Ethylene polymerization by 3-oxa-pentamethylene bridged dinuclear metallocene (Ti, Zr)/MAO systems

Two hetero-atom containing bridged dinuclear metallocene complexes, (CpMCl₂)₂(C₅H₄CH₂CH₂OCH₂CH₂C₅H₄) [M = Ti (1), Zr (2)], have been synthesized by treating the disodium salt of the corresponding ligand (C₅H₅CH₂CH₂)₂O with two equivalents of CpTiCl₃ and CpZrCl₃ · DME, respectively, in THF at 0 °C and characterized by ¹H- and ¹³C-NMR, MS and IR spectroscopy. Homogenous ethylene polymerization by those complexes has been conducted systematically in the presence of methylaluminoxane (MAO). The influences of reaction parameters, such as [MAO]/[Cat] molar ratio, catalyst concentration, ethylene pressure, temperature and time, have been studied in detail. The catalytic activities of the dinuclear complexes 1 and 2 were higher than those of (MeCpTiCl₂)₂(C₅H₄CH₂C₆H₄CH₂C₅H₄) (3), (CpZrCl₂)₂(C₅H₄CH₂C₆H₄CH₂C₅H₄) (4) and the mononuclear metallocenes Cp₂TiCl₂ and Cp₂ZrCl₂, respectively. Complex 2 showed high catalytic activity at high temperature (50-100 °C) and high pressure (6 bar). The molecular weight distributions of polyethylene produced by 1 and 2 (MWD = 2.49 and 5.90) were broader than those using the corresponding mononuclear metallocenes (MWD = 2.05 and 2.15). The melting points of the polyethylene produced ranged from 129 to 133 °C, indicating a high linearity and a high crystallinity.     

New group 4 half sandwich complexes containing triethanolamine ligand for polyethylene

(η⁵-C₅Me₅)M(TEA) (M = Ti, 1; Zr, 2; Hf, 3; TEA = triethanolateamine) was prepared by the reaction of (η⁵-C₅Me₅)MCl₃ with triethanolamine in the presence of NEt₃. The polyethylene catalytic efficiency in terms of activity decreases in the order 1/MAO > 2/MAO ? 3/MAO. In addition, the molecular weight (M_v) and melting temperature (T_m) of all the resulting polyethylene obtained by 2/MAO show the range of M_v = 91,200-356,200 and T_m = 137.0-141.9 °C, respectively; however, 1/MAO and 3/MAO gave polyethylenes with lower molecular weight (M_v = 6800-78,700) and lower melting temperature (T_m = 125.9-136.7 °C). Furthermore, 1/MAO showed significant decrease in the catalytic activity with increasing polymerization temperature though 2/MAO and 3/MAO have no dependence on the polymerization temperature.     

Synthesis, characterization, and catalytic activities in syndiospecific polymerization of styrene for half-sandwich titanium complexes with non-Cp tridentate dianionic ligands MeN(CH2CR2O)2

New half-titanocenes, Cp^∗TiCl[(OCR₂CH₂)NMe(CH₂CR^′₂O)] [R,R′ = H (1), R,R′ = Me, H, (2), R,R′ = Me (3)], were prepared from Cp^∗TiCl₃ (4) with the corresponding alcohols in the presence of triethylamine. X-ray analysis shows that 1 has slightly distorted trigonal bipyramidal geometry around Ti. These complexes exhibited moderate catalytic activities for syndiospecific styrene polymerization in the presence of MAO and the activity increased in the order: 2 > 1 > 4 > 3 (at 50 °C), 1 > 2 > 4 > 3 (at 70 °C and 90 °C).     

Reactions of 2-pyridinethiolate cobalt(III) complexes with pyridinethiolate or benzenethiolate ligands

Four half-sandwich cobalt complexes, Cp^∗Co(2-PyS)₂ (2), Cp^∗Co(2-PyS)₂ · HI (3), Cp^∗Co(2-PyS) (4-PyS) (4), (Cp^∗Co)₂(μ-PhS)₂(μ-2-PyS)I (5) [Cp^∗ = pentamethylcyclopentadienyl, 2-PyS = 2-pyridinethiolate, 4-PyS = 4-pyridinethiolate, PhS = benzenethiolate] were successfully synthesized by the reactions of 2-pyridinethione, lithium 4-pyridinethiolate and lithium benzenethiolate with Cp^∗Co(2-PyS)I (1), respectively. Complexes 2 and 3 have the structures with two 2-pyridinethiolates ligands coordinated to the cobalt atom. Two different pyridinethiolates ligands can be identified in complex 4. The molecular structure of 5 consists of two Cp^∗-Co fragments, which are triply bridged by three sulfur atoms from different ligands. The molecular structures of 3 and 5 were determined by X-ray crystallographic analysis. All the complexes have been well characterized by elemental analysis, NMR and IR spectra.     

