Mild Thermolysis Research Articles

Synthesis of N2-Substituted 1,2,3-Triazoles.

We present a novel synthetic approach for the synthesis of the 1,2,3-triazole core, with a particular focus on the direct and regioselective synthesis of the synthetically more challenging triazoles having additional substituents at the N2 nitrogen atom. Through treatment of readily accessible geminal diazides with organic hydrazines under mild thermolysis conditions, a broad spectrum of N2-alkyl- and N2-aryl-1,2,3-triazoles are easily generated. For example, geminal diazides derived from ketoesters, ketoamides, and ketones were converted under the reaction conditions. The product structures were confirmed via NMR as well as single-crystal structure analysis.

The First Planar, Not Twisted, Distannene - A Structural Alkene Analog. Synthesis, Isolation and X-ray Crystallography Characterization.

The tetrasilyl-substituted distannene, (tBu2 HSi)2 Sn=Sn(SiHtBu2 )2 6, was synthesized by mild thermolysis (70 °C in hexane) of tris(di-tert-butyl-hydridosilyl)stannane 4. The X-ray crystallography structure of 6 reveals the following unusual structural properties: a planar geometry around both Sn atoms (Σ∡Sn=359.87°), a non-twisted Sn=Sn double bond, and the shortest Sn=Sn double bond of 2.599 Å among all acyclic distannenes. Thus, compound 6 is the first reported distannene having a structure closely analogous to a classic alkene. Reactions of 6 with CCl4 or with 2,3-dimethylbuta-1,3-diene to produce 1,2-dichlorodistannane 9 and the [2+4] cycloadduct 10, respectively, are characteristic for a Sn=Sn double bond.

Efficient electrocatalytic oxygen reduction reaction of thermally optimized carbon black supported zeolitic imidazolate framework nanocrystals under low-temperature.

Turning commercially available low-cost conducting carbon black materials into functional electrocatalytic electrode media using simple surface chemical modification is a highly attractive approach. This study reports on remarkably enhanced oxygen electrocatalytic activity of commercially available Ketjenblack (KB) by growing a non-precious cobalt metal-based zeolitic-imidazolate framework (ZIF-67) at room temperature in methanol solution followed by a mild thermolysis. The resulting Co@CoOx nanoparticle decorated nitrogen-doped KB derived from the optimized ZIF-67 : KB weight ratio of hybrid samples at 500-600 °C shows high performance for the oxygen reduction reaction (ORR) with impressive Eonset and E1/2 values of ∼0.90 and ∼0.83 V (vs. RHE), respectively in 0.1 M KOH electrolyte. Such ORR activity is comparable to, or better than many metal@metal-oxide-carbon based electrocatalysts synthesized under elevated carbothermal temperatures and using multicomponent/multistep chemical modification conditions. Therefore, a simple electrocatalyst design reported in this work is an efficient synthesis route that not only utilises earth-abundant carbon black but also comprises scalable room temperature synthesized ZIF-67 following mild thermolysis conditions under 600 °C.

New Aspects of Ruthenium-Mediated Polyhedral Contraction of Monocarbollides

It has been shown that the interaction of tris(triphenylphosphine)ruthenium dichloride RuCl2(PPh3)3 (1) with 10-vertex monocarborane [6-Ph-nido-6-CB9H11]−[Et4N]+ (2) under mild thermolysis conditions is not selective due to the undesired coordination of ruthenium to a phenyl substituent in the carborane and phosphine ligands, giving the series of new classical and non-classical metallacarborane complexes. In contrast, the reaction of 1 and monocarborane [arachno-6-CB9H14]−[Et4N]+ (3) proceeds more selectively with the formation of the only one product, a isocloso-structured metallacarborane. The structures of two ruthenacarboranes were resolved by X-ray diffraction.

