- Why does benzenediazonium chloride get converted to benzene upon reacting with $\ce{H3PO2}$ and not $\ce{LiAlH4}$ ?
- Also, what is the reaction mechanism of the reaction with $\ce{H3PO2}$ ?
This Wikipedia page list all kind of nucleophilic substitution reaction on aromatic compound why can't $\ce{LiAlH4}$ / $\ce{H-}$ react like one of these to give benzene and expel nitrogen.
I just wanted to add that it's up to my knowledge that $\ce{LiAlH4 / H-}$ can't reduce the double bond of Benzene, because when styrene reacts with $\ce{LiAlH4 / H-}$ it gives ethyl benzene.
Update
I was just researching (on google) for the mechanism where I came across this site suggesting the mechanism to be radical and as follow :
But still there is one problem the side products don't match this site states the side product to be $\ce{H3PO3}$ and $\ce{HCl}$ but as stated above the side products must be $\ce{H2PXO2}$.