The ligand influence on olefin hydrogenation using four capping arene ligated Rh(I) catalyst precursors (FP)Rh(η²-C₂H₄)Cl {FP = capping arene ligands, including 6-FP (8,8′-(1,2-phenylene)diquinoline), 6-^NPFP (8,8′-(2,3-naphthalene)diquinoline), 5-FP (1,2-bis(N-7-azaindolyl)benzene) and 5-^NPFP [2,3-bis(N-7-azaindolyl)naphthalene]} has been studied. Our studies indicate that relative observed rates of catalytic olefin hydrogenation follow the trend (6-FP)Rh(η²-C₂H₄)Cl > (5-FP)Rh(η²-C₂H₄)Cl. Based on combined experimental and density functional theory modeling studies, we propose that the observed differences in the rate of (6-FP)Rh(η²-C₂H₄)Cl and (5-FP)Rh(η²-C₂H₄)Cl-catalyzed olefin hydrogenation are most likely attributed to the difference in the activation energies for the dihydrogen oxidative addition step. We are unable to directly compare the rates of olefin hydrogenation using (6-^NPFP)Rh(η²-C₂H₄)Cl and (5-^NPFP)Rh(η²-C₂H₄)Cl as the catalyst precursor since (5-^NPFP)Rh(η²-C₂H₄)Cl undergoes relatively rapid formation of an active catalyst that does not coordinate 5-^NPFP.

We report carbon-hydrogen acetoxylation of nondirected arenes benzene and toluene, as well as related functionalization with pivalate and 2-ethylhexanoate ester groups, using simple copper(II) [Cu(II)] salts with over 80% yield. By changing the ratio of benzene and Cu(II) salts, 2.4% conversion of benzene can be reached. Combined experimental and computational studies results indicate that the arene carbon-hydrogen functionalization likely occurs by a nonradical Cu(II)-mediated organometallic pathway. The Cu(II) salts used in the reaction can be isolated, recycled, and reused with little change in reactivity. In addition, the Cu(II) salts can be regenerated in situ using oxygen and, after the removal of the generated water, the arene carbon-hydrogen acetoxylation and related esterification reactions can be continued, which leads to a process that enables recycling of Cu(II).

A combined synthetic and theoretical investigation of N-heterocyclic carbene (NHC) adducts of magnesium amidoboranes is presented, which involves a rare example of reversible migratory insertion within a normal valent  s -block element . The reaction of (NHC)Mg(N(SiMe 3 ) 2 ) 2  ( 1 ) and dimethylamine borane yields the tris(amide) adduct (NHC-BN)Mg(NMe 2 BH 3 )(N(SiMe 3 ) 2 ) ( 2 ; NHC-BN = NHC – BH 2 NMe 2 ). In addition to Me 2 N=BH 2  capture at the  NHC C–Mg bond, mechanistic investigations suggest the likelihood of aminoborane migratory insertion from an RMg(NMe 2 BH 2 NMe 2 BH 3 ) intermediate. To elucidate these processes, the carbene complexes (NHC)Mg(NMe 2 BH 3 ) 2 ( 8 ) and (NHC)Mg(NMe 2 BH 2 NMe 2 BH 3 ) 2  ( 9 ) were synthesized, and a dynamic migration of Me 2 N=BH 2  between Mg–N and  NHC C–Mg bonds was observed in  9 . This unusual reversible migratory insertion is presumably induced by dissimilar charge localization in the ˉ{NMe 2 BH 2 NMe 2 BH 3 } anion, as well as the capacity of NHCs to reversibly capture Me 2 N=BH 2  in the presence of Lewis acidic magnesium species.

Electrocatalytic CO₂ reduction is an attractive strategy to mitigate the continuous rise in atmospheric CO₂ concentrations and generate value-added chemical products. A possible strategy to increase the activity of molecular systems for these reactions is the co-catalytic use of redox mediators (RMs), which direct reducing equivalents from the electrode surface to the active site. Recently, we demonstrated that a sulfone-based RM could trigger co-electrocatalytic CO₂ reduction via an inner-sphere mechanism under aprotic conditions. Here, we provide support for inner-sphere cooperativity under protic conditions by synthetically modulating the mediator to increase activity at lower overpotentials (inverse potential scaling). Furthermore, we show that both the intrinsic and co-catalytic performance of the Cr-centered catalyst can be enhanced by ligand design. By tuning both the Cr-centered catalyst and RM appropriately, an optimized co-electrocatalytic system with quantitative selectivity for CO at an overpotential (η) of 280 mV and turnover frequency (TOF) of 194 s⁻¹ is obtained, representing a three-fold increase in co-catalytic activity at 130 mV lower overpotential than our original report. Importantly, this work lays the foundation of a powerful tool for developing co-catalytic systems for homogeneous electrochemical reactions.

The first structurally characterized example of a trioxaborinanone (2) is produced by the reaction of a 9-carbene-9-borafluorene monoanion and carbon dioxide. When compound 2 is heated or irradiated with UV light, carbon monoxide (CO) is released, and a luminescent dioxaborinanone (3) is formed. Notably, carbon monoxide releasing molecules (CORMs) are of interest for their ability to deliver a specific amount of CO. Due to the turn-on fluorescence observed as a result of the conversion to 3, CORM 2 serves as a means to optically observe CO loss “by eye” under thermal or photochemical conditions.

