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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.

We report here on two stable polymorphs of the dinuclear complex [Re2(μ-Cl)2(CO)6(μ-4,5- (Me3Si)2pyridazine)]. The compound belongs to the recently reported class of dinuclear luminescent Re(I) complexes of general formula [Re2(μ-Cl)2(CO)6(μ-1,2-diazine)]. In the solid state, the complex exhibits a unique combination of unusual properties: (i) concomitant formation of two highly luminescent polymorphs, and single crystal-to-single-crystal conversion of one form into the other, (ii) remarkable differences in the absorption properties of the two polymorphs due to different redistribution of oscillator strength among the different excitons, and (iii) remarkable differences among the emission properties. In particular, a higher emission quantum yield was found in the solid state than in solution (measured to be 0.52 and 0.56 for the two polymorphs, almost one order of magnitude higher than that of the molecule in solution). Interest in luminescent materials able to efficiently emit in the solid state is continuously growing, because in most applications the dyes are used as solid films. Although rigid environments are expected to freeze rotovibrational relaxation pathways, luminescence efficiency often decreases in the solid state with respect to liquid solution due to concentration quenching, affecting both organic and organometallic emitters. However, an increasing number of molecular-based emitters exhibit enhanced solid state emission. Apart from the importance of bulky substituents in reducing concentration quenching effects, other intra- or inter-molecular phenomena have been invoked as well, such as conformational changes, π-π stacking, hydrogen bonds, or Jaggregates, which cause rearrangements of the energy levels and population. In these two polymorphs the enhancement of the emission with respect to the solution is most likely due to the restricted rotation of the Me3Si groups in the crystals, providing an interesting example of aggregation-induced emission effect (AIE). To provide more insight into the optical properties of the two polymorphs, we present a combined computational and experimental study in the framework of crystal optics in the aim to explore the role of molecular packing on the UV-visible absorption properties of the two known polymorphs of [Re2(μ-Cl)2(CO)6 (μ-4,5-(Me3Si)2pyridazine)].

The synthesis and full characterization of new platinum complexes bearing a bulky asymmetric dianionic tridentate ligand is reported. The hindrance of the ligand prevents detrimental intermolecular interactions yielding to highly emitting species in both crystalline state and thin-film. Such properties prompted their successful use in solution-processed OLEDs, showing remarkable external quantum efficiency up to 5.6%.

A combined computational and experimental study in the framework of crystal optics enables us to rationalize the UV-visible absorption properties and the observed differences among the two polymorphs of [Re 2(μ-Cl) 2(CO) 6-(4,5-(Me 3Si) 2pyridazine)]. In one polymorph, several excitons are allowed originating from the main molecular electronic transition, in contrast to the other polymorph where H-like aggregation is found and only one blue-shifted exciton possesses a measurable oscillator strength. This very different electronic behavior for the two polymorphs is believed to be the key factor, which is responsible for the observed remarkable differences in the energy, polarization, and intensity of the optical bands. © 2011 American Chemical Society.

