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

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

Organometallic Chemistry for Enabling Carbon Dioxide Utilization

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Organometallics, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.organomet.0c00229.In photosynthesis, carbon dioxide is used as the carbon source; indeed, most carbon atoms in the structure of a massive tree—the trunk, the branches, the leaves—originate from CO2. This insight has profound implications for chemical synthesis: complex molecular structures are built from something as simple and inert as CO2. Scientists have long been fascinated by this concept, and chemists have tried to reproduce it by generating artificial systems for the transformation of CO2 into more valuable products. Over the past two decades, chemical conversion of CO2 has developed into a major research field. Several comprehensive reviews have summarized advances on coupling CO2 with nucleophiles to form carboxylic acids, carbonates, or carbamates or on reducing CO2 to C1 species such as formate and methanol. The reviews of this field also emphasize an important point: chemical utilization of CO2 is not a strategy to mitigate climate change. CO2 is, however, a renewable carbon feedstock that can replace nonrenewable fossil-fuel-based starting materials. Therefore, methods for the efficient conversion of CO2 should be viewed as an integral part in the development of sustainable chemical processes. The 22 articles in this Special Issue highlight the many ways in which organometallic chemistry can help solve challenges related to CO2 utilization: organometallic complexes can be used in thermal, electrochemical, or photochemical conversion of CO2 to various products such as formate, carbon monoxide, carboxylic acids, acrylates, and polycarbonates. Remarkably, the work presented here involves the activation of CO2 with 15 different metals, including the first-row transition metals titanium, manganese, iron, cobalt, nickel, and copper, the second-row elements ruthenium and rhodium, the third-row species rhenium, platinum, and iridium, the actinide uranium, and the main-group metals cesium, magnesium, and aluminum. One may think, there are many roads to Rome; however, an important point is that the various metals have distinct strengths in terms of selectivity and activity for chemical CO2 utilization. The behavior of these different metals in CO2 conversion can further be modulated through introduction of different ligands

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

Tris(hydroxypropyl)phosphine Oxide: A Chiral Three-Dimensional Material with Nonlinear Optical Properties

The achiral C_(3v) organic phosphine tris(hydroxypropyl)phosphine oxide (1) crystallizes in the unusual chiral hexagonal space group P6_3. The structure is highly ordered because each phosphine oxide moiety forms three hydrogen bonds with adjacent hydroxy groups from three different molecules. The properties of the crystals and the presence of hydrogen bonding interactions were investigated using single crystal Raman spectroscopy. The crystals show nonlinear optical properties and are capable of efficient second harmonic generation

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

Bulky, electron-rich, renewable: analogues of Beller's phosphine for cross-couplings

In recent years, considerable progress has been made in the conversion of biomass into renewable chemicals, yet the range of value-added products that can be formed from biomass remains relatively small. Herein, we demonstrate that molecules available from biomass serve as viable starting materials for the synthesis of phosphine ligands, which can be used in homogeneous catalysis. Specifically, we prepared renewable analogues of Beller's ligand (di(1-adamantyl)-n-butylphosphine, cataCXium® A), which is widely used in homogeneous catalysis. Our new renewable phosphine ligands facilitate Pd-catalysed Suzuki– Miyaura, Stille, and Buchwald–Hartwig coupling reactions with high yields, and our catalytic results can be rationalized based on the stereoelectronic properties of the ligands. The new phosphine ligands generate catalytic systems that can be applied for the late-stage functionalization of commercial drugs