The stepwise mechanism for the O
2 -dependent oxidative deglycination of the
nonheme [Fe(tpena)]
2+ complex was thus fully elucidated. The presence of a
carboxylato group in the ligand allows an electron transfer from this group to the
metal center (LMCT) upon irradiation. The nature of this band was identified with
TD-DFT techniques. In addition, transient intermediates were characterized with
experimental and computational techniques.
3.2 Light-Driven Insertion of Dioxygen into Pt(II)–C Bonds
Metal-carbon complexes are major intermediates in many catalytic processes. However, the direct functionalization of alkyl ligands into useful products remains still a
challenge. Many efforts have been done in recent years for the use of readily
accessible reactants that can be inserted into the M–C bond and release
functionalized products [73, 74]. In the field of alkene oxidation, Pt(II) and Pd
(II) organometallic complexes have been used for this quest. Several oxidation
agents have been used in combination with the aforementioned catalysts, such as
Cl 2 , [75] PhICl 2 , [76] PhI(OAc) 2 [76], and RSSR, [77] among others. In any case,
the ideal scenario would be the use of environmental benign oxidant such as H 2 O 2 or
O 2 , especially the latter. Dioxygen is, however, a difficult reactant, it is in low
concentration in solution, and it often presents high barriers.
In a collaboration with the group of Britovsek, we carried out a computational
DFT study on the reaction of the 6,6
0 -diaminoterpyridines Pt(II)-methyl complex
with the O 2 molecule upon irradiation of the system [78]. Modifications on the 6,6
0
positions of the terpyridine ligands change the behavior of the system, and the
rationalization of these effects is a challenge.
3.2.1 Photoactivation Step
The photoinduced excitation of square planar Pt(II) and Pd(II) complexes bearing
pyridinic ligands has been previously studied by computational and experimental
methods. These complexes show a long lifetime in the triplet state upon irradiation.
The maximum absorption band is associated with a metal-to-ligand charge transfer
(MLCT). For this reason and to avoid the usage of high expensive multireference
methods, such as CASSCF, we did not study the intersystem crossing (ISC) from the
excited singlet state to the triplet state.
The TD-DFT calculations, at M06 level of theory, showed two strong bands at
404 nm (ƒ ¼ 0.1343) and 364 nm (ƒ ¼ 0.2789). Both bands correspond to a metalto-ligand charge transfer (MLCT) events. These results agree with the experimental
spectrum for the complex [79]. The nature of these bands is associated with the
transfer from a d orbital of the metal to a π* orbital of the terpyridine ligand.
Figure 13 show the key absorption orbitals associated with the photoactivation step.
Computational Modeling of Selected Photoactivated Processes
147
2 -dependent oxidative deglycination of the
nonheme [Fe(tpena)]
2+ complex was thus fully elucidated. The presence of a
carboxylato group in the ligand allows an electron transfer from this group to the
metal center (LMCT) upon irradiation. The nature of this band was identified with
TD-DFT techniques. In addition, transient intermediates were characterized with
experimental and computational techniques.
3.2 Light-Driven Insertion of Dioxygen into Pt(II)–C Bonds
Metal-carbon complexes are major intermediates in many catalytic processes. However, the direct functionalization of alkyl ligands into useful products remains still a
challenge. Many efforts have been done in recent years for the use of readily
accessible reactants that can be inserted into the M–C bond and release
functionalized products [73, 74]. In the field of alkene oxidation, Pt(II) and Pd
(II) organometallic complexes have been used for this quest. Several oxidation
agents have been used in combination with the aforementioned catalysts, such as
Cl 2 , [75] PhICl 2 , [76] PhI(OAc) 2 [76], and RSSR, [77] among others. In any case,
the ideal scenario would be the use of environmental benign oxidant such as H 2 O 2 or
O 2 , especially the latter. Dioxygen is, however, a difficult reactant, it is in low
concentration in solution, and it often presents high barriers.
In a collaboration with the group of Britovsek, we carried out a computational
DFT study on the reaction of the 6,6
0 -diaminoterpyridines Pt(II)-methyl complex
with the O 2 molecule upon irradiation of the system [78]. Modifications on the 6,6
0
positions of the terpyridine ligands change the behavior of the system, and the
rationalization of these effects is a challenge.
3.2.1 Photoactivation Step
The photoinduced excitation of square planar Pt(II) and Pd(II) complexes bearing
pyridinic ligands has been previously studied by computational and experimental
methods. These complexes show a long lifetime in the triplet state upon irradiation.
The maximum absorption band is associated with a metal-to-ligand charge transfer
(MLCT). For this reason and to avoid the usage of high expensive multireference
methods, such as CASSCF, we did not study the intersystem crossing (ISC) from the
excited singlet state to the triplet state.
The TD-DFT calculations, at M06 level of theory, showed two strong bands at
404 nm (ƒ ¼ 0.1343) and 364 nm (ƒ ¼ 0.2789). Both bands correspond to a metalto-ligand charge transfer (MLCT) events. These results agree with the experimental
spectrum for the complex [79]. The nature of these bands is associated with the
transfer from a d orbital of the metal to a π* orbital of the terpyridine ligand.
Figure 13 show the key absorption orbitals associated with the photoactivation step.
Computational Modeling of Selected Photoactivated Processes
147