Structural and electronic analysis of bimetallic thiolate complexes of group-5 transition metal ions

The chemistry of group-5 transition metals, namely vanadium, niobium, and tantalum supported by thiolate ligand framework, has been described. Special emphasis has been given to the electronic and structural properties of binuclear thiolate complexes of group-5 metals exhibiting interesting coordination modes of the chelating thiolate ligands. The mild thermolysis of [(CH2S2)4B]Na5 with [Cp*VCl2]3 afforded the divanadium trithiocarbonate complex, [(Cp*V)2(μ-CS3-κ2S,S')(μ-H2CS2-κ2S'',S''')] (1) along with [{S(CH2S)2}VOCp*] (2). The single crystal X-ray structure of 1 illustrates that the trithiocarbonate and methanedithiolate ligands are symmetrically coordinated to two {Cp*V} units. However, reaction of the heavier group-5 metal precursor, [Cp*NbCl4] with [(CH2S2)4B]Na5 at 60 °C in toluene produced a bimetallic trithiolate complex [(Cp*Nb)2(μ-SCS2-κ1S:κ3C,S',S'')(μ-S)2] (3) along with [(Cp*Nb)2(μ,η2:η2-SH3B)(μ-S)(μ-H2CS2-κ2S,S')]. In a similar manner, [Cp*TaCl4] led to the formation of ditantalum thiolate complexes [(Cp*Ta)2(μ-S)(μ-S2CH2CHS2-κ2S:κ2S',S'')(μ-H)(μ-S2CH2-κ2S''',S'''')] (4) and [Cl(Cp*Ta)2(μ-H)(μ-S2CH2-κ2S,S')(μ-S)(μ-S2CH2-κ2S'':κ1S''')] (5) along with [(Cp*Ta)2(μ-S){μ-(BH2S)(CH2S)2(BS3)-κ2B:κ2S:κ4S',S'',S''',S''''}]. However, the reaction of LiBH4·THF with [Cp*TaCl4] followed by the thermolysis in the presence of S2C·PPh3 led to the formation of [(Cp*Ta)2(μ-S)(μ-S2CH2-κ2S,S')(μ-H)(μ-CHS3-κ2S'':κ2S''',S'''')] (6) along with [(Cp*Ta)2(μ-S2CH2-κ2S,S')2(μ-H)(μ,η2:η2-B2H5)] (I) and [(Cp*Ta)2(μ,η2:η2-B2H6)2] (II). Complex 3 is an example of trithiolate {CS3} stabilized bimetallic niobium complex. The (dimercaptomethyl)-methanedithiolate ligand (C2H3S4) in 4 is coordinated to both the tantalum centres via three sulfur donors and displayed exclusive bonding mode (μ,κ2S:κ2S',S''). Complex 5 consists of two methanedithiolate ligands (S2CH2) with different coordination towards the metal centres, whereas methanetrithiolate (HCS3) and methanedithiolate (S2CH2) units are symmetrically coordinated to both the tantalum centres in complex 6. This study demonstrates that the electronic properties of these complexes vary depending on the metal centres and thiolate ligands. This is reflected in the paramagnetic behaviour of the vanadium complex 1. In contrast, the niobium and tantalum thiolate complexes 3, 4, 5 and 6 are diamagnetic. Further, theoretical investigations provided the insights into the electronic structures and bonding of these group-5 metal thiolate complexes.

Frustrated Lewis Pair Chelation as a Vehicle for Low-Temperature Semiconductor Element and Polymer Deposition.

The stabilization of silicon(II) and germanium(II) dihydrides by an intramolecular Frustrated Lewis Pair (FLP) ligand, PB, i Pr2 P(C6 H4 )BCy2 (Cy=cyclohexyl) is reported. The resulting hydride complexes [PB{SiH2 }] and [PB{GeH2 }] are indefinitely stable at room temperature, yet can deposit films of silicon and germanium, respectively, upon mild thermolysis in solution. Hallmarks of this work include: 1) the ability to recycle the FLP phosphine-borane ligand (PB) after element deposition, and 2) the single-source precursor [PB{SiH2 }] deposits Si films at a record low temperature from solution (110 °C). The dialkylsilicon(II) adduct [PB{SiMe2 }] was also prepared, and shown to release poly(dimethylsilane) [SiMe2 ]n upon heating. Overall, this study introduces a "closed loop" deposition strategy for semiconductors that steers materials science away from the use of harsh reagents or high temperatures.

