Activation of a C−H Bond in Indene by [(COD)Rh(μ_2-OH)]_2

The air- and water-tolerant hydroxy-bridged rhodium dimer [(COD)Rh(μ_2-OH)]_2 cleanly activates the aliphatic C−H bond in indene to generate [(COD)Rh(η^3-indenyl)]. The mechanism involves direct coordination of indene to the dimer followed by rate-determining C−H bond cleavage, in contrast to the previously reported analogous reactions of [(diimine)M(μ_2-OH)]_2^(2+) (M = Pd, Pt), for which the dimer must be cleaved before rate-determining displacement of solvent by indene. Another difference is observed in the reactions with indene in the presence of acid: the Rh system generates a stable η^6-indene 18-electron cation, [(COD)Rh(η^6-indene)]+, that is not available for Pd and Pt, which instead form the η^3-indenyl C−H activation products. The crystal structure of [(COD)Rh(η^6-indene)] is reported

Oxidative aromatization of olefins with dioxygen catalyzed by palladium trifluoroacetate

Molecular oxygen can replace sacrificial olefins as the hydrogen acceptor in the palladium trifluoroacetate catalyzed dehydrogenation of cyclohexene and related cyclic olefins into aromatics. One of the major drawbacks of the homogeneous system is the tendency of the palladium trifluoroacetate to precipitate as palladium(0) at elevated temperatures. The use of better ligands affords catalysts that can operate at higher temperatures, although they are less reactive than palladium trifluoroacetate

A Versatile Ligand Platform that Supports Lewis Acid Promoted Migratory Insertion

A helping hand: Incorporation of Group 2 Lewis acids into a macrocycle appended to a phosphine ligand attached to a rhenium carbonyl complex promotes otherwise unfavorable transformations of coordinated CO (see scheme; M=Ca, Sr). These Lewis acids form relatively weak M-O bonds, thereby enabling release of organic products from the metal center

Oxidation of Organometallic Platinum and Palladium Complexes Obtained from C−H Activation

η^3-Cyclohexenyl and -indenyl Pt(II) and Pd(II) diimine complexes, which are generated via C−H activation of cyclohexene and indene by Pt and Pd hydroxy dimers, are selectively oxidized by Br_2, Na_2PtCl_6, and CuCl_2 to give halogenated organic products along with well-defined Pd(II) and Pt(II) species

Iridium(I) and Iridium(III) Complexes Supported by a Diphenolate Imidazolyl-Carbene Ligand

Deprotonation of 1,3-di(2-hydroxy-5-tert-butylphenyl)imidazolium chloride (1a) followed by reaction with chloro-1,5-cyclooctadiene Ir(I) dimer affords the anionic Ir(I) complex [K][{OCO}Ir(cod)] (2: OCO = 1,3-di(2-hydroxy-5-tert-butylphenyl)imidazolyl; cod = 1,5-cyclooctadiene), the first Ir complex stabilized by a diphenolate imidazolyl-carbene ligand. In the solid state 2 exhibits square-planar geometry, with only one of the phenoxides bound to the metal center. Oxidation of 2 with 2 equiv of [FeCp_2][PF_6] generates the Ir(III) complex [{OCO}Ir(cod)(MeCN)][PF_6] (3). Reaction of 3 with H_2 results in the liberation of cyclooctane and a species capable of catalyzing the hydrogenation of cyclohexene to cyclohexane. Displacement of cyclooctadiene from 3 can be achieved by heating in acetonitrile to form [{OCO}Ir(MeCN)3][PF_6] (4) or by reaction with either PMe_3 or PCy_3 to generate [{OCO}Ir(PMe_3)_3][PF_6] (5) or [{OCO}Ir(PCy_3)_2(MeCN)][PF_6] (6), respectively. 6 reacts with CO in acetonitrile to give an equilibrium mixture of 6 and [{OCO}Ir(PCy_3)_2(CO)][PF_6] (7) and with chloride to generate [{OCO}Ir(PCy_3)_(2)Cl] (8). The solid-state structure of 8 shows that the diphenolate imidazolyl-carbene ligand is distorted from planarity; DFT calculations suggest this is due to an antibonding interaction between the phenolates and the metal center in the highest occupied molecular orbital (HOMO) of the complex. 8 undergoes two successive reversible one-electron oxidations in CH_(2)Cl_2 at −0.22 and at 0.58 V (vs ferrocene/ferrocenium); EPR spectra, mass spectroscopy, and DFT calculations suggest that the product of the first oxidation is [{OCO}Ir(PCy_3)_(2)Cl]+ (8+), with the unpaired electron occupying a molecular orbital that is delocalized over both the metal center and the diphenolate imidazolyl-carbene ligand

