Why does DIBAL-H not reduce esters to alcohols directly?

[This](https://www.masterorganicchemistry.com/2011/08/26/reagent-friday-di-isobutyl-aluminum-hydride-dibal/#:%7E:text=It%20will%20also%20reduce%20other,aldehydes%2C%20ketones%2C%20and%20nitriles.&text=Like%20Lindlar%27s%20catalyst%2C%20DIBAL%20is,stops%20at%20the%20aldehyde%20stage.) source says that DIBAL-H reduces esters to aldehydes. Further, it says that, like NaBH4, it reduces aldehydes too.


Why in reduction of ester, the aldehyde so formed is not converted to alcohol, if it can reduce both ?




It depends on the reduction conditions.


1 eq of Dibal-H takes esters to aldehydes at low temperature. Use multiple eqs at a higher temperature and you get further reduction. This is because of the formation of a hemi-acetal aluminium complex intermediate that is stable at low temperature and resistant to further reduction.



> 
> DIBAL is an “electrophilic” reductant. That is, the first step in the reaction is coordination of a lone pair from the carbonyl oxygen (a nucleophile) to the aluminum (electrophile). It is only after coordinating to its carbonyl host that DIBAL delivers its hydride to the carbonyl carbon, resulting in formation of a neutral hemiacetal intermediate that is stable at low temperatures.
> 
> 
> 


[![enter image description here](https://i.stack.imgur.com/mhC3q.png)](https://i.stack.imgur.com/mhC3q.png)


[source here](https://www.masterorganicchemistry.com/2011/08/26/reagent-friday-di-isobutyl-aluminum-hydride-dibal/)


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