New reactions of 1-alkynes catalyzed by transition metal complexes

Recently discovered catalytic reactions with ruthenium and lanthanide metal complexes have extended the scope of 1-alkynes as useful reagents. The specific formation of aryl-substituted (Z)-1,3-enzymes via the dimerization of HC(triple bond) CR(1) (R(1) = aryl) has been attained using dimeric lanthanide complexes, the catalytic activity of which appears to be unaffected by time. The dimerization of HC(triple bond) CR(2) (R(2) = t-Bu, SiMe(3)) catalyzed by Ru(cod)(cot)/PR(3) or RuH(2)(PPh(3))(3) produces a good yield of butatrienes (Z)R(2)CH=C=C=CHR(2) with a high degree of selectivity. Under certain conditions, HC(triple bond) C=SiMe(3) dimerizes to yield exclusively (Z)-M(3)Si-C(triple bond) C-CH=CH-SiMe(3). The hydration of HC(triple bond)CR(3) (R(3) = alkyl, aryl) catalyzed by RuCl(2)/PR'(3) or CpRuCl(PR"(3))(2) has realized the first example of anti-Markovnikov regioselectivity in an addition reaction of water that produces aldehydes R(3)CH(2)bond;CHO. The application of this reaction to propargylic alcohols has lead to their formal isomerization to alpha,beta-unsaturated aldehydes. In contrast, the addition of amines R(4)bond;NH(2) (R(4) = aryl) to HCtbond;CR(5) (R(5) = alkyl, aryl) conforms to Markovnikov's rule to produce ketimines R(5)bond;(C=NR(4))bond;CH(3) when catalyzed by a Ru(3)(CO)(12)/additive. Since the reaction can be performed in air without the need for any solvents, it enables the practical synthesis of aromatic ketimines, which are difficult to prepare by conventional methods. The synthesis of indoles using deactivated anilines is one practical application of this reaction. The mechanisms of some of these reactions have been analyzed in detail with the aid of theoretical calculations.     

Eta6-mesityl,eta1-imidazolinylidene-carbene-ruthenium(II) complexes: catalytic activity of their allenylidene derivatives in alkene metathesis and cycloisomerisation reactions

The reaction of electron-rich carbene-precursor olefins containing two imidazolinylidene moieties [(2,4,6-Me(3)C(6)H(2)CH(2))NCH(2)CH(2)N(R)Cdbond;](2) (2a: R=CH(2)CH(2)OMe, 2 b R=CH(2)Mes), bearing at least one 2,4,6-trimethylbenzyl (R=CH(2)Mes) group on the nitrogen atom, with [RuCl(2)(arene)](2) (arene=p-cymene, hexamethylbenzene) selectively leads to two types of complexes. The cleavage of the chloride bridges occurs first to yield the expected (carbene) (arene)ruthenium(II) complex 3. Then a further arene displacement reaction takes place to give the chelated eta(6)-mesityl,eta(1)-carbene-ruthenium complexes 4 and 5. An analogous eta(6)-arene,eta(1)-carbene complex with a benzimidazole frame 6 was isolated from an in situ reaction between [RuCl(2)(p-cymene)](2), the corresponding benzimidazolium salt and cesium carbonate. On heating, the RuCl(2)(imidazolinylidene) (p-cymene) complex 8, with p-methoxybenzyl pendent groups attached to the N atoms, leads to intramolecular p-cymene displacement and to the chelated eta(6)-arene,eta(1)-carbene complex 9. On reaction with AgOTf and the propargylic alcohol HCtbond;CCPh(2)OH, compounds 4-6 were transformed into the corresponding ruthenium allenylidene intermediates (4-->10, 5-->11, 6-->12). The in situ generated intermediates 10-12 were found to be active and selective catalysts for ring-closing metathesis (RCM) or cycloisomerisation reactions depending on the nature of the 1,6-dienes. Two complexes [RuCl(2)[eta(1)-CN(CH(2)C(6)H(2)Me(3)-2,4,6)CH(2)CH(2)N- (CH(2)CH(2)OMe)](C(6)Me(6))] 3 with a monodentate carbene ligand and [RuCl(2)[eta(1)-CN[CH(2)(eta(6)-C(6)H(2)Me(3)-2,4,6)]CH(2)CH(2)N-(CH(2)C(6)H(2)Me(3)-2,4,6)]] 5 with a chelating carbene-arene ligand were characterised by X-ray crystallography.     

Isolation of rhenium and ReOx species within ZSM5 channels and their catalytic function in the activation of alkanes and alkanols

