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

Rhodium-NHC-Catalyzed gem-Specific O-Selective Hydropyridonation of Terminal Alkynes

The dinuclear complex Rh(mu-Cl)(eta(2)-coe)(IPr)](2) is an efficient catalyst for the O-selective Markovnikov-type addition of 2-pyridones to terminal alkynes. DFT calculations support a hydride-free pathway entailing intramolecular oxidative protonation of a pi-alkyne by a kappa N-1-hydroxypyridine ligand. Subsequent O-nucleophilic attack on a metallacyclopropene species affords an O-alkenyl-2-oxypyridine chelate rhodium intermediate as the catalyst resting state. The release of the alkenyl ether is calculated as the rate-determining step

Síntesis y reactividad de catalizadores de rodio con ligandos carbeno N-Heterocíclicos

En la presente Memoria se ha llevado a cabo la síntesis y caracterización de nuevos complejos catiónicos y neutros de rodio que poseen un solo ligando carbeno N-Heterocíclico (NHC) con el resto de ligandos lábiles o fácilmente modificables. El ligando de tipo NHC elegido es el 1,3-bis-(2,6-diisopropilfenil)imidazol-2-carbeno (IPr), debido a su alta capacidad electrodadora y su gran protección estérica lo que debería favorecer la estabilidad de los complejos sintetizados. La síntesis de los complejos se ha llevado a cabo haciendo uso de técnicas de atmósfera inerte, usando como producto de partida el complejo [Rh(μ-Cl)(IPr)(η2-olefina)]2, ya que es fácilmente modificable a través de la sustitución controlada de la olefina coordinada, la ruptura de puentes cloro o la extracción del cloro por reacción con diferentes ligandos. En el primer apartado de esta memoria, se han sintetizado complejos RhIII-NHC a partir de [Rh(μ-Cl)(IPr)(η2-coe)]2 por tratamiento de este último con un ácido fuerte, el ácido tríflico, en acetonitrilo. Estos complejos, han sido utilizados como precursores de complejos alquilideno RhIII-NHC, pero el tratamiento con diazocompuestos conduce a la dimerización de los mismos. En el segundo apartado, se ha estudiado la distinta disposición que adquieren ligandos típicos en complejos RhI-NHC plano cuadrados frente al carbeno y su labilidad. Dentro de este apartado se ha estudiado el distinto comportamiento que presentan complejos con etileno y con cicloocteno al someterlos al mismo tratamiento, la distinta labilidad que presenta piridina y acetonitrilo, y por último, se han sintetizado distintos complejos con moléculas pequeñas, O2 y CO

Double hydrophosphination of alkynes promoted by rhodium: The key role of an N-heterocyclic carbene ligand

The regioselective double hydrophosphination of alkynes mediated by rhodium catalysts is presented. The distinctive stereoelectronic properties of the NHC ligand prevent the catalyst deactivation by diphosphine coordination thereby allowing for the closing of a productive catalytic cycle

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

Ligand-controlled regioselectivity in the hydrothiolation of alkynes by rhodium N-heterocyclic carbene catalysts

Rh-N-heterocyclic carbene compounds [Rh(μ-Cl)(IPr)(ν 2- olefin)] 2 and RhCl(IPr)(py)(ν 2-olefin) (IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-carbene, py = pyridine, olefin = cyclooctene or ethylene) are highly active catalysts for alkyne hydrothiolation under mild conditions. A regioselectivity switch from linear to 1-substituted vinyl sulfides was observed when mononuclear RhCl(IPr)(py)(ν 2- olefin) catalysts were used instead of dinuclear precursors. A complex interplay between electronic and steric effects exerted by IPr, pyridine, and hydride ligands accounts for the observed regioselectivity. Both IPr and pyridine ligands stabilize formation of square-pyramidal thiolate-hydride active species in which the encumbered and powerful electron-donor IPr ligand directs coordination of pyridine trans to it, consequently blocking access of the incoming alkyne in this position. Simultaneously, the higher trans director hydride ligand paves the way to a cis thiolate-alkyne disposition, favoring formation of 2,2-disubstituted metal-alkenyl species and subsequently the Markovnikov vinyl sulfides via alkenyl-hydride reductive elimination. DFT calculations support a plausible reaction pathway where migratory insertion of the alkyne into the rhodium-thiolate bond is the rate-determining step. © 2012 American Chemical Society.Financial support from the Ministerio de Ciencia e Innovación (MICINN/FEDER) of Spain (Project CTQ2010-15221), the Diputación General de Aragón (E07), the ARAID Foundation under the program “Jóvenes Investigadores”, and CONSOLIDER INGENIO-2010, Projects MULTICAT (CSD2009-00050) and Factoría de Cristalización (CSD2006-0015) are gratefully acknowledged. R.C. thanks the CSIC and the European Social Fund for his Research Contract in the framework of the “Ramón y Cajal” Program.Peer Reviewe

