I have been taught in class that
DIBAL-H is more reactive towards esters than carboxylic acids while opposite is true for diborane.
Also DIBAL-H mentioned is taken under low temperatures (−78 °C).
I was given no reason for the difference in preference.
Now I would suppose that ester would be slightly more nucleophilic and bulky than acids. From these conditions it is hard to conclude the above mentioned order. According to me opposite order could be true because as DIBAL-H is bulky so it would be easier for it to approach a less bulky molecule.
Who do we rationalise the mentioned order? Besides is the difference between preference very large or is there just slight more preference for one than the other?
