Synthesis of heterodinuclear FeRu(CO)6(R-DAB(6e))(R-DABRNC(H)C(H)NR) Part XV. Comparison of the reactivities of heterodinuclear FeRu(CO)6(R-DAB(6e)) and homodinuclear analogues M2(CO)6(R-DAB(6e)) (M = Fe,Ru). Single-crystal x-ray structures of FeRu(CO)6(i-Pr-DAB(6e)) and FeRu(CO)5(i-Pr-DAB(4e))(C3H4)

The reactions of Fe(CO)₃(R-DAB; R¹, H(4e)) (1a: R = i-Pr, R¹ = H; 1b: R = t-Bu, R¹ = H; 1c: R = c-Hex, R¹ = H; 1e: R = p-Tol, R¹ = H; 1f: R = i-Pr, R¹ = Me) with Ru₃(CO)₁₂ and of Ru(CO)₃(R-DAB; R¹, H(4e)) (2a: R = i-Pr, R¹ = H; 2d: R = CH(i-Pr)₂, R¹ = H) with Fe₂(CO)₉ in refluxing heptane both afforded FeRu(CO)₆(R-DAB; R¹, H(6e)) (3) in yields between 50 and 65%.The coordination mode of the ligand has been studied by a single crystal X-ray structure determination of FeRu(CO)₆(i-Pr-DAB(6e)) (3a). Crystals of 3a are monoclinic, space group P2₁/a, with four molecules in a unit cell of dimensions: a = 22.436(3), b = 8.136(3), c = 10.266(1) Å and β = 99.57(1)°. The structure was refined to R = 0.049 and R_w = 0.052 using 3045 reflections above the 2.5σ(I) level. The molecule contains an FeRu bond of 2.6602(9) Å, three terminally bonded carbonyls to Fe, three terminally bonded carbonyls to Ru and bridging 6e donating i-Pr-DAB ligand. The i-Pr-DAB ligand is coordinated to Ru via N(1) and N(2) occupying an apical and equatorial site respectively (RuN(1) = 2.138(4) RuN(2) = 2.102(3) Å). The C(2)N(2) moiety of the ligand is η²-coordinated to Fe with C(2) in an apical and N(2) in an equatorial site (FeC(2) = 2.070(5) and FeN(2) = 1.942(3) Å).The ¹H and ¹³C NMR data indicate that in all FeRu(CO)₆(R-DAB(6e)) complexes (3a to 3f) exclusively η²-CN coordination to the Fe atom and not to the Ru atom is present irrespective of whether 3 was prepared by reaction of Fe(CO)₃(R-DAB(4e)) (1) with Ru₃(CO)₁₂ or by reaction of Ru(CO)₃(R-DAB(4e)) (2) with Fe₂(CO)₉. In the case of FeRu(CO)₆(i-Pr-DAB; Me, H(6e)) (3f) the NMR data show that only the complex with the C(Me)N moiety of the ligand σ-N coordinated to the Ru atom and the C(H)N moiety η²-coordinated to the Fe atom was formed. Variable temperature NMR experiments up to 140 °C showed that the α-diimine ligand in 3a is stereochemically rigid bonded.FeRu(CO)₆(R-DAB(6e)) (3a and 3e) reacted with allene to give FeRu(CO)₅(R-DAB(4e))(C₃H₄) (4a and 4e). A single crystal X-ray structure determination of FeRu(CO)₅(i-Pr-DAB(4e))(C₃H₄) (4a) was performed. Crystals of 4a are triclinic, space group P1, with two molecules in a unit cell of dimensions: a = 9.7882(7), b = 12.2609(9), c = 8.3343(7) Å, α = 99.77(1)°, β = 91.47(1)° and γ = 86.00(1)°. The structure was refined to R = 0.028 and R_w = 0.043 using 4598 reflections above the 2σ(I) level. The molecule contains an FeRu bond of 2.7405(7) Å and three terminally bonded carbonyls to iron. Two carbonyls are terminally bonded to the Ru atom together with a chelating 4e donating i-Pr-DAB ligand [RuN = 2.110(1) (mean)]. The allene ligand is coordinated in an η³-allylic fashion to the Fe atom while the central carbon of the allene moiety is σ-bonded to the Ru atom (FeC(14) = 2.166(3), FeC(15) = 1.970(2), FeC(16) = 2.127(3) and RuC(15) = 2.075(2) Å). The ¹H and ¹³C NMR data show that in solution the coordination modes of the R-DAB and the allene ligands are the same as in the solid state.Thermolysis reactions of 3a with R-DAB or carbodiimides gave decomposition and did not afford C(imine)C(reactant) coupling products. Thermolysis reactions of 3a with M₃(CO)₁₂ (M = Ru, Os) and Me₃NO gave decomposition. When the reaction of 3a with Me₃NO was performed in the presence of dimethylacetylenedicarboxylate (DMADC) the known complex FeRu(CO)₄(i-Pr-DAB(8e))(DMADC) (5a) was formed in low yield. In 5a the R-DAB ligand is in the 8e coordination mode with both the imine bonds η²-coordinated to iron. The acetylene ligand is coordinated in a bridging fashion, parallel with the FeRu bond.     

