Please read OS X 10.8 removes iTunes sync support with Outlook for Mac by MVP William Smith for details.

Outlook for Mac no longer syncs with Mountain Lion’s Calendar (formerly iCal) and Contacts (formerly Address Book) via iTunes. Outlook for Mac users now have just one option for syncing mail, calendars and contacts with any Apple product: Microsoft Exchange, which is a solution geared more toward enterprise customers. Multiple hosting services offer Exchange for home and small business consumers including Microsoft’s Office 365.