Biogeneration of C13-norisoprenoid compounds: experiments supportive for an apo-carotenoid pathway in grapevines

The first step of the proposed biogenetic pathway in grapes that leads from carotenoids to C₁₃-norisoprenoids involves the enzymatic degradation of carotenoids by regiospecific oxygenases. Chemical, photochemical and oxidase-coupled degradation of carotenoids to norisoprenoids have been studied in vitro and enzymatic systems shown to be involved in mammals. However, no enzymatic system has been shown to be involved in the formation of C₁₃-norisoprenoids in grapes, despite all recent studies carried out on grapevines supporting such a model. These findings include the preponderance of norisoprenoids possessing 13 carbon atoms that thereby indicates the specificity of cleavage, the configuration of the asymmetric centres and axes common to C₁₃-norisoprenoids and the corresponding carotenoids, the negative correlations observed between the levels of norisoprenoids and carotenoids during berry development, and the in vivo transfer of ¹³C markers from carotenoids to norisoprenoids in berries between véraison and berry maturity. All of these findings are major arguments in favour of the hypothesis that glycosylated C₁₃-norisoprenoids derive from carotenoids in grape berries. Carotenoids are mostly synthesised from the first stage of fruit formation until véraison, and then degrade between véraison and maturity to produce glycosylated C₁₃-norisoprenoids and other compounds.     

Rapid tool for assessment of C13 norisoprenoids in wines

Two novel methodologies for quantification of C₁₃ norisoprenoids in wines were developed. The first methodology, method A (reference method) was based on the headspace solid-phase microextraction combined with gas chromatography–quadrupole mass spectrometry operating in selected ion monitoring mode (HS-SPME–GC–qMS–SIM). This methodology allowed to select the GC conditions for an adequate chromatographic resolution of wine components. The second methodology, method B (rapid method) was based on the HS-SPME–GC–qMS–SIM, using GC conditions that allowed to obtain a C₁₃ norisoprenoid volatile signature. In the later, the GC capillary column of 30 m at 220 °C was used acting as a transfer line of the components sorbed by the SPME coating fibre to the mass spectrometer, which acts as a sensor for m/z fragments 142 and 192. It does not require any pre-treatment of the sample, and the C₁₃ norisoprenoid composition of the wine was evaluated based on the chromatographic profile and specific m/z fragments, without complete chromatographic separation of its components. For quantification purposes, external calibration curves were constructed with β-ionone chemical standard. Calibration curves with regression coefficient (r²) of 0.9940 and 0.9968, RSD of 1.08% and 12.51%, and detection limits of 1.10 and 1.57 μg L⁻¹ were obtained for methods A and B, respectively. These methodologies were applied to seventeen white and red table wines. Two vitispirane isomers (158–1529 μg L⁻¹) and 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) (6.42–39.45 μg L⁻¹) were quantified. The data obtained for vitispirane isomers and TDN using the two methods were highly correlated (r² of 0.9756 and 0.9630, respectively). Associated to the fast and robust character of the proposed rapid method B and considering the extraction time, it is important to focus its selectivity and potential applicability if specific m/z fragments would be established for new analytes.     

Volatile composition of Brassica oleracea L. var. costata DC leaves using solid‐phase microextraction and gas chromatography/ion trap mass spectrometry

Volatile and semi‐volatile components of internal and external leaves of Brassica oleracea L. var. costata DC, grown under different fertilization regimens, were determined by headspace solid‐phase microextraction (HS‐SPME) combined with gas chromatography/ion trap mass spectrometry (GC/ITMS). Forty‐one volatiles and non‐volatile components were formally identified and thirty others were tentatively identified. Qualitative and quantitative differences were noticed between internal and external leaves. In general, internal leaves exhibited more aldehydes and sulfur volatile compounds than external ones, and less ketone, terpenes and norisoprenoid compounds. The fertilization regimens influenced considerably the volatile profile. Fertilizations with higher levels of sulfur produced Brassica leaves with more sulfur volatiles. In opposition, N and S fertilization led to leaves with lower levels of norisoprenoids and terpenes. Copyright © 2009 John Wiley & Sons, Ltd.     

