what regex settlement datetime (2008-09-01 12:35:45 )?

what regex settlement datetime (2008-09-01 12:35:45 ) ?

i error:

no finale delimiter '^' found

using:

preg_match('(?n:^(?=\d)((?<day>31(?!(.0?[2469]|11))|30(?!.0?2)|29(?(.0?2)(?=.{3,4}(1[6-9]|[2-9]\d)(0[48]|[2468][048]|[13579][26])|(16|[2468][048]|[3579][26])00))|0?[1-9]|1\d|2[0-8])(?<sep>[/.-])(?<month>0?[1-9]|1[012])\2(?<year>(1[6-9]|[2-9]\d)\d{2})(?:(?=\x20\d)\x20|$))?(?<time>((0?[1-9]|1[012])(:[0-5]\d){0,2}(?i:\ [ap]m))|([01]\d|2[0-3])(:[0-5]\d){1,2})?$)', '2008-09-01 12:35:45');

gives error:

warning: preg_match() [function.preg-match]: gathering failed: zero repeat during homogeneous 0 e:\www\index.php line 19