Ferrocene

I'm reading up on iron (because it's magnetic) in Wikipedia and I come across this line:

Among its organometallic compounds is ferrocene, the first sandwich compound discovered.

which basically means nothing to me because half of the words likewise mean nothing, but somebody thought is was worth mentioning that it was the first of its kind.
    Its kind is a sandwich compound, which just means we've got a tomato sandwich (see picture) made with two pumpernickel muffins. The muffins are a little lumpy and are decorated with Hostess Sno Balls, but you get the picture. The red ball in the center is the iron atom, the two lumpy black blobs on either side are rings made of five carbon atoms each, and the silver balls around the outside edge are hydrogen atoms. Here's a different rendition, except they have made a blueberry sandwich.

    Following links to ever more obscure terms (like Ligand and Coordination Complexes) I stumble across this line:

Coordination complexes were known – although not understood in any sense – since the beginning of chemistry, e.g. Prussian blue and copper vitriol. 

    Prussian blue was invented back in 1706 in Germany. It was the first economical blue dye, economical in that it replaced lapis lazuli, a stone mined in Persia, and Indigo, a dye derived from a plant. I remember a story from elementary school about how the first European settlers in North America discovered Indigo, which also became an important blue dye. Oops, wrongo! Indigo had been imported from India since ancient times. Several American colonists tried to grow it. Eliza Lucas Pickney persisted and eventually met with success.
    I've heard of Prussian blue because machinists use it for marking metal and biologists use it for staining specimens for microscope slides. It is also used as an antitode for some kinds of heavy metal poisoning, like radioactive Cesium, which was the culprit in the Goiânia accident in Brazil back in 1987.
    Copper vitriol, also known as copper sulfate is used as fungicide, pesticide and herbicide. Watch out microbes, copper's comin'! It was used to pressure treat wood to preserve it from rotting. It is also used in swimming pools and aquariums.
    So we've been using stuff that we really didn't understand. No surprise there. All that is really interesting, but here's the clincher:

Ferrocene and its derivatives are antiknock agents used in the fuel for petrol engines; they are safer than tetraethyllead, previously used.^[34] It is possible to buy at Halfords in the UK, a petrol additive solution which contains ferrocene which can be added to unleaded petrol to enable it to be used in vintage cars which were designed to run on leaded petrol.^[35] The iron containing deposits formed from ferrocene can form a conductive coating on the spark plug surfaces.

So ferrocene, invented in 1951, can be used to run your hot-rod engine with today's wimpy gasoline. But it you do it will foul your plugs. Still, replacing fouled plugs in better than having to replace the whole damn engine.