Syntheses of new uranium complexes Cl2U(π-S4N4 and (C5H5)3UClAlCl3·THF

The new bridging complexes Cp₃UClClAlCl₂ and Cp₃UClClAlCl₂·THF were synthesized by reaction of triscyclopentadienyl uranium chloride with aluminum trichloride in the presence of different solvents. The Cp₃UClClAlCl₂·THF complex id proposed to have a square bipyramidal structure with THF occupying the sixth position. A new inorganic cyclooctatetraene uranium complex, UCl₂(S₄N₄), was also synthesized by uranium tetrachloride with tetrasulfur tetranitride.     

Hydride transfer from transition metal hydrides to dihapto acyl ligands

The dihapto acyl ligand in Cp₂Zr[C(O)R]X, (R = Me, Ph; X = Me, Cl) is subject to hydrogen transfer from Cp₂MH₂ (M = Mo, W), Cp₂ReH and CpReH₄(PMe₂Ph). The initial products are bimetallic dimers of the type Cp₂XZrOCH(R)ML_n. The fate of this bimetallic species is highly dependent upon the Group VIB metal when Cp₂MH₂ is the hydride source. For M = Mo, a second hydrogen migrates to the acyl carbon, yielding Cp₂Zr(OEt)Me and products derived from Cp₂Mo. For M = W, CO bond scission occurs with retention of the WC bond, to yield the carbene complexes Cp₂WC(C)R along with various oxyzirconium products. Filled d orbitals are not necessary on the hydride source; Cp₂NbH₃ also readily reduces the acyl in Cp₂Zr[C(O)Me]Me.     

High-spin binuclear cyclopentadienyliron chlorides: a density functional theory study

Theoretical studies on the cyclopentadienyliron chlorides Cp₂Fe₂Cl _n (n?=?6???1) with iron in the formal oxidation states from +1 to +4 indicate that all the high-spin species are predicted to be the lowest energy structures and they are paramagnetic complexes with magnetic moments between 2.8μ _B and 5.9μ _B. The mixed oxidation state derivatives with odd number of chloride atoms have larger magnetic moments than other species. In addition to Cp₂Fe₂Cl, which has the largest magnetic moment, these high-spin species have terminal Cp rings and bridging Cl atoms up to a maximum of two bridges. The Cp₂Fe₂Cl₄, Cp₂Fe₂Cl₃ and Cp₂Fe₂Cl₂ derivatives are predicted to be thermodynamically stable molecules with respect to exothermic reactions for the loss of one Cl atom from Cp₂Fe₂Cl _n . Moreover, the lowest energy Cp₂Fe₂Cl _n (n?=?3, 4) derivatives can be derived by the oxidative addition reactions of Cp₂Fe₂Cl _n?2 + Cl₂ → Cp₂Fe₂Cl _n .

Some new derivatives of organozirconium(IV) and organotitanium(IV) with thiophenecarboxylic acids

The complexes of the type Cp₂M(3-TC)Cl, Cp₂M(3-TC)₂, Cp₂M(3-TA)Cl, Cp₂M(3-TA)₂, Cp₂M(2-TB)Cl, Cp₂M(2-TB)₂ [where Cp = cyclopentadienyl, M = Zr or Ti] were synthesized by the reactions of dichlorobis(cyclopentadienyl)zirconium(IV) and dichlorobis(cyclopentadienyl)titanium(IV) with 3-thiophenecarboxylic acid (3-TCH), 3-thiopheneacetic acid (3-TAH) and 2-thiophenebutyric acid (2-TBH) respectively in different stoichiometric ratios. The new complexes were characterized by their elemental analysis, ¹H NMR, IR, and electronic spectral data.     