Syntheses, structures, and properties of phenyltrihydroborate complexes of zirconocene and titanocene

The phenyltrihydroborate complexes, Cp₂ZrCl{(μ-H)₂BHPh}, 1, and Cp₂Zr{(μ-H)₂BHPh}₂ · (1/2 toluene), 2, were prepared from the reactions of Cp₂ZrCl₂ with one and two moles of LiBH₃Ph. The Zr-H-B bonds in 2 are stable under vacuum at 100 °C for hours without significant decomposition. An inductive effect has been proposed for this strong interaction. This hydrogen bridge bond can be broken upon reacting with the Lewis base N(C₂H₅)₃ to produce (C₂H₅)₃N · BH₂Ph and the zirconium hydride compound Cp₂ZrH{(μ-H)₂BHPh}, 3. Compound 3 also can be prepared from the reaction of Cp₂ZrHCl with LiBH₃Ph. The reaction of 1 with the Lewis acid B(C₆F₅)₃ is solvent dependent, the metathesis product Cp₂ZrCl{(μ-H)₂B(C₆F₅)₂}, 4, was formed in the toluene solution, whereas the ionic complex [Cp₂ZrCl(OEt₂)][HB(C₆F₅)₃], 5, was isolated from the ether solution. The reaction of titanocene dichloride, Cp₂TiCl₂, with LiBH₃Ph produced a 17-electron, paramagnetic complex, Cp₂Ti{(μ-H)₂BHPh}, 6. Single crystal X-ray structures of 1, 2, 3, 4, 5, and 6 were also determined. A coplanar structure of the four bridge hydrogens in 2 was observed.     

From symmetrical to unsymmetrical bimetallic nickel complexes bearing aryl-linked iminopyridines; synthesis, structures and ethylene polymerisation studies

Both symmetrical and unsymmetrical tetramethylphenyl-linked iminopyridines, 1,4-{(2-C₅H₄N)RCN}₂-2,3,5,6-Me₄C₆ [R = H (L1a), Me (L1b)] and 1-{(2-C₅H₄N)HCN}-4-{(2-C₅H₄N)MeCN}-2,3,5,6-Me₄C₆ (L1c), have been prepared in good yield using straightforward condensation strategies. The molecular structures of L1a and L1c reveal the adjacent imino and pyridyl nitrogen atoms to adopt transoid configurations. Interaction of L1x with two equivalents of NiX₂ [NiX₂ = (DME)NiBr₂ (DME = 1,2-dimethoxyethane), NiCl₂] in n-BuOH at elevated temperature affords the paramagnetic bimetallic complexes, [(L1x)Ni₂X₄] [L1x = L1a, X = Br (1a); L1x = L1b, X = Br (1b); L1x = L1c, X = Br (1c); L1x = L1a, X = Cl (1d)] in moderate to good yield. Adduct formation results on treatment of bromide-containing 1a-1c with DMF (dimethylformamide) to yield dicationic [(L1x)Ni₂Br₂(DMF)₆]Br₂ [L1x = L1a (2a), L1b (2b), L1c (2c)], while with chloride-containing 1d the neutral species [(L1a)Ni₂Cl₄(DMF)₄] (3) is obtained. Activation of 1a-1d and 2c with excess methylaluminoxane (MAO) generates active ethylene polymerisation catalysts (1b/MAO > 1c/MAO > 1a/MAO ∼ 1d/MAO > 2c/MAO) affording mixtures of waxes and low molecular weight solid polyethylene. Multinuclear NMR and GC analysis of the waxy components reveal methyl branched materials that contain mostly internal unsaturation along with low levels of α-olefins. Broad molecular weight distributions are observed for all the polymers obtained, with that from 1b/MAO leading to the highest molecular weight. Single crystal X-ray diffraction studies have been performed on L1a, L1c, 2a-2c and 3.     

