Phosphinimido Complexes of Silicon, Tin, and Germanium

Abstract

The preparation of a silyl−phosphinimide of the form (R3PN)SiMe3 (R = Me (1), i-Pr (2), Ph (3), t-Bu (4)) was achieved by the conventional literature methodology of oxidation of phosphine by N3SiMe3. The analogous species (t-Bu3PN)MMe3 (M = Ge (5), Sn (6)) were derived via a stoichiometric reaction of the salt Li[NP-t-Bu3] with Me3MCl. Similarly, the species (t-Bu3PN)2MMe2 (M = Si (7), Ge (8), Sn (9)), (i-Pr3PN)SnMe3 (10), (i-Pr3PN)2SnMe2 (11), and (t-Bu3PN)2SnMeCl (12) were prepared. Subsequent reactions of 12 afforded (t-Bu3PN)3SnMe (13) and (t-Bu3PN)2Sn(Ot-Bu)Me (14). In analogous metathesis reactions R3PNSnPh3 (R = t-Bu (15), i-Pr (16)), (t-Bu3PN)2SnPh2 (17), and (t-Bu3PN)2Sn(t-Bu)2 (18) were also prepared. Reaction of i-Pr3PNH and ClSnMe3 gave (i-Pr3PNH)SnMe3Cl (19), whereas 6 was obtained from the reaction of t-Bu3PNH with Me3SnCl. The reaction of 1 with B(C6F5)3 resulted in the formation of Me3PN(SiMe3)B(C6F5)3 (20), whereas the phosphinimines 2 and 3 react with B(C6F5)3 in a 2:1 ratio to give [R3PNSiMe2(N(PR3)SiMe3)][MeB(C6F5)3] (R = i-Pr (21), Ph (22)). In contrast, reaction of 4 and 6 with B(C6F5)3 afforded [((μ-t-Bu3PN)MMe2)2][MeB(C6F5)3]2 (M = Si (23), Sn (24)). The analogous reaction of 7 and 9 with B(C6F5)3 gave products formulated as [((t-Bu3PN)2MMe)2][MeB(C6F5)3]2 (M = Si (25), Sn (26)) and [((i-Pr3PN)2SnMe)2][MeB(C6F5)3]2 (27). Complexes 7−9, 17, 19, 20, and 24 were characterized crystallographically. The implications of this chemistry with regard to the steric demands of phosphinimide ligands are considered.

Facile Access to Stable Silylium Ions Stabilized by N-Heterocyclic Imines

“…A signal was observed in the 29 Si-NMR spectrum at δ = 17.3 ppm, which is significant low-field shifted compared to that of the precursor 1 (−22.3) [37]. This value is very similar to that of phosphinoimino complex of the silylium ion (δ( 29 Si) = 7.9 ppm) [36], illustrating the existence of dimer 2[MeB(C6F5)3]2 in solution. The calculated chemical shift of optimized structure of 2 (8.1 ppm) corresponds well with the experimental value, supporting the presence of dimeric structure with a tetracoordinate silicon environment in 2[MeB(C6F5)3]2.…”

“…A signal was observed in the 29 Si-NMR spectrum at δ = 17.3 ppm, which is significant low-field shifted compared to that of the precursor 1 (−22.3) [37]. This value is very similar to that of phosphinoimino complex of the silylium ion (δ( 29 Si) = 7.9 ppm) [36], illustrating the existence of dimer 2[MeB(C 6 Herein we describe the facile synthesis of novel imino-substituted silylium ions by the abstraction of methyl group of the trimethylsilyl ligand. Moreover, base-coordinated silylium ion was also prepared by treatment of Me2(OTf)SiNIPr with DMAP by expelling the OTf anion.…”

“…A signal was observed in the 29 Si-NMR spectrum at δ = 17.3 ppm, which is significant low-field shifted compared to that of the precursor 1 (−22.3) [37]. This value is very similar to that of phosphinoimino complex of the silylium ion (δ( 29 Si) = 7.9 ppm) [36] In order to gain deeper insight into the electronic nature of the structure of 2, we performed a Natural Resonance Theory (NRT) analysis. Evaluation of the relative contributions of all important canonical forms for compound 2 shows that the imino-coordinated silylium ion formulation A1 (78.9%) is dominant (Scheme 3).…”

“…Motivated by this report and from the view point of their isoelectronic nature to silylium ions, iminosilylium ions would be an interesting synthetic target. It is noteworthy that the syntheses of phosphinoimido complexes of silylium ions were described by Stephan and co-workers and they exist as a dimer VII or a phosphinoimido-coordinated monomer VIII depending on the steric crowding of the substituents (tBu vs. iPr and Ph) (Scheme 1) [36]. Selected group silylium ions I and II and metallyliumylidenes III and IV as well as bis(imino)stannylenoid V. Dichloroiminoborane VI and its canonical structure VI'.…”

“…It is noteworthy that the syntheses of phosphinoimido complexes of silylium ions were described by Stephan and co-workers and they exist as a dimer VII or a phosphinoimido-coordinated monomer VIII depending on the steric crowding of the substituents (tBu vs. iPr and Ph) (Scheme 1) [36]. Tamm and co-workers developed a facile synthetic method for imidazolin-2-imino ligands and reported a number of metal complexes with these ligands [24][25][26][27].…”