Synthesis protocols, structures, and reactivity of Re-oxo species grafted onto H-ZSM5, and their subsequent conversion to Re-clusters through contact with H2 or CH4 were studied by using Raman, infrared, and X-ray absorption spectroscopies. Reactivity measurements by using alkane and alkanol reactants were also examined. Sublimation of Re(2)O(7) at 723 K led to a stoichiometric exchange with each ReO(x) species replacing one proton. Raman features for Re(2)O(7) disappeared during thermal treatment and Raman bands assigned to distorted-tetrahedral Si-O(f)ReO(3)-Al (O(f): zeolite-lattice oxygen atoms) species emerged; infrared bands for acidic OH groups in H-ZSM5 weakened concurrently. X-ray absorption near-edge and fine-structure spectra detected the formation of distorted-tetrahedral Re7+-oxo species during thermal treatment of Re(2)O(7)/H-ZSM5 mixtures in air, and their subsequent reduction to Re(0) in H2 or CH4 to form encapsulated Re metal clusters similar in diameter (approximately 8 A) to the channel intersections in ZSM5. Si-O(f)ReO(3)-Al species in ReO(x)-ZSM5 catalyzed the oxidative conversion of C(2)H(5)OH to acetaldehyde, acetal, and ethyl acetate with very low selectivity to CO(x) (<1 %). Unprecedented turnover rates were exhibited at temperatures much lower than previously found for ReO(x)-based catalysts, and without deactivation or sublimation processes ubiquitous in crystalline Re7+ compounds at temperatures required for catalysis. Encapsulated Re metal clusters formed by the reduction of Si-O(f)ReO(3)-Al precursors led to CH4 pyrolysis and C(3)H(8) dehydrocyclodimerization rates (per Re) that are higher than those previously reported for zeolite-based catalysts. The rate of CH4 conversion to benzene, by using Re-ZSM5, was approximately 30 % higher than that of the best reported catalysts, based on encapsulated MoC(x) clusters, whereas C(2)H(4) and C6+ arene selectivities were similar. C(3)H(8) activity and selectivity of Re-ZSM5 was significantly higher than that of Ga-ZSM5, the best reported catalyst for these reactions. Reaction rates (per Re) were independent of the Re/Al(f) (Al(f): aluminum framework) ratio for both Re and ReO(x) species. This is consistent with the uniform character of the structures formed during grafting of the ReO(x) species through sublimation and their ability to retain their homogeneity even after their reduction to encapsulated Re-clusters.     

HP-Ca2Si5N8--a new high-pressure nitridosilicate: synthesis, structure, luminescence, and DFT calculations

HP-Ca(2)Si(5)N(8) was obtained by means of high-pressure high-temperature synthesis utilizing the multianvil technique (6 to 12 GPa, 900 to 1200 degrees C) starting from the ambient-pressure phase Ca(2)Si(5)N(8). HP-Ca(2)Si(5)N(8) crystallizes in the orthorhombic crystal system (Pbca (no. 61), a=1058.4(2), b=965.2(2), c=1366.3(3) pm, V=1395.7(7)x10(6) pm(3), Z=8, R1=0.1191). The HP-Ca(2)Si(5)N(8) structure is built up by a three-dimensional, highly condensed nitridosilicate framework with N([2]) as well as N([3]) bridging. Corrugated layers of corner-sharing SiN(4) tetrahedra are interconnected by further SiN(4) units. The Ca(2+) ions are situated between these layers with coordination numbers 6+1 and 7+1, respectively. HP-Ca(2)Si(5)N(8) as well as hypothetical orthorhombic o-Ca(2)Si(5)N(8) (isostructural to the ambient-pressure modifications of Sr(2)Si(5)N(8) and Ba(2)Si(5)N(8)) were studied as high-pressure phases of Ca(2)Si(5)N(8) up to 100 GPa by using density functional calculations. The transition pressure into HP-Ca(2)Si(5)N(8) was calculated to 1.7 GPa, whereas o-Ca(2)Si(5)N(8) will not be adopted as a high-pressure phase. Two different decomposition pathways of Ca(2)Si(5)N(8) (into Ca(3)N(2) and Si(3)N(4) or into CaSiN(2) and Si(3)N(4)) and their pressure dependence were examined. It was found that a pressure-induced decomposition of Ca(2)Si(5)N(8) into CaSiN(2) and Si(3)N(4) is preferred and that Ca(2)Si(5)N(8) is no longer thermodynamically stable under pressures exceeding 15 GPa. Luminescence investigations (excitation at 365 nm) of HP-Ca(2)Si(5)N(8):Eu(2+) reveal a broadband emission peaking at 627 nm (FWHM=97 nm), similar to the ambient-pressure phase Ca(2)Si(5)N(8):Eu(2+).     

Investigations on the coupling of ethylene and alkynes in [IrTp Me2] compounds: water as an effective trapping agent

