Showing papers by "William D. Jones published in 2015"
TL;DR: In this article, acceptorless, reversible dehydrogenation and hydrogenation reactions involving N-heterocycles are reported with a well-defined cobalt complex supported by an aminobis(phosphine) [PN(H)P] pincer ligand.
Abstract: Acceptorless, reversible dehydrogenation and hydrogenation reactions involving N-heterocycles are reported with a well-defined cobalt complex supported by an aminobis(phosphine) [PN(H)P] pincer ligand. Several N-heterocycle substrates have been evaluated under dehydrogenation and hydrogenation conditions. The cobalt-catalyzed amine dehydrogenation step, a key step in the dehydrogenation process, has been independently verified. Control studies with related cycloalkanes suggest that a direct acceptorless alkane dehydrogenation pathway is unlikely. The metal–ligand cooperativity is probed with the related [PN(Me)P] derivative of the cobalt catalyst. These results suggest a bifunctional dehydrogenation pathway and a nonbifunctional hydrogenation mechanism.
197 citations
TL;DR: Iridium-mediated dehydrogenation of ethanol to acetaldehyde has led to the development of an ethanol-to-butanol process operated at a lower temperature.
Abstract: A highly selective (>99%) tandem catalytic system for the conversion of ethanol (up to 37%) to n-butanol, through the Guerbet process, has been developed using a bifunctional iridium catalyst coupled with bulky nickel or copper hydroxides. These sterically crowded nickel and copper hydroxides catalyze the key aldol coupling reaction of acetaldehyde to exclusively yield the C4 coupling product, crotonaldehyde. Iridium-mediated dehydrogenation of ethanol to acetaldehyde has led to the development of an ethanol-to-butanol process operated at a lower temperature.
137 citations
TL;DR: Reversibility of a dehydrogenation/hydrogenation catalytic reaction has been an elusive target for homogeneous catalysis and this reactivity suggests a strategy for the development of reversible fuel cell electrocatalysts for partial oxidation of hydroxyl-containing fuels.
Abstract: Reversibility of a dehydrogenation/hydrogenation catalytic reaction has been an elusive target for homogeneous catalysis. In this report, reversible acceptorless dehydrogenation of secondary alcohols and diols on iron pincer complexes and reversible oxidative dehydrogenation of primary alcohols/reduction of aldehydes with separate transfer of protons and electrons on iridium complexes are shown. This reactivity suggests a strategy for the development of reversible fuel cell electrocatalysts for partial oxidation (dehydrogenation) of hydroxyl-containing fuels.
117 citations
TL;DR: In this paper, a single homogeneous nickel(II) complex, supported by tris(3,5-dimethylpyrazolyl)borate ligand and 2-hydroxyquinoline ancillary ligand, is shown to catalyze both acceptorless dehydrogenation of alcohols and hydrogenation of carbonyl compounds under mild conditions.
91 citations
TL;DR: In this paper, the effect of carboxylate used in a concerted metalation-deprotonation reaction is probed and shows a direct correlation of pKa to observed rate up to a pKa of 4.3, where the rate drops off at higher pKa.
43 citations
TL;DR: In this article, a bis(phosphino)amine pincer ligand was used to catalyse both acceptorless dehydrogenation and hydrogenation of N-heterocycles.
Abstract: A well-defined iron complex (3) supported by a bis(phosphino)amine pincer ligand efficiently catalyzes both acceptorless dehydrogenation and hydrogenation of N-heterocycles. The products from these reactions are isolated in good yields. Complex 3, the active catalytic species in the dehydrogenation reaction, is independently synthesized and characterized, and its structure is confirmed by X-ray crystallography. A trans-dihydride intermediate (4) is proposed to be involved in the hydrogenation reaction, and its existence is verified by NMR and trapping experiments.
38 citations
TL;DR: Intermolecular competition reactions were studied by photoreaction of 1 in C6F6 with benzene and another substrate (HBpin, PhSiH3, or pentafluoropyridine) employing in situ laser photolysis in the NMR probe, resulting in a wide-ranging map of kinetic selectivities.