Measurement of 2J(H,C)- and 3J(H,C)-coupling constants by α/β selective HC(C)H-TOCSY

A new heteronuclear NMR pulse sequence for the measurement of ⁿJ(C,H) coupling constants, the /selective HC(C)H-TOCSY, is described. It is shown that the S³E element (Meissner et al., 1997a,b) can be used to obtain spin state selective coherence transfer in molecules, in which adjacent CH moieties are labeled with ¹³C. Application of the / selective HC(C)H-TOCSY to a 10nt RNA tetraloop 5-CGCUUUUGCG-3, in which the four uridine residues are ¹³C labeled in the sugar moiety, allowed measurement of two bond and three bond J(C,H) coupling constants, which provide additional restraints to characterize the sugar ring conformation of RNA in cases of conformational averaging.     

Bis(heptalene) “submarine” metal dimer sandwich compounds (C12H10)2M2 (M = Ti, V, Cr, Mn, Fe, Co, Ni)

The bis(heptalene)dimetal complexes (C₁₂H₁₀)₂M₂ of the first row transition metals from Ti to Ni are predicted by density functional theory to exhibit “submarine” sandwich structures with a pair of metal atoms sandwiched between the two heptalene rings. For the early transition metal derivatives (C₁₂H₁₀)₂M₂ (M = V, Cr) there are two types of such structures. In one structural type the metals are sandwiched between two heptahapto heptalene rings with metal-metal distances (3.5–3.8 Å) too long for direct metal-metal bonding. The other type of (C₁₂H₁₀)₂M₂ (M = V, Cr, Mn) structure has a pair of bonded metal atoms sandwiched between a fully bonded heptalene ligand and a heptalene ligand bonded to the metals only through an eight-carbon heptafulvene subunit, leaving an uncomplexed cis-1,3-diene unit. The formal metal-metal bond orders in these latter structures are 3, 2, and 1 for M = V, Cr, and Mn with predicted bond lengths of 2.5, 2.7, and 2.8 Å, respectively. For (C₁₂H₁₀)₂Fe₂ a singlet structure with each iron atom sandwiched between a hexahapto and a tetrahapto heptalene ring is energetically preferred over an alternate structure with ferrocene-like iron atoms sandwiched between two pentahapto heptalene rings. Partial bonding of each heptalene ring to the metal atoms occurs in the late transition metal derivatives (C₁₂H₁₀)₂M₂ (M = Co, Ni). This leads to an unsymmetrical structure for the cobalt derivative and a structure for the nickel derivative with each nickel atom sandwiched between a trihapto ligand and a tetrahapto ligand.

Synthesis of [{Os3(CO)10(μ2-H)}2{μ2,μ2-NC6H4C6H4N}] and [{Os3(CO)9(μ2-H)PPh3}2{μ2,μ2-NC6H4C6H4N}]: Carbon–carbon bond formation promoted by organorhodium species

