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We present for the first time a method for the preparation of magnetic halloysite nanotubes (HNT) by loading of preformed superparamagnetic magnetite nanoparticles (SPION) of diameter size ∼6 nm with a hydrodynamic diameter of ∼10 nm into HNT. We found that the most effective route to reach this goal relies on the modification of the inner lumen of HNT by tetradecylphosphonic acid (TDP) to give HNT–TDP, followed by the loading with preformed oleic acid (OA)-stabilized SPION. Transmission electron microscopy evidenced the presence of highly crystalline magnetic nanoparticles only in the lumen, partially ordered in chainlike structures. Conversely, attempts to obtain the same result by exploiting either the positive charge of the HNT inner lumen employing SPIONs covered with negatively charged capping agents or the in situ synthesis of SPION by thermal decomposition were not effective. HNT–TDP were characterized by infrared spectroscopy (ATR-FTIR), thermogravimetric analysis (TGA), and ζ-potential, and all of the techniques confirmed the presence of TDP onto the HNT. Moreover, the inner localization of TDP was ascertained by the use of Nile Red, a molecule whose luminescence is very sensitive to the polarity of the environment. The free SPION@OA (as a colloidal suspension and as a powder) and SPION-in-HNT powder were magnetically characterized by measuring the ZFC-FC magnetization curves as well as the hysteresis cycles at 300 and 2.5 K, confirming that the super-paramagnetic behavior and the main magnetic properties of the free SPION were preserved once embedded in SPION-in-HNT., SPION nanoparticles are selectively loaded into halloysite lumen, keeping their superparamagnetic character.

[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.

In this work, we report the synthesis of [Ru(phen)3 2+]-based complexes and their use as photosensitizers for photodynamic therapy (PDT), a treatment of pathological conditions based on the photoactivation of bioactive compounds, which are not harmful in the absence of light irradiation. Of these complexes, Ru-PhenISA and Ru-PhenAN are polymer conjugates containing less than 5%, (on a molar basis), photoactive units. Their performance is compared with that of a small [Ru(phen)3 2+] compound, [Ru(phen)2BAP](OTf)2 (BAP = 4-(4′-aminobutyl)-1,10-phenanthroline, OTf = triflate anion), used as a model of the photoactive units. The polymer ligands, PhenISA and PhenAN, are polyamidoamines with different acid-base properties. At physiological pH, the former is zwitterionic, the latter moderately cationic, and both intrinsically cytocompatible. The photophysical characterizations show that the complexation to macromolecules does not hamper the Ru(phen)3 2+ ability to generate toxic singlet oxygen upon irradiation, and phosphorescence lifetimes and quantum yields are similar in all cases. All three compounds are internalized by HeLa cells and can induce cell death upon visible light irradiation. However, their relative PDT efficiency is different: the zwitterionic PhenISA endowed with the Ru-complex lowers the PDT efficiency of the free complex, while conversely, the cationic PhenAN boosts it. Flow cytometry demonstrates that the uptake efficiency of the three agents reflects the observed differences in PDT efficacy. Additionally, intracellular localization studies show that while [Ru(phen)2BAP](OTf)2 remains confined in vesicular structures, Ru-PhenISA localization is hard to determine due to the very low uptake efficiency. Very interestingly, instead, the cationic Ru-PhenAN accumulates inside the nucleus in all treated cells. Overall, the results indicate that the complexation of [Ru(phen)2BAP](OTf)2 with a cationic polyamidoamine to give the Ru-PhenAN complex is an excellent strategy to increase the Ru-complex cell uptake and, additionally, to achieve accumulation at the nuclear level. These unique features together make this compound an excellent photosensitizer with very high PDT efficiency.

