Dimerization Of Terminal Alkynes Research Articles

Iron(II) Bis(acetylide) Complexes as Key Intermediates in the Catalytic Hydrofunctionalization of Terminal Alkynes

Nonclassical iron(II) polyhydride complexes supported by PNP-pincer ligands were found to be very active catalysts for the Z-selective hydroboration and head-to-head dimerization of terminal alkynes. Iron(II) bis(acetylide) complexes are identified as catalytically active species in both transformations, which proceed via different reaction pathways, however. These species as well as intermediates relevant for the elucidation of selectivity could be trapped and fully characterized spectroscopically. X-ray structures of key intermediates are presented. Detailed DFT calculations provide a deeper insight into the activation of the precatalysts, and comprehensive catalytic cycles are elucidated. The proposed mechanisms provide a consistent picture of the different reaction pathways and fully explain the stereoselective steps of these transformations.

Dimerization of Terminal Aryl Alkynes Catalyzed by Iron(II) Amine-Pyrazolyl Tripodal Complexes with E/Z Selectivity Controlled by tert-Butoxide.

The catalytic activity of iron(II) complexes with functionalized amine-pyrazolyl tripodal ligands toward dimerization of terminal alkynes in the presence a base (KOtBu or NaOtBu) has been studied. An unusual E/Z selectivity of the reaction determined by tert-butoxide was observed.

Computational insight into the mechanism of the Pd(0)–Brønsted acid cooperatively catalysed head-to-tail dimerization of terminal alkynes

The Pd(0)–Brønsted acid cooperatively catalysed head-to-tail dimerization of terminal alkynes was computationally studied to gain a mechanistic insight.

POP–Pincer Ruthenium Complexes: d6 Counterparts of Osmium d4 Species

A wide range of ruthenium complexes stabilized by the POP-pincer ligand xant(P(i)Pr2)2 (9,9-dimethyl-4,5-bis(diisopropylphosphino)xanthene) were prepared starting from cis-RuCl2{κ-S-(DMSO)4} (1; DMSO = dimethyl sulfoxide). Treatment of toluene solutions of this adduct with the diphosphine under reflux leads to RuCl2{xant(P(i)Pr2)2}(κ-S-DMSO) (2), which reacts with H2 in the presence of a Brønsted base. The reaction in the presence of Et3N affords RuHCl{xant(P(i)Pr2)2}(κ-S-DMSO) (3), whereas NaH removes both chloride ligands to give RuH2{xant(P(i)Pr2)2}(κ-S-DMSO) (4). The stirring of 3 in 2-propanol under 3 atm of H2 for a long time produces the elimination of DMSO and the coordination of H2 to yield the dihydrogen derivative, RuHCl(η(2)-H2){xant(P(i)Pr2)2} (5). In contrast to H2, PPh3 easily displaces DMSO from the metal center of 3 to afford RuHCl{xant(P(i)Pr2)2}(PPh3) (6), which can be also obtained starting from RuHCl(PPh3)3 (7) and xant(P(i)Pr2)2. In contrast to 3, complex 4 does not undergo DMSO elimination to give RuH2(η(2)-H2){xant(P(i)Pr2)2} (8) under a H2 atmosphere. However, the latter can be prepared by hydrogenation of Ru(COD)(COT) (9; COD = 1,5-cyclooctadiene and COT = 1,3,5-cyclooctatriene) in the presence of xant(P(i)Pr2)2. A more efficient procedure to obtain 8 involves the sequential hydrogenation with ammonia borane of the allenylidene derivative RuCl2(═C═C═CPh2){xant(P(i)Pr2)2} (10), which is formed from the reaction of 2 with 1,1-diphenyl-2-propyn-1-ol. The hydrogenation initially gives RuCl2(═C═CHCHPh2){xant(P(i)Pr2)2} (11), which undergoes the subsequent reduction of the Ru-C double bond to yield the hydride-tetrahydroborate complex, RuH(η(2)-H2BH2){xant(P(i)Pr2)2} (12). The osmium complex, OsCl2{xant(P(i)Pr2)2}(κ-S-DMSO) (13), reacts with 1,1-diphenyl-2-propyn-1-ol in a similar manner to its ruthenium counterpart 2 to yield the allenylidene derivative, OsCl2(═C═C═CPh2){xant(P(i)Pr2)2} (14). Ammonia borane also reduces the Cβ-Cγ double bond of the allenylidene of 14. However, the resulting vinylidene species, OsCl2(═C═CHCHPh2){xant(P(i)Pr2)2} (15), is inert. Complex 12 is an efficient catalyst precursor for the hydrogen transfer from 2-propanol to ketones, the α-alkylations of phenylacetonitrile and acetophenone with alcohols, and the regio- and stereoselective head-to-head (Z) dimerization of terminal alkynes.

