Reason for double acylation of ferrocene only occurring with certain reagent combinations Can anyone explain why the acylation of ferrocene produces the following results:

Ferrocene + acetic anhydride + AlCl3 ==> mono-acylated ferrocene

but:

Ferrocene + acetyl chloride + AlCl3 ==> di-acylated ferrocene (an acyl group on each ring).

I have seen various statements confirming this, but not a single explanation for it! My current thoughts are that it must be something to do with the carboxylic acid produced from the reaction with the anhydride somehow hydrogen bonding/blocking the second site, but not really sure how it would work.

Any explanations greatly appreciated!
One factor:  since ferrocene is covalently bonded, the rings "communicate" with each other via the molecular orbitals passing through the iron atom.  Thus the acetyl group placed on one ring not only deactivates that ring, but to some extent deactivates the second ring as well.  The second ring would still be attacked preferentially in the second stage but may require a stronger electrophile, which acetyl chloride is compared with acetic anhydride.