Sciencemadness Discussion Board

Photoredox Catalysts, & My recent preparation of Tris(bipyridine)nickel(II) hydrochloride

Electra - 19-5-2014 at 20:19

No elaborate write up, but preparation was as simple as mixing Nickel (II) Chloride and Bipyridine in a 1:3 molar quantity and refluxing it in acetone. This compound should be air stable, so going to plan on distilling it tonight. I've recently been intrigued by the concept of photoredox catalysts. So far I've only found indications in literature of ppy/bpy ligands with Ruthenium and Iridium. Ruthenium being the more popular one, but I'm not sure why. Most any lewis acid should do the job.

For those of you who don't know what a photoredox catalyst is..... most photochemistry is conducted with UV light, as this is what primarily excites various molecules such as halides, ketones, aldehydes, alkenes, and much more. The UV photons enter the oribitals of the molecule, displacing an electron, often creating a short lived reactive radicals by a sort of outersphere transfer. The downside to this is non-quartz glass, which is what most lab-ware is made of, absorbs light below the 275nm spectrum, sometimes greater. 254 nm is one of the most critical uv wavelengths for photochemistry. Not only that, specialized UV lights are often expensive, and if proper protective gear is not worn, they can be damaging to the body. As well, the set ups can get elaborate without specialized equipment.

Photoredox Catalysts circumvent most all of this. The bipyridine ligand when complexed with a metal is excited by visible 450-500nm+ light. This is light that is produced by most all common light fixtures. This causes an outshell electron transfer that can created either a reducing or oxidizing sort of radical. Now, this might not sound very appealing, but get this: Photoredox Catalysts when excited, can stay in the excited state for up to 10-100x longer than other photoinduced radicals caused by UV light. Having a long half-life gives it an increased opportunity to react with more substrates. So: The photoredox catalyst can become activated by UV light, and then go on to activate multiple substrates that would only be activated by UV light.


What I hope to do:

There is no documentation of this nickel based photoredox catalyst in the literature that I am aware of. The compound is documented, but not its photoredox usage. It should behave very similarly to the other Lewis Acid - Bipyridine complexes.

I do not have any substrates to test this complex on currently, so I will probably vacuum off the acetone and store it. From what I've read these complexes in solid form produce very deep and vibrant colors.

If anyone has any suggestions on what sort of photochemical reaction I can try this on, shout them out. Any UV based reaction should be possibly with visible light when using this type of catalyst. If anyone else has experience with this sort of thing, I would love to hear them!

froot - 20-5-2014 at 11:15

Well not much use but the term 'photoredox' perfectly describes an old idea I had which was the possibility to change the oxidation states of battery electrolyte using solar energy. Seems impossible though, closest I got was photocatalytic properties of TiO2.

mnick12 - 20-5-2014 at 15:39

Coordination chemistry, yay!

Out of curiosity what does the complex look like? Also is refluxing necessary, did simply mixing the compounds result in a color change? Additionally was the nickel salt anhydrous? If not it may have some aqua ligands. Do you have access to NMR, I would guess that this complex would be diamagnetic, and NMR would be a good characterization tool.

Cool stuff.

Electra - 20-5-2014 at 19:15

Quote: Originally posted by mnick12  
Coordination chemistry, yay!

Out of curiosity what does the complex look like? Also is refluxing necessary, did simply mixing the compounds result in a color change? Additionally was the nickel salt anhydrous? If not it may have some aqua ligands. Do you have access to NMR, I would guess that this complex would be diamagnetic, and NMR would be a good characterization tool.

Cool stuff.


I didn't isolate it, yet, still in the solvent, but refluxing is probably not necessary. Though, that is not something that can easily be said without tests. Heating will of course speed up the rate at which the complexing takes place. I do not believe the nickel salt was anhydrous. Aqua ligands... hmm

I do not have access to an NMR or anything fancy like that, but I am also not going to wager that my compound is the purest that it could be. In terms of the coordination, there's not much else that can happen when the two are mixed.
Quote: Originally posted by froot  
Well not much use but the term 'photoredox' perfectly describes an old idea I had which was the possibility to change the oxidation states of battery electrolyte using solar energy. Seems impossible though, closest I got was photocatalytic properties of TiO2.


I've read some interesting things about TiO2 and its photo-properties.

It can be possible to change the oxidation states of battery electrolytes if you possibly took advantage of an additional substrate. If you are talking about a closed system, photo-redox catalysts do exhibit radical-type properties. If you read into you it you may be able to figure out some sort of radical electron transfer from Oxygen in the air to change the oxidation state of your electrolyte, though the energy required to pump air through the battery for it to experience any appreciable energy gain would far exceed the energy gained from the air.