Research Progress on the Indirect Hydrogenation of Carbon Dioxide to Methanol

Xian-Long Du, Zheng Jiang, Dang Shen Su, Jian-Qiang Wang

First published: 21 December 2015   DOI: 10.1002/cssc.201501013

Abstract

Methanol is a sustainable source of liquid fuels and one of the most useful organic chemicals. To date, most of the work in this area has focused on the direct hydrogenation of CO₂ to methanol. However, this process requires high operating temperatures (200–250 °C), which limits the theoretical yield of methanol. Thus, it is desirable to find a new strategy for the efficient conversion of CO₂ to methanol at relatively low reaction temperatures. This Minireview seeks to outline the recent advances on the indirect hydrogenation of CO₂ to methanol. Much emphasis is placed on discussing specific systems, including hydrogenation of CO₂ derivatives (organic carbonates, carbamates, formates, cyclic carbonates, etc.) and cascade reactions, with the aim of critically highlighting both the achievements and remaining challenges associated with this field.

http://onlinelibrary.wiley.com/doi/10.1002/cssc.201501013/full

Conversion of alkanes to linear alkylsilanes using an iridium–iron-catalysed tandem dehydrogenation–isomerization–hydrosilylation

Xiangqing Jia & Zheng Huang

Nature Chemistry Volume: 8, Pages: 157–161  Year published: (2016) doi:10.1038/nchem.2417 Received 04 August 2015    Accepted  11 November 2015  Published online 21 December 2015      

Abstract
The conversion of inexpensive, saturated hydrocarbon feedstocks into value-added speciality chemicals using regiospecific, catalytic functionalization of alkanes is a major goal of organometallic chemistry. Linear alkylsilanes represent one such speciality chemical—they have a wide range of applications, including release coatings, silicone rubbers and moulding products. Direct, selective, functionalization of alkanes at primary C–H bonds is difficult and, to date, methods for catalytically converting alkanes into linear alkylsilanes are unknown. Here, we report a well-defined, dual-catalyst system for one-pot, two-step alkane silylations. The system comprises a pincer-ligated Ir catalyst for alkane dehydrogenation and an Fe catalyst that effects a subsequent tandem olefin isomerization–hydrosilylation. This method exhibits exclusive regioselectivity for the production of terminally functionalized alkylsilanes. This dual-catalyst strategy has also been applied to regioselective alkane borylations to form linear alkylboronate esters.

http://www.nature.com/nchem/journal/v8/n2/full/nchem.2417.html

Reversible Bergman cyclization by atomic manipulation

Bruno Schuler, Shadi Fatayer, Fabian Mohn, Nikolaj Moll, Niko Pavliĉek, Gerhard Meyer, Diego Peña, & Leo Gross

Nature Chemistry Volume: 8, Pages: 220–224 Year published: (2016) doi:10.1038/nchem.2438 Received 20 August 2015 Accepted  11 December 2015 Published online  25 January 2016    

 

Abstract

The Bergman cyclization is one of the most fascinating rearrangements in chemistry, with important implications in organic synthesis and pharmacology. Here we demonstrate a reversible Bergman cyclization for the first time. We induced the on-surface transformation of an individual aromatic diradical into a highly strained ten-membered diyne using atomic manipulation and verified the products by non-contact atomic force microscopy with atomic resolution. The diyne and diradical were stabilized by using an ultrathin NaCl film as the substrate, and the diyne could be transformed back into the diradical. Importantly, the diradical and the diyne exhibit different reactivity, electronic, magnetic and optical properties associated with the changes in the bond topology, and spin multiplicity. With this reversible, triggered Bergman cyclization we demonstrated switching on demand between the two reactive intermediates by means of selective C–C bond formation or cleavage, which opens up the field of radical chemistry for on-surface reactions by atomic manipulation.

