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In this work, unprecedented {dz2-CuIIO4}⋯π-hole interactions are described in the case of a cocrystal of a Cu(ii) bis-β-diketonate complex and 1,4-diiodotetrafluoro-benzene.

The highest degree of interpenetration reported so far of 7- and 8-fold is realized in two luminescent sql 2D networks by self-assembly of a new nanometric-sized ligand with Ag(i) salts.

International audience; Highlights • Nine novel thiazolo[5,4-d]thiazole fluorophores with peripheral pyridines is presented. • The compounds possess either a linear, two-or four-armed molecular structure. • All the compounds display good near-UV to bluish-green fluorescence. • Linear derivatives show better photoluminescence quantum yields compared to nonlinear counterparts up to 0.42. • The nature of the short-lived excited state is confidentially described as p-p*.

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.

Cocrystallization of a bis[1-(4-pyridyl)butane-1,3-dionato]copper(II) (1) complex and 1,4-diiodoperfluorobenzene in the presence of pyridine yields a 1 : 1 cocrystal where both the σ and π-holes of 1,4-diiodoperfluorobenzene play a role. The crystal structure shows short arene CuO

The remarkable emissive properties of cyclic triimidazole (TT), showing crystallization-induced emissive behavior and, in particular, room temperature phosphorescence (RTP), are here combined with its versatility in assembling coordination compounds. A series of Ag(I) coordination polymers (CPs), comprising a 1D chain ([Ag(TT)I]n, 1-Ag) and 3D networks ([Ag(TT)Cl]n, 2-Ag, and [Ag3(TT)4]n(NO3)3n·6nH2O, 3-Ag), have been synthesized and their photophysical behavior thoroughly investigated. They show both fluorescence and multiple RTPs, all simultaneously activated but varied in intensity by changing the excitation energy. Based on DFT/TDDFT calculations and analysis of the X-ray crystal structures, the origin of the different phosphorescences has been ascribed to H-aggregation of the ligand (in 1-Ag and 2-Ag), intermolecular electronic coupling by an extrinsic heavy-atom effect (in 1-Ag) and ligand-centered emissive states (in all three compounds). Comparison with isostructural 1-Cu and 2-Cu CPs reveals that, different from the Ag(I) analogues, non-thermally equilibrated XMLCT and ligand-centered emissive states are active. The isostructural Ag(I) and Cu(I) compounds show comparable emission efficiency, while the phosphorescence lifetimes are longer for the former (ms regime) than the latter (micro-s regime). A Quantum Theory of Atoms In Molecules (QTAIM) topological analysis of electron density allows the interpretation of the different nature of the emissive states of Ag(I) and Cu(I) compounds on the basis of larger shell-shared character of the Cu-N bond with respect to the Ag-N one.

Organic materials with multiple emissions tunable by external stimuli represent a great challenge. TTPyr, crystallizing in different polymorphs, shows a very rich photophyisics comprising excitation-dependent fluorescence and phosphorescence at ambient conditions, and mechanochromic and thermochromic behavior. Transformation among the different species has been followed by thermal and X-ray diffraction analyses and the emissive features interpreted through structural results and DFT/TDDFT calculations. Particularly intriguing is the polymorph TTPyr(HT), serendipitously obtained at high temperature but stable also at room temperature, whose non-centrosymmetric structure guarantees an SHG efficiency 10 times higher than that of standard urea. Its crystal packing, where only the TT units are strongly rigidified by π-π stacking interactions while the Pyr moieties possess partial conformational freedom, is responsible for the observed dual fluorescence. The potentialities of TTPyr for bioimaging have been successfully established.

A novel family of photoactive cationic tris-carbonyl rhenium complexes of general formula fac-[Re (CO)(3)(PYIPY)(L)]PF6, where pyipy is the 2-(pyridyl)-imidazo[1,5-a]pyridyl-3-ylidene ligand and L = pyridine (3.PF6) or PPh3 (4.PF6), is herein presented. Compounds 3.PF6 and 4.PF6 are straightfor-wardly synthetized from the corresponding chloro-derivativefac-[ReCl(CO)(3) (pyipy)] via halogen abstraction with silver(l) salt, followed by coordination of the neutral monodentate L ligand. The target complexes were characterized by H-1 and C-13 NMR as well as FT-IR spectroscopy and high-resolution mass spectrometry (HR-MS). In addition, X-ray diffractometric analysis was carried out by solving the single-crystal structure of compound 3.PF6. For both complexes, dilute samples in CH3CN solution at room temperature display a structured photoluminescence profile in the red region that is ascribed to a long-lived excited state tau = 19.3-30.0 mu s in degassed condition) with mainly triplet ligand-centered ((LC)-L-3) character. This assignment is further corroborated by the minor hypsochromic shift of the emission profile observed for samples in 2-MeTHF at 77 K glassy matrix, in agreement with previous studies on the corresponding neutral counterparts. Electrochemical characterization by cyclic voltammetry (CV) shows two irreversible processes, one in the positive and one in the negative bias, which are associated to the metal-NHC moiety and the chelating NHC ligand, respectively. Finally, both electronic and optical features are further studied by means of computational investigation at density functional theory (DFT) and time-dependent DFT (TD-DFT) level of theory, which supports the attribution of the electronic transitions involved. (C) 2021 Elsevier Ltd. All rights reserved.

Anion recognition by neutral hosts that function in aqueous solution is an emerging area of interest in supramolecular chemistry. The design of neutral architectures for anion recognition still remains a challenge. Among neutral anion receptor systems, urea and its derivatives are considered as "privileged groups" in supramolecular anion recognition, since they have two proximate polarized N-H bonds exploitable for anion recognition. Despite promising advancements in urea-based structures, the strong hydrogen bond drives detrimental self-association. Therefore, immobilizing urea fragments onto the rigid structures of a metal-organic framework (MOF) would prevent this self-association and promote hydrogen-bond-accepting substrate recognition. With this aim, we have synthesized two new urea-containing metal-organic frameworks, namely [Zn(bpdc)(L2)]n·nDMF (TMU-67) and [Zn2(bdc)2(L2)2]n·2nDMF (TMU-68) (bpdc = biphenyl-4,4'-dicarboxylate; bdc = terephthalate; L2 = 1,3-bis(pyridin-4-yl)urea), and we have assessed their recognition ability toward different anions in water. The two MOFs show good water stability and anion affinity, with a particular selectivity toward dihydrogen arsenate for TMU-67 and toward fluoride for TMU-68. Crystal structure characterizations reveal 3-fold and 2-fold interpenetrated 3D networks for TMU-67 and TMU-68, respectively, where all single interpenetrated networks are hydrogen bonded to each other in both cases. Despite the absence of self-quenching, the N-H urea bonds are tightly hydrogen bonded to the oxygen atoms of the dicarboxylate ligands and cannot be directly involved in the recognition process. The good performance in anion sensing and selectivity of the two MOFs can be ascribed to the network interpenetration that, shaping the void, creates monodimensional channels, decorated by exposed oxygen atom sites selective for arsenate sensing in TMU-67 and isolated cavities, covered by phenyl groups selective for fluoride recognition in TMU-68.

