Luminescent Cationic Group 4 Metallocene Complexes Stabilized by Pendant N-Donor Groups.

Cationic group 4 metallocene complexes with pendant imine and pyridine donor groups were prepared as stable crystalline [B(C6F5)4]- salts either by protonation of the intramolecularly bound ketimide moiety in neutral complexes [(η5-C5Me5){η5-C5H4CMe2CMe2C(R)═N-κN}MCl] (M = Ti, Zr, Hf; R = t-Bu, Ph) by PhNMe2H+[B(C6F5)4]- to give [(η5-C5Me5){η5-C5H4CMe2CMe2C(R)═NH-κN}MCl]+[B(C6F5)4]- or by chloride ligand abstraction from the complexes [(η5-C5Me5)(η5-C5H4CMe2CH2C5H4N)MCl2] (M = Ti, Zr) by Li[B(C6F5)4]·2.5Et2O to give [(η5-C5Me5)(η5-C5H4CMe2CH2C5H4N-κN)MCl]+[B(C6F5)4]-. Solid state structures of the new compounds were established by X-ray diffraction analysis, and their electrochemical behavior was studied by cyclic voltammetry. The cationic complexes of Zr and Hf, compared to the corresponding neutral species, exhibited significantly enhanced luminescence predominantly from triplet ligand-to-metal (3LMCT) excited states with lifetimes up to 62 µs and quantum yields up to 58% in the solid state. DFT calculations were performed to explain the structural features and optical and electrochemical properties of the complexes.

Preparation of silyl-terminated branched polyethylenes catalyzed by Brookhart's nickel diimine complex activated with hydrosilane/B(C6F5)3.

Brookhart's nickel α-diimine complex [(κ2-N,N-BIAN)NiCl2] (1) (where BIAN = {Ar-NAceN-Ar}, Ace = acenaphthen-1,2-diyl, and Ar = 2,6-(iPr)2-C6H3) activated with a hydrosilane/B(C6F5)3 (SiHB) adduct forms a highly active catalytic system for ethylene polymerization. Under optimal conditions, the activity of the system depends on the nature of hydrosilane and decreases in the order R3SiH > Ph2SiH2 > PhSiH3. The decrease in system activity within the hydrosilane series is correlated with increasing formation of Ni(I) species. In addition to their activation effect, hydrosilanes act as efficient chain termination/chain transfer agents, with the Si/Ni ratio controlling the molecular weight of the resulting polyethylene (PE). The use of Et3SiH generated elastomeric, highly branched polymers with a saturated chain-end, while systems using Ph2SiH2 and PhSiH3 led to branched end-functionalized PEs terminated with the hydrosilyl functionality (i.e. br-PE-SiPh2H or br-PE-SiPhH2).

"Activated Borane": A Porous Borane Cluster Polymer as an Efficient Lewis Acid-Based Catalyst.

Borane cluster-based porous covalent networks, named activated borane (ActB), were prepared by cothermolysis of decaborane(14) (nido-B10H14) and selected hydrocarbons (toluene, ActB-Tol; cyclohexane, ActB-cyHx; and n-hexane, ActB-nHx) under anaerobic conditions. These amorphous solid powders exhibit different textural and Lewis acid (LA) properties that vary depending on the nature of the constituent organic linker. For ActB-Tol, its LA strength even approaches that of the commonly used molecular LA, B(C6F5)3. Most notably, ActBs can act as heterogeneous LA catalysts in hydrosilylation/deoxygenation reactions with various carbonyl substrates as well as in the gas-phase dehydration of ethanol. These studies reveal the potential of ActBs in catalytic applications, showing (a) the possibility for tuning catalytic reaction outcomes (selectivity) in hydrosilylation/deoxygenation reactions by changing the material's composition and (b) the very high activity toward ethanol dehydration that exceeds the commonly used γ-Al2O3 by achieving a stable conversion of ∼93% with a selectivity for ethylene production of ∼78% during a 17 h continuous period on stream at 240 °C.

Reactions of permethyltitanocene tucked-in derivatives with carbon dioxide.

