Formation and characterization of the oxygen-rich hafnium dioxygen complexes: OHf(eta2-O2)(eta2-O3), Hf(eta2-O2)3, and Hf(eta2-O2)4

Hafnium atom oxidation by dioxygen molecules has been investigated using matrix isolation infrared absorption spectroscopy. The ground-state hafnium atom inserts into dioxygen to form primarily the previously characterized HfO(2) molecule in solid argon. Annealing allows the dioxygen molecules to diffuse and react with HfO(2) to form OHf(eta(2)-O(2))(eta(2)-O(3)), which is characterized as a side-on bonded oxo-superoxo hafnium ozonide complex. Under visible light (532 nm) irradiation, the OHf(eta(2)-O(2))(eta(2)-O(3)) complex either photochemically rearranges to a more stable Hf(eta(2)-O(2))(3) isomer, a side-on bonded di-superoxo hafnium peroxide complex, or reacts with dioxygen to form an unprecedented homoleptic tetra-superoxo hafnium complex: Hf(eta(2)-O(2))(4). The Hf(eta(2)-O(2))(4) complex is determined to possess a D(2d) geometry with a tetrahedral arrangement of four side-on bonded O(2) ligands around the hafnium atom, which thus presents an 8-fold coordination. These oxygen-rich complexes are photoreversible; that is, formation of Hf(eta(2)-O(2))(3) and Hf(eta(2)-O(2))(4) is accompanied by demise of OHf(eta(2)-O(2))(eta(2)-O(3)) under visible (532 nm) light irradiation and vice versa with UV (266 nm) light irradiation.     

Soluble yttrium chalcogenides: syntheses,structures, and NMR properties of Y[eta 3-N(SPPh2)2]3 and Y[eta 2-N(SePPh2)2]2[eta 3-N(SePPh2)2

The compounds Y[N(QPPh2)2]3 (Q = S (1), Se (2)) have been synthesized in good yield from the protonolysis reactions between Y[N(SiMe3)2]3 and HN(QPPh2)2 in methylene chloride (CH2Cl2). The compounds are not isostructural. In 1, the Y atom is surrounded by three similar [N(SPPh2)2]- ligands bound eta 3 through two S atoms and an N atom. The molecule possesses D3 symmetry, as determined in the solid state by X-ray crystallography and in solution by 89Y and 31P NMR spectroscopies. In 2, the Y atom is surrounded again by three [N(SePPh2)2]- ligands, but two are bound eta 2 through the two Se atoms and the other ligand is bound eta 3 through the two Se atoms and an N atom. Although a fluxional process is detected in the 31P and 77Se NMR spectra, a triplet is found in the 89Y NMR spectrum of 2 (delta = 436 ppm relative to YCl3 in D2O, 2JY-P = 5 Hz). This implies that on average the conformation of one eta 3- and two eta 2-bound ligands is retained in solution. Crystallographic data for 1: C72H60N3P6S6Y, rhombohedral, R3c, a = 14.927(5) A, c = 56.047(13) A, V = 10815(6) A3, T = 153 K, Z = 6, and R1(F) = 0.042 for the 1451 reflections with I > 2 sigma(I). Crystallographic data for 2: C72H60N3P6Se6Y.Ch2-Cl2, monoclinic, P2(1)n, a = 13.3511(17) A, b = 38.539(7) A, c = 14.108(2) A, beta = 94.085(13) degrees, V = 7241(2) A 3, T = 153 K, Z = 4, and R1(F) = 0.037 for the 8868 reflections with I > 2 sigma(I).     