[Re3(μ-H)3(μ3-CH3)(CO)9]- (1) reacts with CO at 273 K to quantitatively give the [Re3(μ-H)3(μ-CH3)(CO)10]- derivative (2) through the conversion of the methyl group from triply to doubly-bridging coordination. An NMR isotopic perturbation experiment demonstrates the unsymmetrical bridging of the methyl group on the Re-Re bond, and a fast exchange, in solution, between one agostic and two terminal C H bonds. This is in agreement with X-Ray diffraction analysis performed on single crystals of 2. In solution at room temperature 2 decomposes with CH4 elimination, which is also observed when 2 is treated with CO affording the [Re3(μ-H)2(CO)12]- anion. The opening of the triple bridging methyl coordination in 1 occurs also with other different L ligands, yielding to the syn and anti isomers of unsymmetrically bridged methyl complexes of general formula [Re3(μ-H)3(μ-CH3)(CO)9(L)]- (L = MeCN, PMePh2, THF). The kinetic and thermodynamic stabilities of these isomers vary with the nucleophilicity of the ligand and the polarity of the solvent. In particular, the strong nucleophile PMePh2 affords the quantitative conversion of anion 1 into the thermodynamic syn isomer, which is stable in THF at room temperature for several days. On the contrary, weak nucleophiles, such as MeCN or THF, give equilibrium mixtures containing residual amounts of anion 1. The adducts with MeCN are stable in solution at room temperature for several hours, while decompose fastly in neat MeCN affording mainly the cluster anion [Re3(μ-H)4(CO)9(MeCN)]-. This suggests that cluster stabilization after methane evolution follows a different path with respect to that observed in the reaction of 1 with CO.

Two novel rhenium(I) tricarbonyl complexes of general formula fac-[Re(N^C:)(CO)3X] are herein presented, where N^C: is the pyridoannelated N-heterocyclic carbene (NHC) arising from 2-(2-pyridinyl)imidazo[1,5-a]pyridinium hexafluorophosphate proligand, namely [pyipy]PF6, and X being Cl and Br. The synthetic pathway is a one-pot reaction that starts from the azolium salt as the NHC source and [Re(CO)5X] to yield the desired charge-neutral fac-[Re(pyipy)(CO)3X] complexes (1–2). Both complexes were thoroughly characterized by spectroscopic, electrochemical, theoretical investigation as well as X-ray diffraction analysis. They display a rather similar electronic absorption spectrum in dilute CH2Cl2 solution, which is characterized by a broad profile extending into the blue region. This lowest-lying absorption band is attributed to a transition with admixed metal-to-ligand charge transfer and intraligand charge transfer (1MLCT/1ILCT) character. Degassed samples of the complexes display moderate (Φ ≈ 1.5%) and long-lived (τ = 12.8–13.4 μs) red photoluminescence with highly structured profile independent of the nature of the ancillary halogen ligand and little sensitivity to the solvent polarity, highlighting the markedly different nature of the emitting excited state in comparison with the lowest-lying absorption. Indeed, photoluminescence is ascribed to a long-lived excited state with metal-perturbed triplet ligand-centred (3LC) character as supported by both experimental and density functional theory (DFT) investigations.

The synthesis of a series of neutral dinuclear rhenium complexes of the general formula [Re2(μ-ER)2(CO)6(μ-pydz)] (pydz = pyridazine; E = S, Se or Te; R = methyl or phenyl; the TeMe is not included) has been carried out via new, either one-pot or two-step, procedures. The one-pot synthesis consists of the oxidative addition of RE–ER across the Re–Re bond of [Re2(CO)10], in the presence of 1 equivalent of pyridazine, and affords the corresponding dinuclear complexes in high yields (ca. 85%). Furthermore, a general two-step procedure has been carried out, which involves the synthesis of heterocubane-like [Re4(μ3-ER)4(CO)12] molecules and their reaction with pyridazine, quantitatively affording the corresponding dinuclear species through a symmetric [2+2] fragmentation pathway. The molecular structure of the complexes has been elucidated by single crystal XRD analysis, and TD-DFT calculations predicted the existence of conformers differing in the orientation of the chalcogen substituents with respect to the pyridazine ligand. The relative stabilities and the activation barriers for the interconversion have been calculated, observing a regular trend that has been rationalized depending on the hybridization of the chalcogen atom. Variable temperature NMR studies experimentally confirmed the theoretical prediction, showing, in solution, two conformers with different relative amounts and different interconversion rates between them, depending on the chalcogen nature. From the electrochemical point of view the S, Se and Te complexes display a bi-electronic reversible oxidation peak, differently from the two mono-electronic irreversible oxidation peaks previously observed for the O derivatives. Moreover, a progressive narrowing of the HOMO–LUMO gap on going from O to Te, arising from the increase of the HOMO level, has been observed. This is in line with the decreasing electron-withdrawing strength of the chalcogenide bridging ligand, so that the energy gap for the telluride derivative is 1.64 eV, the smallest value in the whole family of the di-rhenium pyridazine complexes. The spectroscopic HOMO–LUMO gap parallels this trend, with a significant red-shift of the metal-to-ligand charge transfer absorption, making the telluride complex highly promising as a photosensitizer in the field of solar energy conversion. In agreement with the narrow HOMO–LUMO gap, no photoluminescence has been observed upon optical excitation.

