Praise be to Allah.
You do not have to pay zakaah on this money until you take possession of it; when you take possession of it you should count one (hijri) year from the day you took possession of it, then pay zakaah on it after one year.
Shaykh Ibn Baaz (may Allaah have mercy on him) was asked a similar question, and he replied: If property has been seized and its value estimated, but the owner has not been able to take possession of it due to reasons beyond his control, no zakaah is due on it until he takes possession of its price and a full year has passed. End quote.
Majmoo’ Fataawa Ibn Baaz (14/41)
And Allaah knows best.