Frustrated Lewis Pair Chelation as a Vehicle for Low‐Temperature Semiconductor Element and Polymer Deposition

AbstractThe stabilization of silicon(II) and germanium(II) dihydrides by an intramolecular Frustrated Lewis Pair (FLP) ligand, PB, iPr2P(C6H4)BCy2 (Cy=cyclohexyl) is reported. The resulting hydride complexes [PB{SiH2}] and [PB{GeH2}] are indefinitely stable at room temperature, yet can deposit films of silicon and germanium, respectively, upon mild thermolysis in solution. Hallmarks of this work include: 1) the ability to recycle the FLP phosphine‐borane ligand (PB) after element deposition, and 2) the single‐source precursor [PB{SiH2}] deposits Si films at a record low temperature from solution (110 °C). The dialkylsilicon(II) adduct [PB{SiMe2}] was also prepared, and shown to release poly(dimethylsilane) [SiMe2]n upon heating. Overall, this study introduces a “closed loop” deposition strategy for semiconductors that steers materials science away from the use of harsh reagents or high temperatures.

Heterometallic Triply-Bridging Bis-Borylene Complexes.

Triply-bridging bis-{hydrido(borylene)} and bis-borylene species of groups 6, 8 and 9 transition metals are reported. Mild thermolysis of [Fe2 (CO)9 ] with an in situ produced intermediate, generated from the low-temperature reaction of [Cp*WCl4 ] (Cp*=η5 -C5 Me5 ) and [LiBH4 ⋅THF] afforded triply-bridging bis-{hydrido(borylene)}, [(μ3 -BH)2 H2 {Cp*W(CO)2 }2 {Fe(CO)2 }] (1) and bis-borylene, [(μ3 -BH)2 {Cp*W(CO)2 }2 {Fe(CO)3 }] (2). The chemical bonding analyses of 1 show that the B-H interactions in bis-{hydrido (borylene)} species is stronger as compared to the M-H ones. Frontier molecular orbital analysis shows a significantly larger energy gap between the HOMO-LUMO for 2 as compared to 1. In an attempt to synthesize the ruthenium analogue of 1, a similar reaction has been performed with [Ru3 (CO)12 ]. Although we failed to get the bis-{hydrido(borylene)} species, the reaction afforded triply-bridging bis-borylene species [(μ3 -BH)2 {WCp*(CO)2 }2 {Ru(CO)3 }] (2'), an analogue of 2. In search for the isolation of bridging bis-borylene species of Rh, we have treated [Co2 (CO)8 ] with nido-[(RhCp*)2 (B3 H7 )], which afforded triply-bridging bis-borylene species [(μ3 -BH)2 (RhCp*)2 Co2 (CO)4 (μ-CO)] (3). All the compounds have been characterized by means of single-crystal X-ray diffraction study; 1 H, 11 B, 13 C NMR spectroscopy; IR spectroscopy and mass spectrometry.

Optical switching and nanothermochromic studies of VO2(M) nanoparticles prepared by mild thermolysis method

Vanadium dioxide (VO2) has been widely studied due to its promising thermochromic property. VO2 nanoparticles film exhibits a unique nanothermochromic advantage with higher light transmittance (Tlum) and larger solar light transmittance modulation (∆Tsol) than continuous film. In this paper, a mild thermolysis method was developed to prepare VO2 nanoparticles with controlled size and morphology, which was then used to build the nanothermochromic films. By using vanadyl ethylene glycol (VEG) nanorods as a precursor, VO2 nanoparticles can be obtained at a thermolysis temperature as low as 250 °C within 5 min under static argon atmosphere. The VEG nanorods with uniform size and excellent dispersity were prepared from amorphous vanadium oxide nanopowders synthesized by electrochemical anodic-oxidation of vanadium target. The influence of the thermolysis conditions on the microstructure, phase transition and thermochromic properties of VO2 nanoparticles were investigated and discussed. By combining with transparent conductive substrate ITO, the VO2 nanoparticles films demonstrate an active optical switching performance, and the optimal thermochromic properties with Tlum of 48% and ∆Tsol of 11% can be achieved.