Synthesis and characterization of linked cluster [{Os₃(CO)₁₀(μ₂-H)}₂{μ₂,μ₂-NC₆H₄C₆H₄N}] (1) from the reaction of [Os₃Rh(μ-H)₃(CO)₁₂] with aniline in the presence of an excess amount of 4-vinyl phenol in refluxing heptane is reported. A similar reaction with [Os₃(CO)₁₀(NCMe)₂] as starting material gave a known compound, [Os₃(CO)₁₀(μ₂-H)(μ₂-HNC₆H₅)] (2). The treatment of complexes 1 and 2 with Wilkinson’s catalyst in refluxing heptane respectively, yielded [{Os₃(CO)₉(μ₂-H)PPh₃}₂{μ₂,μ₂-NC₆H₄C₆H₄N}] (3). An interesting and unexpected C–C coupling of phenyl-amido ligands was observed in complexes 1 and 3, which is believed to be catalysed by the organometallic rhodium species. The newly synthesized compounds 1 and 3 were fully characterized by IR, ¹H NMR spectroscopy, mass spectroscopy, elemental analysis, and X-ray crystallography. Both structures 1 and 3 comprise two triangles of osmium atoms. The two triangular osmium metal cores are linked by a bi-amido ligand via the two nitrogen atoms N(1) and N(1)* and N(1) and N(2), at their equatorial sites. The electronic absorption spectra of complexes 1, 2, and 3 display both low energy absorption, dπ (Os) → π* (amido) metal-to-ligand charge-transfer (MLCT) transition, and π → π* intra-ligand electronic transitions of the amido and bi-amido ligands.     

Highly cytotoxic trithiophenolatodiruthenium complexes of the type [(η6-p-MeC6H4Pr i )2Ru2(SC6H4-p-X)3]+: synthesis, molecular structure, electrochemistry, cytotoxicity, and glutathione oxidation potential

A series of cationic dinuclear p-cymene ruthenium trithiophenolato complexes of the type [(η(6)-p-MeC(6)H(4)Pr(i))(2)Ru(2)(SC(6)H(4)-p-X)(3)](+) (1 X is H, 2 X is Me, 3 X is Ph, 4 X is Br, 5 X is OH, 6 X is NO(2), 7 X is OMe, 8 X is CF(3), 9 X is F, 10 X is Pr(i), 11 X is Bu(t)) have been synthesized from the reaction of [(η(6)-p-MeC(6)H(4)Pr(i))RuCl(2)](2) with the corresponding thiol, isolated as the chloride salts, and further studied for their electrochemical properties, cytotoxicity towards human ovarian cancer cells, and catalytic activity for glutathione (GSH) oxidation. Complex 1 was also compared with the benzene and hexamethylbenzene analogues [(η(6)-C(6)H(6))(2)Ru(2)(SC(6)H(5))(3)](+) (12) and [(η(6)-C(6)Me(6))(2)Ru(2)(SC(6)H(5))(3)](+) (13). The most active compound [11]Cl was structurally studied by single-crystal X-ray diffraction analysis. The concentrations corresponding to 50 % inhibition of cancer cell growth (IC(50) values) in the A2780 and A2780cisR cell lines of these complexes except for 6 were in the submicromolar range, complex 11 showing an IC(50) value of 0.03 μM in both cell lines. The high in vitro anticancer activity of these complexes may be at least partially due to their catalytic potential for the oxidation of GSH, although there is no clear correlation between the IC(50) values and the turnover frequencies at about 50 % conversion. However, the cytotoxicity is tentatively correlated to the physicochemical properties of the compounds determined by the electronic influence of the substituents X (Hammett constants σ(p)) and the lipophilicity of the thiols p-XC(6)H(4)SH (calculated log P parameters).     

A density functional theory study of phenyl formation initiated by ethynyl radical (C2H•) and ethyne (C2H2)

An ab initio computational density functional theory (DFT) was used to study the formation of the first cyclic molecule (phenyl) initiated by the ethynyl radical (C₂H•). The study covers a competition reaction between the addition reactions of C₂H• with ethyne (C₂H₂) and some molecular re-arrangement schemes. The minimum energy paths of the preferred cyclic formation route were characterized. A thorough thermochemical analysis was performed by evaluating the differences in the energy of activation (ΔE), enthalpy (ΔH), and Gibb's free energy (ΔG) of the optimized stable and transition state (TS) molecules. The reaction temperatures were set to normal (T = 298 K) and combustion (T = 1,200 K) conditions.

