Interplay of Steric and Electronic Effects on the Bonding Components in Aromatic Ring Agostic Interactions

Density functional theory (DFT) calculations on the effect of steric size adjacent to an agostic interaction in ligand assisted Pd–C bond formation involving aromatic rings gives insight into why the synthetic reaction can fail as the size of an alkyl group is increased. In [PdCl₂(1-tetralone oxime)] agostic complexes, changing the C(7)-substituent on the ligand through the series H, Me, CHMe₂, and CMe₃ progressively reduces agostic and syndetic donations. For (N)–CMe₃ imine complexes, CMe₃ steric pressure at C(7) switches off agostic donation and increases syndetic donation significantly, especially where the aromatic ring can rotate. Electron withdrawal from the aromatic ring in this type of system has little effect, but electron donation into the ring invokes η¹-covalency, especially with strong π-donation. This covalency can be switched off by further π-donation and the syndetic donation restored. These steric effects can be expected to impact the success of C–C bond formation chemistry derived from Pd–C cyclometalation reactions involving agostic and syndetic donations

Chasing the CMD/AMLA Mechanism C–H···Pd Interactions in the Cyclopalladation Reaction of <i>N</i>,<i>N</i>‑Dimethylbenzylamine with Pd(OAc)₂

700 MHz 1H NMR spectral examination of the reaction between Me2NCH2Ph and Pd(OAc)2 in CDCl3 reveals that several anagostic complexes form, but an agostic intermediate is not identified by way of a lowered 1JC–H coupling constant. Density functional theory (DFT) calculations were used to compare characteristic features of the putative agostic intermediate when the acetato ligand CO···H–C interaction is present as in the CMD/AMLA mechanism and when it is not. With the CO···H–C interaction present, the agostic C–H bond is significantly longer, the H and C atoms are closer to the metal, natural bond orbital (NBO) analysis indicates that agostic C–Hσ orbital donation to Pd-based orbitals is significantly greater, π-syndetic donation is similar, and coulombic attraction between the agostic carbon and the Pd center is greater as is the repulsion between the H and Pd atoms. Whether the CO···H–C interaction is present or not, the electron withdrawal substituents SO2Cl and NO2 at the para position of the ligand on energy minimization reduce the effect of the interaction, whereas the electron-donating groups B(OH)3– and NMe2 give η1-σ-lone pair donor complexes and S– produces a Pd–C–H σ-bond. Overall, the presence of the CO···H–C interaction enhances the agostic interaction produced during the reaction of the N,N-dimethylbenzylamine with Pd(OAc)2, which gives credence to the importance of the AMLA mechanism

Chasing the CMD/AMLA Mechanism C–H···Pd Interactions in the Cyclopalladation Reaction of <i>N</i>,<i>N</i>‑Dimethylbenzylamine with Pd(OAc)₂

700 MHz 1H NMR spectral examination of the reaction between Me2NCH2Ph and Pd(OAc)2 in CDCl3 reveals that several anagostic complexes form, but an agostic intermediate is not identified by way of a lowered 1JC–H coupling constant. Density functional theory (DFT) calculations were used to compare characteristic features of the putative agostic intermediate when the acetato ligand CO···H–C interaction is present as in the CMD/AMLA mechanism and when it is not. With the CO···H–C interaction present, the agostic C–H bond is significantly longer, the H and C atoms are closer to the metal, natural bond orbital (NBO) analysis indicates that agostic C–Hσ orbital donation to Pd-based orbitals is significantly greater, π-syndetic donation is similar, and coulombic attraction between the agostic carbon and the Pd center is greater as is the repulsion between the H and Pd atoms. Whether the CO···H–C interaction is present or not, the electron withdrawal substituents SO2Cl and NO2 at the para position of the ligand on energy minimization reduce the effect of the interaction, whereas the electron-donating groups B(OH)3– and NMe2 give η1-σ-lone pair donor complexes and S– produces a Pd–C–H σ-bond. Overall, the presence of the CO···H–C interaction enhances the agostic interaction produced during the reaction of the N,N-dimethylbenzylamine with Pd(OAc)2, which gives credence to the importance of the AMLA mechanism

Reservoir Greenhouse Gas Fluxes and Potential Predictor Variables

This data file contains reservoir greenhouse gas emission estimates as well as categorical and continuous data for tested predictors of these fluxes. There is one row reserved for each reservoir included in the study. The associated references for this data are included in a second spreadsheet tab