Nanoparticles (NPs) have received much attention in recent years for their diverse potential biomedical applications. However, the synthesis of NPs with desired biodistribution and pharmacokinetics is still a major challenge, with NP size and surface chemistry being the main factors determining the behavior of NPs in vivo. Here we report on the surface chemistry and in vitro cellular uptake of magnetic iron oxide NPs coated with zwitterionic dopamine sulfonate (ZDS). ZDS-coated NPs were compared to similar iron oxide NPs coated with PEG-like 2-[2-(2-methoxyethoxy)ethoxy]acetic acid (MEEA) to investigate how surface chemistry affects their in vitro behavior. ZDS-coated NPs had a very dense coating, guaranteeing high colloidal stability in several aqueous media and negligible interaction with proteins. Treatment of HepG2 cells with increasing doses (2.5-100 mug Fe/mL) of ZDS-coated iron oxide NPs had no effect on cell viability and resulted in a low, dose-dependent NP uptake, inferior than most reported data for the internalization of iron oxide NPs by HepG2 cells. MEEA-coated NPs were scarcely stable and formed micrometer-sized aggregates in aqueous media. They decreased cell viability for dose >=50 mug Fe/mL, and were more efficiently internalized than ZDS-coated NPs. In conclusion, our data indicate that the ZDS layer prevented both aggregation and sedimentation of iron oxide NPs and formed a biocompatible coating that did not display any biocorona effect. The very low cellular uptake of ZDS-coated iron NPs can be useful to achieve highly selective targeting upon specific functionalization.

The reactions of the hydrido complexes [Re 2 H 2 (μ-H)(CO) 8 ] − ( 1 ) and [Re 4 H 2 (μ-H) 3 (CO) 16 ] − ( 2 ) with 0.5 equivalents of AgOTf (OTf − = CF 3 SO 3 − ) afforded rapidly and selectively the novel cluster anions [Ag(μ-H) 4 {Re 2 (μ-H)(CO) 8 } 2 ] − ( 3 ) and [Ag(μ-H) 4 {Re 4 (μ-H) 3 (CO) 16 } 2 ] − ( 4 ), respectively, formed by donor–acceptor interactions between the rhenium hydrides and the Ag + cation. 1 H and 109 Ag NMR spectroscopies showed that each Ag atom is surrounded by four hydrido ligands, bridging Re–Ag interactions. The Re 2 AgRe 2 cluster 3 therefore adopts the well known "bow-tie" geometry, constituted by two triangular clusters sharing the Ag vertex (spiro bis-cyclopropane). The Re 4 AgRe 4 anion 4 has instead an unprecedented spiro bis-cyclopentane-like structure, which is stable in solution only at temperatures lower than 220 K. The NMR investigation of the behavior in solution of these complexes revealed different intra- and inter-molecular dynamic processes, involving reversible fragmentation of the cyclic structures, with elimination of neutral or anionic hydrido-carbonyl fragments and interconversion among the different spiro derivatives. In particular, at temperature higher than 220 K the onset of a dissociative equilibrium was observed, involving the egress of a Re 2 (μ-H) 2 (CO) 8 fragment from 4 , with formation of the [Ag(μ-H) 4 {Re 2 (μ-H)(CO) 8 }{Re 4 (μ-H) 3 (CO) 16 }] − anion 5 , with a mixed spiro cyclopropane–cyclopentane-like structure, never previously observed. The fragmentation reaction was completely reversible on lowering the temperature. The mixed spiro derivative 5 was obtained (in mixture with the two symmetrical spiro derivatives 3 and 4 ) by either adding 1 equivalent of [Re 2 (μ-H) 2 (CO) 8 ] to 3 , or by reacting 1 equivalent of Ag + with a 1:1 mixture of the free hydrido complexes 1 and 2 . Intermolecular exchanges between the Re 4 H 5 fragments of 4 and 5 , and between the Re 2 H 3 fragments of 3 and 5 were revealed by 2D 1 H EXSY NMR experiments, which also showed exchange between the spiro bis-cyclopropane 3 and the free hydrido complex 1 . Furthermore, a higher binding ability towards Ag + of 1 with respect to 2 was proved, since 1 was found to be able to displace 2 from the spiro bis-cyclopentane adduct 4 and from the mixed spiro cyclopropane–cyclopentane 5 , leading to free hydrido complex 2 and the spiro bis-cyclopropane 3 .

