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A family of dinuclear tricarbonyl rhenium (I) complexes containing bridging 1,2-diazine ligand and halide anions as ancillary ligands and able to catalyze CO2 reduction is presented. Electrochemical studies show that the highest catalytic efficiency is obtained for the complex containing the 4,5-bipenthyl-pyridazine and iodide as ancillary halogen ligands. This complex gives rise to TOF=15 s−1 that clearly outperforms the values reported for the benchmark mononuclear Re(CO)3Cl(bpy) (11.1 s−1). The role of the substituents on the pyridazine ligand and the nature of the bridging halide ligands on the catalytic activity have been deeply investigated through a systematic study on the structure-properties relationship to understand the improved catalytic efficiencies of this class of complexes.

A series of neutral, dinuclear, luminescent rhenium(I) complexes suitable for phosphorescent organic light emitting devices (OLEDs) is reported. These compounds, of general formula [Re2(m-Cl)2(CO)6(m-1,2-diazine)], contain diazines bearing alkyl groups in one or in both the b positions. Their electrochemical and photophysical properties are presented, as well as a combined density functional and time-dependent density functional study of their geometry, relative stability and electronic structure. The complexes show intense green/yellow emissions in toluene solution and in the solid state and some of the complexes possess high emission quantum yields (f=0.18–0.22 for the derivatives with disubstituted diazines). In butyronitrile glass, at 77K, due to the charge transfer character of the lowest (emitting) excited state, strong blue shift of the emission is observed, accompanied by a strong increase in the lifetime values. The highest-performing emitting complex, containing cyclopentapyridazine as ligand, is tested in a polymer-based lightemitting device, with poly(9-vinylcarbazole) as matrix, as well as in a device obtained by vacuum sublimation of the complex in the 2,7bis(diphenylphosphine oxide)-9-(9-phenylcarbazol-3-yl)-9-phenylfluorene (PCF) matrix. This represents the first example of devices obtained with a rhenium complex which can be sublimed and is solution processable. Furthermore, the emission is the bluest ever reported for electrogenerated luminescence for rhenium complexes.

Methanol does not significantly affect the position and the rate of the equilibrium between the monomeric (1m) and cyclic trimeric (1t) forms of bis(pentafluorophenyl)borinic acid, Ar2BOH (1, Ar = C6F5), in CD2Cl2 solution. This contrasts with what was previously observed in the presence of thf and is mainly due to the stabilization of the 1m·MeOH covalent adduct through the formation of the hydrogen-bonded dimer [Ar2B(OH)(MeOH)]2 (7), characterized in solution and by single-crystal X-ray analysis. This dimer can be viewed as the intermediate in the conversion of 1 into its methyl ester 6 by fast proton transfer along the hydrogen bond, which transforms the 1m·MeOH adduct into the 6·H2O adduct. Extrusion of H2O by water scavengers drives the equilibrium toward ester 6. X-ray analysis showed that, at variance with 1, ester 6 in the solid state is a monomer. Hindered rotation [ΔH# = 38(1) kJ mol–1, ΔS# = –35(6) J mol–1] around the B–OMe bond, due to O-to-B π-donation, has been observed. This π-donation lowers the Lewis acidity of 6, as shown by the thermal instability of its adducts with MeOH and thf. Water addition to 6 affords the dimeric adduct 7, in fast equilibrium with both 1m and 6, even at 183 K, as revealed by 2D EXSY analysis. Borinic acid itself can act as a water scavenger at low temperature, so that 6 is formed also in the early stages of the titration of 1 with MeOH. The other main initial product was the adduct [Ar2B(OH)]3·MeOH (3) containing a MeOH molecule bound within an octaatomic –B–O(H)–B–O(Me)–H···O(H)–B–O(H)– ring. Fast proton transfer along the strong hydrogen bond was revealed by 2D EXSY analysis. At variance with thf, the adduct containing MeOH exocyclically hydrogen-bonded to 1t could be obtained in high concentration at 183 K only when due allowance for the kinetic requirements of the slow trimerization equilibrium was made.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