A series of [Re 2(μ-ER) 2(CO) 6(μ-pydz) ] complexes have been synthesized (E = S, R = C 6H 5, 2; E = O, R = C 6F 5, 3; C 6H 5, 4; CH 3, and 5; H, 6), starting either from [Re(CO) 5O 3SCF 3] (for 2 and 4), [Re 2(μ-OR) 3(CO) 6] - (for 3 and 5), or [Re 4(μ 3-OH) 4(CO) 12] (for 6). Single-crystal diffractometric analysis showed that the two μ-phenolato derivatives (3 and 4) possess an idealized C 2 symmetry, while the μ-benzenethiolato derivative (2) is asymmetrical, because of the different conformation adopted by the phenyl groups. A combined density functional and time-dependent density functional study of the geometry and electronic structure of the complexes showed that the lowest unoccupied molecular orbital (LUMO) and LUMO+1 are the two lowest-lying π* orbitals of pyridazine, whereas the highest occupied molecular orbitals (HOMOs) are mainly constituted by the "t 2g" set of the Re atoms, with a strong Re-(μ-E) π* character. The absorption spectra have been satisfactorily simulated, by computing the lowest singlet excitation energies. All the complexes exhibit one reversible monoelectronic reduction centered on the pyridazine ligand (ranging from -1.35 V to -1.53 V vs Fc +|Fc). The benzenethiolato derivative 2 exhibits one reversible two-electron oxidation (at 0.47 V), whereas the OR derivatives show two close monoelectronic oxidation peaks (ranging from 0.85 V to 1.35 V for the first peak). The thioderivative 2 exhibits a very small electrochemical energy gap (1.9 eV, vs 2.38-2.70 eV for the OR derivatives), and it does not show any photoluminescence. The complexes containing OR ligands show from moderate to poor photoluminescence, in the range of 608-708 nm, with quantum yields decreasing (ranging from 5.5% to 0.07%) and lifetimes decreasing (ranging from 550 ns to 9 ns) (3 > 4 > 6 ≈ 5) with increasing emission wavelength. The best emitting properties, which are closely comparable to those of the dichloro complex (1), are exhibited by the pentafluorophenolato derivative (3). © 2012 American Chemical Society.

The dinuclear complex [Re(2)(μ-Cl)(2)(CO)(6)(μ-4,5-(Me(3)Si)(2)pyridazine)] gives in the solid state two polymorphs (yellow, 1Y, and orange, 1O), which can be either concomitantly or separately obtained on varying the crystallization rate. Both crystal phases exhibit intense photoluminescence from the lowest lying triplet metal-to-ligand charge transfer state, much stronger than in solution (quantum yields 0.56 and 0.52, for 1O and 1Y respectively, vs 0.06 in toluene), likely due to the restricted rotation of the Me(3)Si groups in the solid state. A clean, irreversible 1O → 1Y single-crystal-to-single-crystal phase transition occurs at 443 K, as revealed by variable temperature X-ray diffraction analysis. In spite of the absence of any strong intermolecular interactions in both forms, 1O and 1Y show very different absorption and emission maxima (λ(abs) 370 and 393 nm, λ(em) 534 and 570 nm, for 1Y and 1O, respectively). This behavior highlights the importance of the local organization of molecular dipoles in perturbing the photophysical properties of the molecule in the crystal.

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.

One-dimensional metal-organic compounds with cis, trans symmetry-controlled counter anions were synthesized (cis compound {[Cu(azpy)(H2O)2(OTs)2]*2H2O*(acetone)} (1) and trans compound {[Cu(H2O)4Cu(azpy)2(OTs)2(H2O)2]*2(OTs)*2H2O*2EtOH} (2)). Only 2, having trans conformation, exhibited a complete structure-restoration effect with a mechanism involving layering of molecular "bricks" of water and solvent molecules.