The dynamic processes occurring in the triangular clusters [Re 3 (μ-H) 3 (μ-pz- κN 1 : κN 2 )(CO) 10 ] − (pz = pyrazolate, 4 ), [Re 3 (μ-H) 2 (μ-pydz- κN 1 : κN 2 )(CO) 10 ] − (pydz = pyridazine, 5 ) and [Re 3 (μ-H) 3 (μ-pydz- κN 1 : κN 2 )(CO) 10 ] ( 6 ), have been investigated by 1 H and 13 C NMR. In the pyrazolate derivative 4 the exchange ( k ≈ 1 s −1 at 320 K) between the two carbonyls in the trans -diaxial apical positions has been recognized, and its activation parameters, in C 2 D 2 Cl 4 , have been determined ( E a = 68(3) kJ mol −1 ). The exchange has been attributed to the rotation of the apical H 2 Re(CO) 4 fragment with respect to the Re 2 (μ-pz) basal fragment, a process analogous to that previously observed in the unsaturated dianion [Re 3 (μ-H) 3 (CO) 10 ] 2− ( 2 ) and in the monoanion [Re 3 (μ-H) 3 (μ–NC 5 H 4 – κN 1 : κC 6 )(CO) 10 ] − ( 1 ), containing a bridging orthometallated pyridine ligand. The vertex rotation was not observed in the pyridazine derivatives 5 and 6 . An explanation for this different behaviour is presented, based on the view of the fluxional clusters 1 , 2 and 4 as adducts between the apical and basal moieties (π- or σ-complexes). The ΔG # 312K value here measured in acetone for the σ-complex 4 (77 kJ mol −1 ) is very similar to that previously determined for the other σ-complex 1 ( ΔG # 305K = 76 kJ mol -1 ) and significantly higher than the values measured for the π-complex 2 ( ΔG # 260K = 60 kJ mol −1 ). The di-hydrido derivative 5 shows a different much faster dynamic process, namely the hopping of one hydride between the two lateral edges, affording a pseudo C s symmetry in the molecule. The process has been monitored by both 1 H and 13 C analysis, affording quite similar activation parameters ( E a = 44(1) and 45(1) kJ mol −1 , respectively, in THF-d 8 ), that did not significantly change in CD 2 Cl 2 solution, in agreement with an intramolecular process.

Low temperature NMR spectroscopy has been used to characterize the mixtures formed in the oligomerization reactions of the unsaturated complex [Re 2 (μ-H) 2 (CO) 8 ] ( 1 ), promoted by hydrido-carbonyl rhenates. Three families of chain clusters, constituted by Re(CO) 4 units connected through Re(μ-H)Re interactions, have been obtained. The first one, of general formula [(CO) 5 Re-{HRe(CO) 4 } 2 n +1 ] − , was formed using [HRe 2 (CO) 9 ] − as promoter. The nature of the products was confirmed by 13 C NMR of 13 CO enriched samples. The formation of Re 6 and Re 8 chain clusters was recognized. The other two families have general formula [H-{HRe(CO) 4 } 2 n ] − and [H-{HRe(CO) 4 } 2 n +1 ] − and were obtained using as initiators [HB( s Bu) 3 ] − or [H 2 Re(CO) 4 ] − , respectively. Mixtures of oligomers with mean chain lengths higher than 10 have been observed. The addition of a strong acid caused H 2 evolution, leading back to the “monomer” 1 . For all the three families, each oligomerization step was reversible, with the longer oligomers favoured at the lowest temperatures, where, however, the reactions were very slow, usually preventing the attainment of the equilibrium. Variable temperature NMR spectra revealed a dynamic process involving the terminal H 2 Re(CO) 4 moiety(ies), that simultaneously exchanges terminal/bridging hydrides and the carbonyls trans to them (Δ G # 41–44 kJ mol −1 ). At room temperature, the more hydrogen-rich chain clusters also underwent dehydrogenation/cyclization reactions.

