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Electrode density effects on the heterogeneous electron-transfer dynamics of monolayers containing osmium, were examined.

The use of quantum mechanical reference data to develop a transition state force field for the AD reaction is demonstrated. The force field is validated by prediction of experimental enantioselectivities and by comparison to energetic and structural data.

A study was conducted to explore the design and construction of a molecular level electronic set, a set of molecular-level systems capable of performing functions which mimic those of macroscopic components in electronic devices. Nine rodlike compounds of nanometric dimension of the general formula [M(bpy)3-(ph)(sub n)-M'(bpy)3]4+ (M = M' = Ru(II); M = M' = Os(II); M = Ru(II), M' = Os(II); bpy = 2,2'-bipyridine; ph = 1,4-phenylene; n = 3,5,7; the central phenylene unit bears two alkyl chains for solubility reasons). Experimental methods, results and conclusions are discussed.

The vibrational spectra of the binuclear propene complexes: [Os2(CO)8(mu2-eta1,eta1-C2H3CH3)]16, its (3,3,3-d3) and (d6) deuterium-substituted isotopologues and [Os2(CO)4(mu2-C2H3CH3)] were determined and the vibrational modes of the alkene ligands had been designated. It was hoped that the effort can be related to the electron energy loss spectroscopy or the reflection-absorption infrared spectroscopy of ethene-osmium complexes chemisorbed on metal single-crystal surfaces.

A study was conducted on the electrochemistry at very positive potentials in liquid SO2 of RuII and OsII dendritic polynuclear complexes and of several of their lower-nuclearity analogues. The experiments resulted in the observation of several metal- and ligand-centered oxidations which were previously inaccessible. The findings also suggest that the redox properties can also be employed as a powerful tool for the chemical characterization of large and highly charged supermolecules.

A study was conducted on the reaction of the complex of [Os(NH3)5(eta2-anisole)]2+ with acetals or Michael acceptors to produce 4-methoxystyrene complexes that are exclusively coordinated at the arene (eta2). These styrene complexes are active dienes and are involved in Diels-Adler reactions with electron-deficient olefins to form tetrahydronaphthalene complexes. The cycloadducts are produced as single diastereomers and are essential as precursors to functionalized tetralins and decalins.

Previous research has been able to synthesize the high-oxidation-state cyclopentadienyl metal polyhydride known as (pentamethylcyclopentadienyl)osmium(VI) pentahydride. However, whether the complex contains five equivalent hydride ligands or inequivalent hydrides in rapid exchange remains unknown. To remedy this problem, the polyhydride is subjected to ab initio calculations to determine its structure, vibrational spectrum and rearrangement mechanism.

The rotational frequency of the H2 ligand in trans-(Os(H..H)X(L)2)+, where L = phenyl, X = Cl, Br and L = ethyl, X = Cl, is near the Larmor frequency. The complex is octahedral and has an elongated dihydrogen ligand in solid-state and solution. The distance between the hydrogen atoms, d(sub HH), is calculated from coupling constant, J(H,D). The T1(min) value gives the limits for d(sub HH). The acidic character of these complexes is a function of the nature of X ligand.

A study has been conducted to examine the products of osmium-catalyzed asymmetric dihydroxylation reactions. DFT was used to calculate the metallaoxetane ligand complexes. The calculations were compared to those of their corresponding osmium and ruthenium complexes. The results revealed an unusually high level of enantioselectivity. An electrostatic dipole-dipole interaction between the osmaoxetane and the ester moiety of the ligand was also observed.

The monohydride OsHCL(CO)(PiPr3)2 reacts with HCL to form dihydrogen OsCl2(eta squared-H2)(CO)(PiPr3)2. A study of reactivity between hydridoosmium compounds and alkynes shows that specific organometallic compounds can be prepared by reacting these compounds with terminal alkynes when the right number of hydrido ligands and electronic properties of starting material are chosen. New carbene derivatives are produced in the reactions between OsCl2(eta squared-H2)(CO)(PiPr3)2 and terminal alkynes. X-ray crystallography has been used to determine the structure of the carbene derivatives.