Study of the Structure of Benzene- and Alcohol–Benzene-Extractable Resins and Kerogen of Rock Organic Matter (By Example of Bazhenovo Formation Rocks from the North of the Gyda Peninsula)

Mild thermolysis of benzene- and alcohol–benzene-extracted resins and kerogen of the organic matter of Bazhenovo Formation rocks from the northern part of the Gyda Peninsula has been carried out. It has been revealed that macromolecular compounds of the benzene and alcohol–benzene resins and kerogen contain, as moieties, the homologous series of C10–C40n-alkanes, isoprenanes, C10–C30n-alkylcyclohexanes, and C10–C30n-alkylbenzenes; steranes; and terpanes found in crude oils. It has been shown that despite the difference in polarity of the benzene and alcohol–benzene resins, the relative distribution of hydrocarbon biomarkers in thermolysis products is close and differs from that in kerogen thermolysis products. The maturity of benzene and alcohol–benzene resins according to the sterane and terpane indexes is much lower than that of kerogen. As a result of the thermolysis of the resins of both types and kerogen, the unsaturated compounds isoprenene and squalene have been found, and oleanane was found in the thermolysis products of the alcohol–benzene resins. The pattern of distribution of n-alkanes and isoprenanes in the products of thermolysis of resins and kerogen is similar to that observed in the soluble part and in the thermolysates of Thermoplasma sp. archaea biomass in our previous study.

Desulfurization of Heavy Oil by Using Combination of Oxidation and Mild Thermolysis

Desulfurization of Heavy Oil by Using Combination of Oxidation and Mild Thermolysis

New routes to organometallic molecular junctionsviaa simple thermal processing protocol

Gold nanoparticle capped organometallic molecular junctions are prepared from a single source precursor by simple self-assembly and mild thermolysis.

Synthesis in aqueous media of poly(ethylene phosphoric acids) by mild thermolysis of homopolymers and block copolymers based on tert-butyl ethylene phosphate

Poly(ethylene phosphoric acid)s (PEPA)s of different compositions, namely homopolymers, and diblock and triblock copolymers containing poly(ethylene glycol) monomethyl ether, l-lactide, and ε-caprolactone blocks, can be quantitatively obtained by mild thermolysis of polymers based on tert-butyl ethylene phosphate in aqueous media at 80 °C. Thermolysis of poly(tert-butyl ethylene phosphate) in the presence of sodium acetate gave a PEPA with a narrow molecular weight distribution (Ð = 1.10). The salt-like reaction product can be concentrated without the formation of three-dimensional gels. All starting poly(tert-butyl ethylene phosphate) containing homopolymers and block copolymers were effectively prepared with phenolate–Mg catalysts, i.e., [(BHT)MgBu(THF)]2 and [(BHT)Mg(OBn)(THF)]2 (BHT = 2,6-di-tert-butyl-4-methylphenolate). In the synthesis of polyphosphate–polyester block copolymers, the polyphosphate macromonomer inhibits further polymerization of ε-caprolactone. We therefore failed to obtain a copolymer BnO(tBuOEP)n-b-(εCL)mH using a coordination Mg catalyst.

A Dipyrrin Programmed for Covalent Loading with Fullerenes.

We describe here a di‐(β,β′‐sulfoleno)pyrrin programmed for efficient and specific β,β′‐functionalization via [4+2] cycloaddition reactions. At 120 °C and in the presence of an excess of C60‐fullerene the di‐(β,β′‐sulfoleno)pyrrin decomposed cleanly, furnishing a di‐(β,β′‐fullereno)pyrrin and the corresponding monofullereno‐dipyrrin in an overall yield of 96 %. Hence, relatively mild thermolysis of the di‐(β,β′‐sulfoleno)pyrrin induced stepwise extrusion of two equivalents of SO2, producing highly reactive dipyrrin‐β,β′‐diene intermediates readily, providing a very effective path to [4+2]‐cycloadducts. As presented here by the example of the covalent attachment of C60‐fullerene units, a convenient general methodology for the efficient synthesis of covalent dipyrrin β,β′‐cycloadducts is made available.

Synthesis, Structural Characterization, and H2 Evolution Study of a Spheroid‐Shape Hydride‐Rich Copper Nanocluster