A new two-dimensional zinc(II) coordination polymer of 5-aminoisophtalic acid (H2AIP), namely [Zn(AIP)(DMSO)]n (Zn-CP), has been successfully prepared via conventional heating at 100 ​°C in a (2:1) dimethyl sulfoxide/ethanol solvent mixture. The compound has been characterized by FT-IR spectroscopy, elemental and thermogravimetric analyses, powder and single-crystal X-ray diffraction techniques. Crystal structure of Zn-CP shows the presence of neutral layers of composition Zn(AIP) and 63-hcb topology, which are decorated only on one side with dangling DMSO molecules. Moreover, the composite Zn-CP@Foam has also been fabricated growing Zn-CP crystals on the 3D porous structure of a melamine-formaldehyde foam (MF) by immersion of pieces of MF in the precursor solution of the coordination polymer. Both Zn-CP and Zn-CP@Foam materials have been studied for the adsorption in water of cationic dyes, such as Crystal Violet (CV), Victoria Blue (VB) and Malachite Green (MG), and anionic dyes, such as Sunset Yellow (SY), Congo Red (CR) and Aniline Blue (AB). Results show selective sorption of cationic dyes only, with faster and larger adsorption capacity observed for the porous composite material which has an adsorption capacity for Victoria Blue (VB) (102 ​mg ​g−1) more than twice larger than that found for pristine Zn-CP powder (48 ​mg ​g−1). This selectivity towards cationic dyes is attributed to electrostatic interactions between the cationic dye molecules and the negatively charged surface of the zinc coordination polymer, which shows a zeta potential of −13.7 ​mV. Moreover, dye adsorbed Zn-CP and Zn-CP@Foam can be regenerated by immersion in a water/acetic acid solution (1:1) and reused with almost the same efficiency.

Stepwise self-assembly processes using new lanthanide metalloligands (Ln-MLs) and silver salts have been successfully applied to isolate 4f-4d heterometallic coordination networks of four different structural types. In particular, the new lanthanide tetrakis-chelate complexes NEt4[Ln(L1)4] [HL1 = 1,3-bis(4'-cyanophenyl)-1,3-propanedione; Ln = Eu (1a), La (1b), Nd (1c), Tb (1d)] and NEt4[Ln(L2)4] (HL2 = 1,3-bis(4'-pyridyl)-1,3-propanedione; Ln = Eu (1e), Nd (1f)] have been synthesized, characterized, and reacted with different silver salts. The use of NEt4[Ln-(L1)4] allowed then to isolate and characterize i) neutral onedimensional ladder-like species of formula [Ln(L1)4Ag] [Ln = Eu (2a), La(2b), Nd(2c), Tb(2d)] and ii) their supramolecular isomers [Ln(L1)4Ag] [Ln = Eu (3a), La (3b), Nd (3c), Tb (3d)] showing a very unstable 2D network structure, iii) the cationic 2D species [Ln(L1)4Ag2]X [Ln = Eu, X = PF6-, CF3SO3-, ClO4- (4a-4c); Ln = Tb, Nd, La X = PF6 - (4d-4f)], and, only for lanthanum, iv) a fourth 2D species of formula [La(L1)4(H2O)Ag] (5) and SQL topology. Of the eight nitrile groups on the MLs potentially coordinating, only a partial number is used for networking with Ag(I), that is, only two in families 2 and 3 and four in family 4 and in network 5. Finally, the four structural types are rationalized in terms of a new "pincer-like" secondary building unit (SBU) consisting of a silver cation coordinating two central carbon atoms (γ carbon) of two different diketonate ligands on the same ML. Therefore, it is shown that compounds 5, 4, and 2-3 contain, respectively, none, one, or two of such pincer-like SBUs. The luminescence properties of the Ln-MLs and some of their polymeric species have been also investigated in solution and in the solid state.

A new neutral cadmium-organic framework with a pillared layer structure, [Cd3(BTC)2(4-bpdb)2] (H3BTC = benzene-1,3,5-tricarboxylic acid; 4-bpdb = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene), has been synthesized via solvothermal reaction of cadmium nitrate with the tricarboxylic acid H3BTC and the linear bispyridyl linker 4-bpdb. The complex has been characterized by single crystal X-ray diffraction, showing to possess a 3D porous network of jcr7 topology. The capability of the prepared MOF in adsorbing the organic dyes Congo Red (CR) and Neutral Red (NR), together with kinetics and thermodynamics of their adsorption, have been investigated in detail. The adsorption process was well described by pseudo-first order and pseudo-second order kinetics for CR and NR, respectively. In addition, conversion of the MOF 3D architecture into nano-sized cadmium oxide particles has also been studied.

The novel [Re2(μ-H)(μ-OOC-CPDT)(CO)6(μ-3-Me-pydz)] complex (1; OOC-CPDT = 4H-cyclopenta[2,1-b:3,4-b']dithiophene-4-carboxylate, 3-Me-pydz = 3-methylpyridazine) has been prepared and characterized by single-crystal X-ray diffraction, density functional theory (DFT), and time-dependent DFT computations, UV-vis absorption and emission spectroscopy, and cyclic voltammetry (CV). The measured properties indicate the lack of electronic communication in the ground state between the CPDT and the rhenium diazine moieties. Oxidative electropolymerization of 1, achieved by repeated potential cycling (-0.4 to +1.0 V vs Fc(+)/Fc, in acetonitrile) with different supporting electrolytes, on different electrodes, afforded an electroactive and stable metallopolymer (poly-1). In situ measurements of the mass of the growing film (on a gold electrode, with an electrochemical quartz microbalance) confirmed the regularity of the polymerization process. The polymer exhibits two reversible oxidation peaks of the thiophene chain and a broad irreversible reduction peak (-1.4 V, quite close to that observed for the reduction of monomer 1), associated with a remarkably delayed sharp return peak, of comparable associated charge, appearing in close proximity (+0.3 V) to the first oxidation peak of the neutral polythiophene chain. This charge-trapping effect can be observed upon repeated cycles of p and n doping, and the negative charge is maintained even if the charged electrode is removed from the solution for many hours. Electrochemical impedance spectroscopy showed that the main CV oxidation peak corresponds to facile charge transfer, combined with very fast diffusion of both electrons and ions within the polymer. In summary, poly-1 provides a new example of a metallopolymer, in which the conductive properties of the π-conjugated system are added to the redox behavior of the pendant-isolated complexes.