Alkyne reactions with trimethylphosphine complexes of iridium: Lessons for the catalysis of vinyl ester formation and alkyne dimerization

The combination of iridium with trimethylphosphine ligands yields very electron rich iridium compounds that are active for terminal alkyne dimerization chemistry as well as the addition of carboxylic acids to alkynes. The structures, catalytic and stoichiometric chemistry of some iridium tris-trimethlyphosphine compounds with benzoate ligands are detailed in this paper. The roles that these compounds may play in the catalytic cycles involved in the dimerization of terminal alkynes and the addition of benzoic acid to terminal alkynes are examined and possible mechanisms for these catalytic reactions are proposed.

Pyridine‐Enhanced Head‐to‐Tail Dimerization of Terminal Alkynes by a Rhodium–N‐Heterocyclic‐Carbene Catalyst

A general regioselective rhodium-catalyzed head-to-tail dimerization of terminal alkynes is presented. The presence of a pyridine ligand (py) in a Rh-N-heterocyclic-carbene (NHC) catalytic system not only dramatically switches the chemoselectivity from alkyne cyclotrimerization to dimerization but also enhances the catalytic activity. Several intermediates have been detected in the catalytic process, including the π-alkyne-coordinated Rh(I) species [RhCl(NHC)(η(2)-HC≡CCH2Ph)(py)] (3) and [RhCl(NHC){η(2)-C(tBu)≡C(E)CH=CHtBu}(py)] (4) and the Rh(III)-hydride-alkynyl species [RhClH{-C≡CSi(Me)3}(IPr)(py)2] (5). Computational DFT studies reveal an operational mechanism consisting of sequential alkyne C-H oxidative addition, alkyne insertion, and reductive elimination. A 2,1-hydrometalation of the alkyne is the more favorable pathway in accordance with a head-to-tail selectivity.

Z-Selective Dimerization of Aromatic Terminal Alkynes Catalyzed by an Iridium(I)-N-Heterocyclic Carbene-Phosphine System

The development of an iridium-catalyzed regio- and stereoselective dimerization process has enabled the formation of (<i>Z</i>)-enyne products. More specifically, low catalyst loadings of an iridium(I) complex, featuring a bulky N-heterocyclic carbene–phosphine ligand combination, has been successfully employed in this selective head-to-head dimerization of terminal alkynes via C–H activation.

Synthesis and Reactivity of Ruthenium Azido Complexes Containing a Hydridotris(pyrazolyl)borate Ligand and Dimerization of Terminal Alkynes in Organic and Aqueous Media

Facile ligand substitution is observed when the ruthenium azido complex (PPh3)[Ru]-N3 (1; [Ru] = Tp(PPh3)Ru) is treated with CH3CN, yielding the nitrile-substituted ruthenium azido complex (CH3CN)[Ru]-N3 (2). Alkylation, [3 + 2] cycloaddition, and catalytic reactions of complex 2 have been investigated. In the case of [3 + 2] cycloaddition reactions, the metal-bound heterocyclic complexes (CH3CN)[Ru]-N3C2(CO2Me)2 (3a), (CH3CN)[Ru]-N3C2HCO2Me (5), and (CH3CN)[Ru]-N3C2HCN (6) are obtained from dimethyl acetylenedicarboxylate, methyl propiolate, and fumaronitrile, respectively. The tetrazolato complex [(CN)2C═C(CN)2][Ru]-N4C[C(CN)═C(CN)2] (8) is prepared from 2 and TCNE. Alkylation of 3a with organic bromides affords N-alkylated five-membered-ring organic triazoles. The reaction of CS2 with 2 produces the thermally unstable thiothiatriazolate (CH3CN)[Ru]-N3CS(S) (10), which decomposes to the isothiocyanate (CH3CN)[Ru]-NCS (11). On the other hand, several cationic imine complexes {(CH3CN)[Ru]-(NH═CHR)}+ (12a,...

