Is it permissible to purchase a car from a Riba-based bank that first acquires ownership of it and then sells it to me, given that I was compelled by my employer to have my salary account at this bank?

If the bank owns the car and possesses it, then sells it to you in installments without stipulating a late penalty, this transaction is permissible. Sheikh Ibn Uthaymeen was asked about the ruling on buying cars in installments from banks that own them and stipulate salary transfer, and he permitted it.