Politics in forming collaborations as a postdoc
Talk to your boss in general terms at first.  Then you'll get a feeling for whether a "go for it" approach will go down well locally or not.  You may have a good idea of whether you're working with a natural collaborator or not, but an early discussion is still worthwhile because they can warn you in general terms about rivalries/conflicts of interest etc. Try your hardest to keep your boss in the loop at all times. Of course this isn't always possible when you meet people at conferences. 

Don't make promises you don't have the authority to keep -- so discuss possibilities rather than actually inviting someone until you can clear it.  It might not be just your boss but politics/policies that you have to deal with.  Money is always a good get-out: If you don't hold the budget yourself, everyone knows you can't just spend it without authorisation.