1H and 19F NMR spectroscopy, X-ray diffractometry and DFT computations have been used for investigating the interaction between the Lewis base pyridine and bis(pentafluorophenyl)borinic acid Ar2BOH (1, Ar=C6F5). Previous studies showed that the latter species in solution exists as an equilibrium mixture of the monomer (1 m ) and a cyclic trimer (1 t ), in variable ratios, and that the trimer is stabilized in the presence of Lewis bases, by the formation of strong 1 t ···L hydrogen bonds. In the present case, upon addition of 0.33 equivalents of pyridine, low-temperature NMR spectra showed the formation of deprotonated 1 t (anion 3), strongly hydrogen-bonded to the pyridinium cation Hpy+. The presence of this cation was confirmed by the high value of 1JHN (88 Hz). DFT computations confirmed the higher stability of the O-···H–N+ limit form over the neutral O–H···N one. Variable temperature NMR spectra showed that the Hpy+·3 ion pair has high conformational freedom. At temperatures higher than 260 K, 3 underwent reversible partial fragmentation to give 1 m and the Lewis acid-base covalent adducts between pyridine and either 1 m (2 py ), or its anhydride (5 py ). The fragmentation was perfectly reversible on lowering the temperature. The adduct 2 py became the only species in solution in the presence of 1 equivalent of pyridine, showing that the Lewis basicity of pyridine plays the major role, at variance with what previously observed with other bases. Hydrogen bond interactions, however, promote the supramolecular organization of 2 py in the form of a cyclic tetramer, as revealed by X-ray single crystal diffractometric analysis. The formation of the deprotonated trimer 3 was previously observed in the reaction of 1 with 1,8-bis(dimethylamino)naphtalene (DMAN). However the stepwise dearylation processes, which were dominant in the reactions with DMAN, have a very marginal role in the reaction with pyridine, due to its lower Brønsted basicity. For Supplementary Material see online version. Supporting information available: details of the NMR spectroscopic characterization (Figs. S1–S4), computed chemical shifts (Table S1), details of the X-ray diffractometric analysis, and tables of geometrical parameters (Tables S2–S3).

In this contribution we provide an overview of the preparation and of the properties of different classes of luminescent dinuclear tricarbonyl rhenium(I) complexes of general formula [Re 2 (μ-X) 2 (CO) 6 (μ-1,2-diazine)] (X = halide, hydride, alkoxide, and thiolate). Their electrochemical and photophysical properties in solution are presented, as well as combined density functional (DFT) and time-dependent density functional (TDDFT) studies of their geometry, relative stability and electronic structure. The relationships between the structure and the emission properties of the complexes are discussed in detail, showing a modulation effect of the bridging ancillary ligands as well as of the diazine substituents on energy, lifetime and quantum yield of the emission. Photoluminescent quantum yields ( Φ ) up to 0.53 have been measured in fluid solution for the dichloro complexes containing diazines bearing alkyl groups in both the β positions, designed to optimize all the parameters responsible for the radiative decay. The photophysical properties in the solid state are also briefly presented, showing in some cases an increase of the emission intensity, discussed in terms of restriction of intramolecular roto-vibrational motions. These properties, together with their good processability and high stability, allowed the successful use of some of these complexes as a phosphorescent dopant in OLEDs. The good performances of OLED devices prepared both by solution- and vacuum-processing are reported. The preliminary work exploring the potential of these complexes as luminescent labels for bioimaging is also presented.

A number of 2-methyl-4-aryl-5-methoxy-6-alkylindenes and C2-symmetric Me2Si-bridged ansa-zirconocenes based on them were synthesized. Zirconocenes were obtained by means of highly effective and scalable racemo-selective synthetic approach based on the use of a Zr tert-butyl amide complex. The structure of μ-(bis-[η5-6-tert-butyl-5-methoxy-2-methyl-4-tert-butylphenyl-1H-inden-1-yl]dimethylsilanediyl)dichlorozirconium(IV) (14) has been established with X-ray analysis. The introduction of a methoxy group into the indenyl fragment of zirconocene significantly improved its catalytic performance (i.e., its activity, stereoselectivity, molecular mass potential, and thermal stability) in the polymerization and copolymerization of propylene in comparison with the benchmark Spaleck-zirconocene. The role of the methoxy group is proposed to stabilize the cationic catalytic intermediates, which was confirmed using DFT calculations.

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.

The three complexes [Re2(mu-X1)(mu-X2)(CO)6(mu-ppd-kappaN3:kappaN4)] (X1, X2 ) H, 1; X1 ) H, X2 ) Cl, 2; X1, X2 ) Cl, 3; ppd) 2,5-diphenyl-1,3,4-oxadiazole) have been synthesized by different routes, involving the reaction of [Re4(mu3-H)4(CO)12]with ppd for 1, the reaction of 1 with HCl for 2, and the reaction of [ReCl(CO)5] with ppd for 3. The three complexes possess a different number of valence electrons, so the formal Re-Re bond order varies from 2 to 1 to 0 in complexes 1, 2, and 3, respectively. This is reflected in the Re-Re bond distance (277.9, 297.9, and 358.5 pm in the same series)and in the stability of the complexes in the coordinating solvent acetonitrile (t1/2 for ppd displacement 13.6, 4.5, and 3.7 h,for 1, 2, and 3, respectively). Both experimental and calculated structures indicates that coordination induces a distortion from planarity of the diphenyloxadiazole moiety due to the interaction of the equatorial carbonyls with the bridging ppd,which increases on going from 1 to 2 to 3 (dihedral angle between the oxadiazole and the phenyl rings 18.4 degrees, 23.3 degrees, and 45.0 degrees, respectively). The UV spectra show pi-pi* transitions of the oxadiazole ligand (which shift to higher energy on increasing the distortion from the planarity, from 252 to 267 nm) and metal-to-ligand charge transfer absorptions (from 300 to 362 nm). Upon irradiation between 340 and 380 nm, complex 2 only features a weak broad emission at 527 nm(phi)0.02%), whereas upon excitation at 300 nm, the emission typical of free ppd is observed, suggesting photodissociation.Cyclic voltammetry investigations in acetonitrile showed that the three complexes exhibit ligand-centered irreversible reduction peaks (from -1.83 to -1.93 V vs Fc+|Fc), shifted to more positive values with respect to free ppd (-2.50 V). The shift however is smaller than in the analogous derivatives containing 1,2-diazines, suggesting a smaller electron depletion of the heterocycle ligand upon coordination. The complexes also show a metal-centered, bi-electronic, irreversible oxidation peak (from 1.05 to 1.37 V vs Fc+/Fc). A combined density functional and time-dependent density functional (TD DFT)study allowed us to understand the factors affecting the stability of the three complexes and to rationalize their electrochemical and photophysical properties in terms of their electronic structure.

