algebra precalculus - Imaginary numbers and exponent arithmetic

This is a very basic question but it's been driving me crazy for a while... I know that $i^3 = i^2*i = (-1)i = -i$

But why does the following reasoning give me the wrong answer? $i^3 = (i^2)^{3/2} = (-1)^{3/2} = (-1)^{1/2} = i$

Thanks