Hexamethyl Phosphoric Triamide, the solvent for the reaction

In the order of appearance

 1,2-Diphenylethanol. Why was this substrate chosen? This is a dehydration reaction. You remove water

tetramethylphosphorodiamidic chloride

tetramethylphosphorodiamidate ester of 1,2-diphenylethanol

the proton released when the ester is formed is picked up by the solvent

the protonated HMPT fragments to produce dimethyl amine and a phospho cation

trans-Stilbene, the product of the reaction

tetramethylphosphatediamidate ion