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 possible use of some dinuclear rhenium complexes as sensitizers for dye sensitized solar cells (DSSCs) has been investigated. They have general formula [Re2(μ-X)(μ-Y)(CO)6(μ-pyridazine-4-COOH)], with X = Y = Cl (1), X = H, Y = benzoato (2), and X = H, Y = 4-diphenylaminobenzoato (3). An original synthetic strategy has been set for preparing the hydrido-carboxylato derivatives 2 and 3. They have been indicated by DFT and TD-DFT computations as the most promising dyes, endowed with good light harvesting capability. The complexes have absorption maxima in the range of 405–443 nm, on TiO2 films, arising from metal-to-ligand-charge transfer transitions. Cyclic voltammetry experiments have been performed on the derivatives containing the methyl ester of the pyridazine-4-COOH acid, showing electrochemical band gaps in the range of 2.25–1.63 eV. The best DSSC results have been obtained using complex 3, with an overall solar-to-electric conversion efficiency of 1.0%. Noteworthy the presence of a hydrido ligand did not show any detrimental effect on the stability of the sensitizers under the operating conditions.

Polypropene and poly(1-butene) have been synthesized under very similar experimental conditions with a series of MAO-activated C 2 -symmetric and C 1 -symmetric ansa -zirconocenes. The C 1 -symmetric zirconocenes bearing the bilaterally symmetric fluorenyl or bis(2-methylthieno)cyclopentadienyl ligand connected through a dimethylsilyl bridge to substituted indenyl ligands produce isotactic polybutene of similar or higher molecular mass and with noticeably higher isotacticity, compared to isotactic polypropene prepared with the same catalysts under comparable conditions. Structural and mechanistic reasons for such behavior are discussed on the basis of QM/MM calculations.

Bis(pentafluophenyl)borinic acid, Ar2BOH (1, Ar = C6F5), in dichloromethane solution is present as an equilibrium mixture of monomeric (1m) and trimeric (1t) forms. Previous studies showed that water affects both the position and the rate of this equilibrium. Here, the behavior of 1 in the presence of tetrahydrofuran (THF), a nucleophile able to behave as a Lewis base and H-bond acceptor only, has been studied, by monitoring with 1H and 19F NMR the course of titrations performed directly into NMR tubes. The addition, at 183 K, of 0.33 equiv of THF caused the instantaneous and quantitative formation of the hydrogen-bonded adduct between the trimer 1t and one molecule of THF. Homo- and heteronuclear 2D NMR correlation experiments led to a solution structure consistent with the C2-optimized geometry obtained by PM3 computations. The H-bonding of the THF molecule causes major deformations of the molecular geometry of the trimer, so that only one molecule of THF can interact with the trimer, in spite of its th...

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 stereomutations in a class of tris(pentafluorophenyl)borane−benzotriazole adducts are investigated by means of variable-temperature 19F NMR and X-ray crystallography. At low temperature the presence of a pair of conformational enantiomers is confirmed by NMR spectra obtained in a chiral medium. Two different energy barriers, corresponding to an enantiomerization process and a B−N rotation, were observed and their values measured (ΔG⧧ = 10.7 and 12.8 kcal mol-1 in the case of 1). In the case of the bis-adduct 3, two conformational diastereoisomers with different populations were detected at low temperature, while only one diastereoisomer is present in the crystalline state.

Reaction between 7-azaindole and B(C6F5)3 quantitatively yields 7-(C6F5)3B-7-azaindole (4), in which B(C6F5)3 coordinates to the pyridine nitrogen of 7-azaindole, leaving the pyrrole ring unreacted even in the presence of a second equivalent of B(C6F5)3. Reaction of 7-azaindole with H2O−B(C6F5)3 initially produces [7-azaindolium]+[HOB(C6F5)3]- (5) which slowly converts to 4 releasing a H2O molecule. Pyridine removes the borane from the known complexes (C6F5)3B-pyrrole (1) and (C6F5)3B-indole (2), with formation of free pyrrole or indole, giving the more stable adduct (C6F5)3B-pyridine (3). The competition between pyridine and 7-azaindole for the coordination with B(C6F5)3 again yields 3. The molecular structures of compounds 4 and 5 have been determined both in the solid state and in solution and compared to the structures of other (C6F5)3B-N-heterocycle complexes. Two dynamic processes have been found in compound 4. Their activation parameters (ΔH⧧ = 66 (3) kJ/mol, ΔS⧧ = −18 (10) J/mol K and ΔH⧧ = 76 (5)...

The strong Lewis acid tris(pentafluorophenyl)boron, B(C6F5)3, reacts with several nitrogen-containing Lewis bases (nitriles, amines, imines, pyridines, etc.) and also with non-basic substrates (such as pyrroles and indoles) producing in both cases the B N coordination adduct. With particular substrates (some tertiary amines, the imine tBu(Me)C NBn, N-methyl-pyrrole and -indole,) the 1:1 borane/N-compound reaction produces zwitterions where a new B C bond is generated. Some of the borane–N-compound adducts present Bronsted acidity and can be reacted with di-methyl group 4 complexes with generation of weakly associated ion pairs, which are active catalysts for the polymerization of olefins.

