[Rh((R)-DTBM-SEGPHOS)]BF(4) catalyzes the intramolecular hydroacylation of ketones to afford seven-membered lactones in large enantiomeric excess. Herein, we present a combined experimental and theoretical study to elucidate the mechanism and origin of selectivity in this C-H bond activation process. Evidence is presented for a mechanistic pathway involving three key steps: (1) rhodium(I) oxidative addition into the aldehyde C-H bond, (2) insertion of the ketone CO double bond into the rhodium hydride, and (3) C-O bond-forming reductive elimination. Kinetic isotope effects and Hammett plot studies support that ketone insertion is the turnover-limiting step. Detailed kinetic experiments were performed using both 1,3-bis(diphenylphosphino)propane (dppp) and (R)-DTBM-SEGPHOS as ligands. With dppp, the keto-aldehyde substrate assists in dissociating a dimeric precatalyst 8 and binds an active monomeric catalyst 9. With [Rh((R)-DTBM-SEGPHOS)]BF(4), there is no induction period and both substrate and product inhibition are observed. In addition, competitive decarbonylation produces a catalytically inactive rhodium carbonyl species that accumulates over the course of the reaction. Both mechanisms were modeled with a kinetics simulation program, and the models were consistent with the experimental data. Density functional theory calculations were performed to understand more elusive details of this transformation. These simulations support that the ketone insertion step has the highest energy transition state and reveal an unexpected interaction between the carbonyl-oxygen lone pair and a Rh d-orbital in this transition state structure. Finally, a model based on the calculated transition-state geometry is proposed to rationalize the absolute sense of enantioinduction observed using (R)-DTBM-SEGPHOS as the chiral ligand.

The electron transport layer (ETL) has an important influence on the power conversion efficiency (PCE) and stability of n-i-p planar perovskite solar cells (PSCs). This paper presents an N-type semiconductor material, (CH 3) 2 Sn(COOH) 2 (abbreviated as CSCO) that is synthesized and prepared for the first time as an ETL for n-i-p planar PSCs, which leads to a high PCE of 22.21% after KCl treatment, one of the highest PCEs of n-i-p planar PSCs to date. Further analysis reveals that the high PCE is attributed to the excellent conductivity of CSCO because of its more delocalized electron cloud distribution due to its unique −O=C−O− group, and to the defect passivation of the Cs 0.05 (FA 0.85 MA 0.15) 0.95 Pb(I 0.85 Br 0.15) 3 (denoted as CsFAMA) perovskite through the interaction between the O (Sn) atoms of CSCO and the Pb (halogen) atoms of CsFAMA at CSCO/CsFAMA interface, while the traditional ETL materials such as SnO 2 film lack this function. In addition to the high PCE, the optimal PSCs using CSCO as ETL show remarkable stability, retaining over 83% of its initial PCE without encapsulation after 130 days of storage in ambient conditions (≈25 °C at ≈40% humidity), much better than the traditional SnO 2-based n-i-p PSCs.

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This communication describes a new method to achieve reversible light-induced chemical composition and phase structural transitions from polyvinylpyrrolidone-capped orthorhombic CsPbBr to tetragonal CsPbBr nanosheets or vice versa. This work will deepen our understanding of the controlled synthesis, post-processing, and decomposition pathway of cesium lead halide perovskite nanocrystals.

Encouraged by recent advances in revealing significant effects of van der Waals wells on reaction dynamics, many people assume that van der Waals wells are inevitable in chemical reactions. Here we find that the weak long-range forces cause van der Waals saddles in the prototypical C(1D)+D2 complex-forming reaction that have very different dynamical effects from van der Waals wells at low collision energies. Accurate quantum dynamics calculations on our highly accurate ab initio potential energy surfaces with van der Waals saddles yield cross-sections in close agreement with crossed-beam experiments, whereas the same calculations on an earlier surface with van der Waals wells produce much smaller cross-sections at low energies. Further trajectory calculations reveal that the van der Waals saddle leads to a torsion then sideways insertion reaction mechanism, whereas the well suppresses reactivity. Quantum diffraction oscillations and sharp resonances are also predicted based on our ground- and excited-state potential energy surfaces.

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