Synthesis of new organotitanium (IV) complexes Cp2Ti(SeR)2 and Cp2TiCl(SeR) via tandem reactions involving `Cp2Ti' intermediate. Crystal structures of Cp2TiCl(SeR) (R=p-ClC6H4, p-BrC6H4)

A simple and convenient route for synthesizing organotitanium (IV) complexes with a general formula Cp₂Ti(SeR)₂ or Cp₂TiCl(SeR) has been developed. This synthetic route includes reduction of Cp₂TiCl₂ with Mg and an in situ treatment of the intermediate `Cp₂Ti' with diselenides RSeSeR. Interestingly, while the route involving reaction of Cp₂TiCl₂, Mg and RSeSeR in a molar ratio of 1:1:1 produced Cp₂Ti(SeR)₂, (1-5, R=α-C₁₀H₇, o-MeC₆H₄, m-MeC₆H₄, p-ClC₆H₄, p-BrC₆H₄) in 91-97% yields, the route involving reaction of Cp₂TiCl₂, Mg and RSeSeR in a molar ratio of 1: 0.5: 0.5 afforded Cp₂TiCl(SeR) (6-7, R=p-ClC₆H₄, p-BrC₆H₄) in 70% and 92% yields, respectively. 1-7 are new and have been characterized by elemental analysis and spectroscopy, as well as by X-ray diffraction analysis for 6 and 7. A possible pathway for production of these two types of organotitanium (IV) complexes, mainly depending upon the molar ratio of the starting materials, are briefly discussed.     

Reaction behavior of molybdocene dichloride towards ribonucleosides and ribonucleoside monophosphates: Rare example of sugar coordination

The coordination behavior of Cp₂Mo²⁺ towards the ribonucleosides and ribonucleoside monophosphates uridine, adenosine, cytidine, guanosine, 5′-UMP, 5′-AMP, 5′-CMP and 5′-GMP has been studied in solution in the range 4 ? pD ? 9 using NMR spectroscopy. The ribonucleosides were found to bind Cp₂Mo²⁺ exclusively through the ribose moiety giving rise to the chelate complexes [Cp₂Mo(urd-O2′,O3′)], [Cp₂Mo(ade-O2′,O3′)], [Cp₂Mo(cyd-O2′,O3′)], and [Cp₂Mo(gua-O2′,O3′)]. The ribonucleotides form three types of complex with Cp₂Mo²⁺ in neutral solution, namely N,PO-macrochelates, PO,O3′-coordinated species as well as O2′,O3′-chelates, while at pD 9 only sugar coordination is observed.     

Octahedral (cyclopentadienyl)rhodium clusters [Rh6Cp6(μ6-C)] and [Rh6Cp6(μ3-CO)2]: Synthesis, structures and electrochemistry

The 86-electron dicationic octahedral rhodium clusters containing Cp (Cp = C₅H₅) ligands and either an interstitial carbon atom, [Rh₆Cp₆(μ₆-C)]²⁺ ([1]²⁺), or two carbonyl groups, [Rh₆Cp₆(μ₃-CO)₂]²⁺ ([2]²⁺), were synthesized in low yields by reactions of Rh₃Cp₃(μ-CO)₃ with RhCp(C₂H₄)₂ or [RuCp^∗(MeCN)₃]⁺ (Cp^∗ = C₅Me₅), respectively. The structures of [1]²⁺ and [2]²⁺ were determined by X-ray diffraction. Their electrochemical behavior proved that they possess a rather extended electron transfer activity. In accordance with DFT calculations, the nearly octahedral structure of [1]²⁺ and [2]²⁺ is retained both upon oxidation (2+/3+) and the first reduction (2+/+); however, the second reduction (+/0) results in the breaking of one (for [1]⁰) or two (for [2]⁰) Rh-Rh bonds. In the case of the related Dahl’s nickel cluster Ni₆Cp₆ the nearly octahedral structure is retained upon all redox steps (3+/2+/+/0/−/2−).     

