valine, [(1S,2R,4R)-3-(2-amino-6-oxo-1H-purin-9-yl)-2-(hydroxymethyl)cyclobutyl]methyl ester (5), could be obtained by transesterification of lobucavir using ChiroCLEC™ BL (61% yield), or more selectively by using immobilized lipase from Pseudomonas cepacia (84% yield).     

Synthesis and characterization of organomolybdenum and organotungsten halides containing the η-pentabenzylcyyclopentadienyl ligand η-Bz5C5M(CO)3X (M = Mo, W; X = Cl, Br, I). The X-ray molecular structure of η-Bz5C5Mo(CO)3I

An improved synthetic procedure for pentabenzylcyclopentadiene Bz₅C₅H was developed. Six new organomolybdenum and organotungsten halides η⁵-Bz₅C₅M(CO)₃X(M = Mo, W; X = Cl, Br, I) were syntesized through the reaction of η⁵-Bz₅C₅M(CO)₃Li (derived from Bz₅C₅H, n-BuLi and M(CO)₆) with PCl₃, PBr₃ or I₂ and characterized by elemental analysis, IR and ¹H NMR spectroscopy. The structure of η⁵-Bz₅C₅Mo(CO)₃I was determined by single-crystal X-ray diffraction techniques. It crystallized in the monoclinic space groupp P2/c with cell parameters a = 13.294(4), B = 15.147(4), C = 19.027(3) Å, β = 108.32(2)°, V = 3637(2) ų, Z = 4 and D_x = 1.50 g cm⁻³. The final R value was 0.035 for 4564 observed reflections.     

Regiospecific hydroxylation of 3-(methylaminomethyl) pyridine to 5-(methylaminomethyl) -2 (1H) -pyridinone byArthrobacter ureafaciens

Microbial production of a 6-hydroxy-3-pyridylmethyl compound from 3-pyridylmethyl compound was investigated. The hydroxylation of 3-(methylaminomethyl)pyridine to 5-(methylaminomethyl)-2(1H)-pyridinone, tautomer of 2-hydroxy-5(methylaminomethyl)pyridine, by resting cells ofArthrobacter ureafaciens JCM3873 was found to proceed regio- and chemo-selectively with an almost quantitative yield. The addition of molybdate ion and nicotine as an inducer to the culture medium was required for the preparation of cells containing high hydroxylation activity. The optimal temperature and pH for the hydroxylation by using resting cells were 35°C and around 7, respectively. This hydroxylation enzyme does undergo inhibition by the substrate. The inhibitory effect could be eliminated by stepwise feeding of the substrate. Under adequate conditions, 23 mg/ml of 5-(methylaminomethyl)-2(1H)-pyridinone was produced with a molar yield of nearly 100% from 3-(methylaminomethyl)pyridine.     

Kinetics and mechanisms of ligand substitution reactions of molybdenum SO2 complexes. Synthesis and X-ray structure of trans-Mo(CO)2 (dmpe) (PPh3) (SO2)

Kinetic results are reported for intramolecular PPh₃ substitution reactions of Mo(CO)₂(η¹-L)(PPh₃)₂(SO₂) to form Mo(CO)₂(η²-L)(PPh₃)(SO₂) (L = DMPE = (Me)₂PC₂H₄P(Me)₂ and dppe=Ph₂PC₂H₄PPh₂) in THF solvent, and for intermolecular SO₂ substitutions in Mo(CO)₃(η²-L)(η²-SO₂) (L = 2,2′-bipyridine, dppe) with phosphorus ligands in CH₂Cl₂ solvent. Activation parameters for intramolecular PPh₃ substitution reactions: ΔH^≠ values are 12.3 kcal/mol for dmpe and 16.7 kcal/mol for dppe; ΔS^≠ values are −30.3 cal/mol K for dmpe and −16.4 cal/mol K for dppe. These results are consistent with an intramolecular associative mechanism. Substitutions of SO₂ in MO(CO)₃(η²-L)(η²-SO₂) complexes proceed by both dissociative and associative mechanisms. The facile associative pathways for the reactions are discussed in terms of the ability of SO₂ to accept a pair of electrons from the metal, with its bonding transformations of η²-SO₂ to η¹-pyramidal SO₂, maintaining a stable 18-e count for the complex in its reaction transition state. The structure of Mo(CO)₂(dmpe)(PPh₃)(SO₂) was determined crystallographically: P2₁/c, A=9.311(1), B = 16.344(2), C = 18.830(2) Å, ß=91.04(1)°, V=2865.1(7) ų, Z=4, R(F)=3.49%.