Synthesis of highly enantioenriched hydroxy- and dihydroxy-fatty esters: substrate precursors for cytochrome P450BioI

A series of highly enantioenriched hydroxy- and dihydroxy-fatty esters were required as part of our ongoing investigation into cytochrome P450_BioI. This mediates the biosynthesis of pimelic acid via C–C bond cleavage of long chain fatty acids within Bacillus subtilis. Herein we report the synthesis of various stereoisomers of methyl 7-hydroxytetradecanoate, methyl 8-hydroxytetradecanoate, and methyl 7,8-dihydroxytetradecanoate in highly enantioenriched form, using a combination of asymmetric synthesis and a preparative enantioselective HPLC is reported.     

Control Mechanism for Carbon‐Chain Length in Polyunsaturated Fatty‐Acid Synthases

Polyunsaturated fatty acids (PUFAs) such as docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are essential fatty acids. PUFA synthases are composed of three to four subunits and each create a specific PUFA without undesirable byproducts. However, detailed biosynthetic mechanisms for controlling final product profiles have been obscure. Here, the bacterial DHA and EPA synthases were carefully dissected by in vivo and in vitro experiments. In vitro analysis with two KS domains (KS_A and KS_C) and acyl‐acyl carrier protein (ACP) substrates showed that KS_A accepted short‐ to medium‐chain substrates while KS_C accepted medium‐ to long‐chain substrates. Unexpectedly, condensation from C₁₈ to C₂₀, the last elongation step in EPA biosynthesis, was catalyzed by KS_A domains in both EPA and DHA synthases. Conversely, condensation from C₂₀ to C₂₂, the last elongation step for DHA biosynthesis, was catalyzed by the KS_C domain in DHA synthase. KS_C domains therefore determine the chain lengths.     

Exploring Regioselective Bond Cleavage and Cross‐Coupling Reactions using a Low‐Valent Nickel Complex

Recently, esters have received much attention as transmetalation partners for cross‐coupling reactions. Herein, we report a systematic study of the reactivity of a series of esters and thioesters with [{(dtbpe)Ni}₂(μ‐η²:η²‐C₆H₆)] (dtbpe=1,2‐bis(di‐tert‐butyl)phosphinoethane), which is a source of (dtbpe)nickel(0). Trifluoromethylthioesters were found to form η²‐carbonyl complexes. In contrast, acetylthioesters underwent rapid C_acyl?S bond cleavage followed by decarbonylation to generate methylnickel complexes. This decarbonylation could be pushed backwards by the addition of CO, allowing for regeneration of the thioester. Most of the thioester complexes were found to undergo stoichiometric cross‐coupling with phenylboronic acid to yield sulfides. While ethyl trifluoroacetate was also found to form an η²‐carbonyl complex, phenyl esters were found to predominantly undergo C_aryl?O bond cleavage to yield arylnickel complexes. These could also undergo transmetalation to yield biaryls. Attempts to render the reactions catalytic were hindered by ligand scrambling to yield nickel bis(acetate) complexes, the formation of which was supported by independent syntheses. Finally, 2‐naphthyl acetate was also found to undergo clean C_aryl?O bond cleavage, and although stoichiometric cross‐coupling with phenylboronic acid proceeded with good yield, catalytic turnover has so far proven elusive.     

Fully Borylated Methane and Ethane by Ruthenium‐Mediated Cleavage and Coupling of CO

Many transition‐metal complexes and some metal‐free compounds are able to bind carbon monoxide, a molecule which has the strongest chemical bond in nature. However, very few of them have been shown to induce the cleavage of its C?O bond and even fewer are those that are able to transform CO into organic reagents with potential in organic synthesis. This work shows that bis(pinacolato)diboron, B₂pin₂, reacts with ruthenium carbonyl to give metallic complexes containing borylmethylidyne (CBpin) and diborylethyne (pinBC≡CBpin) ligands and also metal‐free perborylated C₁ and C₂ products, such as C(Bpin)₄ and C₂(Bpin)₆, respectively, which have great potential as building blocks for Suzuki–Miyaura cross‐coupling and other reactions. The use of ¹³CO‐enriched ruthenium carbonyl has demonstrated that the boron‐bound carbon atoms of all of these reaction products arise from CO ligands.     