Aqueous Speciation of ansa- and non-ansa- Substituted [Cp2Mo(μ-OH)]2[OTs]2

Titration curves were measured for three molybdocene dimers, [Cp₂Mo(μ-OH)]₂[OTs]₂ (4), [Mo(μ-OH)]₂[OTs]₂ (4′; Cp′ = C₅H₄CH₃), and ansa-[C₂Me₄Cp₂Mo(μ-OH)]₂[OTs]₂ (4^a), and for two monomeric molybdocene complexes, Cp₂MoO (6) and Cp₂MoCl₂ (1). The titration curves for 4, 6, and 1 were identical and showed three equivalence points each. The titration curve for 4′ was also similar in appearance but the equivalence points were shifted higher by ∼0.3, as expected for the more electron-rich Mo center in this molecule. The titration curve for the ansa-[C₂Me₄Cp₂Mo(μ-OH)]₂[OTs]₂ complex showed only two equivalence points. Two of the equivalence points observed in the titration of 4, 6, and 1 were previously reported in potentiometric measurements of aqueous solutions of Cp₂MoCl₂ and were attributed to the Cp₂Mo(OH₂)²⁺ species (pK_a = 5.5 ± 0.1 and 8.3 ± 0.2). The third equivalence point (pK_a = 2.2 ± 0.2) is assigned to protonation/deprotonation of the [Cp₂Mo(μ-OH)]₂[OTs]₂/[Cp₂Mo(μ-OH₂)(μ-OH)MoCp₂]³⁺ dimer. A new equilibrium scheme is proposed for the aquated molybdocenes to provide a more complete picture of the aqueous speciation of the non-ansa molybdocene complexes, specifically by accounting for the third acidic proton in the titration curves and by describing the hydrolysis of Cp₂MoO. Although the titration curve of the ansa-[C₂Me₄Cp₂Mo(μ-OH)]₂[OTs]₂ complex is different from that of [Cp₂Mo(μ-OH)]₂[OTs]₂, ¹H NMR data suggest that the aqueous speciation of the ansa-[C₂Me₄Cp₂Mo(μ-OH)]₂[OTs]₂ complex is analogous to that of the non-ansa molybdocenes.     

Chloride and tropolonato mixed complexes of uranium(IV) and thorium(IV)

The synthesis of some new chloride and tropolonato mixed complexes of the general composition MCl_4?nTrop_n·mL (M = U^IV, Th^IV; n = 1, 2, 3; m = $\text{1}\text{2}$, $\text{2}\text{3}$, 1, 2 and 3; L = DME, THF, LiCl and 18-crown-6) by the reaction of uranium and thorium tetrachlorides with M′Trop (M′ = Tl and Li) is described. The residual chloride atoms in UTropCl₃·THF undergo further substitution reactions involving TlCp, while UTrop₂Cl₂·THF shows a different behaviour toward TlCp, since Cp₃UCl as one of the main reaction products is obtained. Protolysis of Cp₂U(NEt₂)₂ by HTrop affords a mixture of CpUTrop₃ and Cp₂UTrop₂. Finally both UTropCl₃·THF and UCl₄ react directly with HTrop, the nature of the resulting products depending on the reaction solvent.     

Titanocene complexes with nonlinear pseudohalide ligands: Synthesis, spectroscopic characterization and crystal structure

Binuclear titanocene complexes [Cp₂Ti(tcm)]₂O (4), [Cp₂Ti(dca)]₂O (5) and [Cp₂Ti(dcnm)]₂O (6) (tcm⁻ = tricyanomethanide, dca⁻ = dicyanamide and dcnm⁻ = dicyanonitrosomethanide) were synthesized in moderate yields by the reaction of Cp₂TiCl₂ (1) with respective alkali metal pseudohalide salts in the aqueous solution. When the reaction was carried out in dry organic solvents, mononuclear compounds Cp₂Ti(tcm)₂ (2) and Cp₂Ti(dca)₂ (3) were isolated. Preparation of dipseudohalide complex Cp₂Ti(dcnm)₂ by this manner was unsuccessful due to decomposition of dcnm ligand resulting in formation of oxygen-bridged compound 6. All prepared compounds were characterized by elemental analysis, NMR, Raman, infrared and UV-Vis spectroscopy. Molecular structures of 2, 4 and 6 (two polymorphs) have been determined by single-crystal X-ray diffraction analysis.     

A structural investigation of the heterobimetallic carbocation complex [Cp(CO)2Fe{μ-CH2CH(CH2)3}W(CO)3Cp]BPh4

The reaction of [Cp^∗(CO)₂Fe{μ-CH₂CH(CH₂)₃}W(CO)₃Cp]PF₆ with NaBPh₄ in dry acetone gave [Cp^∗(CO)₂Fe{μ-CH₂CH(CH₂)₃}W(CO)₃Cp]BPh₄. The bond Fe-C_β is shorter than that reported for the shorter chain carbocationic complexes. The data suggest that metallacyclopropane character is on the iron side of the molecule both in the solid state and in solution.     

