Pushing the Limits of Organometallic Redox Chemistry with an Isolable Mn(-I) Dianion.

We report an incredibly reducing and redox-active Mn dianion, [Mn(CO)(PhB(NHC))] (NHC = N-heterocyclic carbene), furnished via 2e reduction of the parent 16e Mn complex with Na or K. Cyclic voltammograms show a Mn redox couple at -3.13 V vs Fc in tetrahydrofuran (THF), -3.

Dispersion-corrected r2SCAN based double-hybrid functionals.

The regularized and restored semi-local meta-generalized gradient approximation (meta-GGA) exchange-correlation functional r2SCAN [Furness et al., J. Phys.

Assessment of DLPNO-MP2 Approximations in Double-Hybrid DFT.

The unfavorable scaling () of the conventional second-order Møller-Plesset theory (MP2) typically prevents the application of double-hybrid (DH) density functionals to large systems with more than 100 atoms. A prominent approach to reduce the computational demand of electron correlation methods is the domain-based local pair natural orbital (DLPNO) approximation that is successfully used in the framework of DLPNO-CCSD(T). Its extension to MP2 [Pinski P.

Toward Benchmark-Quality Predictions for 3d Transition Metal Electrocatalysts: A Comparison of CCSD(T) and ph-AFQMC.

Generating accurate ionization energies for transition metal complexes is an important step toward the accurate computational description of their electrocatalytic reactions. Benchmark-quality data is required for testing existing theoretical methods and developing new ones but is complicated to obtain for many transition metal compounds due to the potential presence of both strong dynamical and static electron correlation. In this regime, it is questionable whether the so-called gold standard, coupled cluster with singles, doubles, and perturbative triples (CCSD(T)), provides the desired level of accuracy─roughly 1-3 kcal/mol.

High-throughput screening of spin states for transition metal complexes with spin-polarized extended tight-binding methods.

The semiempirical GFNn-xTB ( ) tight-binding methods are extended with a spin-dependent energy term (spin-polarization), enabling the fast and efficient screening of different spin states for transition metal complexes. While GFNn-xTB methods inherently can not differentiate properly between high-spin (HS) and low-spin (LS) states, this shortcoming is corrected with the presented methods termed spGFNn-xTB. The performance of spGFNn-xTB methods for spin state energy splittings is evaluated on a newly compiled benchmark set of 90 complexes (27 HS and 63 LS complexes) containing 3d, 4d, and 5d transition metals (termed TM90S) employing DFT references at the TPSSh-D4/def2-QZVPP level of theory.

Dispersion corrected rSCAN based global hybrid functionals: rSCANh, rSCAN0, and rSCAN50.

The regularized and restored semilocal meta-generalized gradient approximation (meta-GGA) exchange-correlation functional rSCAN [Furness et al., J. Phys.

Ligand Protonation at Carbon, not Nitrogen, during H Production with Amine-Rich Iron Electrocatalysts.

We present monometallic H production electrocatalysts containing electron-rich triamine-cyclopentadienyl (Cp) ligands coordinated to iron. After selective CO extrusion from the iron tricarbonyl precursors, electrocatalysis is observed via cyclic voltammetry in the presence of an exogenous acid. Contrary to the fact that amines in the secondary coordination sphere are often protonated during electrocatalysis, comprehensive quantum-chemical calculations indicate that the amines likely do not function as proton relays; instead, -Cp ring protonation is most favorable after 1e reduction.

Benchmark Study of Electrochemical Redox Potentials Calculated with Semiempirical and DFT Methods.

The calculation of redox potentials by semiempirical quantum mechanical (SQM) approaches is evaluated with a focus on the recently developed GFN-xTB methods. The assessment is based on a data set comprising 313 experimental redox potentials of small to medium-sized organic and organometallic molecules in various solvents. This compilation is termed as ROP313 (reduction and oxidation potentials 313) and divided for analysis purposes into the organic subset OROP and the organometallic subset OMROP.

Structure Optimisation of Large Transition-Metal Complexes with Extended Tight-Binding Methods.

Large transition-metal complexes are used in numerous areas of chemistry. Computer-aided theoretical investigations of such complexes are limited by the sheer size of real systems often consisting of hundreds to thousands of atoms. Accordingly, the development and thorough evaluation of fast semi-empirical quantum chemistry methods that are universally applicable to a large part of the periodic table is indispensable.

A generally applicable atomic-charge dependent London dispersion correction.

The so-called D4 model is presented for the accurate computation of London dispersion interactions in density functional theory approximations (DFT-D4) and generally for atomistic modeling methods. In this successor to the DFT-D3 model, the atomic coordination-dependent dipole polarizabilities are scaled based on atomic partial charges which can be taken from various sources. For this purpose, a new charge-dependent parameter-economic scaling function is designed.

TEMPO-Mediated Catalysis of the Sterically Hindered Hydrogen Atom Transfer Reaction between (CPh)Cr(CO)H and a Trityl Radical.

We have demonstrated the ability of TEMPO to catalyze H· transfer from (CPh)Cr(CO)H to a trityl radical (tris( p- tert-butylphenyl)methyl radical). We have measured the rate constant and activation parameters for the direct reaction, and for each step in the catalytic process: H· transfer from (CPh)Cr(CO)H to TEMPO and H· transfer from TEMPO-H to the trityl radical. We have compared the measured rate constants with the differences in bond strength, and with the changes in the Global Electrophilicity Index determined with high accuracy for each radical using state of the art quantum chemical methods.

Understanding and Quantifying London Dispersion Effects in Organometallic Complexes.

Quantum chemical methods are nowadays able to determine properties of larger chemical systems with high accuracy and Kohn-Sham density functional theory (DFT) in particular has proven to be robust and suitable for everyday applications of electronic structure theory. A clear disadvantage of many established standard density functional approximations like B3LYP is their inability to describe long-range electron correlation effects. The inclusion of such effects, also termed London dispersion, into DFT has been extensively researched in recent years, resulting in some efficient and routinely used correction schemes.