The previously known anion [(C6F5)3B(mu-OH)B(C6F5)3]- (2) has been prepared by a two-step procedure, involving deprotonation of (C6F5)3BOH2 to give [B(C6F5)3OH]- (1), followed by addition of B(C6F5)3. The solution structure and the dynamics of 2 have been investigated by 1H and 19F NMR spectroscopy. The reaction of [NHEt3]2 with NEt3 resulted in the formation of [NHEt3]+ [(C6F5)3BOH]-, [NHEt3]+ [(C6F5)3BH]-, and (C6F5)3B- (CH2CH=N+ Et2). This indicates that in the presence of a nucleophile anion 2 can dissociate to B(C6F5)3 and 1. The reaction of [HDMAN]2 with 1,8-bis(dimethylamino)naphthalene (DMAN) confirmed this trend. In the presence of water, 2 transformed into the adduct [(C6F5)3BO(H)H...O(H)B(C6F5)3]- (3), containing the borate 1 hydrogen-bonded to a water molecule coordinated to B(C6F5)3. The same compound is formed by treating (C6F5)3BOH2 with 0.5 equiv of a base. A competition study established that for 1 the Lewis acid-base interaction with B(C6F5)3 is about 5 times preferred over H-bonding to (C6F5)3BOH2. The X-ray single-crystal analysis of [2-methyl-3H-indolium]3 provided the first experimental observation of an asymmetric H-bond in the [H3O2]- moiety, the measured O-H and H...O bond distances being significantly different [1.14(2) vs 1.26(2) A]. The reaction of NEt3 with an equimolar mixture of B(C6F5)3 and bis(pentafluorophenyl)borinic acid, (C6F5)2BOH, afforded the novel borinatoborate salt [NHEt3]+ [(C6F5)3BOB(C6F5)2]- ([NHEt3]4). X-ray diffraction showed that the B-O bond distances are significantly shorter than in [(C6F5)3B(mu-OH)B(C6F5)3]-. Variable-temperature 19F NMR revealed high mobility of the five aryl rings, at variance with the more crowded anion 2. 2D NMR correlation experiments showed that in CD2Cl2 the two anions [(C6F5)3BOH]- and [(C6F5)3BH]- form tight ion pairs with [NHEt3]+, in which the NH proton establishes a conventional (BO...HN) or an unconventional (BH...HN), respectively, hydrogen bond with the anion. The diborate anions 2-4, on the contrary, gave loose ion pairs with the ammonium cation, due both to the delocalized anionic charge and to the more sterically encumbered position of the oxygen atoms that should act as H-bond acceptors.

The addition of one equivalent of dimethylamine (DMA) to the 44 valence-electron triangular cluster anion [Re3(μ3-H)(μ-H)3(CO)9]− (1) affords the novel unsaturated derivative [Re3(μ-H)4(CO)9(DMA)]− (2, 46 valence electrons) which contains a dimethylamine molecule terminally coordinated to a cluster vertex. Theoretical calculations (DFT) reveal that in the more stable conformation the dimethylamine NH proton is directed towards the hydride bridging the opposite cluster edge in syn position, the close proximity of the ligands bound to the cluster surface allowing the formation of an unconventional N–H ⋯ (μ-H)Re2 hydrogen bond. The presence of this conformation in the solid state has been proven by an X-ray structural analysis of crystalline [PPh4]2. Spectroscopic evidences (IR and NMR) indicate that the dihydrogen bond is maintained also in solution and, by the evaluation of the proton spin-lattice relaxation rates at variable temperature, a good estimate of the H ⋯ H distance in solution has been determined.

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 1H, 19F, and 11B NMR data indicated that in CD2Cl2 solution monomeric bis(pentafluorophenyl)borinic acid, (C6F5)2BOH (1m), is in equilibrium with the cyclic trimer (1t) observed in the solid state. The position of the association equilibrium shifted to the right on increasing the concentration, on decreasing the temperature, and on decreasing solvent polarity, in the series CD2Cl2, CDCl3, CCl4, in agreement with the higher polarity of the monomer (2.38 D for 1m and 0.65 D for 1t, according to PM3 computations). At temperatures lower than 210 K the 1H and 19F NMR spectra revealed the simultaneous (reversible) formation of two novel compounds, which have been formulated as the (C6F5)2BOB(C6F5)2 anhydride (2) and the trimeric species [(C6F5)2BOH]3·OH2 (3), of C2 symmetry, with a water molecule formally inserted into a B−O(H)−B bridge of 1t, to give a very strong BO(H)···HO(H)B hydrogen bond (δ 18.6). 1H and 19F EXSY experiments at 184 K revealed exchange between 3 and 1m, and not 1t. The data showed that...

The (13)C NMR CP-MAS spectrum of 2-naphthylphenylsulfoxide in the solid state displays line broadening effects due to the restricted rotation about the Ph-S bond. Line shape simulation of the temperature-dependent traces allowed the corresponding barrier to be determined in the solids (14.7 kcal mol(-1)). By making use of the information obtained from single-crystal X-ray diffraction, this barrier could be satisfactorily reproduced by theoretical calculations (14.5 kcal mol(-1)) that take into account the correlated phenyl motion involving a large set of molecules in the crystalline state

Indenyl silyl amido titanium complexes based on indenoindoles, indenopyrrole, and 2-methylindenothiophene have been prepared and tested in propylene polymerization. The indenoindole ligand precursors were prepared in high yields by the acid-catalyzed Fischer condensation of indan-2-one and arylhydrazines. The Ti complexes dimethylsilyl(tert-butylamido)(N-methyl-2-methyl-5,6-dihydroindeno[2,1-b]indol-6-yl)dimethyl titanium (1), dimethylsilyl(tert-butylamido)(N-ethyl-5,6-dihydroindeno[2,1-b]indol-6-yl)dimethyl titanium (2), dimethylsilyl(tert-butylamido)(N-methyl-5,10H-indeno[1,2-b]indol-10-yl) dimethyl titanium (3), dimethylsilyl(tert-butylamido)(N-phenyl-5,10H-indeno[1,2-b]indol-10-yl)dimethyl titanium (4), dimethylsilyl(tert-butylamido)(N-methyl-2-methyl-1,8-dihydroindeno[2,1-b]pyrrol-8-yl)dimethyl titanium (5), and dimethylsilyl(tert-butylamido)(2-methyl-8H-indeno[2,1-b]thiophen-8-yl)dimethyl titanium (6) were prepared by reacting the ligand, a 2-fold excess of MeLi, and TiCl4. The molecular structures ...