Formation of niobium and tantalum ylide complexes

The reactions of tri(bis(ethyl)amino)phosphorus ylide (Et₂N)₃PCH₂ with cyclopentadienyl (Cp) metal (V) tetrachloride CpMCl₄ (M = Nb 1; Ta 3) and pentamethylcycopentadienyl (Cp^∗) metal (V) tetrachloride Cp^∗MCl₄ (M = Nb 2; Ta 4) were investigated. The hexa-coordinate ylide adducts complexes 5 (CpNbCl₄(H₂CP(NEt₂)₃)), 6 (Cp^∗NbCl₄(H₂CP(NEt₂)₃)) and 8 (Cp^∗TaCl₄(H₂CP(NEt₂)₃)) with pseudo-octahedral geometry were structurally analyzed with X-ray diffraction. Compound 4 (Cp^∗TaCl₄) reacted with three molar equivalent of phosphorus ylide to form one ionic complex 9 ([H₃C-P(NEt₂)₃][Cp^∗TaCl₅]) which was also structurally analyzed with X-ray diffraction. The possible formation mechanism of compound 9 has been discussed.     

Synthesis and characterization of half-sandwich iridium complexes containing 2,6(7)-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene and ancillary ortho-carborane-1,2-dichalcogenolato ligands

The binuclear half-sandwich iridium complexes {Cp^∗IrCl₂}₂(μ-2,6(7)-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene) (3) and {Cp^∗Ir[E₂C₂(B₁₀H₁₀)]}₂(μ-2,6(7)-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene) (E = S(5a), Se(5b)) were prepared from the reaction of [Cp^∗IrCl(μ-Cl)]₂ or the “pseudo-aromatic” half-sandwich iridium complex Cp^∗Ir[E₂C₂(B₁₀H₁₀)] (E = S(4a), Se(4b)) with a tetrathiafulvalene (TTF) derivative 2,6-bis(4-pyridyl)-1,4,5,8-tetrathiafulvalene (2) at room temperature. The complexes (3, 5a and 5b) have been fully characterized by IR and NMR spectroscopy, as well as elemental analysis. And the molecular structures of 2 and 5a were established through X-ray crystallography. It is interesting that infinite tunnels are created by repeating ‘buckled bowl’ molecules of 5a.     

New divalent samarocenes for butadiene polymerisation: influence of the steric effect and the electron density on the catalytic activity

Two new divalent samarocenes, Cp^*′₂Sm(THF) (1) and (Cp^Ph3)₂Sm(THF) (2) (Cp^*′=C₅Me₄ⁿPr, Cp^Ph3=H₂C₅Ph₃-1,2,4), were synthesized and characterized by ¹H NMR and elemental analysis. The activity of 1 and 2 as butadiene polymerisation catalysts was studied, in the presence of MAO and MMAO, and compared to this of Cp^*₂Sm(THF)₂ (3) and (Cp⁴ⁱ)₂Sm (4) (Cp^*=C₅Me₅, Cp⁴ⁱ=C₅HⁱPr₄), in the same conditions. The 1/MAO system presents the highest activity. The less active 2/MAO system leads to a high cis-1,4 regular structure up to 97%. The MMAO cocatalyst is found very sensitive to the steric hindrance of the samarocenes: the activity decreases from 1/MAO to 1/MMAO, and no activity is observed in the case of complexes 2 and 4, associated to MMAO. Complexes 1 and 2 can be both oxidized with AlMe₃ to give the corresponding Sm/Al bimetallics and , respectively.     

Synthesis, structure and characterization of dimolybdaheteroboranes

Chalcogen-stabilized dimolybdaboranes 3-5 (3: [(Cp^∗Mo)₂B₄H₅Se(Ph)], 4: [(Cp^∗Mo)₂B₄H₃Se₂(SeCH₂Ph)] and 5: [(Cp^∗Mo)₂B₃H₆(BSR)(μ-η¹-SR)] (R = 2,6-(^tBu)₂-C₆H₂OH)) have been isolated from the mild pyrolysis of dichalcogenide ligands, RE-E‘R (R = Ph: E = S, E‘ = Se; R = CH₂Ph, [2,6-(^tBu)₂-C₆H₂OH]: E = E‘ = Se, S) and [(Cp^∗Mo)₂B₄H₈], 2, an intermediate generated from the reaction of [Cp^∗MoCl₄] (1) (Cp^∗ = η⁵-C₅Me₅), with [LiBH₄.thf]. The geometry of [(Cp^∗Mo)₂B₄H₅Se(Ph)] is similar to that of [(Cp^∗Mo)₂B₅H₉], in which one BH₃ unit on the open face is replaced by a triple bridged selenium atom. All the compounds have been characterized in solution by ¹H, ¹¹B, ¹³C NMR and IR spectroscopy and elemental analysis. The structural types were unequivocally established by X-ray crystallographic analysis of compounds 3-5.     