Both single tucked-in permethyltitanocene 1 and double tucked-in permethyltitanocene 2 react with excess CO2 by insertion into their Ti-CH2 bonds. The former one precipitates instantly a yellow carboxylate-tethered oligomer [3]n which is insoluble in aprotic solvents and in a vacuum it sublimes as a monomer without decomposition. Computations for n ≤ 4 optimised the structure of the monomer [3] and showed that open chain oligomers bound by dative O → Ti bonds were not sterically hindered. The latter bond dissociates when [3]n is oxidized by chlorination with CDCl3 or CD2Cl2 to give Ti(IV) chloride 4 or upon metathesis of [3]n with Me3SiCl yielding Ti(III) chloride 5. Oxidative addition of MeCN affords a C-C coupled dinuclear titanocene diimine 6. Compound [3]n also reacts with 1 to give the tethered carbodiolate 8 or with [Cp*2TiH] (where Cp* = η5-C5Me5) to give the half-tethered carbodiolate 10. The non-tethered carbodiolate 12 was obtained from [Cp*2TiH] and CO2 yielding titanocene formate by reaction of the latter with another equivalent of [Cp*2TiH]. All these carbodiolates contain Ti(III) metal atoms forming electronic triplet states of axial or orthorhombic symmetry. In contrast to the rapidly reacting 1 compound 2 reacts with excess CO2 slowly in m-xylene at 100 °C using only one of its two Ti-CH2 moieties. The structure of the obtained carbodiolate 13 indicates that the primary product analogous to 3 reacts with 2 more rapidly than with CO2.

Helquats, helical extended diquats, as fast electron transfer systems.

Helicene-viologen structural hybrids, like [5]helquat, 6,7,10,11-tetrahydrodipyrido[2,1-a:1',2'-k][2,9]phenanthrolinediium, and its four methylated derivatives, are characterized by electrochemical admittance and EPR spectroscopy. All compounds are reversibly reduced in two one-electron steps. Formal redox potentials correlate with the calculated LUMO energies. The electron transfer is coupled with a weak adsorption of the reactants. The analysis of the frequency dependence of the electrode admittance is used for the separation of Faradaic and double layer contributions and finally to the estimation of heterogeneous rate constants. Heterogeneous rate constants determined this way are in the range 0.1 to 3 cm s(-1). In all cases the second electron transfer is faster than the first redox step by a factor of three. The Frumkin correction for the acceleration by the double layer potential further amplifies this difference. The heterogeneous rate constants of derivatives correlate with the solvent reorganization energy estimated from the Marcus model. EPR spectra confirm the radical cation formation. The radical of [5]helquat participates in an extremely fast self-exchange process with the parent dication characterized by the self-exchange rate constant k(ET) = (2.4 +/- 0.5) x 10(9) M(-1) s(-1).

Hydrodehalogenation of organohalides by Et3SiH catalysed by group 4 metal complexes and B(C6F5)3.

Catalytic hydrodehalogenation (HDH) of aliphatic organohalides such as trifluorotoluenes by Et3SiH proceeds in the presence of readily available group 4 metal compounds: Cp'2MX2 (Cp' = η5-C5H5 or η5-C5Me5; X = F, Cl, or Me; M = Ti, Zr, or Hf), CpTiCl3 and TiCl4 with a catalytic amount of B(C6F5)3. The use of metallocenes in combination with the borane activator leads to a better selectivity of the reaction, i.e., suppression of Friedel-Crafts alkylations of arenes.

Hydrogenation of titanocene and zirconocene bis(trimethylsilyl)acetylene complexes.

