Hydroarylation of olefins catalysed by a dimeric ytterbium(II) alkyl (original) (raw)
Related papers
2011
The mechanism of the hydroarylation reaction between unactivated olefins (ethylene, propylene, and styrene) and benzene catalyzed by [(R)Ir(m-acac-O,O,C 3 )-(acac-O,O) 2 ] 2 and [R-Ir(acac-O,O) 2 (L)] (R = acetylacetonato, CH 3 , CH 2 CH 3 , Ph, or CH 2 CH 2 Ph, and L = H 2 O or pyridine) Ir(III) complexes was studied by experimental methods. The system is selective for generating the anti-Markovnikov product of linear alkylarenes (61 : 39 for benzene + propylene and 98 : 2 for benzene + styrene). The reaction mechanism was found to follow a rate law with first-order dependence on benzene and catalyst, but a non-linear dependence on olefin. 13 C-labelling studies with CH 3 13 CH 2 -Ir-Py showed that reversible b-hydride elimination is facile, but unproductive, giving exclusively saturated alkylarene products. The migration of the 13 C-label from the a to b-positions was found to be slower than the C-H activation of benzene (and thus formation of ethane and Ph-d 5 -Ir-Py). Kinetic analysis under steady state conditions gave a ratio of the rate constants for CH activation and b-hydride elimination (k CH : k b ) of~0.5. The comparable magnitude of these rates suggests a common rate determining transition state/intermediate, which has been shown previously with B3LYP density functional theory (DFT) calculations. Overall, the mechanism of hydroarylation proceeds through a series of pre-equilibrium dissociative steps involving rupture of the dinuclear species or the loss of L from Ph-Ir-L to the solvento, 16-electron species, Ph-Ir(acac-O,O) 2 -Sol (where Sol refers to coordinated solvent). This species then undergoes trans to cis isomerization of the acetylacetonato ligand to yield the pseudo octahedral species cis-Ph-Ir-Sol, which is followed by olefin insertion (the regioselective and rate determining step), and then activation of the C-H bond of an incoming benzene to generate the product and regenerate the catalyst.
Journal of Organometallic Chemistry, 2011
The addition of aromatic CeH bonds across olefin C]C bonds (olefin hydroarylation) is an important synthetic methodology for the preparation of alkylated arenes. Traditional methods utilizing Friedel eCrafts catalysts result in a significant waste stream and substantial polyalkyated products. In order to achieve high overall yield of monoalkylated compounds, Friedel-Crafts catalysis must be combined with a second transalkylation catalytic step. Reactions that incorporate substituted olefins are selective for branched products. In addition, the regioselective synthesis of disubstituted alkyl arenes is difficult to achieve. Recent development of transition metal based catalysts provides non-Friedel-Crafts pathways for the production of alkyl arenes. Systems based on Ru(II), Ir(III), and Pt(II) have been developed, and mechanistic studies have begun to provide insight into the details of these catalysts. Herein, we review recently published results in the area of transition metal catalyzed olefin hydroarylation with a comparison of known catalysts and discussion of challenges yet to be overcome.
Tetrahedron: Asymmetry, 2000
The reaction of 2-(1-naphthyl)-3-methylpyridine with ole®ns in the presence of [RhCl(coe) 2 ] 2 and PCy 3 as the catalyst resulted in the alkylation of the naphthyl ring at the 2-position in good yield. The replacement of PCy 3 with the chiral ferrocenyl phosphine, (R),(S)-PPFOMe, as the ligand resulted in atropselective alkylation of the naphthylpyridine derivatives. Ethylene reacted with the biaryl compounds to give the corresponding addition products in moderate yields with fair to good ee's (up to 49% ee).
Organometallics, 1999
The reactivity of the three hydride compounds [Ta(OC 6 H 3 Ph 2-2,6) 2 (H) 2 Cl(PMe 3) 2 ] (1), [Ta-(OC 6 H 3 Pr i 2-2,6) 2 (H) 2 Cl(PMe 2 Ph) 2 ] (2), and [Ta(OC 6 H 3 Bu t 2-2,6) 2 (H) 2 Cl(PMePh 2)] (3) toward olefins and alkynes has been investigated. The reactivity observed is highly dependent on the nature of the ancillary aryloxide ligands. The 2,6-diphenylphenoxide 1 reacts with styrene to produce 1 equiv of ethylbenzene and the styrene adduct [Ta(OC 6 H 3 Ph 2-2,6) 2 (η 2-CH 2 dCHPh)Cl(PMe 3)] (5). In contrast, 1 reacts with 3-hexyne to eliminate H 2 along with formation of the analogous alkyne complex 6. Structural studies of 5 and 6 show a squarepyramidal geometry with an axial olefin (alkyne) unit lying along the Cl-TaP axis. Structural parameters support a tantalacyclopropane (tantalacyclopropene) bonding picture for these molecules. Compound 5 is converted back into 1 under H 2 along with formation of PhEt. The dihydride 2 reacts with styrene to form 1 equiv of PhEt, H 2 , and the dehydrogenation product [Ta(OC 6 H 3 Pr i-η 2-CMedCH 2)(OC 6 H 3 Pr i 2-2,6)Cl(PMe 2 Ph) 2 ] (7). The related adduct [Ta(OC 6 H 3 Pr i-η 2-CMedCH 2)(OC 6 H 3 Pr i 2-2,6)Cl(PEt 3) 2 ] (9) was isolated by treatment of [Ta(OC 6 H 3 Pr i 2-2,6) 2 Cl 3 ] with PEt 3 /Bu 3 SnH and was structurally characterized. Labeling studies show that the H 2 generated comes exclusively from the aryloxide o-Pr i group which was dehydrogenated. Both hydrides initially attached to the metal are transferred to the olefin substrate. In the case of the 2,6-di-tert-butylphenoxide compound 3, reaction with styrene generates the mono-cyclometalated compound [Ta(OC 6 H 3 Bu t CMe 2 CH 2)(OC 6 H 3 Bu t 2-2,6)(CH 2 CH 2 Ph)Cl] (9). Structural studies of 9 confirm the presence of a phenethyl group. The related trans-phenylvinyl compound 10 is produced when 3 is reacted with phenylacetylene. Addition of 2,6-dimethylphenyl isocyanide (xyNC) to 10 produces the bis-(iminoacyl) derivative 11, in which xyNC has inserted into the cyclometalated carbon as well as the Ta-CHdCHPh bond in 10. Structural studies of 11 confirmed the trans arrangement of the hydrogen atoms in the phenylvinyl group. Mechanistic studies of the formation of 10 and 11 show the presence of two competing pathways. The first involves direct elimination of H 2 from the dihydride and formation of an intermediate olefin/alkyne adduct. The product then arises by CH bond activation of the aryloxide with the hydrogen transferring to a carbon atom of the tantalacyclopropane (tantalacyclopropene) ring. The second pathway involves insertion of olefin/alkyne into a Ta-H bond followed by CH bond activation by the remaining hydride.