Ethylene polymerization by novel phenylenedimethylene bridged homobinuclear titanocene/MAO systems

Reaction of (o, m, p) disodium(phenylenedimethylene)dicyclopentadienide C₆H₄(CH₂C₅H₄Na)₂ with 2 equiv of (MeCp)TiCl₃ yields the phenylenedimethylene bridged binuclear titanocenes complexes [(MeC₅H₄)TiCl₂](C₅H₄CH₂C₆H₄CH₂C₅H₄)[(MeC₅H₄)TiCl₂] (3, 4, 5) in high yield, which were characterized by ¹H NMR and elemental analysis. They were used successfully as efficient catalysts for ethylene polymerization in the presence of methylaluminoxane (MAO). The catalytic activities of 4 and 5 are somewhat higher than that of 3 and the molecular weight distributions (MWD = 4.8-6.2) of the polymers generated from the bimetallic catalytic systems are obviously higher than that obtained by conventional Cp₂TiCl₂.     

Half-sandwich rhodium complexes containing both N-heterocyclic carbene and ortho-carborane-1,2-dithiolate ligands

A new route was used to synthesize half-sandwich rhodium complexes containing both N-heterocyclic carbenes (NHC) and carborane ligands. The rhodium carbene complexes Cp^∗Rh(L)[S₂C₂(B₁₀H₁₀)] (Cp^∗ = pentamethylcyclopentadienyl, L = 1,3-dimethylimidazolin-2-ylidene; 4) can be obtained from the reaction of Cp^∗Rh(L)Cl₂ (2) with Li₂S₂C₂(B₁₀H₁₀) or from the reaction of Cp^∗Rh[S₂C₂(B₁₀H₁₀)] (3) with silver-NHC complex prepared by direct reaction of an imidazolium precursor and Ag₂O. Complexes 2 and 4 were characterized by IR, NMR spectroscopy, element analysis and X-ray structure analyses.     

Synthesis and characterization of hetero-binuclear Co-Rh complexes [CpCoS2C2(B9H10)][Rh(COD)] and [CpCoSe2C2(B10H10)][Rh(COD)]

Two hetero-binuclear complexes [Cp^∗CoS₂C₂(B₉H₁₀)][Rh(COD)] (2a) and [Cp^∗CoSe₂C₂(B₁₀H₁₀)][Rh(COD)] (2b) [Cp^∗ = η⁵-pentamethylcyclopentadienyl, COD = cyclo-octa-1,5-diene (C₈H₁₂)] were synthesized by the reactions of half-sandwich complexes [Cp^∗CoE₂C₂(B₁₀H₁₀)] [E = S (1a), Se (1b)] with low valent transition metal complexes [Rh(COD)(OEt)]₂ and [Rh(COD)(OMe)]₂. Although the reaction conditions are the same, the structures of two products for dithiolato carborane and diselenolato carborane are different. The cage of the carborane in 2a was opened; However, the carborane cage in 2b was intact. Complexes 2a and 2b have been fully characterized by ¹H, ¹¹B NMR and IR spectroscopy, as well as by elemental analyses. The molecular structures of 2a and 2b have been determined by single-crystal X-ray diffraction analyses and strong metal-metal interactions between cobalt and rhodium atoms (2.6260 Å (2a) and 2.7057 Å (2b)) are existent.     

Half-sandwich cyclopentadienyl rhodium complexes bearing pendant sulfur or oxygen ligands and their catalytic behaviors in ethylene polymerization

Two half-sandwich rhodium complexes with sulfur or oxygen functionalized cyclopentadienyl ligands [η⁵-C₅H₄(CH₂)₂SCH₂CH₃]RhI₂3, {[η⁵-C₅H₄(CH₂)₂OCH₃]RhI₂}₂4 have been synthesized and characterized by IR, ¹H-NMR spectra and Elemental analyses. The molecular structures of complexes 3 and 4 have been determined by X-ray crystallographic analysis. Complexes 3, 4 with a pendent arm on cyclopentadienyl ligand have been tested as catalysts for ethylene and norbornene polymerization in the presence of MAO. Complexes 3 and 4 kept high activities of ca. 10⁶ g PE mol⁻¹ Rh h⁻¹ with morderate molecular weight (M_w ≈ 10⁵ g mol⁻¹) of polyethylene in the ethylene polymerization. Catalytic activities, molecular weights of polyethylene have been investigated under the various reaction conditions.     