Water-soluble molybdenocene complexes with both proliferative and antiproliferative effects on cancer cell lines and their binding interactions with human serum albumin

Two water-soluble molybdenocene complexes containing oxygen chelating ligands, maltolato and malonate, have been synthesized to elucidate the role of the ancillary ligands in the molybdenocene cytotoxic activity. The structural characterizations of these species by ¹H NMR and IR spectroscopies suggest that both molybdenocene complexes contain the ligands in a bidentate fashion and elemental analysis and mass spectrometry corroborate the proposed formula for the species to be Cp₂Mo(malonate) and [Cp₂Mo(maltolato)]Cl (Cp is cyclopentadienyl). Metal–albumin binding studies were pursued using UV–vis spectroscopy and cyclic voltammetric techniques. Whereas metal–albumin binding studies using UV–vis spectroscopy did not show any evidence of interaction, cyclic voltammetry experiments showed that molybdenocene complexes may be involved in weak binding interactions with albumin, most likely in hydrophobic interactions. The cytotoxic activities of Cp₂Mo(malonate) and [Cp₂Mo(maltolato)]Cl alone with Cp₂MoCl₂ were investigated in HT-29 colon cancer and MCF-7 breast cancer cell lines using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide cell viability assay. Cp₂Mo(malonate) and [Cp₂Mo(maltolato)]Cl showed slight improvement in terms of cytotoxic activity as compared with Cp₂MoCl₂ in the HT-29 colon cancer cell line, whereas for MCF-7 all the molybdenocene species exhibited a proliferative profile. The molybdenocene-containing chelating ligands showed stronger proliferative effects than Cp₂MoCl₂. There is no correlation between the binding affinity of molybdenocenes for human serum albumin and cytotoxic activity toward HT-29 and MCF-7 cancer cells.     

Cyclopentadienylcobalt sulfide and selenide cluster compounds: synthesis and structural characterizations

The reaction of CpCo(CO)₂ with elemental sulfur yielded the new sulfur-rich compound Cp₄Co₄(μ₃-S)(μ₃-S₂)₃ (1). The structure of 1 contains a Co₄S₇ core composed of three μ₃-disulfido ligands and one μ₃-sulfido ligand. PEt₃ abstracts sulfur from 1 to yield the new compound Cp₄Co₄(μ₃-S)₃(μ₃-S₂) (2). Compound 2 is also a cage compound, but it contains three μ₃-sulfido ligands and only one μ₃-disulfido ligand. Compound 2 is converted back to 1 by reaction with elemental sulfur. The selenium homologue Cp₄Co₄(μ₃-Se)₃(μ₃-Se₂) (3) was obtained from the reaction of CpCo(CO)₂ with elemental selenium. The structures of 1, 2 and 3 were determined by single-crystal X-ray diffraction analyses.     

Unsaturation in binuclear cyclopentadienyliron carbonyl thiocarbonyls: Four-electron donor bridging thiocarbonyl groups versus metal-metal multiple bonds

