Benzonitrile

Calculations were performed using the Orca (version 3.0.3) and Gaussian-09 computational chemistry software packages.¹⁵ Our model uses a corrolazine macrocycle (Scheme 1) with the peripheral aryl substituents replaced with hydrogen atoms (H₈Cz), as previous work showed that the peripheral groups on porphyrin scaffolds have little influence on the spin state ordering and relative energies.^{16 (link)} Reactivities with para-Z-substituted thioanisoles were calculated for Z = N(CH₃)₂, NH₂, OCH₃, CH₃, H, Br, CN, and NO₂. The work was aimed at establishing whether the reaction mechanisms are electrophilic or nucleophilic and how the intrinsic chemical properties of oxidant and substrate affected these reactivity differences. The nature of all transition states, in particular, the singlet spin transition states, was established (i) through frequency calculations that gave a single imaginary mode for the S–O bond formation and (ii) intrinsic reaction coordinate (IRC) scans in both the forward and the reverse directions. The latter unequivocally connected the transition states to the reactants in one direction and to products in the opposite direction.
Enthalpies of activation of the chemical reactions are compared to experimental data reported previously.^{14a (link)} However, it should be noted that generally gas-phase calculations overestimate the entropy of activation and often find higher values than experiment. As such, previous experience of calibrating oxygen transfer reactivities against low-pressure gas-phase measured rate constants gave a better correlation with enthalpies of activation,¹⁷ which we will adopt here.
All initial geometry optimizations (including transition state geometry optimizations) were performed without constraints and used the hybrid generalized gradient approximation (GGA) functional B3LYP that includes the VWN5 local density approximation.¹⁸ Relativistic small effective core potential basis sets SDD or LACVP were used on Mn and the all-electron 6-31G(d) on the rest of atoms: basis set BS1.¹⁹ Long-range dispersion interactions were applied using the D3 procedure of Grimme et al.^{20 (link)} Geometry optimizations were followed by a frequency calculation at the same level of theory and confirmed all structures as local minima or first-order saddle points (transition states). Using Orca, energies were calculated from single-point calculations at the UB3LYP/BS1-optimized geometries using a correlation-consistent basis set of def2-QZVPP on Mn and cc-pVDZ on the rest of the atoms: basis set BS2. The resolution of identity (RI) approximation to the Coulomb integrals was used with corresponding auxiliary basis sets, as implemented in Orca. The integration grid was increased from 3 to 4 (Orca notation) to increase numerical accuracy. Single-point energy calculations on all optimized structures were also performed using the hybrid meta-GGA functional TPSSh with 10% HF exchange and the D3 dispersion correction.^{20 (link),21 (link)} A similar protocol was followed for the results obtained using the Gaussian software program, although it uses the VWN3 local density approximation in B3LYP; furthermore, these calculations utilized the triple-ζ quality LACV3P+* on Mn (with core potential) and 6-311+G* on the rest of the atoms: basis set BS3. Generally, these studies confirmed the B3LYP obtained landscape and conclusions and did not deviate significantly. Solvent effects were included in Orca by applying the conductor-like screening model (COSMO) with a dielectric constant of 26.0 and probe radius of 1.528 Å mimicking benzonitrile.²² An implicit solvent correction in Gaussian was included using the polarized continuum model (CPCM) with a dielectric constant of ε = 35.688 mimicking acetonitrile.
To test the accuracy and reproducibility of the density functional methods, a range of test calculations with alternative density functional methods and the def2-TZVPP basis set (BS4) were performed, including BP86,²³ BLYP,^{18b ,23a} PBE,^{24 (link)} B3LYP,¹⁸ PBE0,²⁵ and TPSSh.^{21 (link)} In addition, the spin state ordering of the [Mn(O)(H₈Cz)-(CN)]⁻ complex was investigated using the complete active space self-consistent field (CASSCF) methods in Orca. Dynamic correlation was recovered by following these CASSCF studies with the N-electron valence second-order perturbation theory (NEVPT2) correction on the converged multiconfigurational wave functions with basis set BS5 (cc-pVTZ/cc-pVDZ). Due to the size of our chemical system, the NEVPT2:CAS studies were performed at the single-point energy level on the UB3LYP/BS1-optimized geometries of the reactant complexes only. The resolution of identity approximation and the chain-of-sphere approximation (RIJCOSX) were applied to the Coulomb and exchange correlation, respectively, with density fitting auxiliary basis set corresponding to each atomic basis set throughout the calculations below.
Single-point energies were calculated on the triplet spin state of the optimized singlet spin transition state geometry using B3LYP. The ZORA Hamiltonian with the model potential due to Van Wuellen²⁶ was used to account for the relativistic effect along with the segmented all-electron relativistically recontracted version of basis sets def2-TZVPP.^{27 (link)} The Ahlrichs (2df,2pd) polarization functions were obtained from the Turbomole basis set library²⁸ for Mn, while the def2-SVP basis set^{27 (link)} was employed on the rest of atoms. The resolution of identity (RI) and the chain-of-sphere approximations were used for the Coulomb and Exchange correlation, respectively. Spin–orbit coupling constants (SOC) were calculated on the converged unrestricted natural orbitals using the spin–orbit mean field Hamiltonian including 1-electron term and local DFT correlation including VWN5.²⁹ Coulomb terms were computed with the RI approximation, and the exchange terms were computed with one-center exact integrals including the spin–orbit interaction.

A Biotage microwave vial was charged with Pd(OAc)₂ (3.4 mg, 0.015 mmol), RuPhos (14 mg, 0.03 mmol) 4-bromobenzonitrile (46.0 mg, 0.25 mmol), potassium furan-2-yltrifluoroborate (46.0 mg, 0.26 mmol) and Na₂CO₃ (53.0 mg, 0.5 mmol). The test tube was sealed with a cap lined with a disposable Teflon septum, evacuated and purged (x 3). Ethanol (0.18 M, 1.4 mL) was added via syringe and the reaction was heated at 85 °C for 12 h. The reaction mixture was allowed to cool to rt and filtered through a thin pad of silica gel (elution with 25% methanol in EtOAc). The solvent was removed in vacuo and the crude product was purified by silica gel column chromatography (elution with hexane/EtOAc 7:1) to yield the pure product in 91% yield (38.49 mg, 0.23 mmol) as a white solid. ¹H NMR (500 MHz, CDCl₃) δ 7.72 (d, 1H, J = 8.5 Hz), 7.63 (d, 1H, J = 8.5 Hz), 7.52 (m, 1H), 6.80 (d, 1H, J = 3.5 Hz), 6.52 (dd, 1H, J = 1.8, 3.4 Hz). ¹³C NMR (125.8 MHz, CDCl₃) δ 152.1, 143.8, 134.8, 132.7, 124.1, 119.0, 112.3, 110.4, 108.3.