When they set out to extinguish life in the universe, the point is to stop the incursions of the warp into the materium. The Necrons want the imaterium and materium to be completely distinct, with no crossover, and them in charge of the materium. They see humans and eldar as warp tainted creatures that allow and cause the imaterium to cross over into the material universe.
So, no. Necrons would never follow Chaos, they are arch enemies.