Handbook of C-H transformations: applications in organic synthesis

Volume 1. Preface. List of Contributors. I. General. 1. What is C-H Bond Activation? (Bengu Sezen and Dalibor Sames). 1.1 Introduction. 1.2 Activation or 1.3 The Origin and Historical Context of the Organometallic Definition. 1.4 What Do We Do With Two Definitions? 1.5 Conclusion. 2. C-H Transformation in Industrial Processes (Leslaw Mleczko, Sigurd Buchholz, Christian Munnich) 2.1 Introduction. 2.2 Alkane Activation. 2.3 C-H Transformation at Olefins. 2.4 Basic Chemicals from Aromatic Hydrocarbons. 2.5 Fine Chemicals. II. C-H Transformation at sp-Hybridized Carbon Atoms. 1. C-H Transformation at Terminal Alkynes. 1.1 Recent Developments in Enantioselective Addition of Terminal Alkynes to Aldehydes (Tobias Ritter and Erick M. Carreira). 1.2 The Sonogashira Coupling Reaction (Herbert Plenio and Anupama Datta). 1.3 Glaser Homocoupling and the Cadiot-Chodkiewicz Heterocoupling Reaction (Peter Siemsen and Beatrice Felber). 1.4 Dimerization of Terminal Alkynes (Emilio Bustelo and Pierre H. Dixneuf). 1.5 anti -Markovnikov Addition to Terminal Alkynes via Ruthenium Vinylidene Intermediates (Christian Bruneau). 2. Asymmetric Hydrocyanation of Alkenes (Jos Wilting and Dieter Vogt). 2.1 Introduction. 2.2 Mechanism. III. C-H Transformation at sp 2 -hybridized Carbon Atoms. 1. C-H Transformations at Arenes. 1.1 Direct Oxidation of Arenes to Phenols and Quinones (Vsevolod V. Rostovtsev). 1.2 Metalation of Arenes. 1.3 Alkylation and Vinylation of Arenes. 1.4 Aryl-Aryl Coupling Reactions. 2. C-H Transformation at Alkenes. 2.1 The Heck Reaction (Lukas Gooben and Kathe Baumann). 2.2 Wacker Oxidation (Lukas Hintermann). 3. C-H Transformation at Aldehydes and Imines. 3.1 Inter- and Intramolecular Hydroacylation (Chul-Ho Jun and Young Jun Park). Volume 2. IV. C-H Transformation at sp 3 -hybridized Carbon Atoms. 1. C-H Transformation at Functionalized Alkanes. 1.1 C-H Transformation in the Position &alpha to Polar Functional Groups. 1.2 C-H Transformation in the Allylic and Benzylic Positions. 1.3 C-H Transformation at Functionalized Alkanes via Palladacycles (Gerald Dyker). 2. C-H Transformation at Unfunctionalized Alkanes. 2.1 C-O Bond Formation by Oxidation. 2.2 Radical Halogenations of Alkanes (Peter R. Schreiner and Andrey A. Fokin). 2.3 Preparative SET C-H Transformations of Alkanes (Andrey A. Fokin and Peter R. Schreiner). 2.4 Photochemical Processes. 2.5 Heterogeneous Catalysts for the C-H Transformation of Unfunctionalized Alkanes (Robert Schlogl). 2.6 Transition-metal Catalyzed Carboxylation of Alkanes (Yuzo Fujiwara and Tsugio Kitamura). 2.7 Photochemical and Thermal Borylation of Alkanes (John F. Harwig and Joshua D. Lawrence). 2.8 Preparation of Olefins by Transition Metal-catalyzed Dehydrogenation (Alan S. Goldman and Rajshekhar Ghosh). 2.9 Rhodium-catalyzed Enantioselective Carbene Addition (Huw M.L. Davies). Index.

Ruthenium-Promoted Z-Selective Head-to-Head Dimerization of Terminal Alkynes in Organic and Aqueous Media

[RuH(CH3CN)(NP3)]OTf effectively catalyzes the dimerization of both aliphatic and aromatic alkynes to give (Z)-enynes in high regio- and stereoselectivity. The catalytic system can tolerate a number of functional groups, which allows for its use in organic and aqueous medium.

Regio- and Stereoselective Dimerization of Terminal Alkynes to Enynes in InCl3-NaBH4-MeCN System

A novel method to prepare (E)-enynes is described in this paper. The InCl 3 -NaBH 4 -MeCN system showed high regio- and stereoselectivity for the dimerization of terminal alkynes to enynes.

Synthesis of Enol Esters and Dimerization of Terminal Alkynes Catalyzed by Neutral and Cationic Vinylidene Ruthenium Complexes

In the current study Ru(II) vinylidene complexes of the general type: Cl 2 Ru{=C=C(H)R}(PR' 3 )L (R = Ph, SiMe 3 , R'=Ph, Cyclohexyl (Cy) and L = phosphine or N-heterocyclic carbene) are synthesized and tested for the addition of carboxylic acids to terminal alkynes. A careful choice of the catalytic system, substrate and carboxylic acid gives access to alk-1-en-2-yl esters, alk-1-en-1-yl esters or enyne dimerization products. Furthermore, an extension was made to synthesize an analogous 14-electron species by treating one of the complexes with AgBF 4 and its influence on the catalytic activity and selectivity are investigated.

ChemInform Abstract: Ruthenium‐Catalyzed Selective anti‐Markovnikov trans Addition of Carboxylic Acids and Tail‐to‐Tail Dimerization of Terminal Alkynes.

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