C60基Ebselen衍生物：合成及尤其对鼠胸腺细胞增强保护效应

丙二酸酯衍生物2用2-氯硒基苯甲酰氯和2-(2-胺基乙氧基)乙醇为原料，经三步合成制得。2与C₆₀的Bingel环加成反应制得C₆₀基Ebselen衍生物3，产率为42% (基于已反应的C₆₀)，¹HNMR、¹³CNMR、IR、FAB-MS和元素分析鉴定了其结构。为了证实3对鼠胸腺细胞的活力具有增强效应，C₆₀衍生物4和2被选择，并采用与3相同的方法来处理鼠胸腺细胞，结果显示：3处理组的MTT(OD)值(0.335 ± 0.021)高于4处理组(MTT(OD): 0.283 ± 0.031)和2处理组(MTT(OD):0.247 ± 0.025)，表明3在促进鼠胸腺细胞活力方面优于2 和 4。     

Copper(II)–Graphitic Carbon Nitride Triggered Synergy: Improved ROS Generation and Reduced Glutathione Levels for Enhanced Photodynamic Therapy

Graphitic carbon nitride (g‐C₃N₄) has been used as photosensitizer to generate reactive oxygen species (ROS) for photodynamic therapy (PDT). However, its therapeutic efficiency was far from satisfactory. One of the major obstacles was the overexpression of glutathione (GSH) in cancer cells, which could diminish the amount of generated ROS before their arrival at the target site. Herein, we report that the integration of Cu²⁺ and g‐C₃N₄ nanosheets (Cu²⁺–g‐C₃N₄) led to enhanced light‐triggered ROS generation as well as the depletion of intracellular GSH levels. Consequently, the ROS generated under light irradiation could be consumed less by reduced GSH, and efficiency was improved. Importantly, redox‐active species Cu⁺–g‐C₃N₄ could catalyze the reduction of molecular oxygen to the superoxide anion or hydrogen peroxide to the hydroxyl radical, both of which facilitated the generation of ROS. This synergy of improved ROS generation and GSH depletion could enhance the efficiency of PDT for cancer therapy.     

One-step fabrication of mesoporous sulfur-doped carbon nitride for highly selective photocatalytic transformation of native lignin to monophenolic compounds

Photocatalytic selective transform native lignin into valuable chemicals is an attractive but challenging task. Herein, we report a mesoporous sulfur-doped carbon nitride (MSCN-0.5) which is prepared by a facile one-step thermal condensation strategy. It is highly active and selective for the cleavage Cα?C_β bond in β?O?4 lignin model compound under visible light radiation at room temperature, achieving 99% substrate conversion and 98% C_α?C_β bond cleavage selectivity. Mechanistic studies revealed that the C_β?H bond of lignin model compounds activated by holes and generate key C_β radical intermediates, further induced the C_α?C_β bond cleavage by superoxide anion radicals (^?O₂^?) to produce aromatic oxygenates. Waste Camellia oleifera shell (WCOS) was taken as a representative to further understand the reaction mechanisms on native lignin. 33.2 mg of monophenolic compounds (Vanillin accounted for 22% and Syringaldehyde for 34%) can be obtained by each gram of WCOS lignin, which is 2.5 times as that of the pristine carbon nitride. The present work offers useful guidance for designing metal-free heterogeneous photocatalysts for C_α?C_β bond cleavage to harvest monophenolic compounds.     

On the Mechanism of Action of Fullerene Derivatives in Superoxide Dismutation

We have studied the mechanism of the antioxidant activity of C₆₀ derivatives at the BP86/TZP level with inclusion of solvent effects (DMSO) by using the COSMO approach. The reaction studied here involves degradation of the biologically relevant superoxide radical (O₂^.?), which is linked to tissue damage in several human disorders. Several fullerene derivatives have experimentally been shown to be protective in cell culture and animal models of injury, but precisely how these compounds protect biological systems is still unknown. We have investigated the activity of tris‐malonyl C₆₀ (also called C₃), which efficiently removes the superoxide anion with an activity in the range of several biologically effective, metal‐containing superoxide dismutase mimetics. The antioxidant properties of C₃ are attributed to the high affinity of C₆₀ to accept electrons. Our results show that once the superoxide radical is in contact with the surface of C₃, its unpaired electron is transferred to the fullerene. This process, which converts the damaging O₂^.? to neutral oxygen O₂, is the rate‐determining step of the reaction. Afterwards, another superoxide radical reacts with C₃^.? to form hydrogen peroxide and in the process takes up the additional electron that was transferred in the first step. The overall process is clearly exothermic and, in general, involves reaction steps with relatively low activation barriers. The capability of C₃ to degrade a highly reactive oxygen species that is linked to several human diseases is of immediate interest for future applications in the field of biology and medicine.     