Journal of Organometallic Chemistry, 2006
This paper reports the results obtained in a study on the radical hydrostannation of mono-and disubstituted alkynes with bulky triorganotin hydrides using triethylborane as initiator. The addition of trineophyl-(1), tris[(phenyldimethylsilyl)methyl]-(2), and 9-tripticyldimethyltin (3) hydride to eight alkynes was carried out at room temperature leading to vinylstannanes in good to excellent yields and, mostly, with complete stereoselectivity. The results obtained in a study on the relative reactivity of trineophyl-(1), tris[(phenyldimethylsilyl)methyl]-(2), 9-triptycyldimethyltin (3) hydrides, and tri-n-butyltin hydride (29) using the radical reactions between these hydrides and 6-bromo-1-hexene (28) are also reported. Full 1 H-, 13 C-, and 119 Sn NMR characteristics are included.
Zinc-Catalyzed Hydrosilylation and Hydroboration of N-Heterocycles
ACS Catalysis, 2017
The zinc hydride NacNacZnH (2; NacNac = [Ar'NC(Me)CHC(Me)NAr'] − , Ar' = 2,6-Me 2 C 6 H 3) catalyzes regioselective hydrosilylation and hydroboration of pyridines, including the unprecedented hydroboration of phenanthroline. Mechanistic studies of hydrosilylation, including labelling, kinetic analysis, and DFT calculations, suggest the possibility of a novel reaction pathway based on hydride transfer from an out-of-sphere activated silane.
Tetrahedron Letters, 2008
A highly efficient palladium-catalyzed Heck coupling reaction of heteroaryl halides with electron-rich vinyl ether and hydroxyalkyl vinyl ethers is described. It was found that the choice of solvent, ligand, and reaction temperature had a fundamental influence on the regioselectivity and reactivity of the reaction, and the combination of Pd(OAc) 2 and DPPF in ethylene glycol led to the most effective catalytic system. Under these conditions, a variety of heteroaryl halides reacted very quickly with electron-rich olefins to afford exclusively the branched products in good to excellent yields without employing triflates, halide scavengers, or ionic liquids.
Organometallics, 2008
Rare-earth metal alkyl complexes with tridentate [OSO]-type and tetradentate [OSSO]-type bis(phenolato) ligands, [Ln(L)(CH 2 SiMe 3)(THF) n ] (LH 2) 2,2′-thiobis(6-tert-butyl-4-methylphenol) (tbmpH 2), 1,3-dithiapropanediylbis(6-tert-butyl-4-methylphenol) (mtbmpH 2), 1,4-dithiabutanediylbis(6-tert-butyl-4-methylphenol) (etbmpH 2); Ln) Y (1-3), Sc (4, 5), Lu (7), Ho (9, 10)), were synthesized from the reactions of the tris(alkyl) complexes [Ln(CH 2 SiMe 3) 3 (THF) 2 ] with the corresponding bis(phenol) via alkane elimination. The alkyl complexes were characterized by NMR spectroscopy (Y, Sc, Lu) and elemental analysis as well as by X-ray crystal structure analysis (5, 7). The reaction of [Lu(CH 2 SiMe 3) 3 (THF) 2 ] with H 2 etbmp in a 1:2 ratio led to the formation of the bis(phenolato)-bridged dinuclear complex [Lu 2 (etbmp) 3 (THF) 2 ] (8). The reaction of the holmium alkyl complexes 9 and 10 with PhSiH 3 resulted in the formation of the corresponding hydrido complexes [Ho(L)(µ-H)(THF) n ] 2 (L) tbmp, n) 3, 11; L) etbmp, n) 2, 12). The formation of the yttrium analogues could be observed by NMR spectroscopy. Complexes 2, 4, and 5 were tested in the hydrosilylation of a wide variety of aliphatic and aromatic 1-alkenes and 1,5-hexadiene with various silanes (PhSiH 3 , n BuSiH 3 , and Ph 2 SiH 2). In the case of terminal aliphatic alkenes an anti-Markovnikov (1,2) addition takes place with 80-99% regioselectivity. The hydrosilylation of styrene afforded the Markovnikov (2,1) addition product PhHC(SiH 2 Ph)Me with 97% regioselectivity. The hydrosilylation of 1,5-hexadiene by PhSiH 3 catalyzed by 2 resulted in the formation of a linear product, 1,6-bis(phenylsilyl)hexane (ca. 90%), and a cyclic product, (phenylsilylmethyl)cyclopentane (ca. 10%), whereas with n BuSiH 3 84% of the cyclic product was obtained.