Both bis(diisopropylphosphino)amine and bis(di-t-butylphosphino)amine react with CS 2 to give bright red zwitterionic adducts of the form R 2 P(CS 2 )NP(R 2 )H (R ¼ i Pr or t Bu). The P-H tautomer is the exclusive species present in solution, and there is no evidence of CS 2 lability. The tautomeric hydrogen can undergo exchange with deuterium in protic solvents such as CD 3 OD. The products were characterized by single-crystal X-ray diffraction, IR and multinuclear ( 1 H, 2 H, 13 C, 31 P) NMR spectroscopies. * In memory of Professor Richard F. Langler, whose students, including DAD, will remember him for the high expectations he set for them in the classroom and in research, and the high standards to which he held them. His work with undergraduates has inspired us to train many young scientists, and we note that our coauthor RPUS was a high school student when he performed many of the experiments described in this work.