 

http://www.nature.com/nchem/journal/v8/n3/full/nchem.2438.html  

A Rhodium–Pentane Sigma-Alkane Complex: Characterization in the Solid State by Experimental and Computational Techniques

A Rhodium–Pentane Sigma-Alkane Complex: Characterization in the Solid State by Experimental and Computational Techniques

1. Dr. F. Mark Chadwick, 
2. Dr. Nicholas H. Rees, 
3. Prof. Andrew S. Weller, 
4. Dr. Tobias Krämer, 
5. Dr. Marcella Iannuzziand
6. Prof. Stuart A. Macgregor
7. 1. 
      

Authors

• 
  
• 
  

Chadwick, F. M., Rees, N. H., Weller, A. S., Krämer, T., Iannuzzi, M. and Macgregor, S. A. (2016), A Rhodium–Pentane Sigma-Alkane Complex: Characterization in the Solid State by Experimental and Computational Techniques. Angew. Chem. Int. Ed..

DOI: 10.1002/anie.201511269

Abstract

The pentane σ-complex [Rh{Cy₂P(CH₂CH₂)PCy₂}(η²:η²-C₅H₁₂)][BAr^F₄] is synthesized by a solid/gas single-crystal to single-crystal transformation by addition of H₂ to a precursor 1,3-pentadiene complex. Characterization by low temperature single-crystal X-ray diffraction (150 K) and SSNMR spectroscopy (158 K) reveals coordination through two Rh⋅⋅⋅H−C interactions in the 2,4-positions of the linear alkane. Periodic DFT calculations and molecular dynamics on the structure in the solid state provide insight into the experimentally observed Rh⋅⋅⋅H−C interaction, the extended environment in the crystal lattice and a temperature-dependent pentane rearrangement implicated by the SSNMR data.

Biaryl Reductive Elimination Is Dramatically Accelerated by Remote Lewis Acid Binding to a 2,2′-Bipyrimidyl–Platinum Complex: Evidence for a Bidentate Ligand Dissociation Mechanism

Biaryl Reductive Elimination Is Dramatically Accelerated by Remote Lewis Acid Binding to a 2,2′-Bipyrimidyl–Platinum Complex: Evidence for a Bidentate Ligand Dissociation Mechanism

Allegra L. Liberman-Martin†, Daniel S. Levine†, Wenjun Liu‡, Robert G. Bergman*†, and T. Don Tilley*†
† Department of Chemistry, University of California−Berkeley, Berkeley, California 94720, United States
‡ Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
Organometallics, Article ASAP
DOI: 10.1021/acs.organomet.5b01003
Publication Date (Web): January 4, 2016








The silicon and zinc Lewis acids Si(cat)2 (cat = catecholato), Si(catF)2 (catF = tetrafluorocatecholato), and Zn(C6F5)2 bind to the remote ligand site of a 2,2′-bipyrimidyl–platinum diaryl complex. This platinum complex provides a platform to systematically evaluate electronic and reactivity differences triggered by Lewis acid binding. The electron density of the bipyrimidine ligand is substantially depleted upon Lewis acid binding, as evidenced by UV–vis spectroscopy and cyclic voltammetry. Biaryl reductive elimination studies allowed quantification of the effect of Lewis acid binding on reactivity, and Lewis acid binding accelerated reductive elimination rates by up to 8 orders of magnitude. Kinetics experiments in combination with DFT studies support an unusual mechanism featuring complete dissociation of the Lewis acid-coordinated bidentate bipyrimidine ligand prior to reductive elimination.

Metal-free electrocatalytic hydrogen oxidation using frustrated Lewis pairs and carbon-based Lewis acids

Metal-free electrocatalytic hydrogen oxidation using frustrated Lewis pairs and carbon-based Lewis acids

Elliot J. Lawrence,a Ewan R. Clark,b Liam D. Curless,b James M. Courtney,a Robin J. Blagg,a Michael J. Ingleson*b and Gregory G. Wildgoose*a

Show Affiliations
Chem. Sci., 2016, Advance Article
DOI: 10.1039/C5SC04564AReceived 27 Nov 2015, Accepted 06 Jan 2016
First published online 06 Jan 2016