Abstract: The photochemical reactions of Tp′Rh(PMe3)H2 (1) and thermal reactions of Tp′Rh(PMe3)(CH3)H (1a, Tp′ = tris(3,5-dimethylpyrazolyl)borate) with substrates containing B–H, Si–H, C–F, and C–H bonds are reported. Complexes 1 and 1a are known activators of C–H bonds, including those of alkanes. Kinetic studies of reactions with HBpin and PhSiH3 show that photodissociation of H2 from 1 occurs prior to substrate attack, whereas thermal reaction of 1a proceeds by bimolecular reaction with the substrate. Complete intramolecular selectivity for B–H over C–H activation of HBpin (pin = pinacolate) leading to Tp′Rh(PMe3)(Bpin)H is observed. Similarly, the reaction with Et2SiH2 shows a strong preference for Si–H over C–H activation, generating Tp′Rh(PMe3)(SiEt2H)H. The Rh(Bpin)H and Rh(SiEt2H)H products were stable to heating in benzene in accord with DFT calculations that showed that reaction with benzene is endoergic. The intramolecular competition with PhSiH3 yields a ∼1:4 mixture of Tp′Rh(PMe3)(C6H4SiH3)H and Tp′Rh...
38 citations
TL;DR: The reactive fragment [Tp′Rh(PMe3) as mentioned in this paper, generated from the thermal precursor Tp′Rrh(Me3)(Me)H, is found to cleave the C-Cl bonds of chlorohydrocarbons under mild conditions.
19 citations
TL;DR: In this article, the reactivity of thiopalladacycles derived from thiophenic substrates was fully characterized by 1H, 31P, and 13C NMR spectroscopy, elemental analysis, and X-ray diffraction.
15 citations
TL;DR: In this paper, the carbon-sulfur activation of phenyl p-tolyl sulfide by a mixture of [Pd(dippe)(μ-H)]2 and dinuclear Pd(0), [μ-Dippe)Pd]2 (1,2-bis(diisopropylphosphino)ethane) was investigated.
11 citations
TL;DR: The mechanism of C-H activation with the Co(III) complex Cp*(PMe3)Co(CH3)(OTf) was studied by DFT at the M06/6-31+G(d) level of theory and was determined to be in very good agreement with experimental data as discussed by the authors.
TL;DR: In this article, photolysis of Pt0-acetylene complexes with η2 coordination of the alkynes was studied and characterized, showing exclusive C-C bond activation through sp−sp2 type C−C bonds.
TL;DR: In this paper, Cp∗Co(C2H4)2 was reacted with benzothiophene and C-S activation of the vinyl-sulfur bond was observed.
TL;DR: In this paper, four new air and water stable, organometallic rhodium(III) complexes trans-RhIII(α-diimine) (CO)I2Me, 1, [RhIII-α-Diimine (C(O)Me) (H2O)3][BF4]2, 2, [Rhodium-III-Me(H 2O) 3] [BF4]-2, 3] 2, 3, 4, and rhIII-β-DiIMine (1,4-bis
01 Jan 2015
TL;DR: In this article, the activation of C-H bonds by oxidative addition in about 30 different substrates has been examined with three closely related metal species, [Tp′RhL], where L = CNneopentyl, PMe3, and P(OMe)3.
Abstract: The activation of C–H bonds by oxidative addition in about 30 different substrates has been examined with three closely related metal species, [Tp′RhL], where L = CNneopentyl, PMe3, and P(OMe)3. Kinetic studies of the reductive elimination of R–H provided data to ascertain the relative metal–carbon bond strengths for a wide range of compounds. Trends in these bond strengths reveal that there are two classes of C–H substrates: parent hydrocarbons and substituted methanes. DFT calculations are used to support the observed trends, and some generalizations are made by comparison to other metal systems.
TL;DR: In this article, the authors examined a number of systems where mechanistic information has been obtained in C-C cleavage, and used them to develop new strategies for breaking C -C bonds and using the products in catalysis.
Abstract: Organometallic compounds have been found to be of use in cleaving C–C bonds, as strong metal–carbon bonds can be formed to replace the bond that is broken. Studies of the mechanism of C–C cleavage can provide insight into how these bonds can be cleaved, and can give valuable information that can be used to develop new strategies for breaking C–C bonds and using the products in catalysis. In this chapter, we will examine a number of systems where mechanistic information has been obtained in C–C cleavage.