AbstractThis study reports on new bis‐2‐butyl dithiophosphate‐stabilized polyhydrido copper nanoclusters, [Cu32(H)20{S2P(O2Bu)2}12], 1H, and [Cu20H11{S2P(O2Bu)2}9], 2H. The clusters 1H and 2H have been characterized by a variety of techniques including multinuclear NMR (1H, 2H, 31P), electrospray ionization mass spectrometry (ESI‐MS), and low temperature X‐ray crystallography. The presence of hydride ligands was supported by the 2H NMR spectrum of the deuteride analogs [Cu32(D)20{S2P(O2Bu)2)12], 1D and [Cu20D11{S2P(O2Bu)2}9], 2D. The metal skeleton of 1H revealed that a hexacapped rhombohedron of fourteen copper atoms was sandwiched between two sets of eighteen (9x2) copper atoms in a cup shape and the entire cluster is an elongated triangular gyrobicupola. The metal core is stabilized by 20 hydride ligands via various (μ3, μ4, μ5)‐H coordination modes and 12 dithiophosphate ligands coordinated either in tetrametallic tetraconnective (η4: μ2, μ2) or trimetallic tetraconnective (η3: μ2, μ2) patterns. The structural motif of 2H showed fascinating correlations with 1H having an elongated triangular orthobicupola framework of eighteen (9x2) copper atoms with an encapsulated linear Cu2 unit along the C3 axis and protected by 11 (μ3, μ4)‐H and 9 dithiophosphate ligands in a tetrametallic tetraconnective (η4: μ2, μ2) mode. The isopropyl derivatives, [Cu32(H)20{S2P(OiPr)2}12], 3H and [Cu20(H)11{S2P(OiPr)2}9], 4H, were used to study H2 evolution under different physico‐chemical conditions and proved to be excellent models for hydrogen storage materials. Additionally, following H2 evolution under sunlight irradiation, mild thermolysis (∼60 oC) and acidification, cluster 3H converted into [Cu8(H){S2P(OiPr)2}6]+, 5H. Intriguingly 5H can react with Cu+ salt in the presence of [BH4]− and re‐form 3H. Cluster 4H also reproducibly re‐formed via the reaction between 5H and [BH4]− from which a continuous cycle of cluster conversion and H2 evolution is proposed. Rhombus‐shaped copper nanoparticles fabricated from further reductions of 3H and 4H showed the intermediary role of metal hydrides in the formation of metal nanoparticles under wet chemical methods.

Isolable endocyclic silenes by thermal Brook rearrangement

In the following study, we investigated thermally and photolytically induced transformations of acylcyclotetrasilanes (Me3Si)2Si4Me8(Me3Si)COR (compounds 9a-c; R = alkyl, aryl). Mild thermolysis of 9a-c below 130 °C cleanly and selectively afforded the corresponding endocyclic silenes 10b-d irrespective of the nature of the substituents at the carbonyl moiety. Thus, the previously unknown heterocyclopolysilane 10b could be isolated by crystallization and fully characterized including single crystal X-ray crystallography. Upon photolysis with light of λ ≥ 300 nm 9a-c showed Brook type 1,3-Si → O migration reactions under formation of the silenes 10a-c with exo- and endocyclic SiC double bonds. In this case the substituent at the carbonyl moiety largely determines the type of the resulting silene. Contrary to alkyl substituted educts, which form both types of silenes, aryl substituted acylcyclotetrasilanes exclusively afford the endocyclic derivative. 10b,c were photochemically unstable and underwent different degradation processes while 10d was surprisingly stable under similar conditions. Photolysis of 9a-c, in the presence of methanol, cleanly afforded the expected 1,2-addition products of the SiC double bond.

Synthesis and Characterization of Bis(sigma)borate and Bis–zwitterionic Complexes of Rhodium and Iridium

AbstractBuilding upon the chemistry of Rh–N,S‐heterocyclic carbene complex, [(Cp*Rh)(L2)(1‐benzothiazol‐2‐ylidene)], 2 (Cp*=η5‐C5Me5; L=C7H4NS2) with various monoboranes‐Lewis adducts, we explored the chemistry of 2 with BH3⋅thf at elevated temperature. As a result, mild thermolysis of 2 with BH3⋅thf led to the formation of bis(sigma)borate [(η4‐C5Me5H)Rh(η2‐H3BL)], 3 and a bis‐zwitterionic species [Cp*RhS(BH2L2)], 4 with the concomitant release of BH3⋅bt (bt=benzothiazole). The RhS3C2N2B2 atoms in 4 generates two six membered rings fused by a common Rh−S bond, which may be considered as a bicycle [4.4.0] cage at the rhodium center. In an effort to generate the iridium analogue of 3, reaction of [Cp*IrCl2]2 with Na[H3B(mbt)] (mbt=2‐mercaptobenzothiazole) was carried out that produced bis(sigma)borate complex [(η4‐C5Me5H)Ir(η2‐H3BL)], 1. The solid state X‐ray structures of 1 and 3 showed that the Cp*H ligand coordinated to the metal center in a η4‐fashion. In compound 3, the methyl group is oriented towards rhodium center, whereas it is away from Ir center in 1. In addition, the DFT computations were performed to shed light on the bonding and electronic structures of these compounds.

