rpy2-2.2.5 belongs to the previous series (2.2.x), and was working with older versions of R (R keeps evolving).
The current releases of rpy2 are in the 2.3.x series (latest is 2.3.6), but they require Python 2.7, or Python 3.3 (if you want the latest R, you'll have to get a recent Python ;-) )