I am not sure that works, I now the reverse works. For example if my iMac is asleep my wife can access iTunes through ATV, iPad, etc. And, I believe iOS 6 will sync in sleep mode. However, I don't believe that the Mac will be looking for the iOS devices, ATV, etc., in sleep mode. In short the Mac can be accessed but is not looking for other devices to sync. I think that the solution is just to plug the iPhone into the Mac via USB and that should start your sync.