Proton and NMR studies of OsH2X2L2 (X = halide and L = PiPr3), synthesized by a halide exchange reaction, show that these molecules exist as two interconverting isomers in solution. One isomer has a C2 symmetry and results from steric interactions between phosphine and chlorine ligands and bonding preference of the chlorine ligands. Replacement of chloride by hydride and slight geometric distortions link the symmetric and nonsymmetric structures.

Phenylene spacers connect the Ru(tpy)(sub 2)(super 2+) complex, where tpy is 2,2':6', 2'-terpyridine, and Os(tpy)(sub 2)(super 2+) binding blocks to produce rigid rod-like Ru(II)/Os(II) terpyridine-type complexes. The two building units exhibit slightly different absorption spectra in the dinuclear compounds. Electrochemical measurements of redox potentials reveal metal-metal and ligand-ligand interactions. Time-resolved luminescence spectroscopic analysis of energy transfer reactions shows that electron exchange through the phenylene linker facilitates energy transfer from the Ru-unit to the Os-unit.

Quantum chemical calculations which use effective core potentials calculate spin-spin coupling constants and binding energies of stretched osmium(II) molecular hydrogen complexes. The results agree with experimental data. Population and complex binding energy analyses examine the nature of Os-H2 bonding. The influence of the trans ligand on the properties of the complexes are related to the spectrochemical constant.

X-ray and neutron diffraction, which were used to determine the structure of certain osmium compounds, revealed a cation in the compound having a low J(H-D) value of 9.0 Hertz. The acetate and the H2 ligands of the structure were found at positions on opposite sides of the OsN4 plane and induced an octahedral coordination. The compound's ethylenediamine ligands demonstrated a trans arrangement.

A study was done on the syntheses, absorption spectra, luminescence properties and electrochemical behavior of supramolecular Ru and/or Os complexes of tris(bipyridine) bridging ligands. All the complexes display very intense, ligand centered absorption bands in the UV region and moderately intense metal-to-ligand charge-transfer bands in the visible. Luminescence data show that electronic energy transfer takes place from the Ru-based to the Os-based components.

The stereochemical nonrigidity of the mu3-benzene/pi-alkene complexes (Os3(CO)8(eta2-CH2CHR)(mu3:eta2:eta2:eta2-C6H6)), where R = H, Me, Ph and (super t)Bu, is investigated using one- and two-dimensional NMR experiments in solution. Of the five processes detected by NMR for the complex with R = H, four are in the solid state. 13C(1H) two-dimensional exchange spectroscopy illustrates a 1,2 ring-hopping motion that alters the nuclei in the face-capping benzene ligands. On the other hand, the pi-bound olefins are fluxional.

Trinuclear metal complexes with benzene in a the face-capping bonding mode mu3:eta2:eta2:eta2-C6H6 are synthesized. The ligand in the triosmium complex Os3(CO)9(mu3:eta2:eta2:eta2-C6H6) is generated from the sequential H-abstraction of the complex (mu-H)Os3(CO)9(mu3-eta2:eta2:eta2-C6H7). The triphenylmethyl cation eliminates the hydride from the dienyl ring in the complex to give ((mu-H)Os3(CO)9(mu3-eta2:eta2:eta2-C6H6))1+. The triosmium complex crystallizes in the space group Im, with the benzene-capped triosmium cluster having a C3v symmetry.

The phenol-dienone equilibrium for a series of eta2-phenol complexes of pentaamineosmium(II) was examined to investigate the degree of dearomatization in these systems. The complexes with the form (Os(NH3)5(2, 3-eta2-phenol))2+ were characterized by 1H NMR spectroscopy and compared with an anisole derivative. Protonation and deprotonation were favored at the ring face opposite the metal accounting for the stereoselectivity of the tautomerization processes.

The isostructural compounds Y4Br4Os and Er4Br4Os were synthesized and characterized by single-crystal X-ray crystallography. The structures consisted of osmium-centered square antiprisms of the host metals with the bromine atoms capping the four adjoining metal triangles. Magnetic susceptibility data for Er4Br4Os followed the Curie-Weiss law while the yttrium analogue proposed a Pauli magnetism.

