Is it Islamically permissible for an employee to buy an apartment allocated to him from the company at a reduced price, then sell it to another party for a higher agreed-upon price, and pay its price to the company from the amount he will receive from the buyer, with the ownership being transferred to the buyer via a "promise to sell" contract after receiving the apartment?

It is not permissible for an employee to sell an apartment before purchasing and taking possession of it, due to the Prophet's (peace be upon him) prohibition of selling what one does not own or has not taken possession of. It is permissible for the employee to promise someone to sell them the apartment after acquiring ownership and taking possession of it, without taking any money in return for the promise. It is not permissible for the employee to borrow from his friend to buy the apartment and then sell it to him, due to the prohibition of combining a loan and a sale. It is permissible for the employee to buy the apartment and receive it, with a delay in paying the price for a few days, then sell it and receive the price, and then pay its price to the company. It is also permissible for him to borrow its price from someone and buy it, then sell it to someone other than the lender, and return the loan to its owner.