Polynuclear magnesium and magnesium-titanium species. Syntheses and crystal structures of [Mg4(mu3,eta2-ddbfo)2(mu,eta2-ddbfo)2(mu,eta1-ddbfo)29eta1-ddbfo2],

Tetranuclear magnesium complexes with chelating alkoxo ligands have been synthesized with the aim of investigating coordinatively unsaturated magnesium sites able to bind TiX4 (X = Cl, OR), of the type necessary for the formation of the active centers in polymerization catalysts. The magnesium compound [Mg4(mu3,eta2-ddbfo)2(mu,eta2-ddbfo)2(mu,eta1-ddbfo)2(eta1-ddbfo)2] x 2CH2Cl2 (1) (ddbfo = 2,3-dihydro-2,2-dimethyl-7-benzofuranoxide) was prepared by the reaction of MgBu2 with ddbfoH in dichloromethane. Complex 1 exists as a centrosymmetric tetranuclear species with two different types of magnesium centers corresponding to octahedral MgO6 and trigonal bipyramidal MgO5 geometry. Compound 1 is monoclinic, space group P2(1/c), with a = 12.053(2) A, b = 13.323(3) A, c = 17.069(3) A, beta = 98.50(3) degrees , and Z = 4. The reaction of 1 with methanol in tetrahydrofuran (THF) gave compound [Mg4(mu3-OMe)2(mu,eta2-ddbfo)2(mu,eta1-ddbfo)2(eta1-ddbfo)2(CH3OH)5] x CH3OH x THF (2). During this reaction one of the two five-coordinate MgO5 centers in 1 is completed by a methanol molecule and becomes octahedral in 2. Species 2 belongs to the P2(1/n) monoclinic space group, with a = 13.323(3) A, b = 20.768(4) A, c = 27.584(6) A, beta = 104.26(3) degrees , and Z = 4. Compound [Mg4(mu3,eta2-thffo)2(mu,zeta2-thffo)2(mu,eta1-thffo)2[mu-OTi(DIPP)3]2] x 2CH2Cl2 (3) is formed as a result of substitution of two thffo (thffo = 2-tetrahydrofurfuroxide) ligands bonded to the five-coordinate magnesium atom in [Mg4(thffo)8] by bulky OTi(DIPP)3 (DIPP = diisopropylphenolate) groups. Crystals of 3 are monoclinic, space group P2(1/n), with a = 17.069(3) A, b = 18.421(4) A, 17.815(4) A, beta = 90.77(3) degrees , and Z = 4. The X-ray crystal structures of complexes 1-3 are discussed in terms of explaining the role of the coordinatively unsaturated magnesium site in chiral catalyst active center formation.     

Micro-eta3:eta4-Lithiocene and eta3:eta3-zincocene incorporating 1,2-diaza-3,5-diborolyl, a cyclopentadienyl analog

A heterocyclic cyclopentadienyl analog containing only one carbon atom in the ring was prepared and a polymeric lithiocene and a monomeric zincocene containing this novel ligand have been isolated and crystallographically characterized.     

Cyclic voltammetry modeling, geometries, and electronic properties for metallofullerene complexes with mu3-eta2:eta2:eta2-C60 bonding mode

Reduction potential (E(red)) values have been calculated and compared with available cyclic voltammetry (CV) data for 10 metallofullerene complexes with the mu(3)-eta(2):eta(2):eta(2)-C(60) (M(3)-C(6)[C(60)]) bonding mode. Consideration of bulk solvent effects is essential for the calculation of the E(red) values. Scaling factors for the electrostatic terms of the solvation energies have been introduced to fully describe the experimental cyclic voltammograms with a small mean deviation of 0.07 V. Multiple electron reductions induce movement of the metal cluster moieties on the C(60) surface, which is accompanied with the changes in some M-C[C(60)] bonds from pi-type to sigma-type mode. However, the changes in M(3)-C(60) distances, as well as the geometric changes of M(3) and C(60), are small for the reductions, which is in harmony with the high chemical and electrochemical stability of the metallofullerenes. Our population analyses reveal that the added electrons are not localized at the C(60) moieties, and electron population in the metal clusters is significant, more than 20% (av. 37%), for all the reductions. Furthermore, we demonstrated that the two close one-electron redox waves in CV diagrams are strongly correlated with significant electron delocalization, about 40-80%, to the metal-cluster moieties in these metallofullerene complexes.     

