Visible light induced formation of a tungsten hydride complex

Area of Science:

• Organometallic Chemistry
• Photochemistry
• Radical Chemistry

Background:

• The dimeric complex [CpW(CO)3]2 undergoes metal-metal bond cleavage upon blue light irradiation in the presence of a Lewis base (L).
• This cleavage leads to the formation of cationic [CpW(CO)3L]+ and anionic [CpW(CO)3]- species.

Purpose of the Study:

• To investigate the further reaction of the [CpW(CO)3]- anion in the presence of pyridinium tetrafluoroborate.
• To elucidate the mechanism of light-driven metal hydride complex formation, specifically CpW(CO)3H.
• To determine the role of photon flux in the reaction pathway.

Main Methods:

• Irradiation of [CpW(CO)3]2 with blue light in the presence of a Lewis base and pyridinium tetrafluoroborate.
• Monitoring the reaction progress using in situ photo 1H NMR spectroscopy.
• Investigating the reaction mechanism by determining quantum yields of CpW(CO)3H formation at varying photon fluxes (I).

Main Results:

• The [CpW(CO)3]- anion reacts to form the metal hydride complex CpW(CO)3H.
• Quantum yields for CpW(CO)3H formation show a correlation with I-1/2, where I is the photon flux.
• This correlation suggests a radical chain mechanism is dominant.

Conclusions:

• The formation of CpW(CO)3H from [CpW(CO)3]2 under blue light irradiation proceeds via a radical chain mechanism.
• The disproportionation of [CpW(CO)3]2 to generate the hydride precursor [CpW(CO)3]- is primarily driven by this radical chain process.
• Photochemistry offers a viable route to synthesize organometallic hydride complexes.