The syntheses and reaction chemistry of two electron mixed-valence diphosphazane-bridged dirhodium and diiridium complexes M-2 (0'II)(tfepma)(2)((CNBu)-Bu-t)(2)Cl-2 [M = Rh (1), Ir (2); tfepma = MeN[P(OCH2CF3)(2)](2), (CNBu)-Bu-t = tert-butyl isocyanide] are described. 1 and 2 undergo addition and two-electron oxidation and reduction chemistries. In the presence of (CNBu)-Bu-t, the addition product with the stoichiometry M-2 (0'II)(tfepma)(2)-((CNBu)-Bu-t)Cl-3(2) [M = Rh (3), Ir (3)] is generated; in the presence of 1 equiv of (CNBu)-Bu-t and 2 equiv of bis(pentamethyl-cyclopentadienypcobalt(II), 1 and 2 are reduced to furnish m(2) (0,0)(tfepma.2) ((CNBu)-Bu-t)(3) [M = Rh (5), Ir (6)1 which feature both four- and five-coordinate M-0 centers. Complexes 1, 2, 5, and 6 all possess coordinatively unsaturated square planar M-0 centers that are reactive: (1) 2 reacts with PhICl2 to produce Ir-2(II)'(II)(tfepma)(2)((CNBu)-Bu-t)(2)Cl-4 (7); (2) protonation of 2 with HX yields Ir-2(II)'(II)(tfepma)2((CNBu)-Bu-t)(2)Cl2HX [X = Cl-(8), OTs- (9)]; (3) protonation of 5 with HOTs produces [Rh-2 (I,1) (tfepina)(2)((CNBu)-Bu-t)(3)(mu-H)](OTs); and (4) the reversible hydrogenation of 2 proceeds smoothly, furnishing the cisdihydride complex Ir2II'II(tfepma)(2)((CNBu)-Bu-t)(2)(H)(2)Cl-2 (11). Substitution of tfepma in 2 with bis(diphenylphsophino)methane dppm) yields the orthometalated complex Ir-2(II),(II)(dPPm)(PPh(o-C6H4)CH2PPh2)((CNBu)-Bu-t)(2)Cl2H (12). The X-ray crystal structures of 11 compounds are presented and discussed, and spectroscopic characterization by multinuclear and variable temperature NMR provides details about solution structures and in some cases the formation of isomeric products. The electronic spectra of the new complexes are also described briefly, with absorption and emission features derived from the bimetallic core.