MQ-HCN-based pulse sequences for the measurement of 13C1′-1H1′, 13C1′-15N, 1H1′-15N, 13C1′-13C2′, 1H1′-13C2′, 13C6/8-1H6/8, 13C6/8-15N, 1H6/8-15N, 13C6-13C5, 1H6-13C5 dipolar couplings in 13C, 15N-labeled DNA (and RNA)

A suite of multiple quantum (MQ) HCN-based pulse sequences has been developed for the purpose of collecting dipolar coupling data in labeled nucleic acids. All the pulse sequences are based on the robust MQ-HCN experiment which has been utilized for assignment purposes in labeled nucleic acids for a number of years and provides much-needed resolution for the dipolar coupling measurements. We have attempted to collect multiple couplings centered on the 13C1' and 13C6/8 positions. Six pulse sequences are described, one each for measurement of one-bond 13C1'-1H1' and 13C6/8-1H6/8 couplings, one for measurement of one-bond 13C1'-15N and two-bond 1H1'-15N couplings, one for measurement of one-bond 13C6/8-15N and two-bond 1H6/8-15N couplings, one for measurement of one-bond 13C1'- 13C2' and two-bond 1H1'-13C2' couplings, and one for measurement of one-bond 13C6-13C5 and two-bond 1H6-13C5 couplings in the bases of C and T. These sequences are demonstrated for a labeled 18 bp DNA duplex in a 47 kDa ternary complex of DNA, CBFbeta, and the CBFalpha Runt domain, thus clearly demonstrating the robustness of the pulse sequences even for a very large complex.     

Solution behaviour and relative stability of the complexes [MCl2(RNCHCHNR)] and [MCl2(py-2-CHNR)] (M=Pd,Pt;R=C6H4OMe-p)

Even though the α-diimino complexes [MCl₂(RNCHCHNR)] and [MCl₂(py-2-CHNR)] (M=Pd, Pt;R=C₆H₄OMe-p) are poorly soluble in chlorinated solvents, such as chloroform and 1,2-dichloroethane, or in acetonitrile, the electronic and ¹H NMR spectra indicate that these compounds are generally present as undissociate monomers with σ, σ′-N,N′ chelate N-ligands in dilute solutions. Only for [PdCl₂(RNCHCHNR)], some dissociation of the α-diimine occurs in acetonitrile. In dimethylsulfoxide, where the solubility is much higher, no dissociation is observed for the pyridine-2-carbaldimine complexes [MCl₂(py-2-CHNR)], whereas the 1,2-bis(imino) ethane derivatives [MCl₂(RNCHCHNR)] are extensively dissociated through a step-wise process involving intermediates with a σ-N monodentate α-diimino group. As is shown by the course of substitution reactions with 2,2′-bipyridine, the higher stability of [MCl₂(py-2-CHNR)] in dimethylsulfoxide is mainly due to thermodynamic factors (ground state stabilization for the presence of stronger MN bonds) rather than by kinetic factors (higher activation energy for steric strain in the activation states or transients).     

DFT study on the reactions of ClO–/BrO– with RCl (R = CH3, C2H5, and C3H7) in gas phase

Gas-phase reactions of ClO^–/BrO^– with RCl (R = CH₃, C₂H₅, and C₃H₇) have been investigated in detail using the popular DFT functional BHandHLYP/aug-cc-pVDZ level of theory. As a result, our findings strongly suggest that the type of reaction is firstly initiated by a typical S_N2 fashion. Subsequently, two competitive substitution steps, named as S_N2-induced substitution and S_N2-induced elimination, respectively, would proceed before the initial S_N2 product ion-dipole complex separates, in which the former exhibits less reactivity than the latter. Those are consistent with relevant experimental results. Moreover, we have also explored reactivity difference for the title reactions in term of some factors derived from methyl group, p-π electronic conjugation, ionization energy (IE), as well as molecular orbital (MO) analysis.