Theoretical studies on the binuclear cyclopentadienyliron carbonyl thiocarbonyl derivatives Cp₂Fe₂(CO)₂(μ-CS)(μ-CO) and Cp₂Fe₂(CO)₂(μ-CS)₂ indicate that the trans and cis isomers are nearly degenerate in energy, consistent with experiment. Structures with bridging CS groups are of lower energy than corresponding structures with bridging CO groups. The corresponding unbridged Cp₂Fe₂(CS)(CO)₃ and Cp₂Fe₂(CS)₂(CO)₂ isomers are predicted to lie 11 and 16 kcal/mol, respectively, above their global minima, indicating increasing activation energies for the cis/trans interconversion as bridging CO groups are replaced by bridging CS groups. The unsaturated species Cp₂Fe₂(μ-CS)(μ-CO)₂ and Cp₂Fe₂(μ-CS)₂(μ-CO) are predicted to have triply bridged triplet spin state structures with FeFe double bonds of lengths 2.26 Å, analogous to the experimentally known triplet (Me₅C₅)₂Fe₂(μ-CO)₃. However, low-lying singlet Cp₂Fe₂(CS)(CO)₂ and Cp₂Fe₂(CS)₂(CO) structures with four-electron donor bridging η²-μ-CS groups and formal Fe-Fe single bonds are also found. The lowest lying Cp₂Fe₂(CS)(CO) and Cp₂Fe₂(CS)₂ structures have two bridging groups and very short FeFe distances of ∼2.14 Å, suggesting formal triple bonds. Several higher energy four-electron donor η²-μ-CS bridged structures are also found for Cp₂Fe₂(CS)(CO) and Cp₂Fe₂(CS)₂. In addition, singlet and triplet structures are found for Cp₂Fe₂(CS)₂ in which the two CS ligands have coupled to form a bridging SCCS group with a carbon-carbon bond. Only a η²-μ-CS bridged singlet structure is predicted for Cp₂Fe₂(CS), rather than the normal bridged structure with a FeFe quadruple bond such as that predicted for the carbonyl analog Cp₂Fe₂(CO).     

Reactions of delocalized dianions with transition metal complexes. Electron transfer in the reaction of the isobutylene dianion with molybdenum carbonyl dihalides

Reaction of the dianion of isobutylene with Mo- (CO)₃(PPh₃)₂X₂ results in the reduction of the metal and concomitant oxidation of the dianion. The reduction parallels the previously reported electrochemical reduction. Reaction of the dianion with Mo(CO)₄X₂ results in reduction of the metal presumably to coordinatively unsaturated Mo(CO)_x (x = 5, 4) which is then trapped by solvent or tertiary amines in solution to give Mo(CO)₄L₂ (L₂ = (THF)₂, TMEDA). The reduction potentials for Mo(CO)₃- (PPh₃)₂X₂ allow an estimate of the oxidation potential of the isobutylene dianion to be greater than −0.35 V versus SCE. Cp₂TiCl₂, which is not reduced by the isobutylene dianion, allows the estimate of the upper limit of the oxidation potential to be evaluated as less that −0.88 V versus SCE. The dianion is therefore by this criterion, less stable than the cyclopentadienyl anion (Ep = −0.18 V versus SCE) but more stable than the allyl anion (Ep = −1.40 V versus SCE).     

Synthesis and characterization of tetrairon-tungsten cluster complex containing a μ4, η-carbonyl ligand

Reaction of [(PPh₂C₅H₄)Cp₃Fe₄(CO)₄] (1) with (CO)₄W(CH₃CN)₂ at ambient temperature affords [(CO)₄W(PPh₂C₅H₄)Cp₃Fe₄(CO)₄] (2) as the major product, together with a small amount of [(CO)₅W(PPh₂C₅H₄)Cp₃Fe₄(CO)₄] (3). Compound 3 can be obtained in good yield by treating (CO)₅W(CH₃CN) with equal molar of 1, and reaction of 3 with Me₃NO in acetonitrile solvent produces 2 exclusively. The crystal structures of 2 and 3 have been determined by an X-ray diffraction study. Compound 2 contains an interesting μ₄, η²-CO ligand, where two electrons donated by the carbon atom are involved to bridge a Fe₃ face and two electrons from oxygen are donated to the tungsten(0) atom.     

