gem-selective cross-dimerization and cross-trimerization of alkynes with silylacetylenes promoted by a Rhodium-Pyridine-N-heterocyclic carbene catalyst

The gem-selective cross-dimerization and -trimerization of silylacetylenes with alkynes through C[BOND]H activation using a rhodium(I)–pyridine–N-heterocyclic carbene catalyst have been developed. This reaction is applied to various aliphatic or aromatic terminal alkynes, internal alkynes, and gem-1,3-disubsituted enynes to afford the corresponding enynes and dienynes with high regio- and stereoselectivities and in good isolated yields (up to 91 %).Financial support from the Spanish Ministerio de Economía y Competitividad (MEC/FEDER) of Spain Project (CTQ2010-15221), the Diputación General de Aragón (E07), the KFUPMUNIZAR agreement, and CONSOLIDER INGENIO-2010, under the Project MULTICAT (CSD2009-00050) are gratefully acknowledged. L. R.-P. thanks CONACyT (Mexico, 186898 and 204033) for a postdoctoral fellowship.Peer Reviewe

Preparation of mixed Bis-N-Heterocyclic Carbene Rhodium(I) Complexes

A series of mixed bis-NHC rhodium(I) complexes of type RhCl(η2-olefin)(NHC)(NHC’) have been synthesized by a stepwise reaction of [Rh(μ-Cl)(η2-olefin)2]2 with two different NHCs (NHC = N-heterocyclic carbene), in which the steric hindrance of both NHC ligands and the η2-olefin is critical. Similarly, new mixed coumarin-functionalized bis-NHC rhodium complexes have been prepared by a reaction of mono NHC complexes of type RhCl(NHC-coumarin)(η2,η2-cod) with the corresponding azolium salt in the presence of an external base. Both synthetic procedures proceed selectively and allow the preparation of mixed bis-NHC rhodium complexes in good yields

Tailor-made poly(vinylidene sulfide)s by Rh(I)–NHC catalyzed regioselective thiol-yne click polymerization

The [Rh(μ-Cl)(IPr)(η2-coe)]2/pyridine system efficiently catalyzes the polyhydrothiolation of a series of dialkynes with dithiols, producing sulfur-rich poly(vinylidene sulfide)s with a typical Mw in the range 20.000–124.000 and vinylidene content of 75–87%. A combination of flexible aliphatic dithiols, including 1,6-hexanedithiol and 2,2′-(ethylendioxy)diethanethiol, and the rigid aromatic dithiol 4,4′-thiobisbenzenethiol, with rigid aromatic dialkynes, 1,3-diethynylbenzene and 1,4-diethynylbenzene, and flexible dialkynes, including propargyl ether and 1,7-octadiyne, have been used to prepare poly(vinylidene sulfide)s. The copolymerization of flexible dithiols with rigid aromatic dialkynes or vice versa results in high molecular weight polymers, Mw up to 259.000, with low polydispersities. However, polyhidrothiolation of flexible dialkynes with flexible dithiols is much less efficient and usually results in the formation of oligomers. The interplay of the IPr and pyridine ligands on the RhCl(IPr)(py)(η2-coe) catalyst, which controls the regioselectivity of the alkyne insertion step towards the branched vinyl sulfide, is key in the preparation of these poly(vinylidene sulfide)s

Rhodium(I)-N-heterocyclic carbene catalyst for selective coupling of N-vinylpyrazoles with alkynes via C-H activation

The complex [Rh(μ-Cl)(IPr)(η2-coe)]2 {IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-carbene, coe = cis-cyclooctene} efficiently catalyzes the coupling of alkynes and N-vinylpyrazole via C–H activation, leading to Markovnikov-selective butadienylpyrazole derivatives under mild conditions. A straightforward approach to cross-conjugated acyclic trienes is also operative through a one-pot alkyne dimerization-hydrovinylation tandem reaction. The proposed mechanism involves C–H activation of vinylpyrazole directed by nitrogen coordination to the metallic center. Subsequent alkyne coordination, insertion, and reductive elimination steps lead to the coupling products. Several key intermediates participating in the catalytic cycle have been detected and characterized, including a κ-N, η2-C═C coordinated vinylpyrazole complex and a RhIII-hydride-alkenyl species resulting from the C–H activation of the vinylpyrazole.Financial support from the Spanish Ministerio de Economía y Competitividad (MEC/FEDER) of Spain Projects (CTQ2010-15221), the Diputación General de Aragón (E07), the ARAID Foundation, and CONSOLIDER INGENIO-2010, under the Project MULTICAT (CSD2009-00050) are gratefully acknowledged. L. R.-P. thanks CONACyT (Mexico, 186898 and 204033) for a postdoctoral fellowship.Peer Reviewe