Ethylene polymerization by rigid benzene ring centered dinuclear metallocene (Ti, Zr)/MAO systems

Two rigid benzene centered dinuclear metallocene complexes C₆H₂[(CH₂C₅H₄)₂MCl₂]₂, M = Ti (1), Zr (2) have been prepared by treating two equivalents of TiCl₄ and ZrCl₄ with the tetralithium salt of the ligand C₆H₂(CH₂C₅H₅)₄-1,2,4,5 in toluene and characterized by ¹H NMR and elemental analysis. Both complexes are effective catalysts for ethylene polymerization in the presence of methylaluminoxane (MAO). The influence of [MAO]/[Cat] molar ratio, catalyst concentration, polymerization temperature and time has been tested in detail. The catalytic activity of complex 2 is more than two times higher than that of complex 1, which is still more active than that of the tetranuclear titanocene C₆H₂[CH₂C₅H₄Ti(C₅H₅)Cl₂]₄-1,2,4,5 (5). On the other hand, the catalytic activities of 1 and 2 is slightly lower than that of the dinuclear metallocene complexes C₆H₄[CH₂C₅H₄Ti(C₅H₄CH₃)Cl₂]₂-1,3 (3) and C₆H₄[CH₂C₅H₄Zr(C₅H₅)Cl₂]₂-1,3 (4), respectively, which is related to the limited intermolecular rotation of the metallocene units in 1 and 2. The melting points above 130 °C indicate a polyethylene formed by complexes 1 and 2 with highly linear and highly crystalline. GPC spectra show that polyethylene produced by complexes 1 and 2 has a broad and even bimodal molecular weight distribution (MWD).     

Synthesis and characterization of heterometallic Rh/Ru complexes supported by 1,2-dichalcogenolato-o-carborane ligands

The 16-electron half-sandwich complexes Cp^∗Rh[E₂C₂(B₁₀H₁₀)] (E = S, 1a; Se, 1b) react with [Ru(COD)Cl₂]_x under different conditions to give different types of heterometallic complexes. When the reactions were carried out in THF for 24 h, the binuclear Rh/Ru complexes [Cp^∗Rh(μ-Cl)₂(COD)Ru][E₂C₂(B₁₀H₁₀)] (E = S, 2a; Se, 2b) bridged by two Cl atoms and the binuclear Rh/Rh complexes (Cp^∗Rh)₂[E₂C₂(B₁₀H₁₀)] (E = S, 3a; Se, 3b) with direct Rh-Rh bond can be isolated in moderate yields. [Ru(COD)Cl₂] fragments in 2a and 2b have inserted into the Rh-E bond. If the [Ru(COD)Cl₂]_x was reacted with 1a in the presence of K₂CO₃ in methanol solution, the product [Cp^∗Rh(COD)]Ru[S₂C₂(B₁₀H₁₀]] (4a), K[(μ-Cl)(μ-OCH₃)Ru(COD)]₄ (5a) and 3a were obtained. The B(3)-H activation in complex 4a was found. However, when the reaction between 1b and [Ru(COD)Cl₂]_x was carried out in excessive NaHCO₃, the carborane cage opened products {Cp^∗Rh[S₂C₂(B₉H₁₀)]}Ru(COD) (6b), {Cp^∗Rh[S₂C₂(B₉H₉)]}Ru(COD)(OCH₃) (7b) and 3b were obtained. All complexes were fully characterized by their IR, ¹H NMR and elemental analyses. The molecular structures of 2a, 2b, 3b, 4a, 5a, and 7b have been determined by X-ray crystallography.     

Alkyne-functionalized metallocene complexes: Synthesis, structure, and catalytic ethylene polymerization

Reactions of phenylethynyl lithium with substituted cyclopentenones gave the corresponding pendant phenylethynyl substituted cyclopentadienes. Subsequent deprotonation and transmetallation with TiCl₄·2THF, ZrCl₄, and Cp^∗ZrCl₃ yielded the alkyne-functionalized metallocene complexes [C₅Me₄(CCPh)]₂MCl₂ [M = Ti (1), Zr (2)], Cp^∗[C₅Me₄(CCPh)]ZrCl₂ (3), and Cp^∗[C₅H₂R′₂(CCPh)]ZrCl₂ [R′ = Me (4), Ph (5)]. These complexes were fully characterized by ¹H NMR, ¹³C NMR, MS spectra, and elemental analysis. The molecular structure of 2 was determined by single crystal X-ray diffraction analysis. Ethylene polymerization was studied with these complexes in the presence of methylaluminoxane (MAO).     

