Question

why isn't necessary to flush the reaction flask with an inert gas (nitrogen or argon) during the hydroboration reaction

Answer 1

Because boron is also inert gas.

Explanation:

We use nitrogen and argon to flush the reaction flask because it is an inert gas and prevent the oxidation of the elements and also prevents chemical nature of the reaction. But, in hydroboration boron does this duty and it behaves an inert gas. Hence, we don’t need other inert gases.