Whilst hydrogen is a potentially clean fuel for energy storage and utilisation technologies, its conversion to electricity comes at a high energetic cost. This demands the use of rare and expensive precious metal electrocatalysts. Electrochemical-frustrated Lewis pairs offer a metal-free, CO tolerant pathway to the electrocatalysis of hydrogen oxidation. They function by combining the hydrogen-activating ability of frustrated Lewis pairs (FLPs) with electrochemical oxidation of the resultant hydride. Here we present an electrochemical–FLP approach that utilises two different Lewis acids – a carbon-based N-methylacridinium cation that possesses excellent electrochemical attributes, and a borane that exhibits fast hydrogen cleavage kinetics and functions as a “hydride shuttle”. This synergistic interaction provides a system that is electrocatalytic with respect to the carbon-based Lewis acid, decreases the required potential for hydrogen oxidation by 1 V, and can be recycled multiple times.

New air stable cationic methallyl Ni complexes bearing imidoyl-indazole carboxylate ligand: Synthesis, characterization and their reactivity towards ethylene

New air stable cationic methallyl Ni complexes bearing imidoyl-indazole carboxylate ligand: Synthesis, characterization and their reactivity towards ethylene

Alan R. Cabreraa, d, , ,
Ivan Martineza,
Constantin G. Daniliucb,
Griselda B. Gallandc,
Cristian O. Salasa,
Rene S. Rojasa,
a Nucleus Millennium of Chemical Processes and Catalysis, Faculty of Chemistry, Pontificia Universidad Católica de Chile, Casilla 306, Santiago, Chile
b Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
c Instituto de Química, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
d Universidad Bernardo O Higgins, Departamento de Ciencias Químicas y Biológicas, Laboratorio de Bionanotecnología, General Gana 1702, Santiago, Chile
Received 4 December 2015, Revised 23 December 2015, Accepted 27 December 2015, Available online 31 December 2015







Three new neutral N,N imidoyl-indazole ligands with a methoxycarbonyl functional group (1–3) and three new air-stable cationic methallyl nickel complexes (4–6) were prepared. These compounds were characterized by NMR, FT-IR and elemental analyses. In addition, compounds 1, 2, 3 and 4 were analyzed using X-ray diffraction. An evaluation of the reactivity of complexes 4–6 toward ethylene was conducted by using 5 equivalents of B(C6F5)3. At 1 bar of ethylene and 20 °C, only complexes 4 and 6 were able to produce butene, showing unusual air stability and dimerizing ethylene even after exposure to air for 48 h. By increasing the pressure to 12 bar at 20 °C, complex 6 showed a catalytic activity of 401 Kg product (mol Ni)−1 h−1, producing a low molecular weight polyethylene (26.6 Kg/mol) with almost exclusively methyl branches (2.3 mol%). By increasing the temperature to 60 °C at 12 bar of ethylene, the system 6/B(C6F5)3 increased its catalytic activity to 487 Kg product (mol Ni−1) h−1, but produced a significant decrease in the molecular weight of the polymer (1.8 Kg/mol) and a broad distribution of branches.

Synthesis of Pincer Hydrido Ruthenium Olefin Complexes for Catalytic Alkane Dehydrogenation

Synthesis of Pincer Hydrido Ruthenium Olefin Complexes for Catalytic Alkane Dehydrogenation

Yuxuan Zhang, Huaquan Fang, Wubing Yao, Xuebing Leng, and Zheng Huang*
The State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, 345 Lingling Road, Shanghai 200032, People’s Republic of China
Organometallics, 2016, 35 (2), pp 181–188
DOI: 10.1021/acs.organomet.5b00912
Publication Date (Web): January 13, 2016








A series of new hydrido Ru(II) olefin complexes supported by isopropyl-substituted pincer ligands have been synthesized and characterized. These complexes are thermally robust and active for catalytic transfer and acceptorless alkane dehydrogenation. Notably, the alkane dehydrogenation catalysts are tolerant of a number of polar functional species.