Reactions following the addition of dihydrogen under maximum atmospheric pressure to bis(trimethylsilyl)acetylene (BTMSA) complexes of titanocenes, [(η5-C5H5-nMen)2Ti(η2-BTMSA)] (n = 0, 1, 3, and 4) (1A-1D), and zirconocenes, [(η5-C5H5-nMen)2Zr(η2-BTMSA)] (n = 2-5) (4A-4D), proceeded in diverse ways and, depending on the metal, afforded different products. The former complexes lost, in all cases, their BTMSA ligand via its hydrogenation to bis-1,2-(trimethylsilyl)ethane when reacted at 80 °C for a prolonged reaction time. For n = 0, 1, and 3, the titanocene species formed in situ dimerised via the formation of fulvalene ligands and two bridging hydride ligands, giving known green dimeric titanocenes (2A-2C). For n = 4, a titanocene hydride [(η5-C5HMe4)2TiH] (2D) was formed, similarly to the known [(η5-C5Me5)2TiH] (2E) for n = 5; however, in contrast to this example, 2D in the absence of dihydrogen spontaneously dehydrogenated to the known Ti(iii)-Ti(iii) dehydro-dimer [{Ti(η5-C5HMe4)(µ-η1:η5-C5Me4)}2] (3B). This complex has now been fully characterised via spectroscopic methods, and was shown through EPR spectroscopy to attain an intramolecular electronic triplet state. The zirconocene-BTMSA complexes 4A-4D reacted uniformly with one hydrogen molecule to give Zr(iv) zirconocene hydride alkenyls, [(η5-C5H5-nMen)2ZrH{C(SiMe3)[double bond, length as m-dash]CH(SiMe3)}] (n = 2-5) (5A-5D). These were identified through their 1H and 13C NMR spectra, which show features typical of an agostically bonded proton, [double bond, length as m-dash]CH(SiMe3). Compounds 5A-5D formed equilibria with the BTMSA complexes 4A-4D depending on hydrogen pressure and temperature.

Decamethyltitanocene hydride intermediates in the hydrogenation of the corresponding titanocene-(η2-ethene) or (η2-alkyne) complexes and the effects of bulkier auxiliary ligands.

1H NMR studies of reactions of titanocene [Cp*2Ti] (Cp* = η5-C5Me5) and its derivatives [Cp*(η5:η1-C5Me4CH2)TiMe] and [Cp*2Ti(η2-CH2[double bond, length as m-dash]CH2)] with excess dihydrogen at room temperature and pressures lower than 1 bar revealed the formation of dihydride [Cp*2TiH2] (1) and the concurrent liberation of either methane or ethane, depending on the organometallic reactant. The subsequent slow decay of 1 yielding [Cp*2TiH] (2) was mediated by titanocene formed in situ and controlled by hydrogen pressure. The crystalline products obtained by evaporating a hexane solution of fresh [Cp*2Ti] in the presence of hydrogen contained crystals having either two independent molecules of 1 in the asymmetric part of the unit cell or cocrystals consisting of 1 and [Cp*2Ti] in a 2 : 1 ratio. Hydrogenation of alkyne complexes [Cp*2Ti(η2-R1C[triple bond, length as m-dash]CR2)] (R1 = R2 = Me or Et) performed at room temperature afforded alkanes R1CH2CH2R2, and after removing hydrogen, 2 was formed in quantitative yields. For alkyne complexes containing bulkier substituent(s) R1 = Me or Ph, R2 = SiMe3, and R1 = R2 = Ph or SiMe3, successful hydrogenation required the application of increased temperatures (70-80 °C) and prolonged reaction times, in particular for bis(trimethylsilyl)acetylene. Under these conditions, no transient 1 was detected during the formation of 2. The bulkier auxiliary ligands η5-C5Me4tBu and η5-C5Me4SiMe3 did not hinder the addition of dihydrogen to the corresponding titanocenes [(η5-C5Me4tBu)2Ti] and [(η5-C5Me4SiMe3)2Ti] yielding [(η5-C5Me4tBu)2TiH2] (3) and [(η5-C5Me4SiMe3)2TiH2] (4), respectively. In contrast to 1, the dihydride 4 did not decay with the formation of titanocene monohydride, but dissociated to titanocene upon dihydrogen removal. The monohydrides [(η5-C5Me4tBu)2TiH] (5) and [(η5-C5Me4SiMe3)2TiH] (6) were obtained by insertion of dihydrogen into the intramolecular titanium-methylene σ-bond in compounds [(η5-C5Me4tBu)(η5:η1-C5Me4CMe2CH2)Ti] and [(η5-C5Me4SiMe3)(η5:η1-C5Me4SiMe2CH2)Ti], respectively. The steric influence of the auxiliary ligands became clear from the nature of the products obtained by reacting 5 and 6 with butadiene. They appeared to be the exclusively σ-bonded η1-but-2-enyl titanocenes (7) and (8), instead of the common π-bonded derivatives formed for the sterically less congested titanocenes, including [Cp*2Ti(η3-(1-methylallyl))] (9). The molecular structure optimized by DFT for compound 1 acquired a distinctly lower total energy than the analogously optimized complex with a coordinated dihydrogen [Cp*2Ti(η2-H2)]. The stabilization energies of binding the hydride ligands to the bent titanocenes were estimated from counterpoise computations; they showed a decrease in the order 1 (-132.70 kJ mol-1), 3 (-121.11 kJ mol-1), and 4 (-112.35 kJ mol-1), in accordance with the more facile dihydrogen dissociation.

