Addition of dimethylphenylphosphine at bridging vinyl,acetylene and phenylacetylide ligands in triosmium clusters

PMe₂Ph readily adds at carbon in the compounds HO_S3 (CHCH₂)(CO)₁₀, HO_S3(CCPh)(CO)₁₀ and O_S3 (CHCH)(CO)₁₀ to give zwitterionic 1:1 adducts; the addition to the vinyl compound is reversible and further reaction leads to O_S3 (CO)₁₀ (PMe₂Ph)₂ with ethylene displacement.     

Hexa- and triosmium carbonyl clusters bearing bridging dppm and capping sulfido ligands

Treatment of [Os₃(CO)₇(μ₃-S)₂(μ-dppm)] (1) with Me₃NO in toluene at 80 °C affords the trinuclear cluster [Os₃(CO)₆(μ₃-S)₂(NMe₃)(μ-dppm)] (2) and the hexanuclear cluster [Os₆(CO)₁₂(μ₃-S)₄(μ-dppm)₂] (3) in 30% and 51% yields, respectively. The reaction of 1 with [Os₃(CO)₁₀(MeCN)₂] in refluxing benzene at 80 °C gives the hexanuclear cluster [Os₆(CO)₁₄(μ₃-S)₂(μ-dppm)] (4) in 15% yield. Compound 2 reacts with CO, PPh₃ and P(OMe)₃ at room temperature to give 1, [Os₃(CO)₆(μ₃-S)₂(μ-dppm)(PPh₃)] (5) and [Os₃(CO)₆(μ₃-S)₂(μ-dppm){P(OMe)₃}] (6), respectively; in high yields indicating that the NMe₃ ligand is weakly bound. Compound 1 reacts with PPh₃ in presence of Me₃NO to afford 5, 2 and 3 in 53%, 6% and 18% yields, respectively, whereas with P(OMe)₃1 gives only 6 in 84% yield. Compound 3 reacts with CO at 98 °C to regenerate 1 by the cleavage of the three unsupported osmium-osmium bonds. The molecular structures of 4 and 6 have been unambiguously determined by single crystal X-ray diffraction studies. The hexanuclear compound 3 appears to be a64-electron butterfly core with four triply bridging sulfido ligands and two bridging dppm ligands based on the spectroscopic and analytical data. The metal core of 4 can be described as a central tetrahedral array capped on two faces with two additional osmium atoms. The triply bridging sulfido ligands face cap the two tetrahedral arrays formed by metal capping of the two faces of the central tetrahedron. The dppm ligand bridges one edge of one of the external tetrahedral arrays. Compounds 5 and 6 are formed by the displacement of equatorial carbonyl group of 1 by a PPh₃ and P(OMe)₃ ligand respectively and their structures are comparable to that of 1.     

Synthesis, structures and reactivity of triosmium clusters containing terminal pyrazines, bridging hydroxy and methoxycarbonyl ligands

Four triosmium carbonyl clusters bearing terminal pyrazines, bridging hydroxy and methoxycarbonyl ligands of general formula [Os₃(CO)₉(μ-OH)(μ-OMeCO)L] (1, L = pyrazine; 2, L = 2-methylpyrazine; 3, L = 2,3-dimethylpyrazine; 4, L = 2,3,5-trimethylpyrazine) were synthesized by the reactions of [Os₃(CO)₁₂] with the corresponding pyrazine derivatives and water in the presence of a methanolic solution of Me₃NO in moderate yields. Compounds [Os₃(CO)₉(μ-OH)(μ-OMeCO)L] react with a series of two electron donor ligands, L′ at ambient temperature to give [Os₃(CO)₉(μ-OH)(μ-OMeCO)L′] (5, L′ = PPh₃; 6, L′ = P(OMe)₃; 7, L′ = ^tBuNC; 8, L′ = C₅H₅N) in good yields by the displacement of the pyrazine ligands. This implies that the pyrazine ligands in 1–4 are relatively labile. Compounds 2, 3, 4, and 8 were characterized by single crystal X-ray diffraction analyses. All the four compounds possess two metal–metal bonds and a non-bonded separation of two osmium atoms defined by Os(1)Os(3), which are simultaneously bridged by OH and MeOCO ligands and a heterocyclic ligand is terminally coordinated to one of the two non-bonded osmium atoms.     

