I need an example of Leibniz algebra that is not a Lie algebra.
I found the following example but it seems that is not true:
$L $ is a $k $-vector space and { $e_1,e_2 $} a basis and the billinear form is defined as follows
$[e_1,e_2]=[e_2,e_2]=e_1$ and $[e_1,e_1]=[e_2,e_1]=0$.
But $[[e_1,e_1],e_2] \neq [[e_1,e_2],e_1] +[[e_1,[e_1,e_2]] $ because
RS=$[0,e_2] $ and LS=0.
The right hand side equals the left hand side in this case, because $[0,e_2]=0$, since it is bilinear. So it should work.