The reaction of the bis(ethylene) complex [Tp(Me(2) )Ir(C(2)H(4))(2)] (1) (Tp(Me(2) ): hydrotris(3,5-dimethylpyrazolyl)borate) with two equivalents of dimethyl acetylenedicarboxylate (DMAD) in CH(2)Cl(2) at 25 degrees C gives the hydride-alkenyl species [Tp(Me(2) )IrH{C(R)=C(R)C(R)=C(R)CH=CH(2)}] (2, R: CO(2)Me) in high yield. A careful study of this system has established the active role of a number of intermediates en route to producing 2. The first of these is the iridium(I) complex [Tp(Me(2) )Ir(C(2)H(4))(DMAD)] (4) formed by substitution of one of the ethylene ligands in 1 by a molecule of DMAD. Complex 4 reacts further with another equivalent of the alkyne to give the unsaturated metallacyclopentadiene [Tp(Me(2) )Ir{C(R)=C(R)C(R)=C(R)}], which can be trapped by added water to give adduct 7, or can react with the C(2)H(4) present in solution generating complex 2. This last step has been shown to proceed by insertion of ethylene into one of the Ir--C bonds of the metallacyclopentadiene and subsequent beta-H elimination. Complex 1 reacts sequentially with one equivalent of DMAD and one equivalent of methyl propiolate (MP) in the presence of water, with regioselective formation of the nonsymmetric iridacyclopentadiene [Tp(Me(2) )Ir{C(R)=C(R)C(H)=C(R)}(H(2)O)] (9). Complex 9 reacts with ethylene giving a hydride-alkenyl complex 10, related to 2, in which the C(2)H(4) has inserted regiospecifically into the Ir--C(R) bond that bears the CH functionality. Heating solutions of either 2 or 10 in CH(2)Cl(2) allows the formation of the allyl species 3 or 11, respectively, by simple stereoselective migration of the hydride ligand to the Calpha alkenyl carbon atom and concomitant bond reorganization of the resulting organic chain. All the compounds described herein have been characterized by microanalysis, IR and NMR spectroscopy, and for the case of 3, 7, 7CO, 8NCMe, 9, 9NCMe, and 10, also by single-crystal X-ray diffraction studies.     

Intermolecular alkene and alkyne hydroacylation with beta-S-substituted aldehydes: mechanistic insight into the role of a hemilabile P-O-P ligand

A straightforward to assemble catalytic system for the intermolecular hydroacylation reaction of beta-S-substituted aldehydes with activated and unactivated alkenes and alkynes is reported. These catalysts promote the hydroacylation reaction between beta-S-substituted aldehydes and challenging substrates, such as internal alkynes and 1-octene. The catalysts are based upon [Rh(cod)(DPEphos)][ClO(4)] (DPEphos=bis(2-diphenylphosphinophenyl)ether, cod=cyclooctadiene) and were designed to make use of the hemilabile capabilities of the DPEphos ligand to stabilise key acyl-hydrido intermediates against reductive decarbonylation, which results in catalyst death. Studies on the stoichiometric addition of aldehyde (either ortho-HCOCH(2)CH(2)SMe or ortho-HCOC(6)H(4)SMe) and methylacrylate to precursor acetone complexes [Rh(acetone)(2)(DPEphos)][X] [X=closo-CB(11)H(6)Cl(6) or [BAr(F) (4)] (Ar(F)=3,5-(CF(3))(2)C(6)H(3))] reveal the role of the hemilabile DPEphos ligand. The crystal structure of [Rh(acetone)(2)(DPEphos)][X] shows a cis-coordinated diphosphine ligand with the oxygen atom of the DPEphos distal from the rhodium. Addition of aldehyde forms the acyl hydride complexes [Rh(DPEphos)(COCH(2)CH(2)SMe)H][X] or [Rh(DPEphos)(COC(6)H(4)SMe)H][X], which have a trans-spanning DPEphos ligand and a coordinated ether group. Compared to analogous complexes prepared with dppe (dppe=1,2-bis(diphenylphosphino)ethane), these DPEphos complexes show significantly increased resistance towards reductive decarbonylation. The crystal structure of the reductive decarbonylation product [Rh(CO)(DPEphos)(EtSMe)][closo-CB(11)H(6)I(6)] is reported. Addition of alkene (methylacrylate) to the acyl-hydrido complexes forms the final complexes [Rh(DPEphos)(eta(1)-MeSC(2)H(4)-eta(1)-COC(2)H(4)CO(2)Me)][X] and [Rh(DPEphos)(eta(1)-MeSC(6)H(4)-eta(1)-COC(2)H(4)CO(2)Me)][X], which have been identified spectroscopically and by ESIMS/MS. Intermediate species in this transformation have been observed and tentatively characterised as the alkyl-acyl complexes [Rh(CH(2)CH(2)CO(2)Me)(COC(2)H(4)SMe)(DPEphos)][X] and [Rh(CH(2)CH(2)CO(2)Me)(COC(6)H(4)SMe)(DPEphos)][X]. In these complexes, the DPEphos ligand is now cis chelating. A model for the (unobserved) transient alkene complex that would result from addition of alkene to the acyl-hydrido complexes comes from formation of the MeCN adducts [Rh(DPEphos)(MeSC(2)H(4)CO)H(MeCN)][X] and [Rh(DPEphos)(MeSC(6)H(4)CO)H(MeCN)][X]. Changing the ligand from DPEphos to one with a CH(2) linkage, [Ph(2)P(C(6)H(4))](2)CH(2), gave only decomposition on addition of aldehyde to the acetone precursor, which demonstrated the importance of the hemiabile ether group in DPEphos. With [Ph(2)P(C(6)H(4))](2)S, the sulfur atom has the opposite effect and binds too strongly to the metal centre to allow access to productive acetone intermediates.     