Some nucleophilic additions to allyl vinyl sulfone

Russian Chemical Bulletin -     

Computational studies of nucleophilic attack and protonation of electron-deficient benzoheterocycle triosmium clusters

The density functional theory method has been applied to gain insights into the regioselectivity of nucleophilic attack and protonation of electron-deficient benzoheterocycle triosmium clusters. We report our computational results on the reaction of the green 46-electron triosmium clusters Os3(CO)(9)(mu3-eta2-(LH))(mu-H) (L = benzoxazole, 1a; benzothiazole, 1b; dihydroquinoline, 1c; 1,3-dehydroindoline, 1d; 4H-3,1-benzoxazine, 1e) with hydride (H-) and proton (H+) in order to elucidate factors affecting the observed differences in the structure of the kinetic products of these reactions. Transition-state calculations for the interconversion of the anionic tautomers resulting from H- attack on the clusters 1a-e show that the activation energies of these anionic clusters are considerably lower than the previously reported barriers for related neutral clusters. Calculations also reveal that the structures of the kinetic products resulting from sequential H-/H+ attack are determined by the protonation process.     

The reaction of triosmium and -ruthenium clusters with bifunctional ligands

The reaction of [Os₃(CO)₁₀(μ-H)(μ-OH)], 1, or [Os₃(CO)₁₀(NCCH₃)₂], 2, with bifunctional ligands carrying -OH, -SH and -COOH groups affords, as the major product, clusters of the general formula [Os₃(CO)₁₀(μ-H)(μ-E^?E′H)] (E, E′ = O, S or COO). In some cases, a minor product with general formula [Os₃(CO)₁₀(μ-H)(μ,μ-E^?E′)Os₃(CO)₁₀(μ-H)] was also obtained. With Ru₃(CO)₁₂, 3b, only the first type of products is obtained. The structures of eight of the compounds have also been determined by single crystal X-ray crystallography.     

Triosmium clusters with bridging terpenic thioureato-like ligands

The reaction of acetone-4-(2-methoxy-phenyl)thiosemicarbazone with triosmium cluster Os₃(CO)₁₁(NCMe) results in the formation of the cluster with the μ₂ chelate-bridging ligand coordinated by S and N¹ atoms, which was studied by X-ray diffraction analysis. Reaction of (3aR, 3bR, 4aR, 5aS)-5a-hydroxy-3,4,4-trimethyl-3a,3b,4,4a,5,5a-hexahydrocyclopropa[3, 4]cyclopenta[1,2-c]pyrazole-1-carbothioic acid amide with Os₃(CO)₁₁(NCMe) gives rise to the complex with the bridging ligand coordinated by sulphur atom. Further transformation of the complex in hot benzene results in tautomeric rearrangement of the organic ligand and the cleavage of the pyrazolinol cycle to form an open chain tautomer. Unusual silica gel induced oxidative cleavage of the cyclopropane ring in the open chain derivative and epoxidation of cycloalcane C-C bond are observed on the air.     

Triruthenium and triosmium carbonyl clusters containing chiral bidentate NHC-thiolate ligands derived from levamisole

The trinuclear complexes [M3(mu-Cl)(mu-S approximately CH)(CO)9] (M=Ru, Os; S approximately CH=1-ethylenethiolate-3-H-4-(S)-phenylimidazolin-2-ylidene) and [M3(mu-H)(mu-S approximately CMe)(CO)9] (M=Ru, Os; S approximately CMe=1-ethylenethiolate-3-methyl-4-(S)-phenylimidazolin-2-ylidene) have been prepared by treating [Ru3(CO)12] and [Os3(CO)10(MeCN)2] with levamisolium chloride or [M3(mu-H)(CO)11]- with methyl levamisolium triflate, respectively. The chiral N-heterocyclic carbene-thiolate ligands S approximately CH and S approximately CMe arise from the oxidative addition of the C-S bond of levamisolium or methyl levamisolium cations to anionic trinuclear clusters.     

Iron-promoted nucleophilic additions to diimine-type ligands: a synthetic and structural study

