[Morphic flip]

(n⁵-C₅H₅)(CO)₂M(CH₂CH₂CMe₃) + CO ----> product A ----> product B
M = metal.
I think possibly the addition of CO changes the (n⁵-C₅H₅) group to
(n⁴-C₅H₅) by way of providing the electrons to give product A (below)
(n⁴-C₅H₅)(CO)₃M(CH₂CH₂CMe₃)
But I don`t know what what product B would be, any help appreciated.

[FeLiXe]

what I could think of ist that CO is in the next step inserted between the alkyl group and metal. so you'd get an acyl group

[Morphic flip]

What would you make product A and B then?

[Dan]

I think possibly the addition of CO changes the (n⁵-C₅H₅) group to
(n⁴-C₅H₅) by way of providing the electrons to give product A (below)
(n⁴-C₅H₅)(CO)₃M(CH₂CH₂CMe₃)
But I don`t know what what product B would be, any help appreciated.

Depends on the metal. It will probably be a 16 electron compound, in which case the cp group will remain n⁵.
Otherwise I agree with your product A
Product B is formed by a migratory insertion
Click on lecture 2 on this page http://www.chem.ox.ac.uk/icl/dermot/organomet98/lectures.html