Society leaders refuse to penetrate heart of legation (10)
I believe the answer is:
glitterati
'society leaders' is the definition.
(people in fashionable society)
'refuse to penetrate heart of legation' is the wordplay.
'refuse' becomes 'litter' (I've seen this before).
'to penetrate' indicates putting letters inside.
'heart of' says to take the centre.
The central letters of 'legation' are 'gati'.
'litter' placed within 'gati' is 'GLITTERATI'.
(Other definitions for glitterati that I've seen before include "Rich, beautiful and fashionable celebs" , "Fashionable people" , "Celebrities" , "Glamorous, rich and famous people?" , "Showbiz types" .)