Synthesis and Characterization of Pincer-Molybdenum Precatalysts for CO2 Hydrogenation

Synthesis and Characterization of Pincer-Molybdenum Precatalysts for CO2 Hydrogenation

Yuanyuan Zhang†‡, Paul G. Williard‡, and Wesley H. Bernskoetter*†‡
† Department of Chemistry, University of Missouri, Columbia, Missouri 65211, United States
‡ Department of Chemistry, Brown University, Providence, Rhode Island 02912, United States
Organometallics, Article ASAP
DOI: 10.1021/acs.organomet.5b00955
Publication Date (Web): January 19, 2016








A family of low-valent molybdenum complexes supported by the pincer ligand PNMeP (PNMeP = MeN(CH2CH2PPh2)2) was prepared and characterized, including (PNMeP)Mo(C2H4)2, which contains an agostic interaction between the metal and the N-methyl substituent. This β-agostic C–H bond was cleaved by molybdenum and produced a cyclometalated molybdenum formate complex, (κ4-PNMeP)Mo(C2H4)(κ2-O2CH), upon exposure to CO2. This species serves as a promotor of CO2 hydrogenation to formate under basic conditions, a rare transformation for group VI metals. The performance of the precatalyst was enhanced with the addition of Lewis acid salts.

Experimental and computational study of alkane dehydrogenation catalyzed by a carbazolide-based rhodium PNP pincer complex

Experimental and computational study of alkane dehydrogenation catalyzed by a carbazolide-based rhodium PNP pincer complex

David Bézier,a Changjian Guan,b Karsten Krogh-Jespersen,b Alan S. Goldman*b and Maurice Brookhart*a

Show Affiliations
Chem. Sci., 2016, Advance Article
DOI: 10.1039/C5SC04794C
Received 11 Dec 2015, Accepted 20 Jan 2016
First published online 20 Jan 2016

A rhodium complex based on the bis-phosphine carbazolide pincer ligand was investigated in the context of alkane dehydrogenation and in comparison with its iridium analogue. (carb-PNP)RhH2was found to catalyze cyclooctane/t-butylethylene (COA/TBE) transfer dehydrogenation with a turnover frequency up to 10 min−1 and turnover numbers up to 340, in marked contrast with the inactive Ir analogue. TONs were limited by catalyst decomposition. Through a combination of mechanistic, experimental and computational (DFT) studies the difference between the Rh and Ir analogues was found to be attributable to the much greater accessibility of the 14-electron (carb-PNP)M(I) fragment in the case of Rh. In contrast, Ir is more strongly biased toward the M(III) oxidation state. Thus (carb-PNP)RhH2 but not (carb-PNP)IrH2 can be dehydrogenated by sacrificial hydrogen acceptors, particularly TBE. The rate-limiting segment of the (carb-PNP)Rh-catalyzed COA/TBE transfer dehydrogenation cycle is found to be the dehydrogenation of COA. Within this segment, the rate-determining step is calculated to be (carb-PNP)Rh(cyclooctyl)(H) undergoing formation of a β-H agostic intermediate, while the reverse step (loss of a β-H agostic interaction) is rate-limiting for hydrogenation of the acceptors TBE and ethylene. Such a step has not previously been proposed as rate-limiting in the context of alkane dehydrogenation, nor, to our knowledge, has the reverse step been proposed as rate-limiting for olefin hydrogenation.

Pd(II) Complexes Ligated by 1,3-Bis(diphenylphosphino)calix[4]arene: Preparation, X-ray Structures, and Catalyses

Pd(II) Complexes Ligated by 1,3-Bis(diphenylphosphino)calix[4]arene: Preparation, X-ray Structures, and Catalyses

Kengo Hirasawa, Shinya Tanaka*, Takeru Horiuchi, Takahiro Kobayashi, Takumi Sato, Naoya Morohashi, and Tetsutaro Hattori*
Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, 6-6-11 Aramaki-Aoba, Aoba-ku, Sendai 980-8579, Japan
Organometallics, Article ASAP
DOI: 10.1021/acs.organomet.5b00999
Publication Date (Web): January 22, 2016