Evidence for stereoelectronic control in the assymetric osmium-catalyzed cis-dihydroxylation of the sterically unbiased 3,3-diarylcyclopentenes is presented. The reactions proceed at room temperature in an 8:1 acetone/water solvent system, with trimethylamine N-oxide as the final oxidant. 2D-NOE 1H NMR and 13C NMR spectroscopies and X-ray crystallographic analysis. The selectivities may be explained by the Cieplack postulate of stereoelectronic control.

An electrochemical investigation of 10e (Os2Cl8)2- is undertaken. Voltammetry of (Os2Cl8)2- at 235 degrees K in CH2Cl2 and butyronitrile reveals a reversible one-electron oxidation and a second reversible oxidation at extreme potential. Spectroelectrochemical characterization of the anion is performed via a cryostatic optically transparent thin-layer electrode cell. Results show that the anion approaches the eclipsed conformation and the presence of an energy gap between the delta and delta* orbitals.

A remarkably diverse reactivity between the series of nitrido complexes at room temperature is reported. The products depend upon the electron content of the starting nitrido complexes.

An efficient preparative protocol of 3-D networked osmium nanomaterial is shown by utilizing the capillary action of mesopores of MCM-48 toward molten organometallic precursors as well as high catalytic activity and excellent reusability in certain oxidation reactions. Other 3-D networked nanostructured metals could also be prepared by a similar method.

New divalent osmium complexes that feature strong red metal-to-ligand-charge-transfer (MLCT) phosphorescence and electrophosphorescence are reported. The best external quantum efficiency of 2.2% is achieved when PVN:PBD is used as the host matrix.

Research is presented concerning the use of hydrolysis for the abstraction of nitrogen from nitriles by osmium(IV) complexes which results in the formation of an osmium(VI) nitrido compound.

A halogen-atom abstraction involving a silylene-mediated redox reaction of a metal center is a new reaction type for transition-metal silylene complexes.

Research is presented describing the use of hydrogen peroxide, as a selective oxidant, in the dihydroxylation of olefins by using nu-methylmorpholine and flavin as cocatalysts. The main catalyst is osmium.

Studies of electron transport in conjugated metallopolymers in which metal sites are in direct electronic communication with a conjugated organic backbone offer insight into long-range electron-transfer mechanisms. A new benzimidazole based conjugated metallopolymer, in which pairs of coordinated Os(III/II) sites interact strongly across a pyrazine bridge, is presented. There is also a much weaker interaction between adjacent binuclear centers through the much longer bibenzimidazole bridge.

The paramagnetic d4 oxo complex trans-[OsCl(O)(dcpe)2]+ was observed and characterized in solution. It was found that this compound was generally highly reactive and unstable toward disproportionation. It also promoted the four-electron reduction of O2 with the intermediacy of [OsCl(n2-O2)(dcpe)2]+ wherein two bioelectronic processes were involved including the oxidation from [OsCl(dcpe)2]+ to [OsCl(O)(dcpe)2]+ and the oxidation of PPh3 or I-.

An experiment was undertaken to explain the mechanism of self-assembly of the neutral, discrete and octahedral osmium(VI) ester-bridged macrocylic box. Self-assembly was considered as an effective technique for the development of supramolecular species or receptors having appropriate subunits bound by noncovalent interactions. Findings indicated that the self-assembly mechanism supplemented the chemistry of discrete molecular and supramolecular assemblies mediated by the metal-ligand coordinate bond.

A study was conducted on the direct attack mechanism of phenyl anion at an electrophilic osmium-nitrido ligand. The findings indicate that phenyl anion is delivered directly to the electrophilic ligand by PhMgCl and related reagents without the intermediacy of osmium aryl complexes or free phenyl radicals. Thus, substrates do not have to coordinate to a metal center prior to oxidation by combining with a multiply bonded ligand.

The energy transfer in a rodlike dinuclear complex, (ttp)Ru(tpy-ph-bco-ph-tpy)Os(ttp)4+ (RuOs) was found to be unaffected both by temperature and state of the solvent. In this species, the coordination environment of both metals is composed of tpy-type tridentate ligands and the spacer is a ph-bco-ph fragment. The complex has a rigid, linear geometry and the metal-to-metal distance is fixed at 2.4 nm.

