.delta.(2,2')-Biimidazolidine, 1,1',3,3'-tetraphenyl- 2179-89-7 Bis(1,3-diphenyl-2-imidazolidinylidene) Imidazolidine, 2-(1,3-diphenyl-2-imidazolidinylidene)-1,3-diphenyl- NSC137944