4 research outputs found
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 [PdCl<sub>2</sub>(1-tetralone oxime)] agostic complexes, changing
the C(7)-substituent on the ligand through the series H, Me, CHMe<sub>2</sub>, and CMe<sub>3</sub> progressively reduces agostic and syndetic
donations. For (N)–CMe<sub>3</sub> imine complexes, CMe<sub>3</sub> 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 η<sup>1</sup>-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)<sub>2</sub>
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)<sub>2</sub>
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