The acid-catalyzed reaction between formaldehyde and 1H-indene, 3-alkyl- and 3-aryl-1H-indenes, and six-membered-ring substituted 1H-indenes, with the 1H-indene/CH2O ratio of 2 : 1, at temperatures above 60° in hydrocarbon solvents, yields 2,2′-methylenebis[1H-indenes] 1–8 in 50–100% yield. These 2,2′-methylenebis[1H-indenes] are easily deprotonated by 2 equiv. of BuLi or MeLi to yield the corresponding dilithium salts, which are efficiently converted into ansa-metallocenes of Zr and Hf. The unsubstituted dichloro{(1,1′,2,2′,3,3′,3a,3′a,7a,7′a-η)-2,2′-methylenebis[1H-inden-1-yl]}zirconium ([ZrCl2(1′)]) is the least soluble in organic solvents. Substitution of the 1H-indenyl moieties by hydrocarbyl substituents increases the hydrocarbon solubility of the complexes, and the presence of a substituent larger than a Me group at the 1,1′ positions of the ligand imparts a high diastereoselectivity to the metallation step, since only the racemic isomers are obtained. Methylene-bridged ‘ansa-zirconocenes’ show a noticeable open arrangement of the bis[1H-inden-1-yl] moiety, as measured by the angle between the planes defined by the two π-ligands (the ‘bite angle’). In particular, of the ‘zirconocenes’ structurally characterized so far, the dichloro{(1,1′,2,2′,3,3′,3a,3′a,7a,7′a-η)-2,2′-methylenebis[4,7-dimethyl-1H-inden-1-yl]}zirconium ([ZrCl2(5′)] is the most open. The mixture [ZrCl2(1′)]/methylalumoxane (MAO) is inactive in the polymerization of both ethylene and propylene, while the metallocenes with substituted indenyl ligands polymerize propylene to atactic polypropylene of a molecular mass that depends on the size of the alkyl or aryl groups at the 1,1′ positions of the ligand. Ethene is polymerized by rac-dichloro{(1,1′,2,2′,3,3′,3a,3′a,7a,7′a-η)-2,2′-methylenebis[1-methyl-1H-inden-1-yl]}zirconium ([ZrCl2(2′)])/MAO to polyethylene waxes (average degree of polymerization ca. 100), which are terminated almost exclusively by ethenyl end groups. Polyethylene with a high molecular mass could be obtained by increasing the size of the 1-alkyl substituent.

The two ion pairs [(4,7-Me(2)indenyl)(2)ZrMe](+)[MeB(C(6)F(5))(3)](-) (1 b) and [(indenyl)(2)ZrMe](+) [MeB(C(6)F(5))(3)](-) (2 b) have been generated in situ by reaction of stoichiometric B(C(6)F(5))(3) with the corresponding dimethyl zirconocenes. It has been shown that molecular mechanics computations, guided by experimental (1)H/(1)H NOE correlations, can provide information on the conformers present in solution. The dynamics of the ion pairs has also been investigated, showing the occurrence of both the processes previously characterized for this class of compounds, namely the B(C(6)F(5))(3) migration between the two methyl groups and dissociation-recombination of the whole [MeB(C(6)F(5))(3)](-) anion, the latter process being much faster than the first one (about three order of magnitude). Moreover, it has been shown that in certain conditions intermolecular processes can occur, which mimic the above-mentioned dissociative exchanges. In particular, the presence of species containing loosely bound [MeB(C(6)F(5))(3)](-) anion fastens the exchange of this anion, while the presence of free B(C(6)F(5))(3) accelerates its exchange between the two methyl sites.

