Well, I'll chime in since I have some experience with trial attorneys. (Used to be one.)
One thing about most male litigators is, the really good ones tend to be very powerful, charismatic guys--no problem creating chemistry there. But if they're on opposing sides of a case, they never let their guard down, ever--every word is designed to give them a superior negotiating position over the other side. (And even the ones who work in the same firm are sometimes in competition with the other guys, vying for the next step up the ladder.) So it makes sense that your characters would not be able to loosen up and get intimate, at least at first. That rings very true to me.
But when a case is over, especially a big one, it changes everything. They don't have to posture to the other side anymore. And especially if they reached a successful settlement after a particularly gruelling round of negotiations, the guys can end up feeling both exhausted and really warm and fuzzy about each other. Especially if each had to make big concessions to get to a reasonable settlement. They might even knock off early and go out for drinks together. So--not knowing many details about your story, I'd suggest that if your characters--after a really heated debate or negotiation session--manage to reach an amicable agreement over a really heated issue, that might be a good way to get them behaving differently. Some of the others here suggested a big change in the status quo, and maybe this is the sort of change that might do the trick.
Another thing--the stereotype about lawyers drinking a lot--well, some of them do. That might help loosen up a character, as well.
Finally, late nights (past midnight) happen a lot, especially for young attorneys, and especially right before a trial. If two opposing attorneys are trying to get the wording right on a settlement agreement to make both clients happy the night before a trial is scheduled to take place--which happened to me plenty--they could be together, very late at night, in a very deserted office.
Hope that helps a little. Good luck with your project!
Katya