You mean complicated like naturally occurring fullerenes? By 'complexity' do you mean specified-complexity?
If I have to explain the possible complexity of manufactured proteins I waste my time.
The same molecule every time.
Not a ball rolling down hill to some different location every time.
Want to know what's amazing? Aspirin. They seem to manufacture it the same way every time. They seem to never sell little pills of strychnine, despite it being only one atom different in the elements that form it.
Do you know how they do that?
I'll tell you one thing they don't do, they don't have a little talk with the ingredients and convince them to do the right thing.
All they have to do is have a reliable set of conditions. A certain temperature, a certain concentration, a certain moisture level.
And they get the same molecule every time.
The chemicals do not care
at all how complex or simple the final product is. Not one single little bit. The only thing that matters is whether conditions favor the next chemically certain action. If the conditions are the same, chemicals, having no "agency" will simply "fall" or "roll downhill" into the chemically favorable situation.
Like a snowflake that has no agency whatsoever, no purpose, no intent. And yet "rolls down hill" into six-sided figures that look remarkably of a family.
When I look at my cold window in the winter, those ice patterns will ALWAYS follow the little specs of dust on the glass, the slight trail left over from a ladybug walking up the glass the week before. The atoms react to the conditions... predictably.
My imagination has no trouble imagining the number of atoms it took to create these patterns. And I can practically count on the same patterns coming up on the same windows. One of these is north-facing and one south facing. The different conditions will dictate a pretty predictable pattern. And the dust and dirt on each window will nucleate in similar way every day that it's cold enough to form these, until I wash the windows in spring.
The creation of complex molecules in similar conditions, as they grow and grow and grow of millions of millions of trials is not actually hard to imagine. It doesn't even have to happen every time. You don't need 100% yield. All you need is 0.0001% yield on a billion trials to get a sizable herd.
So your claim that "it's too complicated to have happened by accident" is just bad math.
And your claim that you have some reason to think it has only happened once is also bad math.