Mac and VIM doesn't play well with alt-key shortcuts. To VIM they just look like extended character keys, there doesn't seem to be any indication of an alt-key modifier.
The following alt level shortcuts have been defined
alt-r i.e. ® => recent files
alt-p i.e. π => project level files
alt-f i.e. ƒ => file level tags
alt-t i.e. † => buffer files
alt-] i.e. ‘ => visual tjump (tag jump plugin)