1,3,5-Triphospha-1,4-pentadiene-2,4-diamine reacts with [M(CO)(4)L] (M = Mo, L = nbd (norbornadiene); M = W, L = 2 CH3CN) to give the chelate complexes [M(CO)(4)(PMes{C(NHCy)PMes}(2)-kappa P-1,P-3)]. In contrast, an unusual intramolecular rearrangement occurred with [Cu(CH3CN)(4)]PF6 leading to the dimeric copper(I) complex [ Cu (CNCy) {PHMesPMesC (NHCy)PMes-kappa P-1,P-3}](2)(PF6)(2). The mechanism of the rearrangement was supported by quantum-mechanical calculations. The transition-metal complexes were characterized by multinuclear NMR spectroscopy, mass spectrometry, infrared spectroscopy, and X-ray crystallography.