The appliance of LAB in amide reduction

Lithium aminoborohydride is a versatile reducing agent. In the scheme below, I don't understand how does unhindered LAB afford an alcohol in the reduction of amides while a hindered LAB affords an amine. Why are two different products obtained and by what mechanisms do these reductions take place?


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




Very interesting question and not very obvious. As can be seen from the picture, LAB's reduce only tertiary amides. It is stated in the publication(1) about LAB reductions: 



> 
> LAB reagents do not
>  reduce primary and secondary amides even in refluxing THF.
> 
> 
> 


In the same publication it is provided reason for different outcomes of reductions. They say that: 



> 
> We found that the outcome of these reductions depends on
>  the sterics of the amide as well as of the LAB reagent
> 
> 
> 


Which means that if LAB and/or amide is sterically hindered it can't interact with nitrogen like in compound **5** 


In lower part of the picture is described reaction where more hindered LAB leads to amine product **9**


[![enter image description here](https://i.stack.imgur.com/iTqj7.jpg)](https://i.stack.imgur.com/iTqj7.jpg)


(1)Pasumansky, L., Goralski, C. T., & Singaram, B. (2006). Lithium aminoborohydrides: powerful, selective, air-stable reducing agents. Organic process research & development, 10(5), 959-970.


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