A series of new (silylamino)phosphines that contain sterically bulky silyl groups on nitrogen were prepared by deprotonation/substitution reactions of the hindered disilylamines t-BuR2Si(Me3Si)NH (1, R = Me; 2, R = Ph) and (Et3Si)(2)NH (3). Sequential treatment of the N-lithio derivatives of 1-3 with PCl3 or PhPCl2 and MeLi gave the corresponding (silylamino)phosphines t-BuR2Si(Me3Si)NP(R')Me (5, R = Me, R' = Ph; 6, R = Ph, R' = Me) and (Et3Si)(2)NP(R)Me (11, R = Me; 12, R = Ph) in high yields. Two of the P-chloro intermediates t-BuR2Si(Me3Si)NP(Ph)Cl (7, R = Ph; 9, R = Me) were also isolated and fully characterized. Hydrolysis of 7 afforded the crystalline PH-substituted aminophosphine oxide t-BuPh2SiN(H)P(Ph)(=O)H (10). Thermal decomposition of 7 occurred with elimination of Me3SiCl and formation of a novel P2N2 four-membered ring system (36) that contains both P(III) and P(V) centers. Reactions of the N-lithio derivatives of amines 1 and 2 with phosphorus trihalides afforded the thermally stable -PF2 derivatives t-BuR2Si(Me3Si)NPF2 (13, R = Me; 14, R = Ph) and the unstable -PCl2 analogue 17 (R = Ph). Reduction (using LiAlH4) of the SiPh-substituted dihalophosphines 14 and 17 gave the unstable parent phosphine t-BuPh2Si(Me3Si)NPH2 (15). The P-organo-substituted (silylamino)phosphines underwent oxidative bromination to afford high yields of the corresponding N-silyl-P-bromophosphoranimines t-BuR2SiN=P(R')(Me)Br (18, R = R' = Me; 19, R = Me, R' = Ph; 20, R = Ph, R' = Me) and Et3SiN=P(R)(Me)Br (23, R = Me; 24, R = Ph). Subsequent treatment of these reactive PBr compounds with lithium trifluoroethoxide or phenoxide produced the corresponding PO derivatives t-BuR2SiN=P(R')(Me)OR" (25 and 26, R" = CH2CF3; 28-30, R" = Ph) and Et3SiN=P(R)(Me)OR' (31 and 33, R' = CH2CF3; 32 and 34, R = Ph), respectively. Many of the new compounds containing the bulky tert-butyldiphenylsilyl group, t-BuPh2Si, were solids that gave crystals suitable for X-ray diffraction studies. Consequently, the crystal structures of three (silylamino)phosphines (6, 7, and 14), one (silylamino)phosphine oxide (10), one N-silylphosphoranimine (30), and the cyclic compound 36 were determined. Among the (silylamino)phosphines, the P-N bond distances [6, N-PMe2, 1.725(3) Angstrom; 7, N-P(Ph)Cl, 1.68(1) Angstrom, 14, N-PF2, 1.652(4) Angstrom] decreased significantly as the electron-withdrawing nature of the phosphorus substituents increased. The N-silylphosphoranimine t-BuPh2SiN=PMe2OPh (30), which is a model system for poly(phosphazene) precursors, had a much shorter P=N distance of 1.512(6) Angstrom and a wide Si-N-P bond angle of 166.4(3)(0). A similar P=N bond distance [1.514(7) Angstrom] and Si-N-P angle [169.9(6)(0)] were observed for the exocyclic P=N-Si linkage in the ring compound 36, while the phosphine oxide 10 had P-N and P=O distances of 1.637(4) and 1.496(3) Angstrom, respectively, and a Si-N-P angle of 134.3(2)(0).