Synthesis, Structure, and Reactivity of Some Sterically Hindered (Silylamino)phosphines

• Published in: Inorganic chemistry Vol. 41; no. 26; pp. 7113 - 7124
• Main Authors: Samuel, Remy C, Kashyap, Ram P, Krawiec, Mariusz, Watson, William H, Neilson, Robert H
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 30-12-2002
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic025951n

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)2NH (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)2NP(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) Å; 7, N−P(Ph)Cl, 1.68(1) Å, 14, N−PF2, 1.652(4) Å] 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) Å and a wide Si−N−P bond angle of 166.4(3)°. A similar PN bond distance [1.514(7) Å] and Si−N−P angle [169.9(6)°] 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) Å, respectively, and a Si−N−P angle of 134.3(2)°.