We report here three examples of the reactivity of protic nucleophiles with diimine-type ligands in the presence of Fe(II) salts. In the first case, the iron-promoted alcoholysis reaction of one nitrile group of the ligand 2,3-dicyano-5,6-bis(2-pyridyl)-pyrazine (L1) permitted the isolation of an stable E-imido-ester, [Fe(L1')(2)](CF(3)SO(3))(2) (1), which has been characterized by spectroscopic studies (IR, ES-MS, M?ssbauer), elemental analysis, and crystallographically. Compound 1 consists of mononuclear octahedrally coordinated Fe(II) complexes where the Fe(II) ion is in its low-spin state. The iron-mediated nucleophilic attack of water to the asymmetric ligand 2,3-bis(2-pyridyl)pyrido[3,4-b]pyrazine (L2) has also been studied. In this context, the crystal structures of two hydration-oxidation Fe(III) products, [Fe(L2')(2)](ClO(4))(3).3CH(3)CN (2) and trans-[FeL2"Cl(2)] (3), are described. Compounds 2 and 3 are both mononuclear Fe(III) complexes where the metals occupy octahedral positions. In principle, L2 is expected to coordinate to metal ions through its bipyridine-type units to form a five-membered ring; however, this is not the case in compounds 2 and 3. In 2, the ligand coordinates through its pyridines and through the hydroxyl group attached to the pyrazine imino carbon after hydration, that is, in an N,O,N tridentate manner. In compound 3, the ligand has suffered further transformations leading to a very stable diamido complex. In this case, the metal ion achieves its octahedral geometry by means of two pyridines, two amido N atoms, and two axial chlorine atoms. Magnetic susceptibility measurements confirmed the spin state of these two Fe(III) species: compounds 2 and 3 are low-spin and high-spin, respectively.     

Oxidation of bridging groups by carboxylate coordinated ligands in palladium clusters

Thermolysis of tetranuclear palladium clusters Pd₄(-Q)₄ Pd₄(-Q)₄(-O₂CR)₄ (Q=CPh₂ or CO;R=Me, CMe₃, Ph, CH₂Cl or CF₃) has been found to involve innersphere oxidation of carbene or carbonyl ligands during which an oxygen atom transfer occurs from the carboxylate group to the carbene or carbonyl ligand. The thermolysis of the carbonyl clusters gives rise to the products of CO₂ insertion into the C–H bond of benzene or toluene used as solvents forming benzoic acid from benzene and a mixture of phenylacetic and toluic acids from toluene. The reaction of [Pd(OAc)₂(PPh₃)]₂ with HCO₂H includes the transfer of an O atom from formate ligand to the P atom and cleavage of the P-Ph bond accompanied by transfer of the Ph group from PPh₃ ligand to the palladium atom. The structure of the complex formed, [Pd(-O₂PPh₂)(C₆H₅)(PPh₃)]₂, has been resolved by X-ray analysis.     

Luminescent hydrido-carbonyl clusters of rhenium containing bridging 1,2-diazine ligands

The reaction of the electronically unsaturated (56 valence electrons, ve) tetrahedral cluster [Re4(mu3-H)4(CO)12] (1) with pyridazine (pydz) gives as the main initial product the tetranuclear cluster [Re4(mu-H)4(mu-pydz)(pydz)2(CO)12] (2a), with 64 ve and four hydrogen-bridged metal-metal interactions, with a spiked-triangle geometry. One of the three pydz ligands bridges, in a cis configuration, the cluster edge opposite to the vertex bearing the spike, as indicated by the X-ray single-crystal analysis. This species slowly decomposes, affording the dinuclear unsaturated (32 ve) complex [Re2(mu-H)2(mu-pydz)(CO)6] (3a) and two isomers of the tetranuclear cluster [Re4(mu-H)4(mu-pydz)2(CO)12] (64 ve), sharing an unusual square cluster geometry and differing in the trans (major, 85%, 4a) or cis (4a') configuration of the bridging pydz ligands. The structures of 3a and 4a have been ascertained by X-ray analysis, while the characterization of 4a' was hampered by its instability (slowly transforming into 3a in THF solution). Both the dimer and the square cluster 4a are also formed directly (and quickly) from 1, being present in solution since the beginning of the reaction. Cluster 4a is the main final reaction product. The reaction with phthalazine follows a similar course, with some differences in the relative amount of the final products 3b and 4b. Most of the novel complexes are able to emit light in solution at room temperature, and photophysical measurements were performed in CH2Cl2 solution on the main stable reaction products (i.e., the dinuclear species 3a and 3b and the trans square clusters 4a and 4b). The emission was in the range of 580-645 nm, from MLCT excited states, with lifetimes on the order of a hundred nanoseconds (50-473 ns). The quantum yields were 1 order of magnitude higher for the squares (1.7 and 1.3% for 4a and 4b, respectively, in CH2Cl2) than for the dinuclear complexes ( approximately 0.1%). In the case of 4a, a blue shift and an increase of the emission intensity were observed upon decreasing the solvent polarity.     

