I2C to IrDA - any pitfalls?
I2C has nearly no protocol requirements.  While IrDA is has a complex protocol requirement:



Consider if the benefits of the IrDA protocol outweigh the costs of implementing it.

If this is a clean (you are not expecting errors due to light obstruction) environment and you are willing to do some engineering (as what follows is only an outline) then consider using SPI to 1 wire bridge chips on both sides and using IR LED transmitters (software driven to transmit ASK type signals) and an IR ASK receivers (a device which usually contains an IR sensitive transistor, a band-pass filter and a PLL decoder - commonly found in remotely controlled appliances).  Again, this last bit is only a suggestion and a fair bit of engineering is needed to get it to work.  But, likely, far less then to implement the IrDA stack.