Impact of steric bulk on photoinduced ligand exchange reactions in Mn(I) photoCORMs

Release of CO and Production of 1O2 from a Mn-BODIPY Photoactivated CO Releasing Molecule with Visible Light

“…As illustrated in Figures A and S13, FTIR irradiation at early time leads to emergence of two new stretches at 1936 and 1857 cm –1 along with a decrease in all three original bands, corresponding to the release of one CO and formation of the first dicarbonyl intermediate (shown by black circles). These values are comparable to our previously reported CO stretches for the first intermediate during photolysis of the Mn­(Me 2 bpy)­(CO) 3 Br compound. , In accordance with our previous studies of CO release, we assigned this intermediate as the exchange of one of the equatorial CO ligands with CH 3 CN to form cis , cis -[Mn­(bpy-R-BDP)­(CO) 2 (CH 3 CN)­Br] (R = H or I). Further irradiation results in the appearance of the second dicarbonyl intermediate at 1963 and 1882 cm –1 .…”

“…44 The photophysical and photochemical properties of these two new complexes have been compared to our previously reported model Mn(Me 2 bpy)(CO) 3 Br complex where Me 2 bpy is 4,4′-dimethyl-2,2′-bipyridine. 45,46 In Figure S5, the model complex Mn(Me 2 bpy)(CO) 3 Br shows a Mn(dπ) → bpy(π*) metal-to-ligand charge transfer (MLCT) band at 411 nm, suggesting that the peaks between 360 and 420 nm in both Mn-bpy-R-BDP (R = H or I) complexes arise from π → π* of BDP ligands with significant contribution from the Mn(dπ) → bpy(π*) transition. This assignment is further supported by the higher intensity of this band in both Mn-bpy-R-BDP (R = H or I) complexes compared to the free ligands seen in Figure 2.…”

Solid-phase synthesis of peptides with azopyridine side-chains for Mn(i)–CO binding and red-light responsive CO release

“…Noting that the Br − ligand was replaced by the HPLC solvent MeCN during the measurements in all cases, and depending on the measuring conditions, the MeCN and CO ligands may not be seen, as also reported by others. 54 Importantly, 8d can be activated to release CO by red-light irradiation within 60 s, as reflected by the disappearance of the ν CO bands and the Mb-assay (Fig. 4A and C), confirming the ability of the azpy-bearing peptide Mn–CO complex as a viable red-light activatable photoCORM.…”

Steric Effects on CO2 Reduction with Substituted Mn(bpy)(CO)3X-Type Catalysts on Multiwalled Carbon Nanotubes Reveal Critical Mechanistic Details

“…The relationship between steric bulk and intermolecular separation was evaluated using the crystal structures of complexes 1 – 4 as a proxy for the packing density of these species on MWCNT. X-ray quality crystals of complex 3 were grown by slow diffusion of diethyl ether into dichloromethane, and the crystal structure of complex 3 was determined by XRD (Figure S8) and compared against those of complexes 1 – 2 and 4 , which are available in the literature. ,, The crystal density of complexes 1 – 4 is seen to decrease monotonically with the size of the bipyridyl substituent (Table S3), indicating that the intermolecular spacing of complexes 1 – 4 on MWCNT is also likely to increase with steric bulk. Thus, we attribute the apparent decrease in electroactive complex across catalysts 1 – 4 to steric bulk insulating intermolecular charge transport, consistent with a recent investigation that showed adding substituent bulk to surface-immobilized Ru­(bpy-R) 2 P (P = 4,4′-diphosphonic acid-2,2′-bipyridine) complexes reduced the rate of self-exchange by increasing intermolecular separation …”