syn-1,3-Bis(diphenylphosphino)-2,4-dimethoxycalix[4]arene (7) was synthesized via an Ullmann-type phosphinoylation of the syn-1,3-bis(triflate ester) (2) of p-tert-butylcalix[4]arene, followed by reduction of the phosphinoyl moieties and subsequent methylation of the remaining hydroxy groups. The treatment of diphosphine 7 with 2 molar equiv of PdCl2(MeCN)2 in benzonitrile afforded di-μ-chloro-bridged dinuclear palladium complex 8, formulated as Pd2(7)Cl4, whereas the same reaction conducted in acetonitrile with 1 molar equiv of PdCl2(MeCN)2 yielded mononuclear palladium complex 9, formulated as [Pd(7)Cl(MeCN)]Cl. Complex 9 was transformed into dicationic complex 11, formulated as [Pd(7) MeCN)2](BF4)2, by treatment with AgBF4 in dichloromethane, followed by the addition of acetonitrile. On the other hand, refluxing complex 9 in 1,2-dichloroethane yielded neutral complex 12, formulated as Pd(7)Cl2. In each of the mononuclear complexes, the palladium ion adopts a tetracoordinated square-planar geometry perpendicular to the mean plane defined by the macrocycle, and two phosphorus atoms occupy trans coordination sites. Consequently, an acetonitrile or chlorine ligand coordinates through the cavity of the calixarene, while another acetonitrile or chlorine ligand occupies the exo position. Dicationic complex 11 promoted Suzuki–Miyaura coupling between aryl chlorides and phenylboronic acid and the ring-opening reaction of an epoxide with thiophenol.

Polymer Coordination Promotes Selective CO2 Reduction by Cobalt Phthalocyanine

Polymer Coordination Promotes Selective CO2 Reduction by Cobalt Phthalocyanine

Wesley W Kramer and Charles McCrory

Chem. Sci., 2016, Accepted Manuscript
DOI: 10.1039/C5SC04015A
Received 22 Oct 2015, Accepted 01 Feb 2016

Cobalt phthalocyanine (CoPc) is a known electrocatalyst for the carbon dioxide reduction reaction (CO2RR) that, when adsorbed onto edge-plane graphite (EPG) electrodes, shows modest activity and selectivity for CO production along with co-generation of H2. In contrast, electrodes modified with CoPc immobilized in a poly-4-vinylpridine (P4VP) film show dramatically enhanced activity and selectivity compared to those modified CoPc alone. CoPc-P4VP films display a Faradaic efficiency of ~90% for CO production, with a turnover frequency of 4.8 s-1 at just -0.75 V vs RHE. Two properties of P4VP contribute to enhancing the activity of CoPc; (1) the ability of individual pyridine residues to coordinate to CoPc and (2) the high concentration of uncoordinated pyridine residues throughout the film which may enhance the catalytic activity of CoPc through secondary and other outer coordination sphere effects. Electrodes modified with polymer-free, five-coordinate CoPc(py) films (py = pyridine) and with CoPc catalysts immobilized in non-coordinating poly-2-vinylpyridine films were prepared to independently investigate the role that each property plays in enhancing CO2RR performance of CoPc-P4VP. These studies show that a synergistic relationship between the primary and outer coordination sphere effects is responsible for the enhanced catalytic activity of CoPc when embedded in the P4VP membrane.

Synthesis, Structure, Spectroscopy and Reactivity of New Heterotrinuclear Water Oxidation Catalysts

Synthesis, Structure, Spectroscopy and Reactivity of New Heterotrinuclear Water Oxidation Catalysts

Lorenzo Mognon, Sukanta Mandal, Carmen E Castillo, Jérôme Fortage, Florian Molton, Guillem Aromi, Jordi Benet-Buchholz, Carole Duboc, Marie-Noëlle Collomb and Antoni Llobet
Chem. Sci., 2016, Accepted Manuscript
DOI: 10.1039/C5SC04672F