ChemInform Abstract: Tandem Bond‐Forming Reactions of 1‐Alkynyl Ethers

AbstractReview: 54 refs.

Tandem Bond-Forming Reactions of 1-Alkynyl Ethers.

Electron-rich alkynes, such as ynamines, ynamides, and ynol ethers, are functional groups that possess significant potential in organic chemistry for the formation of carbon-carbon bonds. While the synthetic utility of ynamides has recently been expanded considerably, 1-alkynyl ethers, which possess many of the reactivity features of ynamides, have traditionally been far less investigated because of concerns about their stability. Like ynamides, ynol ethers are relatively unhindered to approach by functional groups present in the same or different molecules because of their linear geometry, and they can potentially form up to four new bonds in a single transformation. Ynol ethers also possess unique reactivity features that make them complementary to ynamides. Research over the past decade has shown that ynol ethers formed in situ from stable precursors engage in a variety of useful carbon-carbon bond-forming processes. Upon formation at -78 °C, allyl alkynyl ethers undergo a rapid [3,3]-sigmatropic rearrangement to form allyl ketene intermediates, which may be trapped with alcohol or amine nucleophiles to form γ,δ-unsaturated carboxylic acid derivatives. The process is stereospecific, takes place in minutes at cryogenic temperatures, and affords products containing (quaternary) stereogenic carbon atoms. Trapping of the intermediate allyl ketene with carbonyl compounds, epoxides, or oxetanes instead leads to complex α-functionalized β-, γ-, or δ-lactones, respectively. [3,3]-Sigmatropic rearrangement of benzyl alkynyl ethers also takes place at temperatures ranging from -78 to 60 °C to afford substituted 2-indanones via intramolecular carbocyclization of the ketene intermediate. tert-Butyl alkynyl ethers containing pendant di- and trisubstituted alkenes and enol ethers are stable to chromatographic isolation and undergo a retro-ene/[2 + 2] cycloaddition reaction upon mild thermolysis (90 °C) to afford cis-fused cyclobutanones and donor-acceptor cyclobutanones in good to excellent yields and diastereoselectivities. This process, which takes place under neutral conditions and proceeds through an aldoketene intermediate, obviates the need to employ moisture-sensitive and/or unstable acid chlorides under basic conditions for intramolecular [2 + 2] cycloaddition reactions. Furthermore, Lewis acid-catalyzed intramolecular condensations of both ethyl and tert-butyl ynol ethers with tethered acetals efficiently provide protected five-, six-, and seven-membered cyclic Baylis-Hilman adducts. Metalated ethoxyacetylene can also participate in multiple bond-forming reactions that avoid isolation of the alkynyl ether intermediate. Lewis acid-promoted tandem additions employing epoxides/oxetanes and carbonyl compounds give rise to (Z)-α-alkylidene and α-benzylidene lactones stereoselectively in high overall yields. Three new carbon-carbon bonds and a ring are formed in this atom-economical single-flask transformation, resulting in a significant increase in molecular complexity. This Account provides a detailed overview of these useful transformations with the intention of stimulating further interest in and research on ynol ethers and their application in organic synthesis.

Metal-Free Addition/Head-to-Tail Polymerization of Transient Phosphinoboranes, RPH-BH2: A Route to Poly(alkylphosphinoboranes).

Mild thermolysis of Lewis base stabilized phosphinoborane monomers R1R2P–BH2⋅NMe3 (R1,R2=H, Ph, or tBu/H) at room temperature to 100 °C provides a convenient new route to oligo- and polyphosphinoboranes [R1R2P-BH2]n. The polymerization appears to proceed via the addition/head-to-tail polymerization of short-lived free phosphinoborane monomers, R1R2P-BH2. This method offers access to high molar mass materials, as exemplified by poly(tert-butylphosphinoborane), that are currently inaccessible using other routes (e.g. catalytic dehydrocoupling).