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We have employed computational methods to investigate the iridium-catalyzed allylic substitution leading to the formation of enantioenriched allyl carbamates from carbon dioxide (CO 2 ). The reaction occurs in several steps, with initial formation of an iridium-allyl, followed by nucleophilic attack by the carbamate formed in situ from CO 2 and an amine. A detailed isomeric analysis shows that the rate-determining step differs for the ( R )- and ( S )-pathways. These insights are essential for understanding reactions involving enantioselective formation of allyl carbamates from CO 2 ., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

The halogen bond (XB) is a highly directional class of noncovalent interactions widely explored by experimental and computational studies. However, the NMR signature of the XB has attracted limited attention. The prediction and analysis of the solid-state NMR (SSNMR) chemical shift tensor provide useful strategies to better understand XB interactions. In this work, we employ a computational protocol for modeling and analyzing the 19 F SSNMR chemical shifts previously measured in a family of square-planar trans Ni II -L 2 -iodoaryl-fluoride (L = PEt 3 ) complexes capable of forming self-complementary networks held by a NiF···I(C) halogen bond [Thangavadivale, V.; Chem. Sci. 2018, 9, 3767-3781]. To understand how the 19 F NMR resonances of the nickel-bonded fluoride are affected by the XB, we investigate the origin of the shielding in trans -[NiF(2,3,5,6-C 6 F 4 I)(PEt 3 ) 2 ], trans -[NiF(2,3,4,5-C 6 F 4 I)(PEt 3 ) 2 ], and trans -[NiF(C 6 F 5 )(PEt 3 ) 2 ] in the solid state, where a XB is present in the two former systems but not in the last. We perform the 19 F NMR chemical shift calculations both in periodic and molecular models. The results show that the crystal packing has little influence on the NMR signatures of the XB, and the NMR can be modeled successfully with a pair of molecules interacting via the XB. Thus, the observed difference in chemical shift between solid-state and solution NMR can be essentially attributed to the XB interaction. The very high shielding of the fluoride and its driving contributor, the most shielded component of the chemical shift tensor, are well reproduced at the 2c-ZORA level. Analysis of the factors controlling the shielding shows how the highest occupied Ni/F orbitals shield the fluoride in the directions perpendicular to the Ni-F bond and specifically perpendicular to the coordination plane. This shielding arises from the magnetic coupling of the Ni(3d)/F(2p lone pair) orbitals with the vacant σ Ni-F * orbital, thereby rationalizing the very highly upfield (shielded) resonance of the component (δ 33 ) along this direction. We show that these features are characteristic of square-planar nickel-fluoride complexes. The deshielding of the fluoride in the halogen-bonded systems is attributed to an increase in the energy gap between the occupied and vacant orbitals that are mostly responsible for the paramagnetic terms, notably along the most shielded direction.

Selective reduction of CO 2 is an efficient solution for producing nonfossil-based chemical feedstocks and simultaneously alleviating the increasing atmospheric concentration of this greenhouse gas. With this aim, molecular electrocatalysts are being extensively studied, although selectivity remains an issue. In this work, a combined experimental-computational study explores how the molecular structure of Mn-based complexes determines the dominant product in the reduction of CO 2 to HCOOH, CO, and H 2 . In contrast to previous Mn(bpy-R)(CO) 3 Br catalysts containing alkyl amines in the vicinity of the Br ligand, here, we report that bpy-based macrocycles locking these amines at the side opposite to the Br ligand change the product selectivity from HCOOH to H 2 . Ab initio molecular dynamics simulations of the active species showed that free rotation of the Mn(CO) 3 moiety allows for the approach of the protonated amine to the reactive center yielding a Mn-hydride intermediate, which is the key in the formation of H 2 and HCOOH. Additional studies with DFT methods showed that the macrocyclic moiety hinders the insertion of CO 2 to the metal hydride favoring the formation of H 2 over HCOOH. Further, our results suggest that the minor CO product observed experimentally is formed when CO 2 adds to Mn on the side opposite to the amine ligand before protonation. These results show how product selectivity can be modulated by ligand design in Mn-based catalysts, providing atomistic details that can be leveraged in the development of a fully selective system., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

1 H NMR spectroscopy has become an important technique for the characterization of transition-metal hydride complexes, whose metal-bound hydrides are often difficult to locate by X-ray diffraction. In this regard, the accurate prediction of 1 H NMR chemical shifts provides a useful, but challenging, strategy to help in the interpretation of the experimental spectra. In this work, we establish a density-functional-theory protocol that includes relativistic, solvent, and dynamic effects at a high level of theory, allowing us to report an accurate and reliable interpretation of 1 H NMR hydride chemical shifts of iridium polyhydride complexes. In particular, we have studied in detail the hydride chemical shifts of the [Ir 6 (IMe) 8 (CO) 2 H 14 ] 2+ complex in order to validate previous assignments. The computed 1 H NMR chemical shifts are strongly dependent on the relativistic treatment, the choice of the DFT exchange-correlation functional, and the conformational dynamics. By combining a fully relativistic four-component electronic-structure treatment with ab initio molecular dynamics, we were able to reliably model both the terminal and bridging hydride chemical shifts and to show that two NMR hydride signals were inversely assigned in the experiment.