Four heterotrinuclear complexes containing the ligands 3,5-bis(2-pyridyl)pyrazolate (bpp-) and 2,2’:6’,2’’-terpyridine (trpy) of general formula {[RuII(trpy)]2µ-[M(X)2(bpp)2])}(PF6)2, where M = CoII, MnII and X = Cl-, AcO- (M = CoII, X = Cl-: Ru2Co-Cl2; M = MnII, X = Cl-: Ru2Mn-Cl2; M = Co, X = AcO-: Ru2Co-OAc2; M = MnII, X = AcO-: Ru2Mn-OAc2) have been prepared for the first time. The complexes have been characterized using different spectroscopic techniques such as UV-vis and IR, and mass spectrometry. X-Ray diffraction analyses have been used to characterize the Ru2Mn-Cl2 and Ru2Mn-OAc2 complexes. Cyclic voltammograms (CV) for all four complexes in organic solvent (CH3CN or CH2Cl2) display three successive reversible oxidative waves corresponding to one-electron oxidations of each of the three metal centers. The oxidized forms of complexes Ru2Co-OAc2 and Ru2Mn-OAc2 are further characterized by EPR and UV-vis spectroscopy. The magnetic susceptibility measurements of all complexes at temperature range 2-300 K reveal paramagnetic properties due to the presence of high spin Co(II) and Mn(II) centers. The complexes Ru2Co-OAc2 and Ru2Mn-OAc2 act as pre catalysts for water oxidation reaction, since the acetato groups are easily replaced by water at pH = 7 generating the active catalysts, {[Ru(H2O)(trpy)]2(µ-[M(H2O)2(bpp)2])}4+ (M = CoII: Ru2Co-(H2O)4; M = MnII: Ru2Mn-(H2O)4). The photochemical water oxidation reaction is studied using [Ru(bpy)3]2+ as photosensitizer and Na2S2O8 as sacrificial electron acceptor at pH = 7. The Co containing complex generates 50 TON in about 10 minutes (TOFi = 0.21 s-1) whereas the Mn containing one only generates 8 TON. The water oxidation reaction of Ru2Co-(H2O)4 is further investigated using Oxone as sacrificial chemical oxidant at pH = 7. Labelled water oxidation experiments suggest that a nucleophilic attack mechanism is occurring at the Co site of the trinuclear complex with cooperative involvement of the two Ru sites, via electronic coupling through the bpp- bridging ligand and via neighboring hydrogen bonding.

Metal-Free Assembly of Polysubstituted Pyridines from Oximes and Acroleins

Metal-Free Assembly of Polysubstituted Pyridines from Oximes and Acroleins

Huawen Huang*, Jinhui Cai, Lichang Tang, Zilong Wang, Feifei Li, and Guo-Jun Deng*
Key Laboratory of Environmentally Friendly Chemistry and Application of Ministry of Education, College of Chemistry, Xiangtan University, Xiangtan 411105, China

DOI: 10.1021/acs.joc.5b02624
J. Org. Chem. 

Abstract:
 

Transition-metal-catalyzed synthesis of N-heterocycles from oximes has been previously well established. In this paper, for the first time a metal-free protocol with the combinational employment of iodine and triethylamine has been demonstrated to be effective to trigger the oxime-based synthesis of pyridines with high chemo-selectivity and wide functional group tolerance. A broad range of functional pyridines were prepared in moderate to excellent yields. While neither iodine nor triethylamine could trigger this transformation, mechanistic experiments indicated a radical pathway for the reaction. The resultant 2-aryl-substituted pyridines have been proved to be versatile building blocks in a range of transition-metal-catalyzed C−H functionalization reactions.

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Regioselective Electrophilic Fluorination of Rationally Designed Imidazole Derivatives

Regioselective Electrophilic Fluorination of Rationally Designed Imidazole Derivatives

Klaus Albertshofer* and Neelakandha S. Mani
Janssen Research & Development, LLC, 3210 Merryfield Row, San Diego, California 92121, United States

 DOI: 10.1021/acs.joc.5b02592
J. Org. Chem.

Abstract:
 

We report the regioselective and direct functionalization of rationally designed imidazole derivatives through electrophilic fluorina- tion with N-fluorobenzenesulfonimide enabled via in situ deprotonation with lithium 2,2,6,6-tetramethylpiperidine. Aided by a controlled protecting group switch, we were able to effectively target both the reactive 5- as well as the difficult to target 4-position of these molecules, leading to a series of fluorinated polysubstituted imidazoles in gram scale.

TOC: