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, band 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

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

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. 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/H(2)O 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. 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

Synthesis and characterization of non-bridging mono- and bis-σ-η1-alkynyl derivatives of the phosphido-bridged hexaplatinum core [Pt6(μ-PBut2)4(CO)4]2+

Several mono- or bis-alkynyl derivatives of general formula Pt6(μ-PBut2)4(CO)4X(CC–R), Pt6(μ-PBut2)4(CO)4(CC–R)2 or Pt6(μ-PBut2)4(CO)4(CC–R)(CC–R′) were obtained under Sonogashira type conditions. The new clusters have been characterized with microanalysis and using IR and multinuclear NMR spectroscopy. The crystal and molecular structures of Pt6(μ-PBut2)4(CO)4(CC–R)2 (R = H, C6H4-4-n-C5H11) are presented and electrochemical and spectroelectrochemical studies of some representative compounds are also reported

Modular chiral Eu(iii) complexes for efficient circularly polarized OLEDs

Achieving both high dissymmetry factors and strong emission in circularly polarized (CP) luminescent materials and, at the same time, compatibility with manufacturing processes for organic electronic devices, is a crucial issue for reliable applications of CP emitters in many fields, such as chiral electronics and optoelectronics. In this communication, we show that the independent choice of the sensitizing and the chirality inducing ligands allows europium(III) complexes to meet the multiple requirements for solution processed efficient CP electroluminescent devices

Process for the Recovery and Refining of Rhodium

The present invention relates to a process for the recovery and refining of rhodium starting from a mixture containing rhodium and other transition metals, including those of the platinum Group, as well as metals of the main Groups, said process comprising the following passages: a) formation of an adduct between rhodium trichloride and a halide of a metal selected from metals of Groups IIA, IIIA, IVA, IVB, VB and VIB; b) carbonylation of the precipitated adduct, deriving from passage a) with the formation of rhodium halogen carbonyls and c) sublimation of the carbonylated product obtained in the previous passage. The main advantage of the above process consists in the production of an extremely pure product, with excellent yields

Hydridosulphonato, Hydridocarboxylato and Cationic Hydrido Complexes of Carbonylpyridine Ruthenium(II)

The oxidative addition of pyridinium salts of Broensted acids to [Ru3(CO)12 ] provides a straightforward and easy way to a new class of H-RuII complexes. These have the H trans to either N or O donors which increases their hydridic character

Ethene hydroformylation with CO/H2O: nucleophilic attack by water on to a terminal CO of a Ru(II) acylcarbonyl complex

The reaction with water of acyldicarbonyl–Ru(II) complexes relevant to ruthenium catalysed ethene hydrocarbonylation with CO/H2O is shown to consist of a nucleophilic attack and to proceed via coordination of propionate and CO to the Ru(II) species

Homogeneous WGS Reaction Promoted by Rhodium Carbonyls in Aqueous Pyridine: An Acid-Cocatalyzed Reaction Which Proceeds to the Complete Consumption of Water and Is Inhibited by Chloride Ions

Homogeneous WGS catalysis employing Rh4(CO)12 as precursor in aqueous pyridine (py) was investigated in a batch reactor at 80-degrees-C, P(CO) = 1 atm, and [Rh] = 0.02 M. The WGSR has the highest activity in py containing 3% H2O, and can be protracted to the complete consumption of water. [L(x)H][Rh5(CO)13(py)2](L = H2O, py) was found to accumulate during, the catalysis, while protracted WGSR leaves [Rh(CO)n(py)4-n][Rh5(CO)13(py)2] (n = 1, 2) in dehydrated py. Separate experiments confirmed that in anhydrous py at 80-degrees-C [(py)2H][Rh5(CO)13(py) 2] gives H-2 and [Rh(CO)n(py)4-n][Rh5(CO)13(py)2], while in wet py at 30-degrees-C the latter rhodium species is reduced by CO back to [L(x)H][Rh5(CO)13(py)2]. With CO2 formation. Hence, a catalytic cycle is proposed where cis-[Rh(CO)2(py)2]+ and [Rh5(CO)13(py)2]- are the active species, and where H-2 and CO2 production accompanies their mutual interconversion. Direct investigation of the catalytic reaction showed an inhibiting effect by chloride ions at <5% H2O. The reaction resulted to be acid cocatalyzed up to a limiting behavior. Both these aspects are explained on the basis of the chemical properties of the two proposed active species, which were elucidated by separate experiments. While a systematic study was not attempted, a TOF(H2) = 172 (T = 80-degrees-C, P(CO) = 1 atm, [Rh] = 0.02 M) was achieved in py containing 3% H2O when a chloride-free precursor is employed in the presence of added acid (CF3SO3H/Rh = 10)

Ru3(CO)12 in Acidic Media. Intermediates of the Acid-Cocatalyzed Water-Gas Shift Reaction (WGSR)

The elucidation of the WGSR promoted by ruthenium carbonyls in acidic media started with the detection of the Ru(0), Ru(I), and Ru(II) intermediate complexes, namely Ru-3(CO)(12), Ru-2[mu-eta(2)-OC(CF3)O](2)(CO)(6), and fac-[Ru(CF3COO)(3)(CO)(3)](-), which accumulate when CF3COOH is employed as an acid cocatalyst. Under catalytic conditions, the three were found to interconvert through elementary steps which produce CO2 and H-2. In fact, Ru(0) is oxidized by H+ to Ru(I) and half the hydrogen of the catalytic cycle is supplied by this reaction. On the other hand, Ru(I) disproportionates to Ru(0) and Ru(II), and this latter species undergoes nucleophilic attack by H2O. The decomposition of the metallacarboxylic acid intermediate gives back Ru(I), while H-2 and CO2 are produced in a 1/2 molar ratio. The two alternating pathways for dihydrogen formation, namely Ru(0) oxidation by H+ and the decomposition of a metallacarboxylic acid intermediate, involve H-2 reductive elimination from the same RuHCF3COO(CO)(2)L(2) intermediate (L = H2O, ethers). These findings define an acid-cocatalyzed WGSR whose distinctive features are (i) the intervention of a disproportionation reaction to generate a Ru(II) electron poor complex, whose CO ligands can undergo nucleophilic attack by water, (ii) the generation of the hydride intermediate for dihydrogen production through two distinct reaction patways, and (iii) the reductive elimination of H-2 from the hydride intermediate without involving H+ from the medium