Out-of-date tin containing old leaves (6,2)
I believe the answer is:
passes on
'leaves' is the definition.
('pass on' can be a synonym of 'leave')
'out-of-date tin containing old' is the wordplay.
'out-of-date' becomes 'passe' (synonyms).
'tin' becomes 'Sn' (Sn is the chemical symbol for tin).
'containing' indicates putting letters inside.
'old' becomes 'o' (abbreviation).
'sn' enclosing 'o' is 'son'.
'passe'+'son'='PASSES ON'
(Other definitions for passes on that I've seen before include "graduates" , "Dies; transmits" , "Hands to the next person" .)