Synthesis and derivatization of halflanthanidocene aryl(alk)oxide complexes

The reaction of halflanthanidocene aryloxides Cp^R′Ln(OAr^tBu,R)₂ (Ln = Y, La, Lu; Cp^R′ = C₅Me₅, C₄Me₄H; R = H, Me) and halflanthanidocene alkoxides [(C₅Me₅)Ln(OCH₂CMe₃)₂]₂ (Ln = Y, Lu) with trimethylaluminum (TMA) was investigated. Monomeric Cp^R′Ln(OAr^tBu,R)₂, derived from the ortho-tBu-substituted OC₆H₂tBu₂-2,6-R-4 (R = H, Me) ligands, form mono(tetramethylaluminate) complexes Cp^R′Ln(OAr^tBu,R)(AlMe₄) for the smaller lanthanide metal centers yttrium and lutetium. Such an [aryloxide] → [aluminate] ligand exchange was not observed at the larger lanthanum metal center. The mobility of the tetramethylaluminate ligands of complexes Cp^R′Ln(OAr^tBu,R)(AlMe₄) (Ln = Y, Lu) was examined by variable-temperature (VT) ¹H NMR spectroscopy, revealing two signals for bridging and terminal methyl groups at lower temperatures. The treatment of complexes Cp^R′Ln(OAr^tBu,R)(AlMe₄) with donor solvent d₈-THF gave Cp^R′Ln(OAr^tBu,R)(Me)(d₈-THF)₂ (Ln = Y, Lu) with terminal methyl groups, according to a donor-induced aluminate cleavage reaction. Dimeric [(C₅Me₅)Ln(OCH₂CMe₃)₂]₂ (Ln = Y, Lu) was synthesized from (C₅Me₅)Ln(NiPr₂)₂(THF) and reacted with two equivalents of TMA per Ln center to yield monomeric bis(TMA) adduct complexes (C₅Me₅)Ln(OCH₂CMe₃)₂(AlMe₃)₂(Ln = Y, Lu). VT NMR spectroscopic studies confirmed a high mobility of the Ln(μ-OCH₂CMe₃)(μ-Me)AlMe₂ moieties at an ambient temperature. Both bis(TMA) adduct complexes were characterized by X-ray structure analysis.     

Towards [CpRh(bpy)(H2O)]-promoted P450 catalysis: Direct regeneration of CytC

The organometallic complex pentamethylcyclopentadienyl rhodium 2,2′-bipyridin ([Cp^∗Rh(bpy)(H₂O)]²⁺) was applied as regeneration catalyst for cytochrome C (CytC). Direct reduction of CytC-bound Fe^III was achieved in this model system pointing towards a potential usefulness of this concept to promote cell-free P450 catalysis. In addition, controlled in situ provision with hydrogen peroxide was performed using [Cp^∗Rh(bpy)(H₂O)]²⁺ resulting in improved CytC-catalyzed sulfoxidation of thioanisol This work represents the first step towards the direct-[Cp^∗Rh(bpy)(H₂O)]²⁺ catalyzed regeneration of P450 monooxygenases and peroxidases.     

Experimental access to the molecular and electronic structures of organo-f-element complexes by NMR spectroscopy

The main objective of this survey is to demonstrate that by extensive assessment of variable temperature ¹H NMR data obtained on paramagnetic f-element complexes in solution, not only valuable information on details of the molecular structure, but also on the electronic structure may be deduced. One of the most informative quantities to arrive at is the paramagnetic anisotropy term, χ∥ - χ⊥, of axially symmetric molecules from which, if the bulk susceptibility $\text{χ}$ is also known, the crystal-field sensitive parameters χ∥ and χ⊥ can be derived.The majority of the examples considered belong to the widely studied type [Cp₃^fML_n]^q (Cp = η⁵C₅H₄R); ^fM = Pr(III), Nd(III), Yb(III) and U(IV); n = 0, 1 and 2; q = 0 or ?1) and to the uranocene family. The survey also includes the two sub-classes of novel anionic complexes [Cp₃LnL]^? and [(Cp₃Ln)₂(μ-L)]^?, respectively, and different isomers of the general composition [Cp₃UXY]^q (L = lanthanoid).     

Syntheses and characterization of Cp2Ce[η3-N(QPPh2)2] (Q = S,Se) and Cp2Ce[η3-N(SPiPr2)(SePPh2)]

The compounds Cp₂Ce[η³-N(QPPh₂)₂] (Q = S (1), Se (2)) and Cp₂Ce[η³-N(SPⁱPr₂)(SePPh₂)] (3) have been synthesized from the protonolysis reactions between Cp₃Ce and HN(QPPh₂)₂ or HN(SPⁱPr₂)(SePPh₂) in THF. The structures of these compounds have been determined by X-ray crystallographic methods. The three compounds have similar structures in which the ligands are coordinated to Cp₂Ce moiety in an η³ fashion through the two chalcogen atoms and an N atom. Whereas the ⁷⁷Se NMR resonances are normal the ³¹P NMR resonances are shifted to much lower frequencies than in similar rare-earth compounds.