Syntheses and molecular structures of eta3-[(eta5-Cp*)(CO)2Fe-AsPC(SiMe3)2]M(CO)2(eta5-Cp)(M = Mo, W): the first complexes featuring eta3-arsaphosphaallyl ligands

Reaction of (eta5-Cp)(CO)2M=P=C(SiMe3)2 4a (M = Mo) and 4b (M = W) with (eta5-Cp*)(CO)2Fe-As=C(NMe2)2 5 affords the eta3-1-arsa-2-phosphaallyl complexes [(eta5-Cp*)(CO)2Fe-AsPC(SiMe3)2]M(CO)2(eta5-Cp) 6a and 6b, the molecular structures of which were determined by X-ray analyses.     

On the origin of dinitrogen hydrogenation promoted by [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2)

The origin of the hydrogenation of the dinitrogen ligand in [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2) has been investigated by a combined computational and experimental study. Density functional theory calculations on the zirconocene dinitrogen complex demonstrate significant imido character in the zirconium nitrogen bonds, arising from effective pi-back-bonding from the low-valent zirconium and the side-on bound N2 ligand. The twisted ground-state structure of the N2 complex is a key requirement for nitrogen hydrogenation, as calculations on the model complex [(eta5-C5H5)2Zr]2(mu2,eta2,eta2-N2) reveal reduced overlap as the dihedral angle between the zirconocene wedges approaches 0 degrees . Experimentally, isotopic labeling studies on the microscopic reverse are consistent with a 1,2-addition mechanism for nitrogen hydrogenation.     

Theoretical characterization of stable eta1-N2O-, eta2-N2O-, eta1-N2-, and eta2-N2-bound species: intermediates in the addition reactions of nitrogen hydrides with the pentacyanonitrosylferrate(II) ion

The addition of nitrogen hydrides (hydrazine, hydroxylamine, ammonia, azide) to the pentacyanonitrosylferrate(II) ion has been analyzed by means of density functional calculations, focusing on the identification of stable intermediates along the reaction paths. Initial reversible adduct formation and further decomposition lead to the eta(1)- and eta(2)-linkage isomers of N(2)O and N(2), depending on the nucleophile. The intermediates (adducts and gas-releasing precursors) have been characterized at the B3LYP/6-31G level of theory through the calculation of their structural and spectroscopic properties, modeling the solvent by means of a continuous approach. The eta(2)-N(2)O isomer is formed at an initial stage of adduct decompositions with the hydrazine and azide adducts. Further conversion to the eta(1)-N(2)O isomer is followed by Fe-N(2)O dissociation. Only the eta(1)-N(2)O isomer is predicted for the reaction with hydroxylamine, revealing a kinetically controlled N(2)O formation. eta(1)-N(2) and eta(2)-N(2) isomers are also predicted as stable species.     

Practical, scalable, high-throughput approaches to eta3-pyranyl and eta3-pyridinyl organometallic enantiomeric scaffolds using the Achmatowicz reaction

A unified strategy for the high-throughput synthesis of multigram quantities of the eta(3)-oxopyranyl- and eta(3)-oxopyridinylmolybdenum complexes TpMo(CO)(2)(eta(3)-oxopyranyl) and TpMo(CO)(2)(eta(3)-oxopyridinyl) is described (Tp = hydridotrispyrazolylborato). The strategy uses the oxa- and aza-Achmatowicz reaction for the preparation of these organometallic enantiomeric scaffolds, in both racemic and high enantiopurity versions.     

eta1:eta2-Alkynyl-bridged W-Si complexes: formation, structure, and reaction with acetone

Reactions of (eta5-C5Me4R)(CO)2(MeCN)WMe (R = Me, Et) with HPh2SiCCtBu gave the novel alkynyl-bridged W-Si complexes, (eta5-C5Me4R)(CO)2W(mu-eta1:eta2-CCtBu)(SiPh2) (R = Me, Et), whose alkynyl ligands bridge the tungsten and silicon atoms in an eta1:eta2-coordination mode. The structures of these complexes were fully characterized, including X-ray crystallography. Treatment of (eta5-C5Me5)(CO)2W(mu-eta1:eta2-CCtBu)(SiPh2) with acetone resulted in acetone insertion into the silicon-alkynyl linkage followed by intramolecular C-H activation of the tBu group to give the chelate-type alkyl-alkene complex, (eta5-C5Me5)(CO)2W(eta1:eta2-CH2CMe2C=CHSiPh2OCMe2).     

