N,N‘,N‘-[Tris(trimethylsilyl)]hydrazino-diphenylphosphane, (TMS)2N−(TMS)N−PPh2 (1), and N,N‘,N‘-[tris(trimethylsilyl)]hydrazino-phenyl(chloro)phosphane, (TMS)2N−(TMS)N−P(Cl)Ph2 (2), were obtained in the reaction of bis-[lithium-tris(trimethylsilyl)hydrazide] with PhnPCl3 - n (n = 1, 2). The structure and bonding of both species are discussed on the basis of experimentally observed (X-ray, Raman, NMR, and MS) and theoretically obtained data (B3LYP/6-31G(d,p), NBO analysis). Oxidation with sulfur and selenium results in the formation of (TMS)2N−(TMS)N−P(S)Ph2 (4), (TMS)2N−(TMS)N−P(Se)Ph2 (5), (TMS)2N−(TMS)N−P(S)Ph(Cl) (6), and (TMS)2N−(TMS)N−P(Se)Ph(Cl) (7). Moreover, the thermal decomposition of N,N‘,N‘-[tris(trimethylsilyl)]hydrazine-dichlorophosphane, (TMS)2N−(TMS)N−PCl2 (3) and the reaction with magnesium have been investigated. The formation and molecular structure of the novel MgCl2(THF)2·2Mg[(TMS)NP(O)2N(TMS)2](THF) (8) salt containing the hitherto unknown (TMS)NP(O)2N(TMS)22− anion are discussed. DFT calculations (B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d,p)) are used to evaluate the bonding, ground-state structures, and energy landscape for the different isomers of 3:  the thermodynamics and kinetics of the successive elimination of chlorotrimethylsilane (TMS−Cl) resulting in the formation of covalent azide analogues such as TMS−PNN or TMS−NNP.