Enhanced selectivity in the conversion of methanol to 2,2,3-trimethylbutane (triptane) over zinc iodide by added phosphorous or hypophosphorous acid

The yield of triptane from the reaction of methanol with zinc iodide is dramatically increased by addition of phosphorous or hypophosphorous acid, via transfer of hydride from a P–H bond to carbocationic intermediates

Robotic Lepidoptery: Structural Characterization of (mostly) Unexpected Palladium Complexes Obtained from High-Throughput Catalyst Screening

In the course of a high-throughput search for optimal combinations of bidentate ligands with Pd(II) carboxylates to generate oxidation catalysts, we obtained and crystallographically characterized a number of crystalline products. While some combinations afforded the anticipated (L-L)Pd(OC(O)R)_2 structures (L-L = bipyridine, tmeda; R = CH_3, CF_3), many gave unusual oligometallic complexes resulting from reactions such as C−H activation (L-L = sparteine), P−C bond cleavage (L-L = 1,2-bis(diphenylphosphino)ethane, and C−C bond formation between solvent (acetone) and ligand (L-L = 1,4-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene). These findings illustrate potential pitfalls of screening procedures based on assuming uniform, in situ catalyst self-assembly

C-H Bond Activation by [{(Diimine)Pd(μ-OH)}2]2+ Dimers: Mechanism-Guided Catalytic Improvement

These conclusions—that the hydroxy-bridged dimer 1b is the most reactive species in the Pd system, considerably more reactive than either 2a or 2b towards C-H bond activation, and that there is an important solvent-assisted component in the rate law—suggest a way to substantially improve the catalytic conversion of cyclohexene into benzene [Eq. (3)]. Our previous studies involved 2b (or mixtures of 1b and 2b) in the noncoordinating solvent dichloroethane. In a typical experiment, after 24 h under 1 atm of O2 with 5 mol% of 2b as the catalyst, 8% of the cyclohexene had been converted into benzene; furthermore, there was an initiation period before any reaction occurred, and competing disproportionation of cyclohexene to benzene and cyclohexane was a major side reaction.[3] In contrast, under the same conditions but using only 1 mol% of pure 1b as the catalyst and TFE as solvent, conversion was 25% after 24 h, with no induction period or competing isomerization.[7

Fuzzy logic based virtual inertia control of DFIG based wind generator for stability improvement of hybrid power system

Large integration of renewable energy sources (RESs), such as wind power and solar photovoltaic (PV) plants, into the power systems, impacts the system frequency stability. Normally, a wind farm (WF) and PV system do not provide frequency support because of the uncontrollability of the input energy. Moreover, overall system inertia will be reduced due to massive integration of RES because conventional generation units that provide reserve power need to be decreased. To overcome the problems of frequency stability as well as power system transient stability resulting from the insufficient inertia response, this paper proposes a new method to enhance the transient stability of the power system with RESs introduced, in which variable speed wind turbine with doubly fed induction generator (VSWT-DFIG) supplies its kinetic energy (KE) during generation outage to stabilize conventional synchronous generators (SGs). A suitable fuzzy logic based virtual inertia controller (VIC) is proposed to release the stored KE efficiently during transient period. This fuzzy logic controller (FLC) can continuously adjust the VIC gain depending upon the incoming wind speed. To verify the effectiveness of the proposed VIC, simulation analyses are performed on a multi-machine hybrid power system model composed of PV plant, VSWT-DFIG, fixed speed wind turbine with squirrel cage induction generator (FSWT-SCIG), and conventional SGs