To divide by a mixed number, we first have to change the mixed number to an improper fraction. We can do this by multiplying the whole number by the denominator and adding the numerator.
$2\dfrac{1}{4} = 2 + \dfrac{1}{4} = \dfrac{8}{4}+\dfrac{1}{4}=\dfrac{9}{4}$
Now, we can rewrite the expression as
$\dfrac{-2}{3} \div \dfrac{9}{4}$
When dividing fractions, we can multiply by the reciprocal of the second fraction.
$\dfrac{-2}{3} \div \dfrac{9}{4} = \dfrac{-2}{3} \cdot \dfrac{4}{9}$
We can cancel out the common factors of 2 and 3.
$\dfrac{-\cancel{2}}{\cancel{3}} \cdot \dfrac{\cancel{4}}{\cancel{9}} = \dfrac{-1}{1} = \boxed{-1}$