To my understanding, iminium nitrogen is drawn to boron and this interactions lets hydride loose and attacks the double bond carbon, dropping the electron on nitrogen and letting boron go. Correct me here if i am wrong.
What i dont understand is whats going on with the carbons that ive drawn black arrows for. These should be hydrated aswell but i dont get it how? Does the double bond reform with nitrogen somehow and one after another BH4 starts loading the carbons or what?