Synthesis of optically active hydridocarbonyl triosmium clusters with terpene derivatives as ligands. Molecular structure and absolute configuration of a cluster with a bridging dihydroimidazole ligand

Reactions of the triosmium clusters Os₃(CO)₁₁(NCMe) (1) and Os₃(CO)₁₀(NCMe)₂ (2) with terpene derivatives,viz., (1S,3S,4R,6R)-3-(N,N-dimethylamino)-4-amino-3,7,7-trimethylbicyclo [4.1.0]heptane (3). (3bR,4aR)-(3,4,4-trimethyl-3b,4,4a,5-tetrahydrocyclopropa [3,4]cyclopenta[1,2-c]pyrazol-1-yl)acetic acid (4a), and (3bR,4aR)-3-(3,4,4-trimethyl-3b, 4,4a,5-tetrahydrocyclopropa[3,4]cyclopenta[1,2-c]pyrazol-1-yl)propionic acid (4b), were studied. A complex with the terminally coordinated ligand is formed in the first step of the reaction of diamine3 with cluster1. Heating of the resulting complex is accompanied by activation of one of the methyl groups of the ligand to form diastereomers with the bridging tricyclic dihydroimidazole ligand. One of these diastereomers was studied by X-ray diffraction analysis and its absolute configuration was established. Pyrazolycarboxylic acids react with cluster2 as simple organic acids and are coordinated as a bridge at the Os—Os bond through the carboxyl group. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1447–1454, August, 2000.     

A discrete dimer of coordination clusters connected through additional bridging ligands

The combination of directionality and unsaturated metal sites in bowl-shaped coordination clusters [Ag(4)L(3)(SbF(6))](3+){L = 2,4,6-tris(diphenylphosphino)triazine} results in the formation of discrete dimers on reaction with additional bridging ligands.     

Studies on cage-type tetranuclear metal clusters with ferrocenylphosphonate ligands

Reaction of FcCH(2)PO(3)H(2) [Fc=(eta(5)-C(5)H(5))Fe(eta(5)-C(5)H(4))] (H(2)FMPA) and 1,10-phenanthroline (phen) with Cd(OAc)(2).2 H(2)O or ZnSO(4).7 H(2)O in methanol in the presence of triethylamine resulted in the formation of two new ferrocenylphosphonate metal-cage complexes [M(4)(fmpa)(4)(phen)(4)] 7 CH(3)OH (M=Cd 1, M=Zn 2). Both structures contain two kinds of isomeric tetranuclear metal phosphonate cages, which are linked to one another by pi-pi interactions between the phen molecules. In 1, the Cd1, Cd3, and Cd4 atoms are all pentacoordinate, while the Cd2 atom is coordinated by four oxygen atoms from three phosphonate ligands and two nitrogen atoms from the chelating phen in a distorted octahedral geometry. Four Cd atoms from each unit are interconnected through bridging phosphonate ligands with different coordination modes, such as 5.221, 4.211, and 2.11 (Harris notation), yielding a {Cd(4)} cage. In 2, each Zn atom is coordinated by three oxygen atoms from three phosphonate ligands and two nitrogen atoms from phen, leading to a distorted square-pyramidal geometry. The four Zn atoms of each isomeric unit are also interconnected through four bridging phosphonate ligands to yield a {Zn(4)} cage. Fluorescent studies indicate that ligand-to-ligand charge-transfer photoluminescence is observed for 1, while the emission bands of 2 can be assigned to an admixture of ligand-to-ligand and metal-to-ligand charge transfer. Solution-state differential pulse voltammetry indicates that the half-wave potentials of the ferrocenyl moieties in 1 and 2 have different deviations relative to the relevant H(2)FMPA ligand. This may be because the highest occupied molecular orbital (HOMO) in 1 is located in the FMPA(2-) groups, while in 2 the HOMO is located in the phen and Zn(II) groups, so the Fe(II) centers in complex 1 are more easily oxidized to Fe(III) centers than those of 2. The third-order nonlinear optical (NLO) measurements show that both 1 and 2 exhibit strong third-order NLO self-focusing effects; hence, they are promising candidates for NLO materials. By calculating the component of the lowest unoccupied molecular orbitals of 1 and 2, we confirmed that the co-planar phen rings control their optical nonlinearity, while the H(2)FMPA ligands and metal ions have only a weak influence on their NLO properties.     

Stereoselectivity in nucleophilic additions to 3-azidoalkanals

The stereoselectivity of nucleophilic additions to 3-azidoalkanals was investigated. Non-chelating, BF(3)·OEt(2)-mediated Sakurai addition to 3-azidoalkanals afforded 1,3-anti products, whereas use of a chelating Lewis acid, TiCl(4), resulted in 1,3-syn products with moderate selectivity. A boat-like chelation structure of the 3-azidoalkanal with the Lewis acid is proposed to be consistent with the 1,3-syn selectivity of the reactions. Mukaiyama aldol addition to 3-azidohexanal generated 1,3-anti products regardless of the chelating ability of the Lewis acid.     