Synthesis,structure, and reactivity of sp carbon chains with bis(phosphine) pentafluorophenylplatinum endgroups: butadiynediyl (C4) through hexadecaoctaynediyl (C16) bridges,and beyond

The reaction of trans-[(C(6)F(5))(p-tol(3)P)(2)PtCl] (PtCl) and butadiyne (cat. CuI, HNEt(2)) gives trans-[(C(6)F(5))(p-tol(3)P)(2)Pt(Ctbond;C)(2)H] (PtC(4)H, 81 %), which reacts with excess HC(triple bond)CSiEt(3) under Hay coupling conditions (O(2), cat. CuCl/TMEDA, acetone) to yield PtC(6)Si (53 %). A solution of PtC(6)Si in acetone is treated with wet nBu(4)NF to generate PtC(6)H. The addition of ClSiMe(3) (F(-) scavenger) and then excess HC(triple bond)CSiEt(3) under Hay conditions gives PtC(8)Si (39 %). Hay homocouplings of PtC(4)H, PtC(6)H, and PtC(8)H (generated in situ analogously to PtC(6)H) yield PtC(8)Pt, PtC(12)Pt, and PtC(16)Pt (97-92 %). Reactions of PtC(4)H and PtC(6)H with PtCl (cat. CuCl, HNEt(2)) give PtC(4)Pt and PtC(6)Pt (69 %, 34 %). The attempted conversion of PtC(8)H to PtC(10)Si affords mainly PtC(16)Pt, with traces of PtC(20)Pt and PtC(24)Pt. The complexes PtC(x)Pt are exceedingly stable (dec pts 234 to 288 degrees C), and Et(3)P displaces p-tol(3)P to give the corresponding compounds Pt'C(8)Pt' and Pt'C(12)Pt' (94-90 %). The effect of carbon chain lengths upon IR nu(C(triple bond)C) patterns (progressively more bands), UV/Vis spectra (progressively red-shifted and more intense bands with epsilon >600 000 M(-1) cm(-1)), redox properties (progressively more difficult and less reversible oxidations), and NMR values are studied, and analyzed with respect to the polymeric sp carbon allotrope "carbyne". The crystal structure of PtC(12)Pt shows a dramatic, unprecedented degree of chain bending, whereas the chains in PtC(8)Pt, Pt'C(12)Pt', and PtC(16)Pt are nearly linear.     

Ring-borylated 15-electron and 17-electron ansa-chromocene complexes, their physical properties and molecular structures

A detailed study of the thermal decomposition of the zwitterionic, ring-borylated ansa-chromocene hydrido carbonyl complex [Cr(CO)H{Me(4)C(2)(C(5)H(4))[C(5)H(3)B(C(6)F(5))(3)]}] (2) is described. This complex is formed in the reaction between [Cr(CO){Me(4)C(2)(C(5)H(4))(2)}] (1) and B(C(6)F(5))(3) in toluene at -78 degrees C. Above -25 degrees C, 2 decomposes to a 50:50 mixture of the low-spin, 17e Cr(III) complexes [Cr(CO){Me(4)C(2)(C(5)H(4))[C(5)H(3)B(C(6)F(5))(3)]}] (3b) and [Cr(CO){Me(4)C(2)(C(5)H(4))(2)}][HB(C(6)F(5))(3)] (4). Carbon monoxide elimination from 3 b generates high-spin, 15 e [Cr{Me(4)C(2)(C(5)H(4))[C(5)H(3)B(C(6)F(5))(3)]}] (3a), which coordinates two other electron-donating ligands, such as xylyl isocyanide, PMe3, and PPh(2)Me to form the low-spin, 17 e electron complexes 3c, 3d, and 3e, respectively. High-spin, 15 e [Cr{Me(4)C(2)(C(5)H(4))(2)}][HB(C(6)F(5))(3)] (5) is generated by heating 3 b in toluene at 100 degrees C and periodically removing the evolved CO. Efforts to isolate more than a few X-ray quality crystals of 5 were thwarted by its tendency to form an insoluble precipitate (6) with the same molecular formula. Heating the solution of 5 at 120 degrees C results in its partial conversion (ca. 28 %) to 3a, thereby allowing the formation of 3a in yields as high as 74 % from the reaction between 1 and B(C(6)F(5))(3). The X-ray crystal structures of 3 b-e and 5 are described. Cyclic voltammetry measurements on 3 a-e reveal a dramatic reduction in the redox potentials of the complexes relative to their non-borylated analogues. DFT calculations show that this is due primarily to electrostatic stabilization of the oxidized species by the negatively charged borylate group. EPR and 19F NMR spectroscopy allow 3a to be distinguished from its Lewis base adducts 3 b-e and reveal the relative affinities of different Lewis bases for the chromium.     

Effect of the nature of the metal atom on hydrogen bonding and proton transfer to [Cp*MH3(dppe)]: tungsten versus molybdenum