The reactions of the unsaturated cluster anion [Re3(μ-H)4(CO)10]− (1) with 1,2-, 1,3- and 1,4-diazines (used as solvents) have been investigated. The reaction with 1,2-diazine at room temperature gives quantitatively the anion [Re3(μ-H)2(μ-η2-N2C4H4)(CO)10]− (3), containing a diazine bridging through the two N atoms, characterised by single crystal X-ray analysis. The orthometallated isomer [Re3(μ-H)3(μ-η2-N2C4H3)(CO)10]− (4) was obtained by refluxing 3 in toluene. The reaction of [NEt4]1 in molten 1,4-diazine (60 °C) affords the anion [Re3(μ-H)3(μ-η2-N2C4H3)(CO)10]− (5), containing orthometallated pyrazine. The slow reaction of [NEt4]1 with 1,3-diazine at room temperature gives two orthometallated isomers 6, corresponding to the metallation of carbon C2 (6a) and C6 (6b), respectively (6b/6a ratio ca. 1.2). Differently from what previously found for the analogous cluster anion containing orthometallated pyridine, the metallation reaction of diazines showed little reversibility, and poor conversion of 5 and 6 to the starting anion 1 was observed after several days under 100 atm of H2. Competition experiments, performed by dissolving [NEt4]1 in equimolar mixtures of pyridine/pyrazine or pyridine/pyrimidine, showed that the anion with metallated pyridine was the kinetically preferred product and that at longer times it slowly converted to the derivatives with metallated diazines (5 or 6).

Reaction of Li[Cp(CO)2Re(COPh)] (1) with CF3SO3Me afforded, besides the expected carbene complex [Cp(CO)2ReC(OMe)(Ph)] (2) and the alkyl–acyl derivative [Cp(CO)2Re(Me)(COPh)] (3), a third structural isomer [Cp(CO)2Re{OC(Me)Ph}] (4), which contains an acetophenone molecule coordinated to the metal center. The X-ray analysis showed that in solid acetophenone is bound to ‘CpRe(CO)2’ exclusively through an oxygen σ-donor interaction, while in solution an equilibrium between σ-bound (η1) and π-bound (η2) forms occurs, as judged by IR data and 1H and 13C variable temperature NMR spectra (π/σ ratio 2.87 at 183 K and 1.16 at 263 K in CD2Cl2, ΔH°=−4.5 kJ mol−1 for the σ⇔π reaction, Ea 58(1) kJ mol−1). In solvents different from Et2O (n-hexane, THF, acetone) and with alkylating agent different from CF3SO3Me (MeI, Me3OBF4) the formation of 4 was negligible. It has been demonstrated that 4 does not originate by acetophenone reductive elimination from 3. No evidence of the involvement of radicals has been obtained.

The reaction of pyrroles and indoles with B(C(6)F(5))(3) and BCl(3) produces 1:1 B-N complexes containing highly acidic sp(3) carbons, for example, N-[tris(pentafluorophenyl)borane]-5H-pyrrole (1) and N-[tris(pentafluorophenyl)borane]-3H-indole (2), that are formed by a new formal N-to-C hydrogen shift, the mechanism of which is discussed. With some derivatives, restricted rotation around the B-N bond and/or the B-C bonds was observed by NMR techniques, and some rotational barriers were calculated from experimental data. The acidity of the sp(3) carbons in these complexes is shown by their ability to protonate NEt(3), with formation of pyrrolyl- and indolyl-borate ammonium salts. The driving force for this reaction is given by the restoration of the aromaticity of the heterocycle.

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 reactions of the unsaturated anion [Re3(μ-H)4(CO)9(PPh3)]- (1) with the metallic Lewis acids [M(PPh3)]+ (M = Cu, Ag, Au) afford the addition derivatives [Re3{μ-M(PPh3)}(μ3-H)(μ-H)3(CO)9(PPh3)], which have been characterized in solution and in the solid state, by X-ray analysis. The copper derivative is obtained also by reaction of [Re3(μ-H)3(μ3-H)(CO)9]- (as the [Re(CO)3(Me2CO)3]+ salt) with [Cu(PPh3)2NO3]. Treatment with PPh3 extrudes the [M(PPh3)]+ groups, restoring the starting anion 1. Solid-state structures of the adducts show a butterfly Re3M metal skeleton with one hydride bridging the Re2M face and three hydrides spanning the three Re−Re edges. The interaction of the [M(PPh3)]+ cation with 1 leads only to a minor structural perturbation of the unsaturated Re2(μ-H)2 moiety. The solid-state structure is maintained in nondonor solvents, while in acetone partial (Au, Ag) or complete (Cu) reversible ionic dissociation of the adducts is observed, affording 1 and solvated [M(PPh3)]+ cations. Experime...

Protonation of the anion [Re(2)H(CO)(9)](-) (1) with a strong acid at 193 K affords the neutral complex [Re(2)H(2)(CO)(9)] (2), that in THF above 253 K irreversibly loses H(2) to give [Re(2)(CO)(9)(THF)], previously obtained by room-temperature protonation of 1. Treatment of 2 with NEt(4)OH restores the starting anion 1. Variable temperature (1)H and (13)C NMR spectra as well as T(1) measurements agree with the formulation of 2 as a classical [Re(2)H(mu-H)(CO)(9)] complex, in which two dynamic processes takes place. The "windshield-wiper motion" observed in several related complexes equalizes the two carbonyls trans to the hydrides (E(a) = 44(1) kJ mol(-)(1)), while another much faster process equalizes bridging and terminal hydrides already at 172 K. The variable temperature behavior of the (1)H transverse relaxation times revealed also proton exchange between 2, water, and the parent anion 1 (due to the acidity of 2), but such a process is too slow to account for the fast hydrides exchange in 2. The nature of the latter process has been investigated both experimentally and theoretically. Kinetic data, obtained by the analysis of the variable temperature (1)H spectra (E(a) = 24.5(5) kJ mol(-1)), revealed a small normal kinetic isotope effect (ca. 1.5). The (2)H chemical shift of the fully deuterated isotopomer 2-d(2) was found isochronous with 2, thus ruling out the presence of a significant concentration of a nonclassical [Re(2)(eta(2)-H(2))(CO)(9)] tautomer, in fast exchange with the classical dihydride. Density functional theory (DFT) calculations, carried out at the B3LYP level, confirmed the formulation of [Re(2)H(2)(CO)(9)] as a classical complex. However, when DFT was used to obtain a detailed description of the dynamic behavior of 2 in solution, a new type of hydride fast exchange emerged, involving the nonclassical tautomer as a relatively high energy (12.7 kJ mol(-1)) intermediate. Isotopic perturbation of the equilibrium by partial deuteration of 2 indicated the preference of deuterium for the bridging sites, with Delta H degrees = -475(4) J mol(-1) and Delta S degrees = -0.80(2) J K(-1) mol(-1). The same preference was observed in the anion [Re(2)H(mu-H)Cl(CO)(8)](-).

