Relative plenitude did not dictate the elements we and our relatives use, and would not for other life, either. In any case, many other elements are plentiful.

Carbon is a good choice for our temperature range, but there are plenty of temperature ranges as well or better represented. Life will not sneer at the others. Most life on Earth cannot make any use of the carbon in CO2, no matter how much of it there is; in fact, the more of it there is, the worse off most living creatures are, only green plants excepted. You would die in a room with the nitrogen replaced by CO2, despite that you use none of the nitrogen at all. (Only bacteria can "fix" nitrogen, and only some of them.)

Iron is very plentiful in the cosmos and in Earth's constitution, and most life depends on it, but it is practically nonexistent in the open ocean; yet life thrives there. Even where iron is plentiful, life uses hardly any. Silicon is extremely plentiful, too, yet used by our life even less -- until just lately!

So, your argument from plenitude utterly collapses. Life as we know it is a product of history and circumstance. Given different circumstances and different history, you should expect a different product. There will certainly be similarities dictated by physics: e.g., cells are very, very likely, and equally so use of liquids. Aperiodic fibers to encode genes, cognate to our DNA, and others to fold up and carry out processes, cognate to our peptide chains a.k.a. proteins, are quite likely. But there is no reason to imagine that any of the details of the encoding would match.

> Even where Iron is plentiful, life hardly uses any

That’s a huge misconception about biology and evolution. Basic cellular biochemistry is extremely well conserved. There is almost no pressure to use more iron, but significant pressure to use less. Photosynthesis for example is Iron dependent and that acts as a major limiting factor on ocean ecosystems. Yet, we don’t have an iron free alternative adapted to utilize that giant ecological niche. Life is seemingly using as little as possible.

That should suggest why primarily silicon life is such a poor option.

> There are plenty of temperature ranges as well or better represented.

For complex life it’s not just about temperature but also pressure and access to sunlight. Anyway, the normal argument is that silicon based life could thrive in extremely high temperatures. That’s all well and good for silicon but not so much the other chemicals it’s interacting with. Life is dependent on being able to reliably create and break relatively weak chemical bonds. However, when you start to look at the actual chemical options at those temperatures you run into serious problems. The kind of large molecules you want for complex life are either unstable or too stable at those temperatures.

Iron is not the key element in chlorophyll; magnesium is.

We don't know of many interesting Si compounds specifically because we have none of the organisms that would produce them. Our ignorance does not constrain nature.

"Weak", for bonds, is exactly a function of temperature. At higher temperature, life will have chosen constituents that bond with the right strength, wholly ignoring your preconceptions of what it ought to be using.

Chlorophyll contains magnesium, photosynthesis requires Iron at about 1000 magnesium atoms per iron atom. However, Iron still ends up the limiting factor in ocean ecosystems. https://zenodo.org/record/1258477

Anyway, Life can only chose chemical bonds that are possible. It’s perfectly reasonable to pick a specific temperature range and say here this is ideal for silicon lifeforms, but that means every chemical interaction must occur in that temperature range which is a major physical constraint.

We don’t know of many interesting and relevant Si compounds in large part because they don’t exist. It’s not even just chemical compounds life needs a water equivalent for all that cellular machinery to float around in and bump into each other.

Again: Relevant Si compounds don't exist here, because there is no Si-based life here. Our favorite carbon compounds would identically not exist in a Si-based ecosystem. That the useful compounds would not be simple substitutions of Si for C is of no importance. As I noted, some liquid-analog is likely involved in any spontaneously evolved ecology, but it does not need to be water, or even, technically, liquid-as-such.

Nature is not constrained to the limits of your imagination. I am frankly surprised to find you continuing to insist it is.

The tangible existence is irrelevant, computational chemistry is more than capable of exploring this territory. The issue isn’t simply finding giant complex molecules that would make up such hypothetical lifeforms it’s looking for the basic building blocks.

In the end all of chemistry comes down to quantum mechanics it really is quite constrained. Put another way you can list our every possible 2-9 atom molecule containing Silicon plus common elements and look at how the behave.

And, you claim to have not just made such a list, but also explored all of their possible interactions with one another and with what could be common non-Si compounds in their vicinity? You and what ten thousand universities?

You are just making things up. Who do you imagine believes you? Why do you want them to believe you?

No, can is not did. My point was it’s a finite space.

People have explored some of this space and found nothing.