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

Bis(hydrosulfido)-bridged dinuclear rhodium(I) complexes as a platform for the synthesis of trinuclear sulfido aggregates with the core [MRh2(μ3-S2)] (M = Rh, Ir, Pd, Pt, Ru)

The reaction of [Rh(μ-SH)(CO)(PPh3)]2 or [Rh(μ-SH){P(OPh)3}2]2 with [Cp*MCl2]2 (M = Rh, Ir) in the presence of NEt3 afforded the Rh3 and IrRh2 sulfido-bridged compounds [Cp*M(μ3-S)2Rh2(CO)2(PPh3)2] (M = Rh, 1; Ir, 2) and [Cp*Rh(μ3-S)2Rh2{P(OPh)3}4] (3). The reaction with [MCl2(cod)] (M = Pd, Pt), cis-[PtCl2(PPh3)2] or [(η6-C6H6)RuCl2]2 under the same experimental conditions gave [(cod)M(μ3-S)2Rh2{P(OPh)3}4] (M = Pd, 6; Pt, 7), [(cod)M(μ3-S)2Rh2(CO)2(PPh3)2] (M = Pd, 8; Pt, 9), [(PPh3)2Pt(μ3-S)2Rh2(CO)2(PPh3)2] (10) and [(η6-C6H6)Ru(μ3-S)2Rh2(CO)2(PPh3)2] (12), with PdRh2, PtRh2 and RuRh2 trimetallic cores. The aggregates derived from [Rh(μ-SH)(CO)(PPh3)]2 were isolated as a mixture of trans and cis isomers in which the trans isomer predominates. The reaction of [Rh(μ-SH){P(OPh)3}2]2 with 2 equiv. of n-BuLi at 253 K followed by addition of [Cp*IrCl2]2 gave [Cp*Ir(μ3-S)2Rh2{P(OPh)3}4] (4) and [Cp*2ClIr2(μ3-S)2Rh{P(OPh)3}2] (5) in a 3:2 ratio. The RuRh2 compound [(η6-C6H6)Ru(μ3-S)2Rh2{P(OPh)3}4] (11) was prepared similarly from [Rh(μ-SH){P(OPh)3}2]2 and [(η6-C6H6)RuCl2]2 using n-BuLi as a deprotonating agent. The molecular structures of compounds 3, 6, 7, 9 and 11 have been determined by X-ray analysis. The trinuclear complexes exhibit an asymmetric triangular metal core with two triply bridging sulfido ligands resulting in a distorted trigonal-bipyramidal M3(μ3-S)2 heterometallic metal–sulfur core.Financial support from the Ministerio de Ciencia e Innovación (MICINN/FEDER) of Spain (Project CTQ2010-15221), the Diputación General de Aragón (E07), and CONSOLIDER INGENIO-2010, Projects MULTICAT (CSD2009-00050) and Factoría de Cristalización (CSD2006-0015) is gratefully acknowledged.Peer Reviewe

Synthesis of a square-planar rhodium alkylidene N-heterocyclic carbene complex and its reactivity toward alkenes

The first rhodium alkylidene square-planar complex stabilized by an N-heterocyclic carbene ligand, RhCl(-CHPh)(IPr)PPh3 (2; IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-carbene), has been prepared by reaction of RhCl(IPr)(PPh3)2 (1) with phenyldiazomethane and its dynamic behavior in solution studied. Treatment of 2 with alkenes results in the formation of the ¿2-olefin complexes RhCl(¿2-CH2-CHR)(IPr)PPh3 (3, R = H; 4, R = Ph; 5, R = OEt) and new olefins arising from the coupling of the alkylidene with the alkenes, likely via a metallacyclobutane intermediate