Novel eta1-N,eta2-C,C-binding mode between pyridinyl-functionalized cyclopentadienyl ligands and iridium

The reaction between 2-(2,3,4,5-tetramethyl-cyclopenta-1,3-dienyl)-pyridine 1 and IrCl3 was performed in an attempt to synthesize a cyclometalated system with decreased pi conjugation in the ligand. An unexpected reduction and rearrangement of bis-pyridinyl-cyclopentadienyl cyclometalated Ir(III) intermediate 2 took place yielding bis-pyridinyl-fulvene Ir(I) complex 4, which exhibits a novel bis-eta1-N,eta2-C,C-binding mode between the pyridinyl-functionalized fulvene ligand and iridium. The iridium atom in 4 is not sandwiched between two cyclopentadienyl moieties; rather, the two cyclopentadienyl groups adopt a pi-pi stacking arrangement with a centroid-centroid distance of 3.494 A. The Cl/P(wedge)O ligand-exchange reaction between 4 and 2-[(diphenylphosphanyl)-methyl]-1,1,1,3,3,3-hexafluoro-propan-2-ol 5 led to loss of one pyridinyl-functionalized fulvene ligand and produced complex 6, in which the remaining pyridinyl-functionalized fulvene ligand exhibits the mono-eta1-N,eta2-C,C-binding mode.     

Syntheses,reactivity, and crystal structures of molybdenum complexes with pyridine-2-thionate (pyS)-containing ligands: crystal structures of [Mo(eta(3)-C(3)H(5))(CO)(2)](2)(mu-eta(1),eta(2)-pyS)(2), exo-[Mo(eta(3)-C(3)H(5))(CO)(eta(2)-pyS)(eta(2)-dppe)], [Mo(CO)(3)(eta(1)-SC(5)H(4)NH)(eta(2)-dppm)], and [Mo(CO)(eta(2)-pyS)(2)(eta(2)-dppm)

The doubly bridged pyridine-2-thionate (pyS) dimolybdenum complex [Mo(eta(3)-C(3)H(5))(CO)(2)](2)(mu-eta(1),eta(2)-pyS)(2) (1) is accessible by the reaction of [Mo(eta(3)-C(3)H(5))(CO)(2)(CH(3)CN)(2)Br] with pySK in methanol at room temperature. Complex 1 reacts with piperidine in acetonitrile to give the complex [Mo(eta(3)-C(3)H(5))(CO)(2)(eta(2)-pyS)(C(5)H(10)NH)] (2). Treatment of 1 with 1,10-phenanthroline (phen) results in the formation of complex [Mo(eta(3)-C(3)H(5))(CO)(2)(eta(1)-pyS)(phen)] (3), in which the pyS ligand is coordinated to Mo through the sulfur atom. Four conformational isomers, endo,exo-complexes [Mo(eta(3)-C(3)H(5))(CO)(eta(2)-pyS)(eta(2)-diphos)] (diphos = dppm, 4a-4d; dppe, 5a-5d), are accessible by the reactions of 1 with dppm and dppe in refluxing acetonitrile. Homonuclear shift-correlated 2-D (31)P((1)H)-(31)P((1)H) NMR experiments of the mixtures 4a-4d have been employed to elucidate the four stereoisomers. The reaction of 4 and pySK or [Mo(CO)(3)(eta(1)-SC(5)H(4)NH)(eta(2)-dppm)] (6) and O(2) affords allyl-displaced seven-coordinate bis(pyridine-2-thionate) complex [Mo(CO)(eta(2)-pyS)(2)(eta(2)-dppm)] (7). All of the complexes are identified by spectroscopic methods, and complexes 1, 5d, 6, and 7 are determined by single-crystal X-ray diffraction. Complexes 1 and 5d crystallize in the orthorhombic space groups Pbcn and Pbca with Z = 4 and 8, respectively, whereas 6 belongs to the monoclinic space group C2/c with Z = 8 and 7 belongs to the triclinic space group Ponemacr; with Z = 2. The cell dimensions are as follows: for 1, a = 8.3128(1) A, b = 16.1704(2) A, c = 16.6140(2) A; for 5d, a = 17.8309(10) A, b = 17.3324(10) A, c = 20.3716(11) A; for 6, a = 18.618(4) A, b = 16.062(2) A, c = 27.456(6) A, beta = 96.31(3) degrees; for 7, a = 9.1660(2) A, b = 12.0854(3) A, c = 15.9478(4) A, alpha = 78.4811(10) degrees, beta = 80.3894(10) degrees, gamma = 68.7089(11) degrees.     

