Group 4 Metallocene Complexes Supported by a Redox-Active <i>O</i>,<i>C</i>‑Chelating Ligand

Group 4 metallocene complexes Cp2M­[OC] (Cp = η5-C5H5; M = Ti (1) or Zr (2); [OC] = κ2-O,C-OC6H2-2-CPh2-4,6-tBu2) supported with a redox-active bidentate O,C-ligand were successfully synthesized through salt metathesis. X-ray crystallographic results showed that both complexes maintained similar bent metallocene coordination geometry. A close inspection of the structural parameters revealed a remarkably long Ti–C bond in 1, indicating concomitant intramolecular charge transfer upon metathesis and coordination. The electronic structure of 1 was investigated by electron paramagnetic resonance (EPR) measurements, revealing the presence of a Ti­(III) center and one [OC]•– radical anion. In contrast, the diamagnetic complex 2 was found to comprise a Zr­(IV) center and an alkyl/aryloxo dianion. Divergent catalytic reactivity was observed for the two group 4 derivatives in the reaction between alkenes and HBpin. Specifically, dehydrogenative boration products (i.e., vinyl boronate esters) were obtained exclusively in the presence of the Zr complex (18 examples, up to 90% yield), while the Ti compound selectively promoted the formation of alkyl boronate esters via hydroboration (19 examples, up to 99% yield)

Group 4 Metallocene Complexes Supported by a Redox-Active <i>O</i>,<i>C</i>‑Chelating Ligand

Group 4 metallocene complexes Cp2M­[OC] (Cp = η5-C5H5; M = Ti (1) or Zr (2); [OC] = κ2-O,C-OC6H2-2-CPh2-4,6-tBu2) supported with a redox-active bidentate O,C-ligand were successfully synthesized through salt metathesis. X-ray crystallographic results showed that both complexes maintained similar bent metallocene coordination geometry. A close inspection of the structural parameters revealed a remarkably long Ti–C bond in 1, indicating concomitant intramolecular charge transfer upon metathesis and coordination. The electronic structure of 1 was investigated by electron paramagnetic resonance (EPR) measurements, revealing the presence of a Ti­(III) center and one [OC]•– radical anion. In contrast, the diamagnetic complex 2 was found to comprise a Zr­(IV) center and an alkyl/aryloxo dianion. Divergent catalytic reactivity was observed for the two group 4 derivatives in the reaction between alkenes and HBpin. Specifically, dehydrogenative boration products (i.e., vinyl boronate esters) were obtained exclusively in the presence of the Zr complex (18 examples, up to 90% yield), while the Ti compound selectively promoted the formation of alkyl boronate esters via hydroboration (19 examples, up to 99% yield)

Heptanuclear Co^II₅Co^III₂ Cluster as Efficient Water Oxidation Catalyst

Inspired by the transition-metal-oxo cubical Mn₄CaO₅ in photosystem II, we herein report a disc-like heptanuclear mixed-valent cobalt cluster, [Co^II₅Co^III₂(mdea)₄­(N₃)₂(CH₃CN)₆(OH)₂­(H₂O)₂·4ClO₄] (<b>1</b>, H₂mdea = <i>N</i>-methyldiethanolamine), for photocatalytic oxygen evolution. The topology of the Co₇ core resembles a small piece of cobaltate protected by terminal H₂O, N₃^–, CH₃CN, and multidentate <i>N</i>-methyldiethanolamine at the periphery. Under the optimal photocatalytic conditions, <b>1</b> exhibits water oxidation activity with a turnover number (TON) of 210 and a turnover frequency (TOF_initial) of 0.23 s^–1. Importantly, electrospray mass spectrometry (ESI-MS) was used to not only identify the possible main active species in the water oxidation reaction but also monitor the evolutions of oxidation states of cobalt during the photocatalytic reactions. These results shed light on the design concept of new water oxidation catalysts and mechanism-related issues such as the key active intermediate and oxidation state evolution in the oxygen evolution process. The magnetic properties of <b>1</b> were also discussed in detail

Heptanuclear Co^II₅Co^III₂ Cluster as Efficient Water Oxidation Catalyst

Inspired by the transition-metal-oxo cubical Mn₄CaO₅ in photosystem II, we herein report a disc-like heptanuclear mixed-valent cobalt cluster, [Co^II₅Co^III₂(mdea)₄­(N₃)₂(CH₃CN)₆(OH)₂­(H₂O)₂·4ClO₄] (<b>1</b>, H₂mdea = <i>N</i>-methyldiethanolamine), for photocatalytic oxygen evolution. The topology of the Co₇ core resembles a small piece of cobaltate protected by terminal H₂O, N₃^–, CH₃CN, and multidentate <i>N</i>-methyldiethanolamine at the periphery. Under the optimal photocatalytic conditions, <b>1</b> exhibits water oxidation activity with a turnover number (TON) of 210 and a turnover frequency (TOF_initial) of 0.23 s^–1. Importantly, electrospray mass spectrometry (ESI-MS) was used to not only identify the possible main active species in the water oxidation reaction but also monitor the evolutions of oxidation states of cobalt during the photocatalytic reactions. These results shed light on the design concept of new water oxidation catalysts and mechanism-related issues such as the key active intermediate and oxidation state evolution in the oxygen evolution process. The magnetic properties of <b>1</b> were also discussed in detail