Splitting 1/2 and 1/2

I have a Dark Ale that just got put into a primary fermentation bucket. Considering moving 1/2 out after 2 weeks into a secondary 5 gallon carboy and adding coco nibs, vanilla bean, and coffee to it, and leaving the other half in the primary alone.

Question is about airspace. If I do this, I'll have 2 1/2 gallons in a 5 gallon containers that will have air above it. (I dont have co2 bottles to blow the air out of the buckets or anything like that).

Will splitting into 2 containers adversely affect the beers taste?

as long as you don't age it a real long time the oxygen shouldn't do too much damage. If you were going for 3 months or so then it might be an issue