If you're talking about securing insurance for someone else's vehicle? Who is the beneficiary of the insurance policy of something happens to the car? There are also issues about authority to drive the motor vehicle that an insurance company probably would not want to touch.
Most reputable insurance companies won't insure you, unless you hold an insurability interest. In the case of autos, that would be proof you own (or are buying) the car. That means title/registration. Most insurers will issue binders until you can collect the proof, but they expect a title or registration to be forthcoming.
If anyone tells you there are ways around that,ignore them. You don't want to get around it, for financial liability reasons.