The reaction of the chalcogen-substituted diazenes trans-[PhEN(4-CH3C6H4)CN=NC(4-CH3C6H4)NEPh] (E = S, Se) with Pd(PPh3)4 or Pt(C2H4)(PPh3)2 in toluene produces the complexes M[PhEN(4-CH3C6H4)CN-NC-(4-CH3C6H4)NEPh](PPH3) (2a, M = Pd, E = S; 2b, M = Pt, E = S; 2c, M = Pd, E = Se; 2d, M = Pt, E = Se). The H-1 NMR spectra of 2a-d show two singlets at 2.26-2.29 and 2.35-2.39 ppm for the 4-CH3 protons, and the Se-77 NMR spectrum of 2c exhibits two equally intense singlets at 872 and 882 ppm. The P-31{H-1} NMR spectra exhibit a singlet at 25-26 ppm for 2a and 2c and at 19-20 ppm [1J(P-31-Pt-195) = 3610-3630 Hz] for 2b and 2d. X-ray structural determinations have revealed that the coordination sites of the approximately square planar metal complexes 2a-d are occupied by a single PPh3 molecule and a tridentate (N, N, E) ligand. The N-N bond distances in these complexes are 1.40-1.42 angstrom, indicating formal reduction of the diazene to an azine. Crystals of 2c are monoclinic, P2(1)/c, with a = 14.354(1) angstrom, b = 19.007(3) angstrom, c = 16.157(2) angstrom, beta = 104.92(1)degrees, V = 4259(1) angstrom3, Z = 4, R = 0.040, and R(w) = 0.024. Crystals of 2d are monoclinic, P2(1)/c, with a = 14.410(3) angstrom, b = 19.003(3) angstrom, c = 16.169(2) angstrom, beta = 105.72(1)degrees, V = 4261(1) angstrom3, Z = 4, R = 0.040, R(w) = 0.025. The FAB mass spectra for the sulfur complexes 2a and 2b show a strong molecular ion peak whereas this peak either is absent (2c) or is of low intensity (2d) for the selenium complexes. The complexes 2a and 2b undergo reversible one-electron oxidations at ca. 0.65 V vs SCE, but the oxidation product has a lifetime of only a few seconds.