The hydrogen-bonding and proton-transfer pathway to complex [Cp*W(dppe)H(3)] (Cp*=eta(5)-C(5)Me(5); dppe=Ph(2)PCH(2)CH(2)PPh(2)) was investigated experimentally by IR, NMR, UV/Vis spectroscopy in the presence of fluorinated alcohols, p-nitrophenol, and HBF(4), and by using DFT calculations for the [CpW(dhpe)H(3)] model (Cp=eta(5)-C(5)H(5); dhpe=H(2)PCH(2)CH(2)PH(2)) and for the real system. A study of the interaction with weak acids (CH(2)FCH(2)OH, CF(3)CH(2)OH, (CF(3))(2)CHOH) allowed the determination of the basicity factor, E(j)=1.73+/-0.01, making this compound the most basic hydride complex reported to date. A computational investigation revealed several minima for the [CpW(dhpe)H(3)] adducts with CF(3)CH(2)OH, (CF(3))(2)CHOH, and 2(CF(3))(2)CHOH and confirms that these interactions are stronger than those established by the Mo analogue. Their geometries and relative energies are closely related to those of the homologous Mo systems, with the most stable adducts corresponding to H bonding with M-H sites, however, the geometric and electronic parameters reveal that the metal center plays a greater role in the tungsten systems. Proton-transfer equilibria are observed with the weaker proton donors, the proton-transfer step for the system [Cp*W(dppe)H(3)]/HOCH(CF(3))(2) in toluene having DeltaH=(-3.9+/-0.3) kcal mol(-1) and DeltaS=(-17+/-2) cal mol(-1) K(-1). The thermodynamic stability of the proton-transfer product is greater for W than for Mo. Contrary to the Mo system, the protonation of the [Cp*W(dppe)H(3)] appears to involve a direct proton transfer to the metal center without a nonclassical intermediate, although assistance is provided by a hydride ligand in the transition state.     

Solid-state natural abundance 25Mg NMR studies of Na2MgEDTA x 4 H2O--a possible new reference compound for 25Mg NMR spectroscopy

Natural abundance solid-state (25)Mg NMR measurements were made of the disodium salt of magnesium ethylenediaminetetraacetate tetrahydrate (Na(2)MgEDTA x 4 H(2)O). Both magic angle spinning (MAS) and static experiments were employed to determine the quadrupole coupling constant (C(q)) and the asymmetry parameter (eta(q)) of the electric field gradient (EFG) tensor associated with (25)Mg in this compound, giving the values C(q) = 1.675(5) MHz and eta(q) = 0.15(1). The isotropic chemical shift was determined to be delta(iso) = 0.25(10) ppm (relative to 11 M MgCl(2) aqueous solution) and a small chemical shift anisotropy (CSA) contribution (approximately -13 ppm) was detected, one of the first CSA reports in (25)Mg NMR. This compound exhibited remarkably good (25)Mg NMR sensitivity, due to its fast spin-lattice relaxation and modest quadrupole coupling, which allowed its use as a secondary shift reference and as a test sample for the implementation and optimisation of signal-enhancement methods in (25)Mg NMR spectroscopy, such as double frequency sweeps (DFS) and the use of adiabatic hyperbolic secant (HS) and WURST pulses.     

Electron-transfer reduction of dinuclear copper peroxo and bis-μ-oxo complexes leading to the catalytic four-electron reduction of dioxygen to water

The four-electron reduction of dioxygen by decamethylferrocene (Fc*) to water is efficiently catalyzed by a binuclear copper(II) complex (1) and a mononuclear copper(II) complex (2) in the presence of trifluoroacetic acid in acetone at 298 K. Fast electron transfer from Fc* to 1 and 2 affords the corresponding Cu(I) complexes, which react at low temperature (193 K) with dioxygen to afford the η(2):η(2)-peroxo dicopper(II) (3) and bis-μ-oxo dicopper(III) (4) intermediates, respectively. The rate constants for electron transfer from Fc* and octamethylferrocene (Me(8)Fc) to 1 as well as electron transfer from Fc* and Me(8)Fc to 3 were determined at various temperatures, leading to activation enthalpies and entropies. The activation entropies of electron transfer from Fc* and Me(8)Fc to 1 were determined to be close to zero, as expected for outer-sphere electron-transfer reactions without formation of any intermediates. For electron transfer from Fc* and Me(8)Fc to 3, the activation entropies were also found to be close to zero. Such agreement indicates that the η(2):η(2)-peroxo complex (3) is directly reduced by Fc* rather than via the conversion to the corresponding bis-μ-oxo complex, followed by the electron-transfer reduction by Fc* leading to the four-electron reduction of dioxygen to water. The bis-μ-oxo species (4) is reduced by Fc* with a much faster rate than the η(2):η(2)-peroxo complex (3), but this also leads to the four-electron reduction of dioxygen to water.     

Energetic and topological analysis of the reaction of Mo and Mo2 with NH3, C2H2, and C2H4 molecules

The Density functional theory has been applied to characterize the structural features of Mo(1,2)-NH(3),-C(2)H(4), and -C(2)H(2) compounds. Coordination modes, geometrical structures, and binding energies have been calculated for several spin multiplets. It has been shown that in contrast to the conserved spin cases (Mo(1,2)-NH(3)), the interaction between Mo (or Mo(2)) and C(2)H(4) (or C(2)H(2)) are the low-spin (Mo-C(2)H(4) and -C(2)H(2)) and high-spin (Mo(2)-C(2)H(4) and -C(2)H(2)) complexes. In the ground state of Mo(1,2)-C(2)H(4) and -C(2)H(2), the metal-center always reacts with the C-C center. The spontaneous formation of the global minima is found to be possible due to the crossing between the potential energy surfaces (ground and excited states with respect to the metallic center). The bonding characterization has been performed using the topological analysis of the Electron Localization Function. It has been shown that the most stable electronic structure for a pi-acceptor ligand correlates with a maximum charge transfer from the metal center to the C-C bond of the unsaturated hydrocarbons, resulting in the formation of two new basins located on the carbon atoms (away from hydrogen atoms) and the reduction of the number of attractors of the C-C basin. The interaction between Mo(1,2) and C(2)H(4) (or C(2)H(2)) should be considered as a chemical reaction, which causes the multiplicity change. Contrarily, there is no charge transfer between Mo(1,2) and NH(3), and the partners are bound by an electrostatic interaction.     