Diseño de nuevos catalizadores organometálicos basados en complejos heterocíclicos con aplicación en reacciones de acoplamiento Carbono-Carbono

El trabajo presentado en esta Tesis Doctoral se ha centrado en la síntesis de nuevos complejos de rodio con ligandos carbeno N-heterocíclicos (NHC) y en el estudio de su actividad catalítica en reacciones de acoplamiento carbono-carbono vía activación C-H. La adición de diferentes ligandos N-dadores al complejo dinuclear [Rh(¿-Cl)(NHC)(¿2-coe)]2 produce la ruptura del sistema de puentes cloruro y ha permitido la preparación de nuevos complejos mononucleares en los que el ligando N-dador se coordina trans al ligando NHC. Este tipo de compuestos son catalizadores eficientes en reacciones de acoplamiento carbono-carbono vía activación C-H en diferentes compuestos que incluyen alquinos, compuestos aromáticos y vinil-derivados. En este sentido, la presencia del ligando NHC es fundamental para alcanzar buenas actividades y selectividades. La alta densidad electrónica aportada por el ligando NHC al metal es clave en la actividad y la influencia estérica de los sustituyentes es determinante para la selectividad.Peer Reviewe

Rhodium (I)-N-heterocyclic carbene catalyst for selective coupling of aromatic heterocycles with olefins and alkynes by C-H activation

Resumen del póster presentado al Organometallic Chemistry Directed Towards Organic Synthesis (OMCOS) IUPAC International Symposium, celebrado en Sitges-Barcelona (España) del 28 de junio al 2 de julio de 2015.The development of new and selective catalytic methodologies has been the focus of intense research. Particularly, rhodium catalyzed C-C bond formation via C-H activation continues to be a powerful tool in organic shynthesis. Substitution of classical ligands such as phosphines by NHC carbene ligands in the metal center has a significant influence on the selectivity control over the catalytic outcome. Herein, we present the selective coupling of heteroarenes with alkenes and alkynes mediated by a Rh[sup]I[/sup]-NHC catalyst. The proposed mechanism involves C-H activation, migratory insertion reactions and reductive elimination steps (Scheme 1 - Control of selectivity in the aromatic heterocycles functionalization).Peer Reviewe

A new access to 4 H-quinolizines from 2-vinylpyridine and alkynes promoted by rhodium-N-heterocyclic-carbene catalysts

Forging the lock that autolocks! Rh-NHC catalysts promote a new access to 4 H-quinolizine species from 2-vinylpyridine and terminal and internal alkynes through C-H activation and C-C coupling reactions (see figure). N-Bridgehead heterocycle formation is favored for internal- over terminal-substituted butadienylpyridine derivatives in a thermal 6π-electrocyclization process. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Financial support from the Ministerio de Economía y Competitividad of Spain Project CTQ2010–15221), the Diputación General de Aragón (E07), the ARAID Foundation under the program “Jóvenes Investigadores”, and CONSOLIDER INGENIO-2010, under the Project MULTICAT (CSD2009–00050) are gratefully acknowledged.Peer Reviewe

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 RhI species [RhCl(NHC)(η2-HC ≡CCH2Ph)(py)] (3) and [RhCl(NHC){η2-C(tBu) ≡C(E)CH=CHtBu}(py)] (4) and the RhIII-hydride-alkynyl species [RhClH{-C ≡CSi(Me) 3}(IPr)(py)2] (5). Computational DFT studies reveal an operational mechanism consisting of sequential alkyne Ci£ 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.Financial support from the Spanish Ministerio de Economía y Competitividad (MEC/FEDER) Projects (CTQ2010-15221, CTQ2012-35665), the Diputación General de Aragón (E07), the ARAID Foundation under the program “Jóvenes Investigadores”, and CONSOLIDER INGENIO-2010 under the Project MULTICAT (CSD2009-00050) is gratefully acknowledged. L.R.-P. thanks CONACyT (Mexico, 186898) for a postdoctoral fellowship.Peer Reviewe