Multinuclear NMR spectroscopy has been used to study the solution properties of several perfluoroaryl borane derivatives. The information obtained from all the NMR active isotopes present in these molecules made it possible to establish not only chemical identity, structure and dynamics of their reaction products, but also the complexity of the solution speciation. In other words, multinuclear NMR helped in unravelling the real forms in which they are present in solution, that in some cases can change dramatically according to even slight changes of the solution conditions. Examples will be presented related to the chemistry of tris(pentafluorophenyl)borane, B(C6F5)3, and bis(pentafluorophenyl)borinic acid, B(C6F5)2OH.

The reaction of Ar2BOH (1, Ar = C6F5) with the proton sponge bis(dimethylamino)naphthalene (DMAN) in CD2Cl2 solution caused a series of strictly interlaced processes that have been investigated by variable-temperature 1H and 19F NMR spectroscopy. The very slow equilibrium between the monomeric and cyclic trimeric forms of Ar2BOH was strongly accelerated by the presence of a catalytic amount of DMAN. Upon addition of stoichiometric DMAN (0.33 equiv.), all Ar2BOH was converted into a mixture of two boroxinate anions, namely [Ar6B3O3H2]– (2) and [Ar5B3O3H]– (3), in which the ratio of the two anions varied according to the reaction conditions. The formation of the dearylated anion 3 (accompanied by equimolar pentafluorobenzene) has been attributed to a reaction process parallel to that leading to the hexaaryl anion 2, involving base-catalyzed hydrolysis of monomeric perfluoroborinic acid to its boronic analogue, followed by aggregation and condensation. Water plays a catalytic role in this process. In the presence of a small excess of DMAN, complete and instantaneous dearylation of 2 to 3 was observed. At temperatures lower than 233 K, the pentaaryl anion 3 was in equilibrium with its conjugate base. Slow further dearylation occurred at temperatures higher than 263 K, cleanly affording the tetraaryl anion [Ar4B3O3]– (5). Anions 3 and 5 have also been obtained in high yields from the condensation reaction between Ar2BOH and ArB(OH)2 (in the ratio 2:1 and 1:2, respectively), in the presence of stoichiometric DMAN. Mechanisms responsible for the stepwise dearylation from 2 to 3 and then from 3 to 5 have been discussed.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

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)

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...

A polymer complex (1P) was synthesized by binding bis(cyclometalated) Ir(ppy)2(+) fragments (ppy = 2-phenylpyridyl) to phenanthroline (phen) pendants of a poly(amidoamine) copolymer (PhenISA, in which the phen pendants involved ∼6% of the repeating units). The corresponding molecular complex [Ir(ppy)2(bap)](+) (1M, bap = 4-(butyl-4-amino)-1,10-phenanthroline) was also prepared for comparison. In water solution 1P gives nanoaggregates with a hydrodynamic diameter of 30 nm in which the lipophilic metal centers are presumed to be segregated within polymer tasks to reduce their interaction with water. Such confinement, combined with the dilution of triplet emitters along the polymer chains, led to 1P having a photoluminescence quantum yield greater than that of 1M (0.061 vs 0.034, respectively, in an aerated water solution) with a longer lifetime of the (3)MLCT excited states and a blue-shifted emission (595 nm vs 604 nm, respectively). NMR data supported segregation of the metal centers. Photoreaction of O2 with 1,5-dihydroxynaphthalene showed that 1P is able to sensitize (1)O2 generation but with half the quantum yield of 1M. Cellular uptake experiments showed that both 1M and 1P are efficient cell staining agents endowed with two-photon excitation (TPE) imaging capability. TPE microscopy at 840 nm indicated that both complexes penetrate the cellular membrane of HeLa cells, localizing in the perinuclear region. Cellular photodynamic therapy tests showed that both 1M and 1P are able to induce cell apoptosis upon exposure to Xe lamp irradiation. The fraction of apoptotic cells for 1M was higher than that for 1P (74 and 38%, respectively) 6 h after being irradiated for 5 min, but cells incubated with 1P showed much lower levels of necrosis as well as lower toxicity in the absence of irradiation. More generally, the results indicate that cell damage induced by 1M was avoided by binding the iridium sensitizers to the poly(amidoamine).