The reaction of the electronically unsaturated (56 valence electrons, ve) tetrahedral cluster [Re4(mu3-H)4(CO)12] (1) with pyridazine (pydz) gives as the main initial product the tetranuclear cluster [Re4(mu-H)4(mu-pydz)(pydz)2(CO)12] (2a), with 64 ve and four hydrogen-bridged metal-metal interactions, with a spiked-triangle geometry. One of the three pydz ligands bridges, in a cis configuration, the cluster edge opposite to the vertex bearing the spike, as indicated by the X-ray single-crystal analysis. This species slowly decomposes, affording the dinuclear unsaturated (32 ve) complex [Re2(mu-H)2(mu-pydz)(CO)6] (3a) and two isomers of the tetranuclear cluster [Re4(mu-H)4(mu-pydz)2(CO)12] (64 ve), sharing an unusual square cluster geometry and differing in the trans (major, 85%, 4a) or cis (4a') configuration of the bridging pydz ligands. The structures of 3a and 4a have been ascertained by X-ray analysis, while the characterization of 4a' was hampered by its instability (slowly transforming into 3a in THF solution). Both the dimer and the square cluster 4a are also formed directly (and quickly) from 1, being present in solution since the beginning of the reaction. Cluster 4a is the main final reaction product. The reaction with phthalazine follows a similar course, with some differences in the relative amount of the final products 3b and 4b. Most of the novel complexes are able to emit light in solution at room temperature, and photophysical measurements were performed in CH2Cl2 solution on the main stable reaction products (i.e., the dinuclear species 3a and 3b and the trans square clusters 4a and 4b). The emission was in the range of 580-645 nm, from MLCT excited states, with lifetimes on the order of a hundred nanoseconds (50-473 ns). The quantum yields were 1 order of magnitude higher for the squares (1.7 and 1.3% for 4a and 4b, respectively, in CH2Cl2) than for the dinuclear complexes ( approximately 0.1%). In the case of 4a, a blue shift and an increase of the emission intensity were observed upon decreasing the solvent polarity.

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 (DeltaH = 66 (3) kJ/mol, DeltaS = -18 (10) J/mol K and DeltaH = 76 (5) kJ/mol, DeltaS = -5 (18) J/mol K) are comparable with those of other (C6F5)3B-based adducts. The nature of the intramolecular interactions that result in such energetic barriers is discussed.

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

The quantitative addition of pyrazole (Hpz) to the 44 valence-electron, triangular cluster anion [Re3(mu 3-H)-(mu-H)3(CO)9]- gives the novel unsaturated anion [Re3(mu-H)4(CO)9(Hpz)]- (1, 46 valence electrons), which contains a pyrazole molecule that is terminally coordinated on a cluster vertex. Solidstate 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 (delta H degree = -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 mu-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 N-H...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(mu 3-H)-(mu-H)3(CO)9]- and [Re3(mu-H)3(CO)9-(mu-eta 2-pz)(Hpz)]-, with H2 evolution. Slow H2 evolution also leads to the formation of the anion [Re3(mu-H)3-(CO)9(pz)]- (5), in which the pyrazolate anion adopts a novel mu 3-eta 2-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(mu-H)3(CO)9(mu 3-CH3)]- through the intermediate formation of two isomeric addition derivatives and following CH4 evolution.

Group 4 dimethylmetallocenes are catalyst precursors for the methylmetallocenium/borate catalyst systems for olefin polymerization, and they are usually prepared by methylation (with MeMgCl or MeLi) of the parent metallocene dichlorides. We describe here a simpler preparation of a series of bisindenyldimethylmetallocenes carried out by reacting the pi-ligand with a 2-fold excess of MeLi, and then MtCl(4) (Mt = Ti, Zr, Hf). This simple, one-pot method produces the dimethylated complexes in higher overall yield, and saves on reaction time and solvents. Ind(2)MtMe(2) (1, Mt = Ti; 2a, Mt = Zr; 3, Mt = Hf), (4,7-Me(2)Ind)(2)ZrMe(2) (4), rac/meso-[C(2)H(4)(Ind)(2)]ZrMe(2) (5), meso-[C(2)H(4)(4,7-Me(2)Ind)(2)]ZrMe(2) (m-6a), and meso-[C(2)H(4)(4,7-Me(2)Ind)(2)]HfMe(2) (m-7a) have been prepared in 40-80% isolated yields. 2a reacts with 1-4 equiv of t-BuOH to give the mono-tert-butoxy derivative 2b, Ind(2)ZrMe(O-t-Bu), while reaction with 2 equiv of C(6)F(5)OH cleanly affords Ind(2)Zr(OC(6)F(5))(2) (2c). Analogously, in the presence of 2 equiv of t-BuOH, m-6a gives meso-[C(2)H(4)(4,7-Me(2)Ind)(2)]ZrMe(O-t-Bu) (m-6b) with replacement of the outward methyl group only, as established by NMR analysis; meso-[C(2)H(4)(4,7-Me(2)Ind)(2)]Zr(OC(6)F(5))(2) (m-6c) is obtained by reaction with 2 equiv of C(6)F(5)OH. The molecular structures of m-6a and m-6c are also described.