Probing platinum azido complexes by 14N and 15N NMR spectroscopy

Metal azido complexes are of general interest due to their high energetic properties, and platinum azido complexes in particular because of their potential as photoactivatable anticancer prodrugs. However, azido ligands are difficult to probe by NMR spectroscopy due to the quadrupolar nature of (14)N and the lack of scalar (1)H coupling to enhance the sensitivity of the less abundant (15)N by using polarisation transfer. In this work, we report (14)N and (15)N NMR spectroscopic studies of cis,trans,cis-[Pt(N(3))(2)(OH)(2)(NH(3))] (1) and trans,trans,trans-[Pt(N(3))(2)(OH)(2)(X)(Y)], where X=Y=NH(3) (2); X=NH(3), Y=py (3) (py=pyridine); X=Y=py (4); and selected Pt(II) precursors. These studies provide the first (15)N NMR data for azido groups in coordination complexes. We discuss one- and three-bond J((15)N,(195)Pt) couplings for azido and am(m)ine ligands. The (14)N(α) (coordinated azido nitrogen) signal in the Pt(IV) azido complexes is extremely broad (W(1/2)≈2124 Hz for 4) in comparison to other metal azido complexes, attributable to a highly asymmetrical electric field gradient at the (14)N(α) atom. Through the use of anti-ringing pulse sequences, the (14)N NMR spectra, which show resolution of the broad (14)N(α) peak, were obtained rapidly (e.g., 1.5 h for 10 mM 4). The linewidths of the (14)N(α) signals correlate with the viscosity of the solvent. For (15) N-enriched samples, it is possible to detect azido (15)N resonances directly, which will allow photoreactions to be followed by 1D (15)N NMR spectroscopy. The T(1) relaxation times for 3 and 4 were in the range 5.7-120 s for (15)N, and 0.9-11.3 ms for (14)N. Analysis of the (1)J((15)N,(195)Pt) coupling constants suggests that an azido ligand has a moderately strong trans influence in octahedral Pt(IV) complexes, within the series 2-pic相似文献   

First investigation of non-classical dihydrogen bonding between an early transition-metal hydride and alcohols: IR, NMR, and DFT approach

The interaction of [NbCp(2)H(3)] with fluorinated alcohols to give dihydrogen-bonded complexes was studied by a combination of IR, NMR and DFT methods. IR spectra were examined in the range from 200-295 K, affording a clear picture of dihydrogen-bond formation when [NbCp(2)H(3)]/HOR(f) mixtures (HOR(f) = hexafluoroisopropanol (HFIP) or perfluoro-tert-butanol (PFTB)) were quickly cooled to 200 K. Through examination of the OH region, the dihydrogen-bond energetics were determined to be 4.5+/-0.3 kcal mol(-1) for TFE (TFE = trifluoroethanol) and 5.7+/-0.3 kcal mol(-1) for HFIP. (1)H NMR studies of solutions of [NbCp(2)H(2)(B)H(A)] and HFIP in [D(8)]toluene revealed high-field shifts of the hydrides H(A) and H(B), characteristic of dihydrogen-bond formation, upon addition of alcohol. The magnitude of signal shifts and T(1) relaxation time measurements show preferential coordination of the alcohol to the central hydride H(A), but are also consistent with a bifurcated character of the dihydrogen bonding. Estimations of hydride-proton distances based on T(1) data are in good accord with the results of DFT calculations. DFT calculations for the interaction of [NbCp(2)H(3)] with a series of non-fluorinated (MeOH, CH(3)COOH) and fluorinated (CF(3)OH, TFE, HFIP, PFTB and CF(3)COOH) proton donors of different strengths showed dihydrogen-bond formation, with binding energies ranging from -5.7 to -12.3 kcal mol(-1), depending on the proton donor strength. Coordination of proton donors occurs both to the central and to the lateral hydrides of [NbCp(2)H(3)], the former interaction being of bifurcated type and energetically slightly more favourable. In the case of the strong acid H(3)O(+), the proton transfer occurs without any barrier, and no dihydrogen-bonded intermediates are found. Proton transfer to [NbCp(2)H(3)] gives bis(dihydrogen) [NbCp(2)(eta(2)-H(2))(2)](+) and dihydride(dihydrogen) complexes [NbCp(2)(H)(2)(eta(2)-H(2))](+) (with lateral hydrides and central dihydrogen), the former product being slightly more stable. When two molecules of TFA were included in the calculations, in addition to the dihydrogen-bonded adduct, an ionic pair formed by the cationic bis(dihydrogen) complex [NbCp(2)(eta(2)-H(2))(2)](+) and the homoconjugated anion pair (CF(3)COO...H...OOCCF(3))(-) was found as a minimum. It is very likely that these ionic pairs may be intermediates in the H/D exchange between the hydride ligands and the OD group observed with the more acidic alcohols in the NMR studies.     

