Tiziana Funaioli

Pyridine induced disproportionation reaction of Co2(CO)8 in THF: Homonuclear ion pairs and dihydrogen activation

Abstract The IR spectra of the Co 2+ /Py/Co(CO) 4 − , system in THF reveal complex associative phenomena. Three kinds of homonuclear ion pairs were distinguished by means of variable temperature IR spectroscopy. Under the conditions in which these associative equilibria exist cobalt(II) is reduced by dihydrogen to cobalt( −I) under 1 atm of syngas at room temperature.

Bioreductively Activated Lysyl Oxidase Inhibitors against Hypoxic Tumours

Most human cancers consist of solid tumours that are significantly less oxygenated than normal tissues. Once their dimensions reach certain values (>1 cm3) they contain hypoxic regions generally surrounding necrotic areas. Hypoxic cells are normally resistant to anticancer chemotherapy and radiotherapy. Hypoxia has also been shown to predispose tumours to increased invasion and metastatic processes,[1] leading to poor prognosis.

Disproportionation of homoleptic rhodium carbonyls

Abstract Both [Rh4(CO)12] and [Rh6(CO)16] disproportionate in pyridine to cis-[Rh(CO)2(py)2]+ and [Rh5(CO)13(py)2]−. In the same solvent, cis-[Rh(CO)2(py)2]+ is reduced by CO/H2O to [(py)2H][Rh5(CO)13-(py)2], which has been structurally characterized.

Co2(CO)8-promoted dihydrogen activations under unusually mild conditions by highly polarizing Co2+ cations

Abstract The reaction between Co2(CO)8 and CoX2 (X = C1, I, O2CC2H5) in THF involves in a P(CO)-dependent disproportionation of the neutral carbonyl: 3 2 Co2(CO)8 + CoX2 ⇆ 2[Co(CO)4]− + 2[CoX]+ + 4CO For X− = I−, a stable CoII, Co−I homonuclear ion-pair (HNIP) is the only product at room temperature, while for X− = C1− and O2CC2H5− is also formed. For X = C1− or O2CC2H5− the solutions obtained activate dihydrogen under unusually mild conditions; highly polarizing Co2+ cations, insufficiently stabilized by [Co(CO)4]− and the X ligand, are suggested to be the active species in this activation. This picture would also account for the catalytic effect of small amounts of pyridine on the formation of HCo(CO)4 from Co2(CO)8 and dihydrogen in toluene.

On the Chiroptical Behavior of Conjugated Multichromophoric Compounds of a New Pseudoaromatic Class: Bicolchicides and Biisocolchicides

Background It is well known that, stemming from the mutual interplay between chromophores, circular dichroism (CD) is a powerful technique to deal with structural problems for both the small organic molecule and the biopolymer. However, quantitative interpretations of the spectroscopic and structural terms that give rise to the exciton couplet are usually presented for ideal cases, or a few CD bands only are taken into account, overlooking the role of the solvent medium. Methodology/Principal Findings Circular dichroism and UV absorption spectra were carried out for colchicide (3) and isocolchicide (6), as well as their coupling products, 10,10′-bicolchicide (2) and 9,9′-biisocolchicide (5), in both hydrogen bonding and non hydrogen bonding solvents, as well as MeCN/H2O mixtures. A dramatic control by the solvent emerged, as even tiny changes in the composition of solvent mixtures, at ca 1 water molar fraction, induced a dramatic modification of their CD bands. A mutarotation phenomenon - long known for isocolchicine (8) - was also observed for 5, and can be attributed to the interconversion between atropisomers (R a,7S),(R a,7′S)-5a and (R a,7S),(S a,7′S)-5b. Conclusions/Significance Our data show that with molecules built on two structurally identical moieties which embody both hydrophilic and hydrophobic groups, even tiny changes in the composition of solvent mixtures cause a dramatic modification of the CD bands. Their analysis arrives at a qualitative rationalization of the observed CD couplets from the coupling of high energy transitions, while attempts at a quantitative interpretation of these phenomena through time-dependent density functional theory allowed to reproduce satisfactorily the CD spectrum in the 300–450 nm region only. Failure with higher energies probably reflects currently inadequate specific theoretical treatments of the solvent medium.

Reductive elimination of dimethylcarbonate from (dimethoxycarbonyl) tricarbonyl cobaltates. Isolation and crystal structures of Cs[Co(COOCH3)2(CO)3] and K[(dibenzo-18-crown-6)][Co(COOCH3)2(CO)3]

Abstract Salts of the anion [Co(COOCH 3 ) 2 (CO) 3 ] − with Cs + and K + (with the latter cation complexed by dibenzo-18-crown-6 ether) have been isolated and structurally characterized. In the trigonal bipyramidal cobaltate two C-coordinated COOCH 3 groups occupy trans -axial positions. There are ionic interactions between the cation and the terminal oxygen atoms of methoxycarbonyl involving both of the coordinated COOCH 3 groups in the case of the Cs salt but only one of them in the case of the K salt. One methoxy group of the anion [Co(COOCH 3 ) 2 (CO) 3 ] − is strongly nucleophilic, as shown by the reactions with Co 2 (CO) 8 or CO 2 . Under an inert atmosphere [Co(COOCH 3 ) 2 (CO) 3 ] − undergoes elimination of dimethylcarbonate.

Homoleptic and heteroleptic Au(I) complexes containing the new [Co5C(CO)12](-) cluster as ligand.

