One of the basic requirements in a 1031 exchange is the way title is held in the old property must be exactly the same way it is held in the new property. Therefore if the rental is held as his sole and separate property as a single man, the new property will have the title held the same way. One way your client may be able to circumvent this is to Quitclaim and undivided interest to his spouse and change the title on the rental before the exchange occurs. It is best to check with the accommodator on timing and the mechanics. Transfers between spouses is a tax-free event.