The structures and energetics of the osmium-catalyzed asymmetric dihydroxylation of olefins, for the transition states and products for the (2 + 2) and (2 + 3) cycloaddition steps without base and with one and two NH3 ligands as model bases, were theoretically determined. Experimental structures for some related cyclic ether intermediates were in good agreement with the theoretical values.

The addition of a bromonium ion reagent to metal carbonyl cluster compounds readily afforded triruthenium and triosmium dodecacarbonyl ions. Structural characterization of these compounds indicated that the ruthenium derivative can be considered as an organometallic analogue of the bromonium ion of ethylene, while the osmium cation can be considered as the corresponding ion of cyclopropane.

A novel method involving a combination of osmium-based asymmetric dehydroxylation and rhenium-based oxidative cyclization helps prepare polyoxygenated aliphatic structures such as (+)-solamin, (+)-reticulatacin, bullatenin and trilobacin. The reaction involves an oxidation step which is very selective when Re(VII) is used, and two cyclization stages. The first cyclization being much faster than the second gives the advantage of stopping the reaction after the first stage. This enables the preparation of many useful intermediates.

Reduction of Os(III)(NH3)4(CF3SO3)3 in a medium of cyclic ether produces a dihydrogen complex of tetraammineosmium(II) having carbene as a coligand. NMR experiments reveal the cis position of the carbene coligand and confirm the presence of eta2-H2 ligand. The dihydrogen complex undergoes a slow decomposition in D2O or CD3OD, generating paramagnetic species.

The reaction of hexabromoosmic acid with 1.5 equiv of C5Me5H under refluxing conditions in methanol or t-butyl alcohols produces the osmium II dimer (C5Me5)2Os2Br4. Reaction of (C5Me5)2Os2Br4 with LiAlH4, followed by methanolysis, produces the osmium(VI) hydride (C5Me5)OsH5 and the dinuclear tetrahydride (C5Me5)2Os2H4. X-ray studies of the osmium III dimer suggest that two bromide ligands bridge the two osmium centers. Various spectroscopic studies help characterize the diosmium complex and osmium (VI) hydride complex.

An aldol condensation reaction between acetone and a 4,5-eta(2)-pyrrole precursor yields a 3-vinylpyrrole complex of osmium(II) by a reaction involving deprotonation of an azafulvenium intermediate. 1H and 13C NMR methods help characterize the complex and cyclic voltammetric studies of a pseudoreversible Os(III/II) reduction potential reveal that the metal is bound to the pyrrole ring. A stereoselective Diels-Alder reaction of the complex yields a highly-substituted tetrahydroindole nucleus.

Os(IV) and Os(V) hydrazido2- complexes are prepared from Os(IV) imido intermediate, which is a trapped product in the presence of secondary amines. The electrochemical property of this Os(IV) complex is relevant to the N-N bond cleavage in nitrogenase enzyme function. The complexes are relatively electron deficient and rigidly coordinated.

Chemical oxidation of eta-2-H2 complexes of osmium(II) amines results in monohydrido complexes of Os(IV), and the metal can bear six ligands besides H-. Oxidation in methanol of (Os(NH3)5(eta-2-H2))2+ by FeCp2(CF3SO3) does not involve the release of H2 or NH3.

X-ray and kinetic studies probe into the origin of high enantioselectivity in the Sharpless asymmetric dihydroxylation of chiral olefins. Notwithstanding contrary evidence from the crystal structure of an OsO4-ligand complex, kinetic experiments strongly suggest a mechanism in which the stereofacial attack proceeds through a mu-oxo-bridged bisosmium(VIII) species where the dihydroquinine ether ligand is bonded to the hexacoordinate Os via the bridgehead nitrogen of its bicycloazaoctane arms.

The synthesis of a stable ethene-ethyne metal complex from the eta2-dihydrogen osmium(II) complex is described. Ethylene was bubbled through a solution of the osmium(II) complex in a nitrogen atmosphereand subsequently heated under N2 at 50 degrees centigrade. Nuclear magnetic resonance spectroscopy was then performed to analyze the decomposition of the compound. Results reveal that the reaction of the eta2-dihydrogen osmium(II) complex with ethyne led to the formation of a trans-bis(ethyne) complex.