The reaction of the carbene complex [Cp(CO)(2)Re=C(OMe)(Ph)] with [Pt(COD)(2)] affords in high yield the novel complex [Cp(Co)(2)Re{mu-C(OMe)(Ph)}Pt(COD)] (2), containing a bridging carbene ligand. Reaction of 2 with (Me3O)BF4 results in removal of the carbene-bound methoxy group, with formation of the cation [Cp(CO)(2)Re{mu-CPh}Pt(COD)](+) (3), in which a bridging carbyne is present. Both the complexes contain only ligands coordinated through carbon atoms and represent the highest members, as far as the Pt:Re ratio is concerned, of the small family of phosphorous-free Pt-Re mixed metal complexes containing Pt-Re bonds. Their full H-1 and C-13 NMR characterization in solution and their single-crystal solid state diffractometric analysis are reported and discussed. The X-ray analysis evidenced the substantially symmetric nature of the carbene bridge in the dimetalla-cyclopropane ring of complex 2 [Re-Pt 2.7188(3), Re-(mu-C) 2.166(4) and Pt-(mu-C) 2.055(4) Angstrom]. In complex 3 the bond length pattern within the three-membered ring is suggestive of a significant double-bond character for the Re-(mu-C) interaction [Re-Pt 2.707(1), Re-(mu-C) 1.904(9) and Pt-(mu-C) 1.981(8) Angstrom]. Both complexes show a semi-bridging CO ligand, with Pt...C distances of 2.452(4) and 2.299(9) Angstrom, in 2 and 3, respectively. The C-13 NMR characterization showed that the Pt...CO interaction is also maintained in solution in both complexes. In cation 3 a libration of the ReCp(CO)(2) fragment around the Pt-Re axis, fast down to 193 K, interchanges the two carbonyl locations observed in the solid state, as well as the environments of couples of COD carbon atoms, leading to an apparent C-s symmetry. The correlation between spectroscopic data and structural features (concerning bridging carbenes or carbynes and semi-bridging carbonyls) in the class of heterodimetallic M-Pt complexes is discussed. (C) 2000 Elsevier Science S.A. All rights reserved.

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 first five-membered rings of metal atoms connected by M-M or M-H-M bonds only have been obtained by a Re

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.

A general, computationally easy method for minimizing the steric energy of a molecule, polymer, surface, or net within the field of a fixed, or periodically updated, crystal lattice has been devised. The goal has been obtained by coupling molecular mechanics (MM) to Kitaigorodsky’s atom-atom pairwise potential (AAPP). The primary outcomes of such MMAAPP computations are the “solid state” conformation of the molecule, its intramolecular steric energy and its interaction energy with the surrounding lattice. These computations are ideally suited for studying relative stabilities of different polymorphs, plastic deformations of a whole crystal lattice, and molecular motions of flexible guest molecules in host crystal lattices. The proposed approach can help in understanding solid-state dynamics, factors controlling reactivity in crystal lattices, and crystals as “supramolecular entities”. In addition, the capability of building “hypothetical” crystals with sterically reasonable geometries can be exploited in the process of solving crystal structures from partial diffraction data.

A chair conformation comparable to that observed for six-membered rings composed of tetrahedral carbon atoms is found for the cluster anion [Re6(μ- H)5(CO)24]- (see picture; black spheres: Re, white spheres: μ-H; CO ligands omitted for clarity) in spite of the octahedral coordination at the Re centers. This is the first example of a carbonyl cluster exhibiting a cyclohexane-like geometry of the metallic framework.