Atmospheric pressure chemical vapour deposition of selenium and tellurium films by UV laser photolysis of diethyl selenium and diethyl tellurium

Excimer laser‐induced photolysis of gaseous diethyl selenium and diethyl tellurium (C₂H₅)₂M (M = Se, Te) is controlled by cleavage of both M? C bonds, it yields C₁–C₄ hydrocarbons (ethene as major product) and results in chemical vapour deposition of selenium films and nanosized tellurium powder. The selenium and tellurium properties were characterized by X‐ray photoelectron spectroscopy and Scanning electron Microscopy techniques. Copyright © 2001 John Wiley & Sons, Ltd.     

Comparative Studies of Thermally Induced Homolytic CarbonCarbon Bond Cleavage Reactions of Strained Dicarba[2]ferrocenophanes and Their Ring‐Opened Oligomers and Polymers

Reactivity studies of dicarba[2]ferrocenophanes and also their corresponding ring‐opened oligomers and polymers have been conducted in order to provide mechanistic insight into the processes that occur under the conditions of their thermal ring‐opening polymerisation (ROP) (300 °C). Thermolysis of dicarba[2]ferrocenophane rac‐[Fe(η⁵‐C₅H₄)₂(CHPh)₂] (rac‐ 14 ; 300 °C, 1 h) does not lead to thermal ROP. To investigate this system further, rac‐ 14 was heated in the presence of an excess of cyclopentadienyl anion, to mimic the postulated propagating sites for thermally polymerisable analogues. This afforded acyclic [(η⁵‐C₅H₅)Fe(η⁵‐C₅H₄)‐CH₂Ph] ( 17 ) through cleavage of both a Fe?Cp bond and also the C?C bond derived from the dicarba bridge. Evidence supporting a potential homolytic C?C bond cleavage pathway that occurs in the absence of ring‐strain was provided through thermolysis of an acyclic analogue of rac‐ 14 , namely [(η⁵‐C₅H₅)Fe(η⁵‐C₅H₄)(CHPh)₂‐C₅H₅] ( 15 ; 300 °C, 1 h), which also afforded ferrocene derivative 17 . This reactivity pathway appears general for post‐ROP species bearing phenyl substituents on adjacent carbons, and consequently was also observed during the thermolysis of linear polyferrocenylethylene [Fe(η⁵‐C₅H₄)₂(CHPh)₂]_n ( 16 ; 300 °C, 1 h), which was prepared by photocontrolled ROP of rac‐ 14 at 5 °C. This afforded ferrocene derivative [Fe(η⁵‐C₅H₄CH₂Ph)₂] ( 23 ) through selective cleavage of the ?H(Ph)C?C(Ph)H? bonds in the dicarba linkers. These processes appear to be facilitated by the presence of bulky, radical‐stabilising phenyl substituents on each carbon of the linker, as demonstrated through the contrasting thermal properties of unsubstituted linear trimer [(η⁵‐C₅H₅)Fe(η⁵‐C₅H₄)(CH₂)₂(η⁵‐C₅H₄)Fe(η⁵‐C₅H₄)(CH₂)₂(η⁵‐C₅H₄)Fe(η⁵‐C₅H₅)] ( 29 ) with a ?H₂C?CH₂? spacer, which proved significantly more stable under analogous conditions. Evidence for the radical intermediates formed through C?C bond cleavage was detected through high‐resolution mass spectrometric analysis of co‐thermolysis reactions involving rac‐ 14 and 15 (300 °C, 1 h), which indicated the presence of higher molecular weight species, postulated to be formed through cross‐coupling of these intermediates.     

Total Synthesis of Enantiopure Pyrrhoxanthin: Alternative Methods for the Stereoselective Preparation of 4‐Alkylidenebutenolides

A new stereocontrolled total synthesis of the configurationally labile C₃₇‐norcarotenoid pyrrhoxanthin in enantiopure form has been completed. A highly stereoselective Horner–Wadsworth–Emmons (HWE) condensation of a C₁₇‐allylphosphonate and a C₂₀‐aldehyde was used as the last conjunctive step. Both a Sonogashira reaction to form the C₁₇‐phosphonate and the final HWE condensation proved to be compatible with the sensitive C7–C10 enyne E configuration. Regioselective (5‐exo‐dig) silver‐promoted lactonization reactions of three alternative pent‐2‐en‐4‐ynoic acid precursors with increased complexity, including a fully functionalized C₂₀‐fragment, were explored for the preparation of the γ‐alkylidenebutenolide fragment. This survey extends the existing methodologies for the preparation of oxygen‐containing carotenoids (xanthophylls) and streamlines the synthesis of additional members of the C₃₇‐norcarotenoid butenolide family of natural products.     

