Auto insurance providers will sell you car insurance even if you can't submit a title yet. Most insurance companies will allow you to start a policy without the title as long as you can provide proof of ownership. This can be shown with a bill of sale, a lease agreement or a bank statement showing that you have a loan on the vehicle.
Depending on where you live and how you bought the car, you may need to show proof of insurance before the title transfer.
Even if you haven't transferred the title yet, having insurance ready is a good idea. This will ensure you're covered immediately, especially if you plan to drive the car right after buying it.