Sadly I haven’t heard of anyone getting a i7 series CPU to work in this older system.
Apple never offered an i7 in the 21.5” model and the i7 (I7-870) the 27” offered won’t work in your system as its a higher TDP chip. The Ivy Bridge version of CPU’s is the first lower TDP version of i7 CPU’s (I7-2600S) but it requires a different micro-code which is not present in your systems EFI.