Structure and Isotope Effects of the β‐H Agostic (α‐Diimine)Nickel Cation as a Polymerization Intermediate

Single‐crystal X‐ray characterization of cationic (α‐diimine)Ni‐ethyl and isopropyl β‐agostic complexes, which are key intermediates in olefin polymerization and oligomerization, are presented. The sharp Ni‐C_α‐C_β angles (75.0(3)° and 74.57(18)°) and short C_α−C_β distances (1.468(7) and 1.487(5) Å) provide unambiguous evidence for a β‐agostic interaction. An inverse equilibrium isotope effect (EIE) for ligand coordination upon cleavage of the agostic bond highlights the weaker bond strength of Ni−H relative to the C−H bond. An Eyring plot for β‐hydride elimination–olefin rotation–reinsertion is constructed from variable‐temperature NMR spectra with ¹³C‐labeled agostic complexes. The enthalpy of activation (ΔH ^≠) for β‐H elimination is 13.2 kcal mol⁻¹. These results offer important mechanistic insight into two critical steps in polymerization: ligand association upon cleavage of the β‐agostic bonds and chain‐migration via β‐H elimination.     

Estimation of peptide N–Cα bond cleavage efficiency during MALDI‐ISD using a cyclic peptide

Matrix‐assisted laser desorption/ionization in‐source decay (MALDI‐ISD) induces N–C_α bond cleavage via hydrogen transfer from the matrix to the peptide backbone, which produces a c′/z? fragment pair. Subsequently, the z? generates z′ and [z + matrix] fragments via further radical reactions because of the low stability of the z?. In the present study, we investigated MALDI‐ISD of a cyclic peptide. The N–C_α bond cleavage in the cyclic peptide by MALDI‐ISD produced the hydrogen‐abundant peptide radical [M + 2H]⁺? with a radical site on the α‐carbon atom, which then reacted with the matrix to give [M + 3H]⁺ and [M + H + matrix]⁺. For 1,5‐diaminonaphthalene (1,5‐DAN) adducts with z fragments, post‐source decay of [M + H + 1,5‐DAN]⁺ generated from the cyclic peptide showed predominant loss of an amino acid with 1,5‐DAN. Additionally, MALDI‐ISD with Fourier transform‐ion cyclotron resonance mass spectrometry allowed for the detection of both [M + 3H]⁺ and [M + H]⁺ with two ¹³C atoms. These results strongly suggested that [M + 3H]⁺ and [M + H + 1,5‐DAN]⁺ were formed by N–C_α bond cleavage with further radical reactions. As a consequence, the cleavage efficiency of the N–C_α bond during MALDI‐ISD could be estimated by the ratio of the intensity of [M + H]⁺ and [M + 3H]⁺ in the Fourier transform‐ion cyclotron resonance spectrum. Because the reduction efficiency of a matrix for the cyclic peptide cyclo(Arg‐Gly‐Asp‐D‐Phe‐Val) was correlated to its tendency to cleave the N–C_α bond in linear peptides, the present method could allow the evaluation of the efficiency of N–C_α bond cleavage for MALDI matrix development. Copyright © 2016 John Wiley & Sons, Ltd.     

外源铜增强天然铜锌超氧化物歧化酶断裂DNA的活性

铜锌超氧化物歧化酶（CuZnSOD）作为一种抗氧化酶, 最重要的功能是催化超氧阴离子歧化为过氧化氢和氧气。然而最近研究发现CuZnSOD具有过氧化物酶活性,能导致核酸、蛋白质和细胞膜的损伤。本工作采用光谱学和酶学方法研究外源Cu(Ⅱ)与CuZnSOD之间的相互作用,以及H₂O₂存在下外源Cu(Ⅱ)对 CuZnSOD断裂DNA活性的增强效应。比较CuZnSOD + nCu(Ⅱ) (n=0, 1, 2, 4, 6, 8)和单独Cu(Ⅱ)分别断裂DNA的活性,表明外源Cu(Ⅱ)的加入可显著增强CuZnSOD断裂DNA的活性。相对酶活力和稳态动力学的测定证实了这种增强效应。pH依赖性实验表明断裂DNA的最适pH范围为pH3.6-5.6和pH9.0-10,在不同的pH区域CuZnSOD + nCu(Ⅱ)断裂DNA途径可能不同。     