Atmospheric chemistry of 4:2 fluorotelomer alcohol (n-C4F9CH2CH2OH): products and mechanism of Cl atom initiated oxidation in the presence of NOx

Smog chamber/FTIR techniques were used to study the Cl atom initiated oxidation of 4:2 fluorotelomer alcohol (C(4)F(9)CH(2)CH(2)OH, 4:2 FTOH) in the presence of NO(x) in 700 Torr of N(2)/O(2) diluent at 296 K. Chemical activation effects play an important role in the atmospheric chemistry of the peroxy, and possibly the alkoxy, radicals derived from 4:2 FTOH. Cl atoms react with C(4)F(9)CH(2)CH(2)OH to give C(4)F(9)CH(2)C(*)HOH radicals which add O(2) to give chemically activated alpha-hydroxyperoxy radicals, [C(4)F(9)CH(2)C(OO(*))HOH]*. In 700 Torr of N(2)/O(2) at 296 K, approximately 50% of the [C(4)F(9)CH(2)C(OO(*))HOH]* radicals decompose "promptly" to give HO(2) radicals and C(4)F(9)CH(2)CHO, the remaining [C(4)F(9)CH(2)C(OO(*))HOH]* radicals undergo collisional deactivation to give thermalized peroxy radicals, C(4)F(9)CH(2)C(OO(*))HOH. Decomposition to HO(2) and C(4)F(9)CH(2)CHO is the dominant atmospheric fate of the thermalized peroxy radicals. In the presence of excess NO, the thermalized peroxy radicals react to give C(4)F(9)CH(2)C(O(*))HOH radicals which then decompose at a rate >2.5 x 10(6) s(-1) to give HC(O)OH and the alkyl radical C(4)F(9)CH(2)(*). The primary products of 4:2 FTOH oxidation in the presence of excess NO(x) are C(4)F(9)CH(2)CHO, C(4)F(9)CHO, and HCOOH. Secondary products include C(4)F(9)CH(2)C(O)O(2)NO(2), C(4)F(9)C(O)O(2)NO(2), and COF(2). In contrast to experiments conducted in the absence of NO(x), there was no evidence (<2% yield) for the formation of the perfluorinated acid C(4)F(9)C(O)OH. The results are discussed with regard to the atmospheric chemistry of fluorotelomer alcohols.     

Ferromagnetic versus antiferromagnetic exchange interactions in tetrathiafulvalene-based 3d/4f heterobimetallic complexes

(TTF-salphen)M compounds (TTF-salphen(2-)=4,5-bis(propylthio)tetrathiafulvalene-N,N'-phenylenebis(salicylideneimine) dianion; M=Cu(II) and Ni(II)) have been treated with Ln(hfac)(3)·2H(2)O precursors (hfac(-)=1,1,1,5,5,5-hexafluoroacetylacetonate anion; Ln=Gd(III), Tb(III), and Dy(III)) to elaborate unprecedented 3d/4f TTF-based heterobimetallic complexes of formula [(TTF-salphen)MLn(hfac)(3)]. All the structures of these compounds have been resolved by X-ray diffraction on single crystals. The structures of these complexes are formed by a TTF-salphen(2-) ligand coordinated to the 3d metal ions in the inert tetradentate N(2)O(2) site. The Ln(hfac)(3) fragment is coordinated to the (TTF-salphen)M one through the two phenolate bridges. Even if the complexes are similar in both Cu(II) and Ni(II) families, the crystal packing is different. In the first case, dimers of TTF-salphen(2-) donors constitute the organic network. In the other case, a reminiscent organic network is observed with S···S contacts. The photophysical properties of [(TTF-salphen)CuDy(hfac)(3)] (3) in chloroform solution highlight the redshift of the TTF→salphen charge transfer (400 cm(-1)) relative to the analogue excitations in (TTF-salphen)Cu, which attest to the stability of these structures in solution. Static magnetic measurements have allowed us to quantify the ferromagnetic interactions (J=+1.29 cm(-1)) between Cu(II) and Gd(III) in the [(TTF-salphen)CuGd(hfac)(3)] complex. Finally, an empirical method that consists of the comparisons of the magnetic properties of [(TTF-salphen)CuTb(hfac)(3)] with [(TTF-salphen)NiTb(hfac)(3)] and [(TTF-salphen)CuDy(hfac)(3)] with [(TTF-salphen)NiDy(hfac)(3)] has established that ferromagnetic interactions take place between Cu(II) and Tb(III) ions, whereas unusual antiferromagnetic interactions have been identified between Cu(II) and Dy(III) ions.     