Host-guest Interactions in Intercalates Zr(HPO4)2·2C2H5OH and VOPO4·2C2H5OH

Molecular mechanics simulations using Cerius² modelling environment combined with vibrational spectroscopy (IR and Raman) have been used to study the host-guest interactions in zirconium and vanadyl phosphate intercalated with ethanole. The strategy of investigation is based on the comparison of vibrational spectra for the host compound, intercalate and guest species. This comparison confirmed the rigidity of VOPO₄- and Zr(HPO₄)₂-layers during the intercalation and provided us with the basis for the strategy of modelling. Molecular mechanics simulations revealed the structure of intercalates and enabled to analyse the host-guest interaction energy and bonding geometry. The bilayer arrangement of ethanole molecules in the interlayer space with two differently bonded ethanole molecules has been found in both intercalates. The average interaction energy ethanole-layer for two differently bonded ethanole molecules is : 127.5 and 135.7 kcal·mol^-1 in Zr(HPO₄)₂·2C₂H₅OH, respectively 94.0 and 104.4 kcal·mol^-1 in VOPO₄·2C₂H₅OH. The Coulombic contribution to the ethanole-layer interaction energy is predominant in all cases, but the hydrogen bonding contribution is much higher in Zr(HPO₄)₂·2C₂H₅OH than in VOPO₄·2C₂H₅OH. Present results of modelling enabled the interpretation of vibrational spectra and explanation of small changes in positions and shapes of spectral bands, in infrared and Raman spectra, proceeding from the host structure to intercalates.     

Influence of ligands on the fac⇌Δhνmer isomerization in [RuCl3(NO)(P–P)] complexes, [P–P = R2P(CH2)nPR2 (n = 1–3) and R2P(CH2)POR2, PR2–CHCH–PR2, R = Ph and (C6H11)2P-(CH2)2-P(C6H11)2]

[RuCl₃(NO)(P–P)], [P–P = R₂P(CH₂)_nPR₂ (n = 1–3) and R₂P(CH₂)POR₂, PR₂–CHCH–PR₂, R = Ph and (C₆H₁₁)₂P-(CH₂)₂-P(C₆H₁₁)₂] were obtained and characterized by ³¹P {¹H} NMR, IR spectroscopies and cyclic voltammetry. The structures of fac-[RuCl₃(NO)(P–P)], P–P = dppm (1), dppe (2), c-dppen (3) and dppp (4), mer-[RuCl₃(NO)(dcpe)] (6a) and mer-[RuCl₃(NO)(dppmO)] (7) have been determined by X-ray diffraction. Photochemical isomerization of fac- to mer-[RuCl₃(NO)(P–P)] was observed under white light in a CH₂Cl₂ solution and in solid state. The isomerization processes were followed by IR and ³¹P {¹H} spectra. The mer-[RuCl₃(¹⁵NO)(dppb)] isomer was used for the definition of the phosphorus atoms in the structure of the complex in solution. The electrochemical study shows that the oxidation/reduction processes observed in these complexes are dependent on both the isomer (fac or mer) and the solvent. In CH₂Cl₂, the NO⁺ reduction potentials are less negative for the mer-isomers than for the fac ones, while in CH₃CN solvent these potentials are, in general, very close for both isomers.     

A (U)MP2(full) and (U)CCSD(T) theoretical investigation into the substituent effects on the intermolecular T-shaped F–H…π interactions between HF and LBBL (L = ?H, ∶CO, :NN, –Cl, –CN and –NC)

The substituent effects on the intermolecular T-shaped F-H...π interactions are investigated between HF and LBBL (L = -H, : CO, :NN, -Cl, -CN and -NC) using the (U)MP2(full) and (U)CCSD(T) methods with the 6-311++G(2 d,p) basis set. The B ≡ B triple-bond contraction is found in the complexes with lone-pair-electron donors while the B = B double-bond is lengthened in the systems with the single-electron substituents upon complexation. The T-shaped F-H...π interaction energies follow the order of ClB = BCl...HF>HB = BH...HF>NNB ≡ BNN...HF>OCB ≡ BCO...HF>CNB = BNC...HF>NCB = BCN...HF. The electron-donating substituents : CO and :NN increases electron density of the B ≡ B triple bond by the delocalization interaction E ((2)) π ((CO/NN) → Lp(B)) while the electron-withdrawing substituents -CN and -NC decrease electron density of the B = B double bond by means of the π-π conjugative effect. The analyses of the APT atomic charge, "truncated" model, natural bond orbital (NBO), atoms in molecules (AIM) and electron density shifts reveal the nature of the substituent effect and explain the origin of the B ≡ B bond contraction.     