Divergent reactivity of 2-vinylpyridine and 1-vinylpyrazole in rhodium-phosphine systems: C-H activation and dinuclear chemistry

[EN]: The RhI-RhIII mixed valence dinuclear complex Rh2- Cl2(μ-H)(μ-η2,κ2-C,N-NC5H4-2-(Z)CH=CH)(PPhMe2)3 has been prepared by reaction of [Rh(μ-Cl)(η2-coe)2]2 with 2-vinylpyridine in the presence of dimethylphenylphosphine as a result of C-H activation of the terminal olefinic proton. The X-ray structure presents anagostic Rh···HC and π-π interactions between aromatic rings. In contrast, 1-vinylpyrazole does not undergo a C-H activation process, resulting in the formation of dinuclear species supported by 1-vinylpyrazole bridges. Anagostic Rh···HC interactions and CH···Cl hydrogen bonds are responsible for the 3D packing of the complex.[ES]: El complejo dinuclear de valencia mixta RhI-RhIII Rh2-Cl2(μ-H)(μ-η2,κ2-C,N-NC5H4-2-(Z)CH=CH)(PPhMe2)3 ha sido preparado por reacción de [Rh(μ-Cl)(η2-coe)2]2 con 2-vinilpiridina en presencia de dimetilfenilfosfina, como resultado de la activación C-H del protón terminal de la olefina. La estructura de rayos-X presenta enlaces anagósticos Rh···HC, así como interacciones π-π entre anillos aromáticos. Por otro lado, la reacción con 1-vinilpirazol no da lugar a una activación C-H sino que se observa la formación de una especie dinuclear soportada por ligandos 1-vinilpirazol puente. Diferentes interacciones anagósticas Rh···HC y de enlace de hidrógeno CH···Cl son responsables del empaquetamiento tridimensional del complejo.Financial support from the Ministerio de Economía y Competitividad (MINECO/FEDER) of Spain (Proyect CTQ2013-42532-P), the Diputación General de Aragón and Fondo Social Europeo (DGA/FSE-E07), and CONSOLIDER INGENIO-2010 under the Project MULTICAT (CSD2009-00050) is gratefully acknowledged.Peer Reviewe

Preparation of butadienylpyridines by iridium-NHC-catalyzed alkyne hydroalkenylation and quinolizine rearrangement

Iridium(I) N-heterocyclic carbene complexes of formula Ir(κ2O,O’-BHetA)(IPr)(η2-coe) [BHetA=bis-heteroatomic acidato, acetylacetonate or acetate; IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-carbene; coe=cyclooctene] have been prepared by treating Ir(κ2O,O’-BHetA)(η2-coe)2 complexes with IPr. These complexes react with 2-vinylpyridine to afford the hydrido-iridium(III)-alkenyl cyclometalated derivatives IrH(κ2O,O’-BHetA)(κ2N,C-C7H6N)(IPr) through the iridium(I) intermediate Ir(κ2O,O’-BHetA)(IPr)(η2-C7H7N). The cyclometalated IrH(κ2O,O’-acac)(κ2N,C–C7H6N)(IPr) complex efficiently catalyzes the hydroalkenylation of aromatic and aliphatic terminal alkynes and enynes with 2-vinylpyridine to afford 2-(4R-butadienyl)pyridines with Z,E configuration as the major reaction products (yield up to 89 %). In addition, unprecedented (Z)-2-butadienyl-5R-pyridine derivatives have been obtained as minor reaction products (yield up to 21 %) from the elusive 1Z,3gem-butadienyl hydroalkenylation products. These compounds undergo a thermal 6π-electrocyclization to afford bicyclic 4H-quinolizine derivatives that, under catalytic reaction conditions, tautomerize to 6H-quinolizine to afford the (Z)-2-(butadienyl)-5R-pyridine by a retro-electrocyclization reaction.Financial support from the Spanish Ministerio de Ciencia e Innovación (MICINN/FEDER) under Project PID2019-103965GB-I00, and the Departamento de Ciencia, Universidad y Sociedad del Conocimiento del Gobierno de Aragón (group E42_20R) is gratefully acknowledged. I.G. thanks the Humboldt Foundation for a research fellowship.Peer reviewe