The quantitative addition of pyrazole (Hpz) to the 44 valence-electron, triangular cluster anion [Re3(μ3-H)(μ-H)3(CO)9]− gives the novel unsaturated anion [Re3(μ-H)4(CO)9(Hpz)]− (1, 46 valence electrons), which contains a pyrazole molecule that is terminally coordinated on a cluster vertex. Solid-state X-ray and IR analyses reveal a rather weak hydrogen-bonding interaction between the NH proton and one of the hydrides bridging the opposite triangular cluster edge (ΔH°=−3.1 kcal mol−1 from the Iogansen equation). Both IR and NMR data indicate that such a proton–hydride interaction is maintained in the major conformer present in CD2Cl2, but also provide evidence of the presence of minor conformers of 1 in which the NH proton is involved in an intermolecular hydrogen bond with the solvent. The μ-H⋅⋅⋅HN bond length evaluated in solution through the T1 minimum value (2.07 A) and that determined in the solid state by X-ray diffraction (2.05 A) are in good agreement. NMR experiments show that, in acetone, intermolecular NH⋅⋅⋅solvent interactions replace the intramolecular dihydrogen bond. At room temperature in CH2Cl2, the pyrazole ligand in 1 is labile and 1 slowly “disproportionates” to [Re3(μ3-H)(μ-H)3(CO)9]− and [Re3(μ-H)3(CO)9(μ-η2-pz)(Hpz)]−, with H2 evolution. Slow H2 evolution also leads to the formation of the anion [Re3(μ-H)3(CO)9(pz)]− (5), in which the pyrazolate anion adopts a novel μ3-η2-coordination mode, as revealed by a single-crystal X-ray analysis. The analysis of the bond lengths indicates that the pyrazolate anion in 5 acts as a six-electron donor, with loss of the aromaticity. The formation of 5 from 1 is much faster in solvents with a high dielectric constant, such as acetone or DMF. Anion 5 was also obtained from the reaction of pyrazole with [Re3(μ-H)3(CO)9(μ3-CH3)]− through the intermediate formation of two isomeric addition derivatives and following CH4 evolution.

The first five-membered rings of metal atoms connected by M-M or M-H-M bonds only have been obtained by a Re2 +Re3 condensation in which a polyhydride acts as a bridging bidentate ligand toward a coordinatively unsaturated fragment (see scheme below). In spite of the octahedral coordination of the Re centers, the Re5 rings display conformations (twisted and envelope) comparable with those observed for organic five-membered rings of tetrahedral carbon atoms.

A large range of bis(Rn-3-indenyl)methanes were obtained in good to fair yields with the base-catalyzed condensation between formaldehyde and (substituted) indenes. For example, bis(indenyl)methane...

The synthesis and propene polymerization performance of the novel rac-[CH2(3-tert-butyl-1-indenyl)2]ZrCl2 (2) and rac-[CH2(3-tert-butyl-1-indenyl)2]ZrMe2 (2-Me2) are described. The ligand precursor, bis(1-tert-butyl-3-indenyl)methane (L2), is obtained in ca. 80% conversion from the condensation of 3-tert-butylindene and formaldehyde in DMF at room temperature and is isolated as a yellow powder by washing with pentane. Red 2 is obtained in 50−60% yield and free from its meso stereoisomer by reacting an Et2O solution of the ligand dianion, (L2)Li2(Et2O)x, with a slurry of ZrCl4 in either pentane or toluene. Yellow 2-Me2 is prepared in 90% yield by reaction of 2 with excess MeMgCl in toluene. Alternatively, 2-Me2 (contaminated with about 5% of its meso isomer) can be obtained directly from the ligand L2, by reacting L2 in Et2O with 4 equiv of MeLi and then 1 equiv of ZrCl4 in toluene. Both 2 and 2-Me2 are remarkably soluble in pentane (2, ca. 1.7 g/L; 2-Me2, ca. 13 g/L) and toluene (2, ca. 50 g/L). 2/MAO and...

Die ersten funfgliedrigen Ringe aus Metallatomen, die nur durch M-M- oder M-H-M-Bindungen verknupft sind, wurden durch eine Re2+Re3-Kondensation erhalten, bei der ein Polyhydrid gegenuber einem koordinativ ungesattigten Fragment als verbruckender zweizahniger Ligand auftritt (siehe unten). Trotz der oktaedrischen Koordination der Re-Zentren liegen die Re5-Ringe in Konformationen vor (Twist- und Briefumschlag-Konformation), die denen organischer funfgliedriger Ringe aus tetraedrisch umgebenen Kohlenstoffatomen ahneln.