The corp is acting as a collection agent on behalf of the charity, they don't get to deduct it as a charitable donation. Even if they did, they would have to then count the money as income, which would offset any tax deduction they would get, giving the corp 0 net tax benefit.
...Though they may get some publicity benefit from it, which is why I don't go out of my way to donate using corps as a proxy. If its a small amount that I may not otherwise make, for a good cause, sure. But for my more deliberate giving, I would avoid corp proxies. So I don't give through my employer (unless they are offering to match it with their own funds).
The corp is acting as a collection agent on behalf of the charity, they don't get to deduct it as a charitable donation. Even if they did, they would have to then count the money as income, which would offset any tax deduction they would get, giving the corp 0 net tax benefit.