[CrimpJiggler]

Is there a standard method of drawing catalytic cycles? For example, heres the Monsanto process:

I can see that the catalytically active species starts at the top of the cycle. The steps that don't involve the transitional metal are inside the circle. Heres the Heck reaction:

which is kinda similar. The catalytically active species (PdL2) starts at the top and is labelled step 1. Is this the standard way of drawing catalytic cycles? In other words, is the first step always one of the reactants (or derivative of one of the reactants) adding to the coordinatively unsaturated metal complex?

[Yakimikku]

Hello!

I don't really have a good answer to your question, but I don't want you to go unanswered!

Bottom line, I don't think there are any rules (that I know about) concerning drawing catalytic cycles. I can comment on a couple things however. On the top of my head, I can't think of a catalytic cycle that was drawn counter-clockwise. It wouldn't change the meaning at all, but I feel that it might just be a sort of "social norm" in drawing catalytic cycles clockwise. Also, I think typically you start at the top with the initial form of the catalyst--what it's like before any of the catalytic process has started, before it has interacted with anything (in practice, some catalysts are not initially active, but that's all in the nitty-gritty details). Anyway, with that in mind, I'd say the tendency is to start with the initial catalyst before any chemistry, and start with the first step going clockwise. Other fancy things such as the center of Monsanto process probably rise case by case--of course aesthetics and understandably are undoubtedly important factors.

[fledarmus]

I agree with Yakimikku

You draw a catalytic cycle to make a point, and usually the point that you are trying to make is the process that the catalyst is going through. Like starting a cell cycle drawing from the resting state of a single cell, you usually start with the catalyst in the form that you find it in the bottle.

There are certainly other ways to draw the cycle - if you are more interested in the chemical reaction, you might drawing the starting material and product across the top, with the catalytic intermediate over the arrow in the middle, and a catalytic cycle below that showing the regeneration fo the catalyst. It all depends on the point that you are trying to make.

And like Yakimikku, I've never seen one drawn counter-clockwise.

[CrimpJiggler]

That pretty much sums it up. Thanks.