You still have to spin up the planet. An earth-like atomosphere would freeze solid on the dark side, and air from the light side would be rushing into the dark side, where it would freeze, until the light side was stripped of its atmosphere too. So the atmosphere would just be a mobile ice cap on the far side, rotating around the planet once per year, with the only gaseous atmosphere being a small, constantly-moving region of sublimation at the terminator betwen the light and dark sides.

Make the atmosphere thick enough to not freeze on the far side, and it'll be absolutely boiling on the near side. The slow rotation means that there is no happy medium: either you've got an atmosphere freezing solid, or you're cooking half the planet at any given moment.