If you have all your stuff still on the PC, you can just copy over the media folders that contain your music and apps and place them on the Mac, actually anywhere and populate that itunes by adding the folder to your library.
If you only have the stuff on your iphone....I believe the only way of doing so it to purchase a program that will do it for you, google there are several.
Only one's ive seen are paid....but I havent looked lately.
I had to do that a time ago when my PC harddrive crashed and I hadnt backed everything up.....I spent prolly $15 on some program but I also recovered thousands of songs and pictures.....well worth it.