Synthesis of phthalide derivatives using nickel-catalyzed cyclization of o-haloesters with aldehydes

The reaction of o-bromobenzoate (1 b) with benzaldehyde (2 a) in the presence of [NiBr(2)(dppe)] (dppe=1,2-bis(diphenylphosphino)ethane) and zinc powder in THF (24 hours, reflux temperature), afforded 3-phenyl-3H-isobenzofuran-1-one (3 a) in an 86 % yield. Similarly, o-iodobenzoate reacts with 2 a to give 3 a, but in a lower yield (50 %). A series of substituted aromatic and aliphatic aldehydes (2 b, 4-MeC(6)H(4)CHO; 2 c, 4-MeOC(6)H(4)CHO; 2 d, 3-MeOC(6)H(4)CHO; 2 e, 2-MeOC(6)H(4)CHO; 2 f, 4-CNC(6)H(4)CHO; 2 g, 4-(Me)(3)CC(6)H(4)CHO; 2 h, 4-C(6)H(5)C(6)H(4)CHO; 2 i, 4-ClC(6)H(4)CHO; 2 j, 4-CF(3)C(6)H(4)CHO; 2 k, CH(3)(CH(2))(5)CHO; 2 l, CH(3)(CH(2))(2)CHO) also underwent cyclization with o-bromobenzoate (1 b) producing the corresponding phthalide derivatives in moderate to excellent yields and with high chemoselectivity. Like 1 b, methyl 2-bromo-4,5-dimethoxybenzoate (1 c) reacts with tolualdehyde (2 b) to give the corresponding substituted phthalide 3 m in a 71 % yield. The methodology can be further applied to the synthesis of six-membered lactones. The reaction of methyl 2-(2-bromophenyl)acetate (1 d) with benzaldehyde under similar reaction conditions afforded six-membered lactone 3 o in a 68 % yield. A possible catalytic mechanism for this cyclization is also proposed.     

Capillary electrophoresis on-line coupled with hydride generation-atomic fluorescence spectrometry for speciation analysis of selenium

A new method for speciation analysis of two inorganic selenium species was developed by on-line coupling of capillary electrophoresis (CE) with hydride generation-atomic fluorescence spectrometry (HG-AFS) and on-line conversion of Se(VI) to Se(IV). Baseline separation of Se(VI) and Se(IV) was achieved by CE in a 50 cm x 75 microm inside diameter (ID) fused-silica capillary at -20 kV using a mixture of 15 mmol.L(-1) NaH2PO4 and 0.5 mmol.L(-1) cetyltrimethylammonium bromide (pH 7.5) as electrolyte buffer. Se(VI) was on-line reduced to Se(IV) by mixing the CE effluent with concentrated HCl. The precision (relative standard deviation, RSD, n=7) ranged from 0.7 to 1.3% for migration time, 6.4 to 3.7% for peak height response, and 5.9 to 6.1% for peak area for the two selenium species at the 500 microg.L(-1) (as Se) level. The detection limits were 33 and 25 microg.L(-1) (as Se) for Se(VI) and Se(IV), respectively. The recoveries of the two selenium species in five locally collected water samples ranged from 88 to 114%. The developed method was applied to speciation analysis of inorganic selenium species in spiked natural water samples.     

甲基丙烯醛氧化酯化制甲基丙烯酸甲酯催化剂的制备与应用

甲基丙烯醛氧化酯化制甲基丙烯酸甲酯催化剂的制备与应用;催化剂; 甲基丙烯酸甲酯; 甲基丙烯醛; 氧化-酯化反应     

Cyclopentadienyl ruthenium, rhodium, and iridium vertices in metallaboranes: geometry and chemical bonding

Most cyclopentadienylmetallaboranes containing the vertex units CpM (M = Co, Rh, Ir; Cp = eta(5)-cyclopentadienyl ring, mainly eta(5)-Me(5)C(5)) and CpRu donating two and one skeletal electrons, respectively, have structures closely related to binary boranes or borane anions. Smaller clusters of this type, such as metallaborane analogues of arachno-B(4)H(10) (e.g., (CpIr)(2)B(2)H(8)), nido-B(5)H(9) (e.g., (CpRh)(2)B(3)H(7) and (CpRu)(2)B(3)H(9)), arachno-B(5)H(11) (e.g., CpIrB(4)H(10)), B(6)H(6)(2)(-) (e.g., (CpCo)(4)B(2)H(4)), nido-B(6)H(10) (e.g., CpIrB(5)H(9) and (CpRu)(2)B(4)H(10)), and arachno-B(6)H(12) (e.g., (CpIr)(2)B(4)H(10)), have the same skeletal electron counts as those of the corresponding boranes. However, such clusters with eight or more vertices, such as metallaborane analogues of B(8)H(8)(2)(-) (e.g., (CpCo)(4)B(4)H(4)), arachno-B(8)H(14) (e.g., (CpRu)(2)B(6)H(12)), and nido-B(10)H(14) (e.g., (CpRu)(2)B(8)H(12)), have two skeletal electrons less than those of the corresponding metal-free boranes, analogous to the skeletal electron counts of isocloso boranes relative to those of metal-free deltahedral boranes. Some metallaboranes have structures not analogous to metal-free boranes but instead analogous to metal carbonyl clusters such as 3-capped square pyramidal (CpRu)(2)B(4)H(8) and (CpRu)(3)B(3)H(8) analogous to H(2)Os(6)(CO)(16) and capped octahedral (CpRh)(3)B(4)H(4) analogous to Os(7)(CO)(21). In the metallaborane structures closely related to metal-free boranes, the favored degrees of BH and CpM vertices appear to be 5 and 6, respectively.