Thunderbolt not working between MacbookPro 10.9 and Imac 10.6

Hello, I have a macbook pro running 10.9 and a 27 iMac which is running 10.6.

I would like to use the iMac as a display and purchased a thunderbolt cable and connected the two but can get the MacBook Pro to power the Imac display or even link them.

Please help, what am I doing wrong.

Command F2 on the iMac wont switch the displays and powering off the macbook pro and restarting wont make the iMac do anything either.

imac

Model Name: iMac

Model Identifier: iMac11,3

Processor Name: Intel Core i5

Processor Speed: 2.8 GHz

Number Of Processors: 1

Total Number Of Cores: 4

L2 Cache (per core): 256 KB

L3 Cache: 8 MB

Memory: 4 GB

MacBook Pro OSX 10.9.5