Search

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.

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).

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.

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.

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 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 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...

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...

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 title molecule in the solid state exists as a cyclic trimer, with B−O(H)−B bridges and a cyclohexane-like structure (C2 twist-boat conformation); dissolution in toluene-d8 affords the B(C6F5)2OH monomer, in which the low-temperature 19F NMR data reveal restricted rotation of the OH substituent around the Ar2B−OH bond (Ea = 39 kJ mol-1), as a result of the partial double-bond character of this interaction.

A large range of bis(R-n-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 and bis(4,7-dimethylindenyl)methane have been synthesized in 70% and 50% yield, respectively, from the corresponding indenes. Typical reaction conditions are as follows: indene in DMF or DMSO, 0.5 equiv of CH2O, 0.2-0.5 equiv of EtONa, room temperature. This process provides an inexpensive and atom-efficient protocol for the synthesis of methylene-bridged ligands, providing a facile entry into methylene-bridged ansa-zirconocenes: MAO-activated Ca-symmetric rac-dichloro[methylenebis(eta(5)-1-indenyl)]zirconium (1) and rac-dichloro[methylenebis(4,7-dimethyl-eta(5)-1-indenyl)]zirconium (2) polymerize ethylene to low molecular weight, vinyl-terminated linear polyethylene, and liquid propylene to low molecular weight, low isotacticity polypropylene. The microstructure, molecular weight, and end-group structure of these isotactic polypropylenes (i-PP) are compared to those from rac-[isopropylidenebis(1-indenyl)]ZrCl2 (3), rac-[ethylenebis(1-indenyl)]ZrCl2 (4), rac-[ethylenebis(4,7-dimethyl-1-indenyl)]ZrCl2 (5), and the silicon-bridged rac-[dimethylsilylbis(1-indenyl)]ZrCl2 (6). The molecular structures of 1 and 2 have been determined and compared to those of 3-6. In liquid monomer at 50 degrees C, the amount of secondary insertions increases on going from the more open to the more hindered systems. At the same time, there is an increase of the fraction of secondary units undergoing isomerization from the normal 2,1 unit to the 3,1 unit (tetramethylene sequence).

The addition of [Re2H(CO)(9)](-) to the electronically unsaturated complex [Re-2(mu-H)(2)(CO)(8)] rapidly and selectively gives the anion [Re4H(mu-H)(2)(CO)(17)](-) (2), containing an open chain tetranuclear metal skeleton, as revealed by a single-crystal X-ray analysis of its [NEt4](+) salt. In the solid state the three metal-metal interactions display a staggered-eclipsed-staggered conformation, while in solution H-1 and C-13 NMR spectra have shown conformational freedom around the three Re-Re interactions and a dynamic process exchanging the two hydrides bound to the terminal H2Re(CO)(4) moiety, as well as the carbonyls trans to them (E-a = 48(1) kJ/mol). A windshield-wiper motion of the H2Re(CO)(4) fragment around the two trans diaxial carbonyls, analogous to that previously observed in the related anions [Re3H(mu-H)(CO)(13)](-) and [Re2H2(mu-H)(CO)(8)](-), is likely responsible for this exchange. The tetrametallic skeleton of the anion 2 in solution easily undergoes fragmentation to trinuclear species. Under CO atmosphere the clean formation of [ReH(CO)(5)] and [Re3H(mu-H)(CO)(13)](-) has been recognized. The anion 2 is formed (even if in lower yields) also by reaction of [Re2H2(mu-H)(CO)(8)](-) with ''Re-2(CO)(9)(THF)'', obtained by treatment of [Re-2(CO)(10)] with Me3NO in THF. A C-13 NMR investigation has clarified that such ''Re-2(CO)(9)(THF)'' reagent is indeed a mixture of three eq-[Re-2(CO)(9)L] species, containing THF, H2O, and, in a minor amount, NMe3, as labile L ligands. The reaction of the same eq-[Re-2(CO)(9)L] species with [Re2H(C0)(9)](-) affords in good yields the tetranuclear cluster anion [Re-4(mu-H)(CO)(18)}](-) (3). The single-crystal X-ray analysis of [NEt4]3 has revealed also in this case a Re-4 chain, with an all-staggered conformation, of idealized C-2 symmetry. The low-temperature C-13 NMR spectrum of the carbonyls has shown a higher symmetry in solution, suggesting conformational freedom around all of the Re-Re interactions.