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Abstract

The title compound (1) was obtained by salt-metathesis reaction of iPr 3 SiPLi 2 with two molar equiv. of iPr 3 SiOTf (OTf = OSO 2 CF 3 ) in 34% yield. Surprisingly, (1) consists of an 4 : 1 mixture of the two diastereomers (1 a) and (1 b), which do not interconvert to each other even at their decomposition temperature (> 70°C). They represent different iPr-rotational isomers which are separated by an unusual high rotational barrier (> 25 kcal mol ±1 ), resulting from hindered rotations around the Si±C and C±C bonds. The unexpectedly small magnitude of the 1 J(Si, P) coupling constant of (1 a) (9.4 Hz) and (1 b) (9.0 Hz) reflects unusual electronic properties of the Si 3 P skeleton. Hitherto only (1 a) could be isolated in the form of single-crystals and its structure was determined by X-ray diffraction analysis. The Patom in (1 a) is almost planar coordinated (sum of bond angles = 359.789(3)°), but the Si±P-distance (2.264(7) A Ê ) resembles those values of related silylphosphanes with pyramidally coordinated P atoms. Although MNDO calculations revealed two other iPr-rotational isomers with similar energy, they prove that the Si 3 P skeleton prefers the trigonal-planar arrangement due to steric congestion. P(SiiPr 3 ) 3 : Das erste Trisilylphosphanderivat mit einem fast planar dreifachkoordinierten PhosphoratomInhaltsu È bersicht. Die Titelverbindung (1) wurde durch Salzmetathesereaktion von iPr 3 SiPLi 2 mit zwei Mola È quivalent iPr 3 SiOTf (OTf = OSO 2 CF 3 ) in 34% Ausbeute erhalten. Ûberraschenderweise besteht (1) aus einer 4 : 1 Mischung der zwei Diastereomere (1 a) und (1 b), die sich auch bis zu ihrer Zersetzungstemperatur (70°C) nicht ineinander umwandeln. Sie repra È sentieren verschiedene iPr-Rotamere, die durch eine ungewo È hnlich hohe Rotationsbarriere (> 25 kcalḿ ol ±1 ) voneinander getrennt sind und die von gehinderten Rotationen um die Si±C-und C±C-Bindungen herru È hren. Der unerwartet kleine Betrag der 1 J(Si, P)-Kopplungskonstante von (1 a) (9.4 Hz) und (1 b) (9.0 Hz) spiegelt die unge-wo È hnlichen elektronischen Eigenschaften des Si 3 P-Geru È sts wider. Bisher konnte nur (1 a) in einkristalliner Form isoliert werden, und seine Struktur wurde durch Ro È ntgenbeugungsanalyse bestimmt. Das P-Atom in (1 a) ist anna È hernd planar koordiniert (Summe der Bindungswinkel = 359.789(3)°), aber der Si±P-Abstand (2.264(7) A Ê ) gleicht den Werten von verwandten Silylphosphanen mit pyramidal-koordinierten P-Atomen. Obwohl MNDO-Berechnungen zwei andere Rotamere ergaben, beweisen sie, dass das Si 3 P-Geru È st die trigonal-planare Anordnung wegen der sterischen Ûberladung bevorzugt.

Tetraphosphanylsilane - A Mild PH2-Transfer Reagent and Building Block for the Synthesis of a Rhombododecahedral Li6P6Si2-Cluster Framework

“…However, non-basic and mild PH 2 transfer reagents are still relatively rare. One of the classical and appropriate PH 2 transfer reagents represents the lithium salt of the Al(PH 2 ) 4 ± complex anion [1] which is suitable for the synthesis of organotriphosphanylsilanes RSi(PH 2 ) 3 [2], Si(PH 2 ) 4 (1) and Ge(PH 2 ) 4 [3]; the latter are accessible from the corresponding chlorosilanes and germanes, respectively. However, the use of LiAl(PH 2 ) 4 , which is only preserved in etheral solutions, is strongly limited due to its thermal lability and aggregation processes between the products and the final lithium salts (LiAlX 4 ) from which the isolation of the products is difficult.…”

“…Reaction of the PH 2 -transfer reagent Si(PH 2 ) 4 (1) with SiCl 4 affords a mixture of the Cl n Si(PH 2 ) 4±n compounds (2 a, n = 1), (2 b, n = 2), and (2 c, n = 3) which were characterized by 1 H-31 P-COSY NMR spectroscopy. The formation of (2 a) is drastically accelerated by using GeCl 4 instead of SiCl 4 as PH 2 acceptor, but a stable molecular GeCl 4±n (PH 2 ) n containing product could not be obtained.…”

“…Lithiation of 1 with four molar equiv. of LiNiPr 2 in THF/Et 2 O at ±80°C, surprisingly, leads to insoluble Si(PHLi) 4 (8 a) which was tetrasilylated with iPr 3 SiOSO 2 CF 3 , affording the tetrakis(triisopropylsilylphosphaneyl)silane (8 b). However, attempts to achieve the tetralithiation of the P atoms in 8 b through reaction with four molar equiv.…”

“…Reaktion des PH 2 -Transferreagenz Si(PH 2 ) 4 (1) mit SiCl 4 ergibt eine Mischung der Cl n Si(PH 2 ) 4±n Verbindungen (2 a, n = 1), (2 b, n = 2), and (2 c, n = 3), die durch 1 H-31 P-COSY-NMR-Spektroskopie charakterisiert wurden. Die Bildung von 2 a ist drastisch beschleunigt durch den Einsatz von GeCl 4 statt SiCl 4 als PH 2 -Acceptor, aber ein stabiles, molekulares GeCl 4±n (PH 2 ) n -enthaltendes Produkt konnte nicht erhalten werden.…”

“…However, the use of LiAl(PH 2 ) 4 , which is only preserved in etheral solutions, is strongly limited due to its thermal lability and aggregation processes between the products and the final lithium salts (LiAlX 4 ) from which the isolation of the products is difficult. As we have shown recently, the salt-free molecular iBuAl 2 PH 2 , which is readily and quantitatively formed by conversion of iBu 2 AlH with PH 3 , represents a true alternative to LiAl(PH 2 ) 4 , since it retains also in unpolar solvents like toluene and acts, in the presence of a small amount THF, as a highly efficient PH 2 transfer reagent toward chlorosilanes [4]. Thus the reaction of SiCl 4 with iBu 2 AlPH 2 furnishes the tetraphosphanylsilane (1) after fractional condensation in 80% yield, whereas the analogous phosphanylation of RSiCl 3 compounds leads to the respective RSi(PH 2 ) 3 derivatives in larger than 80% yield.…”