On the reaction of aromatic phosphanes with electrons. IV. Significance of low-lying orbitals at phosphorus for the mobility and coordinative characteristics of PR2 substituents in reduced p-phenylenediphosphanes. Zeitschrift fuer Anorganische und Allgemeine Chemie, (579):47--56, 1989. [PUMA: arom elec electrochem orbital;redox oxidn phosphane phosphane;electron phosphorus potential reaction redn transfer]