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Anti-Markovnikov additions to alkenes have been a longstanding goal of catalysis, and anti-Markovnikov addition of arenes to alkenes would produce alkylarenes that are distinct from those formed by acid-catalysed processes. Existing hydroarylations are either directed or occur with low reactivity and low regioselectivity for the n-alkylarene. Herein, we report the first undirected hydroarylation of unactivated alkenes with unactivated arenes that occurs with high regioselectivity for the anti-Markovnikov product. The reaction occurs with a nickel catalyst ligated by a highly sterically hindered N-heterocyclic carbene. Catalytically relevant arene- and alkene-bound nickel complexes have been characterized, and the rate-limiting step was shown to be reductive elimination to form the C–C bond. Density functional theory calculations, combined with second-generation absolutely localized molecular orbital energy decomposition analysis, suggest that the difference in activity between catalysts containing large and small carbenes results more from stabilizing intramolecular non-covalent interactions in the secondary coordination sphere than from steric hindrance.The anti-Markovnikov hydroarylation of unactivated alkenes with unactivated arenes has been achieved with high selectivity by using nickel catalysts bearing large N-heterocyclic carbene ligands. Energy decomposition analysis indicates that the high activity of the catalysts with large carbene ligands arises from stabilizing non-covalent interactions rather than steric effects.

The focus of this work is OS-CCSD-SPT(2), which is a second-order similarity transformed perturbation theory correction to opposite spin coupled cluster singles doubles, where in the latter the same-spin amplitudes are removed and the opposite-spin ones are solved self consistently. We demonstrate that, for non-multireference molecules, OS-CCSD-SPT(2) produces relative energies that rival the accuracy of higher-order methods like CCSD(T). For example, using PBE0 orbitals in the reference, OS-CCSD-SPT(2) exhibits a mean absolute deviation (MAD) of 0.66 kcal/mol with respect to CCSD(2) benchmark values for the non-multireference subset of W4-08 atomization energies (c.f. a MAD > 6 kcal/mol for CCSD). OS-CCSD-SPT(2) is free of empirical parameters, has an instrinsic scaling of \\(O(N^6)\\), and makes no use of triples. It is also naturally amenable to higher order corrections: the associated third-order correction, OS-CCSD-SPT(3), which does involve connected triples and quadruples, exhibits a MAD of 0.44 kcal/mol for the same benchmark.

In this work, we revisited the idea of using the coupled-cluster ground state formalism to target excited states. Our main focus was targeting doubly excited states and double core hole states. Typical equation-of-motion (EOM) approaches for obtaining these states struggle without higher-order excitations than doubles. We showed that by using a non-aufbau determinant optimized via the maximum overlap method the CC ground state solver can target higher energy states. Furthermore, just with singles and doubles (i.e., CCSD), we demonstrated that the accuracy of \\(\\)CCSD and \\(\\)CCSD(T) far surpasses that of EOM-CCSD for doubly excited states. The accuracy of \\(\\)CCSD(T) is nearly exact for doubly excited states considered in this work. For double core hole states, we used an improved ansatz for greater numerical stability by freezing core hole orbitals. The improved methods, core valence separation (CVS)-\\(\\)CCSD and CVS-\\(\\)CCSD(T), were applied to the calculation of the double ionization potential of small molecules. Even without relativistic corrections, we observed qualitatively accurate results with CVS-\\(\\)CCSD and CVS-\\(\\)CCSD(T). Remaining challenges in \\(\\)CC include the description of open-shell singlet excited states with the single-reference CC ground state formalism as well as excited states with genuine multi-reference character. The tools and intuition developed in this work may serve as a stepping stone towards directly targeting arbitrary excited states using ground state CC methods.

We report the failure of coupled-cluster valence-bond (CCVB) theory with two-pair configurations [J. Chem. Phys. 2009, 130, 084103 (2009)] for open-shell (OS) spin-frustrated systems where including three-pair configurations is necessary to properly describe strong spin-correlations. We extend OS-CCVB by augmenting the model with three-pair configurations within the independent amplitude approximation (IAA). The resulting new electronic structure model, OS-CCVB+i3, involves only a quadratic number of independent wavefunction parameters. It includes the recently reported closed-shell CCVB+i3 as a special case. Its cost is dominated by integral transformations and it is capable of breaking multiple bonds exactly for all systems examined so far. The strength of OS-CCVB+i3 is highlighted in realistic systems including the [CaMn\\(_3\\)O\\(_4\\)] cubane subunit of the oxygen-evolving complex and a molecular magnet with the [Cr\\(_9\\)] core unit as well as model systems such as N\\(_3\\), V\\(_3\\)O\\(_3\\), and P\\(_5\\). We show that OS-CCVB+i3 is only slightly dependent on the underlying perfect-pairing reference while OS-CCVB shows a stronger dependence. We also emphasize the compactness of the OS-CCVB+i3 wavefunction compared to the heat-bath configuration interaction wavefunction, a recently introduced soft exponential-scaling approach.

RADM Reilly closed out his own 34-year Navy career when he retired during an Oct. 16 ceremony on the USNS Comfort in Baltimore, Md. The ceremony's program included the family trees of RADM Reilly and his wife, former Navy LT Carol Lynn Jacob Reilly - a family that includes 21 servicemen and -women dating back to the Civil War.