How to close applications on sleep?
It's hard for me not to to question the validity of your setup (broken sync!), but ... for doing something on sleep or wake, you should try SleepWatcher by Bernhard Baehr (more context at Mac OS X Hints). It is using launchd for monitoring.


  [SleepWatcher] is a command line tool (daemon) […] that monitors sleep, wakeup
  […] of a Mac. It can be used to execute a Unix command when the Mac
  […] goes to sleep mode or wakes up, […]


If you have a bit of terminal experience, I think you can set it up. Make sure you read the well-hidden "Installation for new SleepWatcher users" section in ReadMe.rtf