The new [{Co5C(CO)12}Au{Co(CO)4}](-), , cluster has been obtained from the reaction of [Co6C(CO)15](2-) with two equivalents of [AuCl4](-). reacts with an excess of HBF4 resulting in the formation of [{Co5C(CO)12}2Au](-), . The new derivatives [Co5C(CO)12(AuPPh3)], , and [Co5C(CO)11(AuPPh3)3], , have been obtained by reacting with two and four equivalents of [Au(PPh3)Cl], respectively. All the new species have been structurally characterised by means of X-ray crystallography as their [NEt4][], [NEt4][], [NMe3(CH2Ph)][], and thf·0.5C6H14 salts and solvates. may be viewed as a homoleptic Au(i) complex containing two [Co5C(CO)12](-) clusters as ligands. Similarly, and are heteroleptic Au(i) complexes containing one [Co5C(CO)12](-) cluster ligand as well as [Co(CO)4](-) or PPh3. Conversely, contains the [Co5C(CO)11](3-) cluster stabilized by three [AuPPh3](+) fragments. and have been investigated in solution by means of electrochemical and spectroelectrochemical methods, revealing a very rich redox propensity to form the closely related (n = 1-3) and (n = 0-3) species.

Ligand-interchange reactions between M(iv) (M = Ti, V) oxide bis-acetylacetonates and halides of high-valent group 4 and 5 metals. A synthetic and electrochemical study

The reactions of M′O(acac)2 [M′ = Ti, V; acac = acetylacetonato anion] with equimolar amounts of MF5 (M = Nb, Ta) in CH2Cl2 afforded Ti(acac)2F2, 1a, and [V(acac)3][MF6] (M = Nb, 4a; M = Ta, 4b), respectively. MOF3 (M = Nb, 2a; M = Ta, 2b) were co-produced from MF5/TiO(acac)2. The intermediate species [TaF4{OTi(acac)2}2][TaF6], 3, was intercepted in the course of the formation of 1a from TiO(acac)2/TaF5. NbCl5 reacted with TiO(acac)2 yielding selectively the previously reported [NbO(acac)Cl2]x, 5, and Ti2(acac)2(μ-Cl)2Cl4, 6. Complex 6 was alternatively obtained from the addition of a two-fold excess of TiCl4 to VO(acac)2. The 1:1 reactions of TiX4 (X = F, Cl) with TiO(acac)2 in dichloromethane gave Ti(acac)2X2 (X = F, 1a; X = Cl, 1b) and TiOX2 (X = F, 7a; X = Cl, 7b). The 1:1 combination of TiX4 (X = F, Cl) with VO(acac)2 led to 1a,b and VOX2 (X = F, 8a; X = Cl, 8b). The μ-oxido compounds (C6F5)3B–O–M′(acac)2 (M′ = Ti, V) underwent fragmentation by [PF6]− in chlorinated solvent, yielding POF3, 9, and [B(C6F5)3F]−, 10, according to NMR studies; 1a and V(acac)3(+), respectively, were detected as the metal-containing species. Electrochemical studies were carried out aiming at the full characterization of the products and the observation of possible degradation pathways.

Ligand lability in and electron transfer of [Co(py)6]+; cyclotrimerisation of alkynes and synthesis, structure, and properties of (η6-C6Ph6)Co(η2-C2Ph2)(py = pyridine)

In pyridine the ionic CoI complex [Co(py)6][BPh4](py = pyridine) catalyses the cyclotrimerisation of but-2-yne and hex-I-yne at room temperature; under the same conditions, diphenylacetylene promotes an irreversible disproportionation of the CoI complex to give [Co(py)6][BPh4]2 and (η6-C6Ph6)Co(η2-C2Ph2), this compound having been structurally characterised and its reaction with CO investigated.

Unprecedented Tris-Phosphido-Bridged Triangular Clusters with 42 Valence Electrons. Chemical, Electrochemical and Computational Studies of their Formation and Stability

This paper presents the synthesis and structural characterization of the unprecedented tris-phosphido-bridged compounds Pt3(μ-PBu(t)2)3X3 (X = Cl, Br, I), having only 42 valence electrons, while up to now analogous clusters typically have 44e(-). The new species were obtained by an apparent bielectronic oxidation of the 44e(-) monohalides Pt3(μ-PBu(t)2)3(CO)2X with the corresponding dihalogen X2. Their X-ray structures are close to the D3h symmetry, similarly to the 44e(-) analogues with three terminal carbonyl ligands. The products were also obtained by electrochemical oxidation of the same monohalides in the presence of the corresponding halide. In a detailed study on the formation of Pt3(μ-PBu(t)2)3I3, the redox potentials indicated that I2 can only perform the first monoelectronic oxidation but is unsuited for the second one. Accordingly, the 43e(-) intermediate [Pt3(μ-PBu(t)2)3(CO)2I](+) was ascertained to play a key role. Another piece of information is that, together with the fully oxidized product Pt3(μ-PBu(t)2)3I3, the transient 44e(-) species [Pt3(μ-PBu(t)2)3(CO)3](+) is formed in the early steps of the reaction. In order to extract detailed information on the formation pathway, involving both terminal ligand substitutions and electron transfer processes, a DFT investigation has been performed and all the possible intermediates have been defined together with their associated energy costs. The profile highlights many important aspects, such as the formation of an appropriate couple of 43e(-) intermediates having different sets of terminal coligands, and suitable redox potentials for the transfer of one electron. Optimizations of 45e(-) associative intermediates in the ligand substitution reactions indicate their possible involvement in the redox process with reduction of the overall energy cost. Finally, according to MO arguments, the unique stability of the 42e(-) phosphido-bridged Pt3 clusters can be attributed to the simultaneous presence of three terminal halides.