Oxidative addition of 2-formyl-furan and related pyrrole and thiophene compounds at triosmium clusters

The bridging acyl complexes [Os₃H(μ-COC₄H₃X)(CO)₁₀] (X = NH, O, or S) have been prepared by oxidative addition of the 2-formyl derivatives of pyrrole, furan, or thiophene (C₄H₃XCHO) at [Os₃(CO)₁₀(MeCN)₂] with cleavage of the aldehydic CH bonds. On heating double decarbonylation of the acyl complexes occurs, to afford high yields of the compounds [Os₃H₂(CO)₉(μ₃-C₄H₂X)], reported previously for X = NH or O. For X = NH, two isomers with this formulation were characterised by ¹H NMR and IR data; the one containing the μ₃-2,3-C₄H₃N ligand isomerises to one containing μ₃-1,2-C₄H₃N. The direct reaction of pyrrole with [Os₃(CO)₁₂] has been re-examined at lower temperatures than before, and observed to give new products, including [Os₃H(CO)₁₀(C₄H₄N)], which contains a bridging non-aromatic tautomeric form of pyrrole. The ability of Os₃ clusters to stabilize non-aromatic tautomers of aromatic ligands is discussed.     

Dynamic processes in hydrido-carbonyl trirhenium clusters containing bridging nitrogen heterocyclic ligands: An NMR investigation

The dynamic processes occurring in the triangular clusters [Re₃(μ-H)₃(μ-pz-κN¹:κN²)(CO)₁₀]⁻ (pz = pyrazolate, 4), [Re₃(μ-H)₂(μ-pydz-κN¹:κN²)(CO)₁₀] ⁻ (pydz = pyridazine, 5) and [Re₃(μ-H)₃(μ-pydz-κN¹:κN²)(CO)₁₀] (6), have been investigated by ¹H and ¹³C NMR. In the pyrazolate derivative 4 the exchange (k ≈ 1 s⁻¹ at 320 K) between the two carbonyls in the trans-diaxial apical positions has been recognized, and its activation parameters, in C₂D₂Cl₄, have been determined (E_a = 68(3) kJ mol⁻¹). The exchange has been attributed to the rotation of the apical H₂Re(CO)₄ fragment with respect to the Re₂(μ-pz) basal fragment, a process analogous to that previously observed in the unsaturated dianion [Re₃(μ-H)₃(CO)₁₀] ²⁻ (2) and in the monoanion [Re₃(μ-H)₃(μ-NC₅H₄-κN¹:κC⁶)(CO)₁₀]⁻ (1), containing a bridging orthometallated pyridine ligand. The vertex rotation was not observed in the pyridazine derivatives 5 and 6. An explanation for this different behaviour is presented, based on the view of the fluxional clusters 1, 2 and 4 as adducts between the apical and basal moieties (π- or σ-complexes). The ΔG^#_312K value here measured in acetone for the σ-complex 4 (77 kJ mol⁻¹) is very similar to that previously determined for the other σ-complex 1 (ΔG^#_305K = 76 kJ mol^-1) and significantly higher than the values measured for the π-complex 2 (ΔG^#_260K = 60 kJ mol⁻¹). The di-hydrido derivative 5 shows a different much faster dynamic process, namely the hopping of one hydride between the two lateral edges, affording a pseudo C_s symmetry in the molecule. The process has been monitored by both ¹H and ¹³C analysis, affording quite similar activation parameters (E_a = 44(1) and 45(1) kJ mol⁻¹, respectively, in THF-d₈), that did not significantly change in CD₂Cl₂ solution, in agreement with an intramolecular process.     

Complexation and C-H bond activation of 1,5-cyclooctadiene on triosmium carbonyl clusters

Reaction of Os₃(CO)₁₀(NCMe)₂ and 1,5-cyclooctadiene (C₈H₁₂) affords the diene complex Os₃(CO)₁₀(η⁴-C₈H₁₂) (1) with the two alkene moieties coordinated to an equatorial and an axial positions of one osmium atom. Thermolysis of 1 in refluxing n-hexane results in a vinylic C-H bond activation to form (μ-H)Os₃(CO)₉(μ,η⁴-C₈H₁₁) (2) in good isolated yield. The crystal structures of 1 and 2 have been established by an X-ray diffraction study.