Chiroptical properties of diastereomeric five-coordinate Pt(II)–olefin complexes. Molecular structure of [PtCl2{(S,S)-(E)-CNCHCHCN}(R,R)-{C6H5CH(CH3)N(CH3)CH2}2]·C6H6

The chiroptical properties of five-coordinate diastereomeric complexes of general formula [PtCl₂(R,R)-{C₆H₅CH(CH₃)N(CH₃)CH₂}₂{olefin}], with olefin ligands having electron-withdrawing substituents, have been investigated. The sign of CD bands in the 28 000–30 000 cm⁻¹ region appears to be correlated to the absolute configuration of the prochiral coordinated alkene. Single-crystal X-ray diffraction structure determination has been performed on the single diastereomer [PtCl₂(E-but-2-enedinitrile)(R,R)-{C₆H₅CH(CH₃)N(CH₃)CH₂}₂]· C₆H₆. The compound crystallizes in the monoclinic space group C2 with a = 17.842(2), b = 8.466(1), c = 10.464(1) Å, β = 109.34(1)°, Z = 2. The number of observed reflections was 1943 and the final R and R_w values were 0.020 and 0.028 respectively. Trigonal-bipyramidal geometry is observed around the Pt atom, with the two Cl atoms in axial positions. The unsaturated ligand lies in the equatorial plane disclosing S,S absolute configuration.     

New coordination polymers based on a novel polynitrile ligand: Synthesis,structure and magnetic properties of the series [M(tcnoetOH)2(4,4′-bpy)(H2O)2] (tcnoetOH− = [(NC)2CC(OCH2CH2OH)C(CN)2]−; M = Fe,Co and Ni)

A novel polynitrile anionic ligand, tcnoetOH^?(=[(NC)₂CC(OCH₂CH₂OH)C(CN)₂]^?), has been synthesized by a one-pot reaction from a cyclic acetal and malononitrile. This ligand has been successfully used to prepare, with 4,4′-bpy as co-ligand, a novel series of coordination polymers formulated as [M(tcnoetOH)₂(4,4′-bpy)(H₂O)₂] with M(II) = Fe (1), Co (2) and Ni (3). These isostructural compounds present a linear chain structure consisting of octahedrally coordinated metal ions bridged by trans 4,4′-bpy ligands. The coordination sphere of the metal ions is completed with two terminal tcnoetOH^? ligand and two water molecules. The magnetic properties indicate that the three compounds are paramagnetic, as expected from the long 4,4′-bpy bridge connecting the metal atoms. Their magnetic properties have been fitted with a model of isolated ions including a zero field splitting for the Fe(II) and Ni(II) derivatives.     

Fast atom bombardment,electron impact and chemical ionization mass spectrometry of the neutral 18-electron species M(CO)2(CNR)2(PR′3)2 (MMo or W)

The molybdenum(0) and tungsten(O) complexes of the type M(CO)₂(CNR)₂(PR′₃)₂ have been studied using a variety of mass spectral techniques, viz. fast atom bombardment (FAB), electron impact (EI), and both positive- and negative-ion chemical ionization (PICI and NICI) mass spectrometry. The FABMS technique gave the most structurally informative spectra with the observation of the molecular ions M⁺ (100% relative abundance in the case of MW) and in some instances the pseudomolecular ion (M + H)⁺. Fragmentation ions arising from competitive ligand loss (CO versus RNC versus PR′₃) were observed, as well as those formed by loss of H from fragment ions and dealkylation of RNC ligands. The EI and PICI spectra were not especially useful due to the relatively low thermal stability of these complexes, while the NICI spectra gave an abundance of ions that resulted from ligand redistribution reactions. Of special note were anions that contained M(CO)₄ and M(CO)₃ fragments. Dealkylation of the RNC ligands to give cyanometallate anions was also prevalent.     

Preparation of (±)-2-(2,3-2H2)Jasmonic Acid and Its Methyl Ester,Methyl (±)-2-(2,3-2H2)Jasmonate

For use as the internal standards in a quantitative analysis of natural jasmonic acid (JA) and methyl jasmonate (JAMe) by gas chromatography-mass spectrometry-selected ion monitoring, (±)-2-(2,3–²H₂)JA and its methyl ester, (±)-2-(2,3–²H₂)JAMe, were efficiently prepared from 2-(2–pentyl)-2-cyclopentenone through catalytic semi-deuteriogenation of acetylenic intermediates with deuterium gas in pyridine.