Superior Activity of Isomorphously Substituted MOFs with MIL-100(M=Al, Cr, Fe, In, Sc, V) Structure in the Prins Reaction: Impact of Metal Type.

The catalytic behavior of isomorphously substituted MIL-100(M) (M=Al, Cr, Fe, In, Sc, V) is investigated for the synthesis of nopol through the Prins condensation of ß-pinene with paraformaldehyde. The large mesoporous cages of the metal-organic frameworks provide a sustainable confinement for the formation of the target product (100 % selectivity for nopol over all materials studied). MIL-100(Sc) and MIL-100(V) exhibit the highest yields (up to 90 %) of nopol after just 20 min from the beginning of the reaction, owing to their high concentrations of accessible Lewis sites possessing intermediate acidity. The high catalytic activity (reaching almost 90 % ß-pinene conversion) even upon decreasing the amount of catalyst from 100 to 25 mg (0.025 and 0.0063 gcatalyst mmolsubstrate -1 , respectively), the stability of its structure, and the possibility to use it several times, make MIL-100(V) a promising material for applications in acid-catalyzed reactions under mild reaction conditions.

Hydrosilane-B(C6F5)3 adducts as activators in zirconocene catalyzed ethylene polymerization.

Hydrosilane-B(C6F5)3 adducts were found to activate zirconocene dihalides and generate ternary catalytic systems possessing moderate to high activity in ethylene polymerization to high density polyethylene (HDPE). The activation efficacy of the adducts increased with increasing hydride donor ability and decreased with steric crowding of the particular hydrosilane used. NMR investigation of the HSiEt3/B(C6F5)3/Cp*2ZrF2 system (Cp* = η(5)-C5Me5) revealed the formation of a stable intermediate [Cp*2ZrF(FSiEt3-κF)](+)[HB(C6F5)3](-), whereas a crucial role of the [HB(C6F5)3](-) anion as a hydride donor for generation of an active cationic zirconium hydride center was elucidated.

Impact of retransfusion of blood processed in cell-saver on coagulation versus cardiopulmonary bypass: a prospective observational study using thromboelastography.

AIMS: To compare an impact of retransfusion of blood processed in cell-saver (CS) with that of cardiopulmonary bypass (CPB) on blood coagulation in patients undergoing cardiac surgery. METHODS: Prospective observational study using thromboelastography (TEG). RESULTS: TEG samples from 170 patients were analyzed. Cardiopulmonary bypass was used in 100 patients while 70 patients were operated off-pump. In 20 off-pump patients collected blood was processed by cell-saver and returned. In all patients clot formation after heparin neutralization by protamine was unimpaired. However, there was a significant increase in fibrinolysis defined by the TEG parameter Lysis time 30 min after the maximum amplitude of the clot was reached (Ly30) in groups with CPB or CS but this increase still did not exceed the threshold for clinical fibrinolysis (Ly30 > 7.5%). In the group without CPB there was no significant impact on coagulation. CONCLUSION: Surgery that avoids CPB and/or CS is the gentlest method for inducing blood coagulation.

Displacement of ethene from the decamethyltitanocene-ethene complex with internal alkynes, substituent-dependent alkyne-to-allene rearrangement, and the electronic transition relevant to the back-bonding interaction.