Syntheses and spectra of chromium-titanium complexes bridged by carboxylate substituted cyclopentadienyl group: The structure of Cp2Ti(CH3){[OC(O)C5H4]Cr(NO)2Cl}

Mono-demethylation of Cp₂Ti(CH₃)₂ in dichloromethane with 1 M equivalent of [η⁵-(C₅H₄COOH)]Cr(CO)₂NO (5), [η⁵-(C₅H₄COOH)]Cr(NO)₂X] (X = Cl 6, X = I 7) and [η⁵-(C₅H₄COOH)]W(CO)₃CH₃ (8) gives Cp₂Ti(CH₃){[OC(O)C₅H₄]Cr(CO)₂NO} (9), Cp₂Ti(CH₃){[OC(O)C₅H₄]Cr(NO)₂Cl} (10), Cp₂Ti(CH₃){[OC(O)C₅H₄]Cr(NO)₂I} (11) and Cp₂Ti(CH₃){[OC(O)C₅H₄]W(CO)₃CH₃} (12), respectively. The structure of 10 has been solved by X-ray diffraction studies. One of the nitrosyl groups is located at the site away from the exocyclic carbonyl carbon of the Cp(Cr) ring with twist angle of 178.1°. All the data reveals that Cp₂Ti(CH₃)- is a strong electron-donating group. The opposite correlation was observed on the chemical shift assignments of C(2)-C(5) in compounds 5-12, using HetCOR NMR spectroscopy, as compared with the NMR data of their ferrocene analogues. The electron density distribution in the cyclopentadienyl ring is discussed on the basis of ¹³C NMR data and those of 10 are compared with the calculations via density functional B3LYP correlation- exchange method.     

Synthesis and structure of functional spherosilicate building block molecules for materials synthesis

Cubic, trialkyl tin functionalized spherosilicates Si₈O₂₀(SnR₃)₈ (R = Me, ⁿBu) and the pentagonal prismatic tin-spherosilicate Si₁₀O₂₅(SnMe₃)₁₀ have been synthesized and characterized. Single crystal X-ray structures were obtained for Si₈O₂₀(SnMe₃)₈ (I), Si₈O₂₀(SnMe₃)₈ · 4H₂O (I · 4H₂O), and Si₁₀O₂₅(SnMe₃)₁₀ · 4H₂O (II). Structural metrics for the silicate cores observed in these structures were compared to other Si₈O₁₂ and Si₁₀O₂₅ cores reported in the CSD database. A pronounced tetragonal distortion of the Si₈O₂₀ cage leads to Si-O-Si bond angles that are considerably distorted in I · 4H₂O when compared to other analogous Si₈O₁₂ structures described in the literature. These octameric stannylated spherosilicates readily react with metal chlorides to produce mesocopically interesting metal oxide and hybrid materials. An illustration of this is found in the reaction of the octameric anhydrous tin compound I with titanocene dichloride to give the octatitanocene derivative Si₈O₂₀(Cp₂TiCl)₈ · 3CH₂Cl₂ (III). The single crystal structure of III is also described.     

Synthesis and characterization of binuclear μ-oxo and μ-telluro molybdenum(V) complexes, [CpMo(O)(μ-Te)]2

Pyrolysis of an in-situ generated intermediate, produced in the reaction of [Cp^∗MoCl₄], 1, (Cp^∗ = η⁵-C₅Me₅) with [LiBH₄·THF], with an excess of difuryl ditelluride in toluene at 90 °C yielded syn and anti isomers of [Cp^∗Mo(O)(μ-Te)]₂ (2, 3) and [Cp^∗₂Mo₂O₂(μ-O)(μ-Te)] (4, 5). In a similar fashion, dibenzyl diselenide yielded syn and anti isomers of [Cp^∗Mo(O)(μ-Se)]₂ (6, 7), along with the known nido-[(Cp^∗Mo)₂B₄H₈Se₂]. Note that in parallel with 2-7, [(Cp^∗Mo)₂B₅H₉] was isolated as the major product in both cases. Compounds 2-7 have been isolated in modest yield as orange to brown crystalline solids. All the new compounds have been characterized in solution by mass, IR, ¹H, ¹³C, ⁷⁷Se and ¹²⁵Te NMR spectroscopy, and the structural types were unequivocally established by crystallographic analysis of 2-4 and 7.