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High-valent metal oxo complexes are prototypical intermediates for the activation and hydroxylation of alkyl C–H bonds. Substituting the oxo ligand with other functional groups offers the opportunity for additional C–H functionalization beyond C–O bond formation. However, few species aside from metal oxo complexes have been reported to both activate and functionalize alkyl C–H bonds. We herein report the first example of an isolated copper( iii ) cyanide complex (LCu III CN) and its C–H cyanation reactivity. We found that the redox potential ( E ox ) of substrates, instead of C–H bond dissociation energy, is a key determinant of the rate of PCET, suggesting an oxidative asynchronous CPET or ETPT mechanism. Among substrates with the same BDEs, those with low redox potentials transfer H atoms up to a million-fold faster. Capitalizing on this mechanistic insight, we found that LCu III CN is highly selective for cyanation of amines, which is predisposed to oxidative asynchronous or stepwise transfer of H + /e − . Our study demonstrates that the asynchronous effect of PCET is an appealing tool for controlling the selectivity of C–H functionalization. 

Algebraic diagrammatic construction (ADC) theory is a computationally efficient and accurate approach for simulating electronic excitations in chemical systems. However, for the simulations of excited states in molecules with unpaired electrons, the performance of ADC methods can be affected by the spin contamination in unrestricted Hartree–Fock (UHF) reference wavefunctions. In this work, we benchmark the accuracy of ADC methods for electron attachment and ionization of open-shell molecules with the UHF reference orbitals (EA/IP-ADC/UHF) and develop an approach to quantify the spin contamination in charged excited states. Following this assessment, we demonstrate that the spin contamination can be reduced by combining EA/IP-ADC with the reference orbitals from restricted open-shell Hartree–Fock (ROHF) or orbital-optimized Møller–Plesset perturbation (OMP) theories. Our numerical results demonstrate that for open-shell systems with strong spin contamination in the UHF reference, the third-order EA/IP-ADC methods with the ROHF or OMP reference orbitals are similar in accuracy to equation-of-motion coupled cluster theory with single and double excitations. 

We present a new theoretical approach for the simulations of X-ray photoelectron spectra of strongly correlated molecular systems that combines multireference algebraic diagrammatic construction theory (MR-ADC) [ J. Chem. Phys. , 2018, 149 , 204113] with a core–valence separation (CVS) technique. The resulting CVS-MR-ADC approach has a low computational cost while overcoming many challenges of the conventional multireference theories associated with the calculations of excitations from inner-shell and core molecular orbitals. Our results demonstrate that the CVS-MR-ADC methods are as accurate as single-reference ADC approximations for predicting core ionization energies of weakly-correlated molecules, but are more accurate and reliable for systems with a multireference character, such as a stretched nitrogen molecule, ozone, and isomers of the benzyne diradical. We also highlight the importance of multireference effects for the description of core–hole screening that determines the relative spacing and order of peaks in the XPS spectra of strongly correlated systems.