The titanocene-ethene complex [Ti(II)(η(2)-C2H4)(η(5)-C5Me5)2] (1) with simple internal alkynes R(1)C≡CR(2) gives complexes [Ti(II)(η(2)-R(1)C≡CR(2))(η(5)-C5Me5)2] {R(1), R(2): Ph, Ph (3), Ph, Me (4), Me, SiMe3 (5), Ph, SiMe3 (6), t-Bu, SiMe3 (7), and SiMe3, SiMe3 (8). In contrast, alkynes with R(1) = Me and R(2) = t-Bu or i-Pr afford allene complexes [Ti(II)(η(2)-CH2=C=CHR(2))(η(5)-C5Me5)2] (11) and (12), whereas for R(2) = Et a mixture of alkyne complex (13A) and minor allene (13) is obtained. Crystal structures of 4, 6, 7 and 11 have been determined; the latter structure proved the back-bonding interaction of the allene terminal double bond. Only the synthesis of 8 from 1 was inefficient because the equilibrium constant for the reaction [1] + [Me3SiC≡CSiMe3] ⇌ [8] + [C2H4] approached 1. Compound 9 (R(1), R(2): Me), not obtainable from 1, together with compounds 3­6 and 10 (R(1), R(2): Et) were also prepared by alkyne exchange with 8, however this reaction did not take place in attempts to obtain 7. Compounds 1 and 3­9 display the longest-wavelength electronic absorption band in the range 670-940 nm due to the HOMO → LUMO transition. The assignment of the first excitation to be of predominantly a b2 → a1 transition was confirmed by DFT calculations. The calculated first excitation energies for 3­9 followed the order of hypsochromic shifts of the absorption band relative to 8 that were induced by acetylene substituents: Me > Ph ≫ SiMe3. Computational results have also affirmed the back-bonding nature in the alkyne-to-metal coordination.

Synthetic transformations of a pendant nitrile moiety in group 4 metallocene complexes.

Functional group transformations at the group 4 metallocene framework have been demonstrated, which have provided relatively straightforward access to otherwise synthetically challenging derivatives. The pendant nitrile group in Ti and Zr metallocene complexes of the type [(η(5)-C5Me5)(η(5)-C5H4CMe2CH2CN)MCl2] was converted into an intramolecularly bound ketimido moiety by alkylation, which took place not only at the nitrile, but also at the metal centre. The choice of an alkylating reagent (alkyl/aryl lithium, Grignard reagent) was crucial: e.g., 2 equiv. of MeMgBr effected the alkylation only at the metal, yielding selectively complexes [(η(5)-C5Me5)(η(5)-C5H4CMe2CH2CN)MMe2], while the use of PhMgBr, PhLi, or MeLi instead gave selectively the ketimido complexes. Organyl lithium reagents were, however, not compatible with the titanocene derivatives. The metal-bound ketimides were subsequently cleaved off by the reaction with HCl, which afforded metallocene dichlorides with a pendant imino group. These compounds were easily protonated again at the nitrogen atom to produce a cationic iminium moiety. Aqueous hydrolysis of the imine or its respective hydrochloride proved to be viable in the case of Zr and it finally afforded a pendant ketone group attached to the zirconocene framework.

Is allogeneic blood transfusion a risk factor for sternal dehiscence following cardiac surgery? A prospective observational study.

Sternal dehiscence following cardiac surgery has a multifactorial etiology. Significant risk factors contributing to sternal dehiscence include chronic obstructive pulmonary disease (COPD), obesity, or re-exploration due to bleeding or pericardial tamponade. We have focused on the role of allogeneic blood transfusion as a factor leading to the poor healing of surgical wounds. A prospective observational study of 1553 elective and emergency cardiac surgery patients was performed between January 2003 and June 2007. All of the patients enrolled in this study underwent median sternotomy. We studied the relationship between sternal dehiscence following cardiac surgery and the total number of packed red blood cells transfused. The incidence of sternal dehiscence in the study group was 3.4%. Diabetic patients did not have a higher incidence of wound dehiscence. Although COPD, obesity, and re-exploration contributed to sternal dehiscence, the number of allogeneic blood transfusions during the perioperative period was an important independent risk factor for sternal dehiscence. Patients with sternal dehiscence received an average of 7.6 transfusion units (TU) of allogeneic blood versus 1.6 TU of allogeneic blood in the group without sternal dehiscence (P < 0.00005). The dehiscence affected patients without any other significant risk factor who received 6 or more TU, or patients with at least one significant risk factor who received 4 or more TU of allogeneic blood. According to our results, the total amount of allogeneic blood transfused is an important risk factor contributing to sternal dehiscence. Regardless of other risk preconditions, the transfusion of 6 or more TU could result in sternal dehiscence following cardiac surgery.