Three and tetranuclear ring clusters have been obtained by treatment of [Re2(CO)8(THF)2] with carbonyl-rhenates containing two terminal hydrides. The reaction with [ReH2(CO)4]- provided a selective route to the previously known [Re3(μ-H)2(CO)12]- triangular cluster anion 1. The reaction with [Re2H2(μ-H)(CO)8]- gave the novel [Re4(μ-H)3(CO)16]- anion 2, containing a rare example of a puckered-square metal cluster. Protonation of 1 is known to afford the neutral [Re3(μ-H)3(CO)12] species 3. Analogously the reaction of 2 with a strong acid afforded the previously known square metal clusters [Re4(μ-H)4(CO)16] 4. The reaction could not be reversed by treatment with bases. Photolysis of 4 gave the unsaturated complex [Re2(μ-H)2(CO)8] 5: this is the reverse of the dimerization reaction, that in THF at room temperature produces 4 from 5. Thermal treatment (reflux in cyclohexane for 24 h) left 4 almost unchanged. A single crystal X-ray analysis of [NEt4]2 showed a s/e/s/s (e=eclipsed, s=staggered) conformation of the Re(CO)4 units, leading to a puckered geometry of the ring, at variance with the square-planar geometry of 4 (all eclipsed). Two of the three hydrides of 2 have been located as bridging the Re–Re edges from inside the metal ring, as previously observed in 4. Density functional computations indicated a puckered conformation as the most stable for both 2 and 4, with very low activation energies for ring inversion (6.6 and 2.2 kcal·mol-1, respectively), but ruled out solid state fluxionality for 4, whose observed planar geometry must be attributed to packing stabilization.

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...

Molecular mechanics simulations within the field of the mean (when disorder is present) crystal lattice have been used to settle most of the ambiguities inherent to the interpretation of the diffra...

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.

The reaction of the unsaturated anion [Re-3(mu-H)(4)(CO)(10)](-) with pyrazole: (used as solvent at 80 degrees C) proceeds in a stepwise manner, at first giving the [Re-3(mu-H)(3)(mu-eta(2)-pz)(CO)(10)](-) anion (2, pz pyrazolate), with Hz evolution. Spectroscopic characterization has shown that 2 contains a pz ligand bridging through the two N atoms, one edge of the triangular cluster. At longer times, CO is evolved and 2 transforms into the novel species [Re-3(mu-H)(3)(mu-eta(2)-pz)(CO)(9)(Hpz)](-)(3), containing one pz ligand bridging a cluster edge and a second pyrazole molecule terminally bonded on the third vertex of the triangle, replacing an axial carbonyl of. The treatment with CO (atmospheric pressure, room temperature) slowly restores 2. A single-crystal X-ray analysis of 3 has revealed the syn coordination of the two heterocycles with respect to the metal triangle plane and an intramolecular hydrogen bond between the N-H proton of the pyrazole ligand and the aromatic pi-electrons of the bridging pyrazolate. There is NMR evidence that this intramolecular hydrogen bond is maintained in CD2Cl2 solution: (i) the N-H protonic resonance is significantly shifted upfield, with respect to the values typical of complexes containing Hpz, due to the screening effect Of the pi-electron cloud; (ii) a 2D NOESY experiment has shown a dipolar interaction between H-alpha of the pyrazolate and the N-H protonic resonance (and, to a lesser extent, H-alpha of the pyrazole). In acetone, intermolecular N-H ... solvent interactions replace, in part, the intramolecular H bond and different conformers are populated in different ratios on varying the temperature; as shown by variable-temperature and nOe (1D and 2D) experiments. Further reacting 1 in molten pyrazole causes fragmentation of the triangular cluster moiety with formation of the novel dinuclear anion [Re-2(mu-H)(mu-eta(2)-pz)(2)(CO)(6)](-) (4) and of the neutral complex [Re(pz)(CO)(3)(Hpz)(2]). A single-crystal X-ray analysis of the [NEt4](+) Salt of 4 showed that the dinuclear anion contains two fac-Re(CO)(3) units linked by one hydride and two pyrazolato bridging Ligands, with the two mu-eta(2)-pz units almost orthogonal to each other. A more selective route to anion 3 is provided by the reaction of the 46 valence electron complex [Re-3(mu-H)4(CO)(9)(Hpz)](-) (6) with Hpz. On using pyrazole deuterated in the nitrogen site. HD evolution has been demonstrated. The treatment of 6 with MeCN affords, even if very slowly, another derivative containing a bridging pyrazolate, namely the anion [Re-3(mu-H)(3)(mu-eta(2)-pz)(CO)(9)(NCMe)](-), characterized spectroscopically. Also, the unsaturated anion [Re-3(mu-H)(4)(CO)(9)(PMe2Ph)](-) reacts with Hpz, giving two isomers of the [Re-3(mu-H)(3)(mu-eta(2)-pz)(CO)(9)(PMe2Ph)](-) anion (with the phosphine in an axial and equatorial position, respectively). The reactions rates of the 46 valence electron complexes [Re-3(mu-H)(4)(CO)(9)L](-) with pyrazole increase on increasing the electron density on the cluster (in the order L = Hpz > PMe2Ph > CO), suggesting that the rate is controlled by the interaction of a "hydridic" H ligand with the acidic N-H bond of pyrazole. In no case has activation of the ortho C-H bond of pyrazole been observed.

The dummy atom formalism, originally proposed by Doman, Landis, and Bosnich for metallocenes, has been generalized in order to deal with any kind of π-bonding ligands and cluster faces (which can also be seen as polyhapto moieties). A modified VESCF approach has been used to derive a general force field for ηn-coordinated π-bonding ligands whose performances are comparable with those of the best current force fields for cyclopentadienyl derivatives but can be used also for μ3-η2:η2:η2 and even complex coordination modes. This approach, which can be considered a further step in the building up of a general force field for metal (carbonyl) clusters, has been tested by rationalizing the dynamic stereochemistry in solution of two classes of triangular clusters: M3L3(CO)3 (M = Co, Rh, Ir; L = η5-Cp, η5-Cp*, η5-Ind) and Co3(η5-Cp)3(μ3-η2:η2:η2-RR‘C6H4) (R = R‘ = H, Me, Et and R = Me, Et, iPr; R‘ = H).