This work explores the potential of iridium complexes of the N-heterocyclic carbene oxazoline ligands 1 in asymmetric hydrogenations of arylalkenes. The accessible carbene precursors, imidazolium salts 2, and robust iridium complexes 5 facilitated a discovery/optimization approach that featured preparation of a small library of iridium complexes, parallel hydrogenation reactions, and automated analysis. Three of the complexes (5ab, 5ad, and 5dp) and a similar rhodium complex (6ap) were studied by single-crystal X-ray diffraction techniques. This revealed molecular features of 6ap, and presumably the corresponding iridium complex 5ap, that the others do not have. In enantioselective hydrogenations of arylalkenes complex 5ap was the best for many, but not all, substrates. The enantioselectivities and conversions observed were sensitive to minor changes to the catalyst and substrate structure. Ligands with aliphatic N-heterocyclic carbene substituents gave complexes that are inactive, and do not lose the 1,5-cyclooctadiene ligands under the hydrogenation conditions. Experiments to investigate this unexpected observation imply that it is of a steric, rather than an electronic, origin. Temperature and pressure effects on the conversions and enantioselectivities of these reactions had minimal effects for some alkenes, but profound effects for others. In one case, the enantioselectivities obtained at high-pressure/low-temperature conditions were opposite to those obtained under high-temperature/low-pressure conditions (-64% enantiomeric excess versus +89% enantiomeric excess); a transformation from one prevalent mechanism to another is inferred from this. The studies of pressure dependence revealed that many reactions proceeded with high conversions, and optimal enantioselectivities in approximately 2 h when only 1 bar of hydrogen was used. Deuterium-labeling experiments provide evidence for other types of competing mechanisms that lead to D-incorporation at positions that do not correspond to direct addition to the double bond.

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Density functional theory (PBE and B3LYP) was used to study asymmetric hydrogenations of alkenes catalyzed by an iridium imidazolylidine oxazoline complex. The calculation predicts that the alkene preferentially coordinates to the site trans to the carbene. The coordinated alkene then reacts first with the H2 ligand, then with the hydride to form alkane. Finally, the alkane is released by equilibrating with extrinsic H2 and alkene. Enantioface selectivities for hydrogenations of trisubstituted alkenes seem to be driven primarily by steric interactions with the adamantyl part of the ligand; only the smallest substituents can adopt a site close to it. Application of this theoretical model leads to correct predictions regarding the experimentally observed sense and magnitude of the enantioselectivities.

and cracks between the Li metal and the SE (such as Li 7 La 3 Zr 2 O 12 , LLZO, and Li phosphorus oxynitride, LiPON), and eventually penetrate the SE. [5][6][7] Another critical problem is the interfacial instability arising from the contact loss at the Li/SE interface during stripping, which lowers the battery's cyclability and ultimately causes cell failure. [8][9][10][11][12] Thus, the dynamic behavior of the mechanical contact at the Li/SE interface needs to be understood to design a better battery cell.A challenge to maintain mechanical contact at the Li/SE interface is void formation. [13][14][15][16] Void formation leads to interfacial porosity, surface roughness, and consequently contact loss. [17][18][19] Recently, experimental characterization has shown that the stack pressure is an important factor in preventing void formation during stripping in SSBs. [18,20,21] It has been proposed that the pressuredriven creep deformation of Li metal replenishes the void at the Li/SE interface. [18,22] However, void formation at the solid-solid interface involves stress, contact, reaction, and Li/Li + transport, which are challenging to observe and measure experimentally. Therefore, the understanding of contact issues during stripping is still in its infancy. Specifically, the fundamental questions as to how the external pressure and current as well as intrinsic material properties impact the internal void formation at the Li/SE interface are unanswered.Taking a deeper insight into the mechanism of interfacial void formation, when applying current density and stack pressure, the stripping current removes electrons from Li metal and releases Li + into the SE to migrate away from the interface (i.e., the flux of Li + migration away from the interface, J migration ). This generates a large number of vacancies in Li metal near the interface. The flux of the vacancies contributed by the Li metal creep, J creep , and diffusion, J diffusion , can transport the vacancies away from the interface and towards the bulk Li metal, as illustrated in Figure 1a. Recent kinetic Monte Carlo (KMC) simulations [23] show that for an ideal flat Li/SE interface, J diffusion is high enough to transport the vacancies away from the interface and maintain a smooth Li/Li 2 O surface even without the stack pressure (i.e., J diffusion > J migration where J # represents the magnitude of the flux), as illustrated in Figure 1b. However, such an ideal flat interface is unlikely due to the limitation of the experimental conditions and techniques, and pre-existing interfacial defects such as Interfacial instability from void formation at the solid-solid interface is one of the crucial challenges in solid-state batteries. However, the fundamental mechanism as to how stress is generated in lithium and thus impacts void formation has not been established. A general creep/contact electro-chemomechanical model is herein developed to reveal the mechanisms of void formation at the Li/solid electrolyte (SE) interface during stripping. Li stress calculation is ...

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