Ferroelectric HfO₂ holds promise for many applications, including non-volatile on-chip memory and ferroelectric field-effect transistors. One challenge preventing the integration of ferroelectric HfO₂ into devices is the difficulty to unambiguously prepare phase-pure material without the benefits of epitaxy. Here, a new method for preparing ferroelectric HfO₂ is presented using High-Power Impulse Magnetron Sputtering (HiPIMS). HiPIMS offers a unique combination of processing parameters such as incident ion energy and gas atmosphere that are inaccessible through conventional HfO₂ synthesis by atomic layer deposition (ALD). In this work, the impact of plasma oxygen content on the crystallization, phase constitution, microstructure, and ferroelectric properties of undoped HfO₂ films deposited by HiPIMS is investigated. HfO₂ thin films were reactively sputtered with plasma oxygen content varied from 7.1 to 8.0 %. The impact of grain size on performance and phases present was assessed, and the results show that the microstructure does not strongly vary between ferroelectric and non-ferroelectric samples. It will be shown that the oxygen content in the plasma directly relates to the oxygen content in the films, as assessed by electron energy-loss spectroscopy, X-ray photoelectron spectroscopy, and positron annihilation spectroscopy. This oxygen content strongly influences phase formation and ferroelectric performance. High concentrations of neutral oxygen vacancies are identified in crystalline ferroelectric samples and allow for low leakage currents. These results show that oxygen content can be used to dictate phase nucleation and provide a path toward phase-pure polycrystalline ferroelectric HfO₂.

Silica-supported Pd, Rh and Pt metal nanoparticles catalyze the hydrogenolysis of the Pt−OPh bond of (^tbpy)Pt(OPh)Cl to release PhOH. Based on kinetic studies monitored by ¹H NMR spectroscopy, the reactivity trend is Pd>Rh>Pt. Kinetic studies with Pd/SiO₂ are consistent with a first-order dependence on the catalyst and the molecular Pt(II) complex (^tbpy)Pt(OPh)Cl. Using TEM-EDS mapping and ICP-OES measurements of a recovered Pd catalyst, after 1 hour of hydrogenolysis of (^tbpy)Pt(OPh)Cl, approximately 10–16 % Pt deposition (relative to Pd mol %) on the Pd/SiO₂ surface was quantified.

A recent advance in the synthesis of alkenylated arenes was the demonstration that the Pd(OAc)₂ catalyst precursor gives >95% selectivity toward styrene from ethylene and benzene under optimized conditions using excess Cu(II) carboxylate as the in situ oxidant [ Organometallics 2019, 38(19), 3532−3541]. To understand the mechanism underlying this catalysis, we applied density functional theory (DFT) calculations in combination with experimental studies. From DFT calculations, we determined the lowest-energy multimetallic Pd and Pd–Cu mixed metal species as possible catalyst precursors. From the various structures, we determined the cyclic heterotrinuclear complex PdCu₂(μ-OAc)₆ to be the global minimum in Gibbs free energy under conditions of excess Cu(II). For cyclic PdCu₂(μ-OAc)₆ and the parent [Pd(μ-OAc)₂]₃, we evaluated the barriers for benzene C–H activation through concerted metalation deprotonation (CMD). The PdCu₂(μ-OAc)₆ cyclic trimer leads to a CMD barrier of 33.5 kcal/mol, while the [Pd(μ-OAc)₂]₃ species leads to a larger CMD barrier at >35 kcal/mol. This decrease in the CMD barrier arises from the insertion of Cu(II) into the trimetallic species. Because cyclic PdCu₂(μ-OAc)₆ is likely the predominant species under experimental conditions (the Cu to Pd ratio is 480:1 at the start of catalysis) with a predicted CMD barrier within the range of the experimentally determined activation barrier, we propose that cyclic PdCu₂(μ-OAc)₆ is the Pd species responsible for catalysis and report a full reaction mechanism based on DFT calculations. For catalytic conversion of benzene and ethylene to styrene at 120 °C using Pd(OAc)₂ as the catalyst precursor and Cu(OPiv)₂ (OPiv = pivalate) as the oxidant, an induction period of ∼1 h was observed, followed by catalysis with a turnover frequency of ∼2.3 × 10^–3 s^–1. In situ¹H NMR spectroscopy experiments indicate that during the induction period, Pd(OAc)₂ is likely converted to cyclic PdCu₂(η²-C₂H₄)₃(μ-OPiv)₆, which is consistent with the calculations and consistent with the proposal that the active catalyst is the ethylene-coordinated heterotrinuclear complex cyclic PdCu₂(η²-C₂H₄)₃(μ-OPiv)₆.

Ruthenium(II) complexes with the general formula TpRu(L)(NCMe)Ph (Tp = hydrido(trispyrazolyl)borate, L = CO, PMe₃, P(OCH₂)₃CEt, P(pyr)₃, P(OCH₂)₂(O)CCH₃) have previously been shown to catalyze arene alkylation via Ru-mediated arene C–H activation including the conversion of benzene and ethylene to ethylbenzene. Previous studies have suggested that the catalytic performance of these TpRu(II) catalysts increases with reduced electron-density at the Ru center. Herein, three new structurally related Ru(II) complexes are synthesized, characterized, and studied for possible catalytic benzene ethylation. TpRu(NO)Ph₂ exhibited low stability due to the facile elimination of biphenyl. The Ru(II) complex (Tp^Br3)Ru(NCMe)(P(OCH₂)₃CEt)Ph (Tp^Br3 = hydridotris(3,4,5-tribromopyrazol-1-yl)borate) showed no catalytic activity for the conversion of benzene and ethylene to ethylbenzene, likely due to the steric bulk introduced by the bromine substituents. (Ttz)Ru(NCMe)(P(OCH₂)₃CEt)Ph (Ttz = hydridotris(1,2,4-triazol-1-yl)borate) catalyzed approximately 150 turnover numbers (TONs) of ethylbenzene at 120 °C in the presence of Lewis acid additives. Here, we compare the activity and features of catalysis using (Ttz)Ru(NCMe)(P(OCH₂)₃CEt)Ph to previously reported catalysis based on TpRu(L)(NCMe)Ph catalyst precursors.