You have 50/50 owners of a property and one owner sells their share to the other owner.
If the property was the primary residence of the seller for at least 2 of the last 5 years they owned it, then the seller will not pay taxes on a maximum $250,000 gain. Keep in mind that the seller (you) also has a cost-basis in the property. So while you may get $300,000 for your share, when you subtract your cost basis from that it's perfectly possible your "gain" will be under the $250,000 exemption threshold anyway.
Note that this will not be a "quit claim", as it will be a sale and would be recorded as such, provided the buyer is in fact, taking out a mortgage to buy it. Now this sale "may" raise flags with the IRS, only because the seller is selling to a related party. But even so, I don't see any problems or issues with the IRS on that.