Structural isomers of aryl-substituted eta(3)-propargyl complexes: eta(2)-1-Metalla(methylene)cyclopropene and eta(3)-benzyl complexes

Hydride abstraction from C(5)Me(5)(CO)(2)Re(eta(2)-PhC triple bond CCH(2)Ph) (1) gave a 3:1 mixture of eta(3)-propargyl complex [C(5)Me(5)(CO)(2)Re(eta(3)-PhCH-C triple bond CPh)][BF(4)] (5) and eta(2)-1-metalla(methylene)cyclopropene complex [C(5)Me(5)(CO)(2)Re(eta(2)-PhC-C=CHPh)][BF(4)] (6). Observation of the eta(2)-isomer requires 1,3-diaryl substitution and is favored by electron-donating substituents on the C(3)-aryl ring. Interconversion of eta(3)-propargyl and eta(2)-1-metalla(methylene)cyclopropene complexes is very rapid and results in coalescence of Cp (1)H NMR resonances at about -50 degrees C. Protonation of the alkynyl carbene complex C(5)Me(5)(CO)(2)Re=C(Ph)C triple bond CPh (22) gave a third isomer, the eta(3)-benzyl complex [C(5)Me(5)(CO)(2)Re[eta(3)(alpha,1,2)-endo,syn-C(6)H(5)CH(C triple bond CC(6)H(5))]][BF(4)] (23) along with small amounts of the isomeric complexes 5 and 6. While 5 and 6 are in rapid equilibrium, there is no equilibration of the eta(3)-benzyl isomer 23 with 5 and 6.     

Synthesis, structural characterization, and properties of chromium(III) complexes containing amidinato ligands and eta2-pyrazolato, eta(2)-1,2,4-triazolato, or eta1-tetrazolato ligands

Treatment of anhydrous chromium(III) chloride with 2 or 3 equivalents of 1,3-di-tert-butylacetamidinatolithium or 1,3-diisopropylacetamidinatolithium in tetrahydrofuran at ambient temperature afforded Cr(tBuNC(CH3)NtBu)2(Cl)(THF) and Cr(iPrNC(CH3)NiPr)3 in 78% and 65% yields, respectively. Treatment of Cr(tBuNC(CH3)NtBu)2(Cl)(THF) with the potassium salts derived from pyrazoles and 1,2,4-triazoles afforded Cr(tBuNC(CH3)NtBu)2(X), where X=3,5-disubstituted pyrazolato or 3,5-disubstituted 1,2,4-triazolato ligands, in 65-70% yields. X-Ray crystal structure analyses of Cr(tBuNC(CH3)NtBu)2(Me2pz) (Me2pz=3,5-dimethylpyrazolato) and Cr(tBuNC(CH3)NtBu)2(Me2trz) (Me2trz=3,5-dimethyl-1,2,4-triazolato) revealed eta2-coordination of the Me2pz and Me2trz ligands. Treatment of Cr(tBuNC(CH3)NtBu)2(Cl)(THF) with trifluoromethyltetrazolatosodium (NaCF3tetz) in the presence of 4-tert-butylpyridine afforded Cr(tBuNC(CH3)NtBu)2(CF3tetz)(4-tBupy) in 30% yield. An X-ray crystal structure determination showed eta1-coordination of the tetrazolato ligand through the 2-nitrogen atom. The complexes Cr(iPrNC(CH3)NiPr)3 and Cr(tBuNC(CH3)NtBu)2(X) are volatile and sublime with <1% residue between 120 and 165 degrees C at 0.05 Torr. In addition, these complexes are thermally stable at >300 degrees C under an inert atmosphere such as nitrogen or argon. Due to the good volatility and high thermal stability, these new compounds are promising precursors for the growth of chromium-containing thin films using atomic layer deposition.     

