$\bullet$ $\mathrm{PEt}_3$ and $\mathrm{AsPh}_3$ as ligands can form $$\mathrm{d} \pi-\mathrm{d} \pi$$ bond with transition metals.

$\bullet$ The N – N single bond is weaker than the single P – P bond because of high inter-electronic repulsion of the non-bonding electrons.

$\bullet$ Nitrogen has unique ability to form p$\pi$-p$\pi$ multiple bonds with itself, carbon and oxygen.

$\bullet$ Nitrogen cannot form d$\pi$-p$\pi$ bond as other heavier elements of its group.