Cytotoxicity of tantalum(V) and niobium(V) small carborane complexes and mode of action in P388 lymphocytic leukemia cells

The metallacarboranes (Et₂C₂B₄H₄)‐­TaCl₂(C₅H₅) ( 1 ), (Et₂C₂B₄H₄)NbCl₂(C₅H₅) ( 2 ), (Et₂C₂B₄H₄)TaCl₂(C₅Me₅) ( 3 ), [(Me₃Si)₂­C₂B₄H₄]TaCl₂(C₅H₅) ( 4 ) and (Me₂C₂B₄H₄)‐­TaCl₂(C₅H₅) ( 5 ) are potent cytotoxic agents against suspended tumors, producing cell death in several tissue culture lines; for example, all were effective against murine L1210 lymphoid leukemia, and all except 5 against murine P388 lymphocytic growth. Human leukemic growth is also retarded since 1–4 were effective against Tmolt₃ cell leukemia, all except 4 against Tmolt₄ leukemia, and 1, 2 , and 5 against HI‐60 leukemia. Cytotoxicity was found towards HuT‐8 lymphoma, THP‐1 acute monocytic leukemia and suspended HeLa‐S³ uterine carcinoma. Some but not all of the complexes were active against Sk‐2 melanoma and Mcf‐7 breast effusion growth. Mode‐of‐action studies in P388 lymphocytic leukemia cells showed that de novo purine synthesis was inhibited; this inhibition reduces DNA and RNA syntheses. Purine synthesis was reduced by compounds 3 and 4 at the regulatory enzymes, i.e. phosphoribosyl pyrophosphate (PRPP) amidotransferase and dihydrofolate reductase. The agents lowered d[ATP] and d[CTP] pools, further reducing DNA synthesis. The complexes afforded DNA fragmentation leading to apoptosis, but this was not by a mechanism of nucleoside alkylation, intercalation between base‐pairs or cross‐linking of the DNA strands. Copyright © 2000 John Wiley & Sons, Ltd.     

Azafullerene C59N–Phthalocyanine Dyad: Synthesis,Characterisation and Photoinduced Electron Transfer

The synthesis of a new azafullerene C₅₉N–phthalocyanine (Pc) dyad is described. The key step for the synthesis of the C₅₉N–Pc dyad was the formation of the C₅₉N‐based carboxylic acid, which was smoothly condensed with hydroxy‐modified Pc. The structure of the C₅₉N–Pc dyad was verified by ¹H and ¹³C NMR spectroscopy, IR spectroscopy, UV/Vis spectroscopy and MS measurements. The photophysical and electrochemical properties of the C₅₉N–Pc dyad were investigated in both polar and non‐polar solvents by steady state and time‐resolved photoluminescence and absorption spectroscopy, as well as by cyclic voltammetry. Different relaxation pathways for the photoexcited C₅₉N–Pc dyad, as a result of changing the solvent polarity, were found, thus giving rise to energy‐transfer phenomena in non‐polar toluene and charge‐transfer processes in polar benzonitrile. Finally, the detailed quenching mechanisms were evaluated and compared with that of a C₆₀–Pc dyad, which revealed that the different excited‐state energies and reduction potentials of the two fullerene spheres (i.e. C₅₉N vs. C₆₀) strongly diverged in the deactivation pathways of the excited states of the corresponding phthalocyanine dyads.     

Activation of Molecular Hydrogen by Bis(η5,η1‐pentafulvene)‐titanium Complexes – Efficient Formation of Titanium(III)hydrides

The synthesis and crystal structures of two dinuclear titanocene hydride complexes are reported. Both complexes, namely bis(η⁵‐(di‐para‐tolylmethyl)cyclopentadienyl)titanium hydride dimer, [(η⁵‐C₂₀H₁₉)₂Ti(μ‐H)]₂ ( 2a ), and bis(η⁵‐2‐adamantylcyclopentadienyl)‐titanium hydride dimer, [(η⁵‐C₁₅H₁₉)₂Ti(μ‐H)]₂ ( 2b ), are formed via activation of molecular hydrogen by the corresponding bis(η⁵,η¹‐pentafulvene)titanium complexes 1a and 1b at ambient temperatures and pressures in high yields. The hydride complexes 2a and 2b exhibit planar [Ti₂H₂] cores and, as a result of the heterolytic cleavage of molecular hydrogen, substituted Cp Ligands were formed during the reaction.