The regiochemistry of the bisosmylation of C60 and the description of difunctionalized C60 frameworks is presented. The untethered bisosmylation of C60 yields 54 regioisomers, but the addition of the first OsO4 decreases the number to 24. Five of these regioisomers are considered and the possibility that the second OsO4 adds to a 6,6 ring fusion to give eight regioisomers is advanced. The C60(OsO4(py)2)2 regioisomers are transformed into their 4-tert-butylpyridine analogs and then analyzed by 1D NMR spectroscopy.

The synthesis of osmahexatriene provides more insight into the chemistry of metal carbene complexes. Heating the triflate salt of the osmacyclopentatriene complex Os(en)2(C4Me4) (en = ethylenediamine) in tetrabutylamine yields, upon evaporation of t-BuNH2, a new complex in which the cyclic carbene ligand has isomerized into a conjugated hexatriene. Treatment with hydrochloric acid yields a crystallizable form of the complex. The reaction mechanism involves deprotonation of an alpha-methyl moiety in a 1,2-hydrogen shift that eventually protonates the Os-C single bond.

The preparation and structures of the new metallacyclopentatrienes cis-(Os(C4Me4)(en)2)2+ and cis-(Os(C10H14)(en)2)2+, where en = ethylenediamine, are presented. The first compound is prepared from the reaction of an acetone solution of trans-(Os(en)2(eta2-H2)(H2O))(CF3SO3)2 with 2-butyne, heated at 59 degrees C. The 1H NMR spectrum of the complex reveals that the planar symmetry has been transformed to C2. Meanwhile, the second complex is formed via the intramolecular alkyne cyclization of cis-(Os(C10H14)(en)2)(CF3SO3)2 when treated with 2,8-decadiyne.

The complexes Os3(CO)11(mu-CNCF3)2 (1) and Os3(CO)10(mu-CNCF3)2 (2) were synthesized and characterized by single-crystal X-ray diffraction and IR and 19F NMR spectroscopy. The complexes were obtained from the reaction of Os3(CO)11(NCMe) with excess CNCF3 in CH2Cl2. Displacement of the NCMe ligand of Os3(CO)11(NCMe) followed by the addition of two molecules of CNCF3 led to the formation of 1. Compound 2 was obtained from decarbonylation of compound 1.

The preparation of osmium (VI) complex TpOs(N)Cl2 from K[Os(N)O3] and KTp in aqueous ethanolic HCl is described.

A study was undertaken to analyze experimental data for a series of mixed-valence mu-N2 osmium (Os) complexes having properties similar with both localization and delocalization although they were at localized OsIII-OsII oxidation states. It was established that delocalized oxidation states exist in known mixed-valence mu-N2 complexes. Results revealed that localized-to-delocalized transition was induced by electronic coupling across the bridge and that the appearance of a vibrational marker and molecular structure indicated residual localization.

Research was conducted to examine the hydrogen bonding between the unsaturated 16-electron complex OsHCl(CO)(P(super t)Bu2Me2) and a sufficiently strong hydrogen bond donor. The objectives were to find the preferred accepting site and to determine the extent that the electronic structure of the complex can be modified through intermolecular hydrogen bonding. Results demonstrate the formation of a 1:1 adduct between OsHCl(CO)(P(super t)Bu2Me2) and (CF3)2(CHOH) in solution, bound exclusively through an (O)H***Cl(Os) hydrogen bond.

The synthesis and characterization of iron(II), ruthenium(II) and osmium(II) carbonyl derivatives of (1-methylimidazole)(5,10,15,20-tetraphenylporphyrinate) were conducted using single-crystal X-ray diffraction methods. This permits a comparative study of the six CO complexes that can be made from TPP, Fe/Ru/Os, 1-methylimidazole and pyridine. Results suggest an rms error between theory and experiment of 0.20 MHz for values that range from (+)1.0 to (1)0.40 MHz.