Limitation of Duration of Work Visa for US Citizen (Istanbul)

I am a US citizen and plan to work in Istanbul late in the summer for a JV company we just set up in Turkey. However, I heard that due to lack of reciprocity for social security between US and Turkey, the meximum time a US citizen is allowed to work in Turkey is 18 months. I would like to work as an expat in Istabul for at least three years due to my older daughter's school situation (don't want to move one or two years into high school).

Could you please advise how I can get around this problem based on your experiece? Your help is greatly appreciated.