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 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 reaction of the ansa-zirconocene meso-[C2H4(4,7-Me2Indenyl)2]ZrMe2 with B(C6F5)3 afforded, besides the expected ion pair with outward MeB ( C 6 F 5 ) 3 - anion, also a minor isomer (molar fraction 0.043) with the bulky methylborate anion in the inward site. 2D 1H EXSY experiments revealed exchange between the two isomers, at T > 320 K, through the migration of the MeB ( C 6 F 5 ) 3 - anion between outward and inward sites. The presence of free B(C6F5)3 fastened the exchange, suggesting B(C6F5)3 attack on the zirconium bound methyl ligand of the two ion pairs.

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 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.

Titrations of B(C6F5)3 (1) with water, in toluene-d8 solution, monitored by 19F and 1H NMR at 196 K, showed first the formation of the adduct [(C6F5)3B(OH2)] (2) and then its stepwise transformation into the two aqua species [(C6F5)3B(OH2)]·H2O (3) and [(C6F5)3B(OH2)]·2H2O (4) containing, respectively, one or two water molecules hydrogen-bonded to the protons of the B-bound water molecule. The NMR data show that in each titration step only two species were present in significant concentration: 1 and 2 up to 1 equiv, 2 and 3 between 1 and 2 equiv, 3 and 4 between 2 and 3 equiv. Above 3 equiv the solutions rapidly attained saturation and phase separation occurred (although there was evidence of interaction of 4 with more water molecules). Titrations at room temperature indicated an analogous stepwise course. Variable-temperature experiments demonstrated water exchange between the different aqua species and between the different water sites in the adducts 3 and 4 (“internal” or B-bound and “external” or H-b...

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 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.

A new amphoteric copolymer, PhenISA, has been obtained by copolymerization of 4-(4′-aminobutyl)-1,10-phenanthroline (BAP) with 2-methylpiperazine and bis(acrylamido)acetic acid (BAC) (6% of phenanthroline-containing repeating units). The copolymer showed excellent solubility in water, where it self-aggregated to give clear nanoparticle suspensions (hydrodynamic diameter = 21 ± 2 nm, by dynamic light scattering (DLS) analysis). The phenanthroline pendants of the polymer stably coordinated either Re(CO) 3+ or Ru(phen)22+ fragments, affording luminescent Re-PhenISA, Re-Py-PhenISA, and Ru-PhenISA polymer complexes, emitting from triplet metal-to-ligand charge transfer ( 3MLCT) excited states (with λem = 608, 571, and 614 nm, respectively, and photoluminescence quantum yields φem = 0.7%, 4.8%, and 4.1%, in aerated water solution, respectively). DLS analyses indicated that the polymer complexes maintained the nanosize of PhenISA. All the complexes were stable under physiological conditions (pH 7.4, 0.15 M NaCl) in the presence of an excess of the ubiquitous competitor cysteine. In vitro viability assays showed no toxicity of Re-Py-PhenISA and Ru-PhenISA complexes, at concentrations in the range of 0.5-50 μM (calculated on the metal-containing unit), toward HEK-293 (human embryonic kidney) cells. A preliminary investigation of internalization in HEK-293 cells, by means of fluorescence confocal microscopy, showed that Ru-PhenISA enters cells via an endocytic pathway and, subsequently, homogeneously diffuse within the cytoplasm across the vesicle membranes. © 2012 American Chemical Society.