Theoretical study of the mechanism of hydrogenation of side-on coordinated dinitrogen activated by Zr binuclear complexes ([(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2))

The reaction mechanism of the reduction of dinitrogen coordinated side-on to a binuclear Zr complex, [(eta(5)-C(5)Me(4)H)(2)Zr](2)(mu(2),eta(2),eta(2)-N(2)) (T1), was investigated theoretically using a model complex, [(eta(5)-C(5)H(5))(2)Zr](2)(mu(2),eta(2),eta(2)-N(2)) (A1), employing density functional theory calculations. The effectiveness of A1 in describing T1 was confirmed by comparing the structures, distributions of charge, and frontier molecular orbitals. Our calculations showed that A1 has a twisted structure, resembling that of T1, which results in similar properties. The calculations for A1 and its derivatives on H(2) addition clearly explain the reaction mechanism and the reaction path that T1 follows, as well as the experimentally required reaction conditions. The immediate reaction of the first and second H(2) additions produces [(eta(5)-C(5)Me(4)H)(2)ZrH](2)(mu(2),eta(2),eta(2)-N(2)H(2)) (T2), and this is explained by the barrier heights of the reaction, which were calculated to be 20.4 and 10.9 kcal/mol, respectively. The latter barrier was below that of A1 + 2H(2). Complex T2 may be the initial complex for further H(2) addition under proper conditions, or it could lose one H(2) molecule followed by H migration from the Zr site to the N site. Both reactions are expected to occur, because of the closeness of the barrier heights (25.1 and 36.5 kcal/mol, respectively). Gentle warming is required for further H(2) additions, which can be understood from the energetics as well. The high reactivity of T1 with H(2) has been discussed by the comparison of the calculation of A1 and another complex with different ligands, presenting an interesting indication on the effects of the ligands. These theoretical results and discussion explaining the experiment should provide insight into the nature of the hydrogenation mechanism.     

Dimers of delocalized Ru3O clusters linked by ortho-metallated 2,2'-bipyrimidine in mu4-eta1(C),eta1(C),eta2(N,N),eta2(N,N) mode

A remarkable cluster-cluster interaction is operative in dimers of delocalized Ru3O(OAc)5(py)2 clusters with ortho-metallated 2,2'-bipyrimidine (bpym) in an unprecedented mu4-eta1(C),eta1(C),eta2(N,N),eta2(N,N) bonding mode; interconversion of the dimeric species [{Ru3O(OAc)5(py)2}2(micro4-bpym)]n+ (n = 0, 1 or 2) with different charges is attainable by chemical oxidation or reduction.     

Relative rates for the amination of eta3-allyl and eta3-benzyl complexes of palladium

Reactions of nucleophiles with metal-bound hydrocarbyl pi-ligands bound in an eta3-fashion are key steps in a variety of carbon-carbon and carbon-heteroatom bond-forming reactions. To reveal factors that control the rates of reaction of nucleophiles with this type of ligand, the rates of reactions of an aromatic and an aliphatic amine with a series of eta3-allyl, eta3-benzyl, and eta3-phenethyl palladium complexes ligated by the bisphosphine (R)-BINAP to form allylic and benzylic amines were measured. These data showed that the less common addition to an eta3-benzyl complex is faster than the more common addition to an eta3-allyl complex. The relative rates of reaction followed the trend naphthylmethyl > naphthylethyl > benzyl > 1,1-dimethylallyl > allyl. Computational studies suggest that there is a correlation between the amount of positive charge at the site of nucleophilic attack and the rate of C-N bond formation.     

A tris-pyrazolylborate ligand with hemilabile O-donor groups. Examples of eta3, eta5, eta6 and bridging modes of bonding to Li+, Na+, K+, Tl+ and Ca2+ ions

A tris-pyrazolylborate ligand bearing ether appendages is shown to be a potential hemilabile ligand based on NMR studies and structural characterization of its eta3, eta5, eta6, and micro-binding modes in coordination with Li+, Na+, K+, Tl+, and Ca2+ ions.