If you start a business and have only startup expenses and no income, you don't report it on your tax return at all. Your report your startup expenses in the year you first have operating income. Your startup expenses are then either expensed, or amortized over 15 years, or both, depending on the amount and nature of the expense.
So no, you can't purchase a business vehicle and use it to reduce your non-business income if you don't have any other business income.
