Silyl phosphanes

The reaction of Me jCPCSiMe 3) j with phosgene occurs with the elimination of Me3SlCl and CO, and the formation via several detectable intermediates) of a cyclic phospha-urea derivative, (10.31), as illustrated in the following scheme [71]  

The heterocycle (10.31) may also be formed by the reaction of phosgene with the tetraphosphorus compound depicted below [71]  

Treatment of Me3SiP=C(OSiMe3)(CMe3) with COCI, gave an unexpected reaction product, a diphosphacyclobutene, (10.32) [70]  

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The transmetalation of trimethylsilylphosphanes with germanium and tin halides is a useful way to prepare compounds with P—Ge and P—Sn bonds by simple chlorosilane elimination. The reverse reaction, i. e. formation of P—Si bonds by chlorosilane cleavage of germyl- and stannylphosphanes has not yet been reported. Recently, we observed that hexachlorodisilane "transsilylates di-r-butyl(trimethyl-silyl)phosphane 1 much faster than tetrachlorosilane to give trichlorosilylphosphane 2 ... 

The 1,4-diphospha-l,3-butadienes are suitable as ligands for cr-coordi-nated complexes with transition metals. Attempts to carry out pericy-clic reactions with maleinic anhydride, acetylene dicarboxylate esters, dimethylbutadiene, or cyclopentadiene failed, but Diels-Alder reactions with norbornadienes were successful (94). Earlier attempts to synthesize 1,4-diphosphabuta-l,3-dienes with oxalychloride and phenyl-bis(silyl)phosphane proceeded via ring closure [Eq. (42)] (89), where R = Ph (a) or [Pg.285]

By pyrolysis of a mixture of hydrogen phosphide and silicon hydride, it was Fritz [1] who first succeeded in the preparation of a simple compound with an Si-P bond. About forty years ago, neither the author nor his colleagues anticipated that the silyl phosphane H3S1-PH2 would become the parent compound of a widely used class of starting materials. On the contrary, silylphosphanes remained peculiarities imtil a convenient synthesis of the tris(trimethylsilyl) derivative (Me3Si)3P had been developed [2]. 

Table 1. p and Si-NMR shifts and coupling constants jp si of the bis(trichloro-silyl)phosphanes. 

MePHSiH3 methyl(silyl)phosphane, not (methylphosphanyl)silane or (silylphosphanyl)methane... 

Carboxylic acid chlorides reacted with (2,3-di-terr-butylcycloprop-2-enylidene)(trimethyl-silyl)phosphane in diethyl ether to give acylphosphatriafulvenes 1 in ca. 50% yield. ... 

Two new silyl phosphanes, (Me3Si)3P7 and (Me3Si)4Pi4, can be isolated from the products of the reaction between white phosphorus and trimethylchlorosilane in the presence of Na-K alloy at ca. 80 The P7 species forms colourless crystals that are readily decomposed by oxygen but stable to ca. 300 °C in the absence of air the P14 compound is isolated as a yellow powder which decomposes at ca. 210 °C. 

Fig. 14. Contour plot of the 2D 120 MHz P/ H HETCOR experiment for tris(tri-methyl-silyl)phosphane, P(SiMc3)3, in C5D5. The experiment was modified by using a z-filter in order to suppress most of the intensity of the central signal. This allows to observe the satellite signals almost undisturbed. The path of PT is indicated for each isotopomer. The active spins are P and in each case, and the passive spin is either Si or C. In the case of Si, there are two types of pairs of cross peaks for Si satellites shown. The pair with lower intensity has a significant positive tilt which means that A i( P, Si) and Al( Si, HMe) have alike signs. Since 2 ( Si, HMe)<0, it holds that A ( P, Si) < 0 ( J( P,2 Si)>0 ). The pair of crosspeaks with higher intensity results from PT across magnetically non-active silicon isotopes, and there is no tUt because of the small magnitude of Al( Si,P,Si,C, H). A very small tilt is indicated for C satellites. (B. Wrackmeyer and U. Klaus, unpublished results).

Triisopropylsilylamine (la) [1], -phosphane (lb) [2] and -arsane (Ic) are easily accessible by the metathesis reaction of alkali metal amide, phosphanide [3] and arsanide [4], respectively, with chlorotriisopropylsilane according to Eq. 1. Redistribution reactions were not observed. The sterically less demanding trimethylsilylphosphane (2) is prepared by protolysis of tris(trimethyl-silyl)phosphane with methanol [5]. 

Reeently, condensation polymerization has been used for preparing poly(p-phenylene phosphaalkene) which contains P=C double bonds in the polymeric backbone. Thus, the reaction between the silylated phosphane, (Me3Si)2P-C6H4-p-P(SiMe3)2 and a diacid chloride affords an E/Z mixture of poly(p-phenylene phosphaalkene) [37]. 

In 1987, a new class of phosphorus heterocyclic compounds was developed by Cowley and coworkers, incorporating keto groups within various phosphorus-containing rings [37]. At the time, only the synthesis of these compounds was reported via reaction between a silylated phosphane and an acyl chloride (Scheme 12.7). More recently, we developed the diketophosphepin as a multifunctional material involving the seven-membered phosphorus ring (28a-d Figure 12.19)... 

The fe-ester derivatives of trithiophosphinic acids, RP(S)(SR )2, have also been studied and, similar to the metal and ammonium salts, show enhanced thermal stability compared to their parent acids. Trithiophosphonic acid Zj zA (tr im e t lr y 1 s i 1 y 1) esters have been synthesised from organo-/u.v(trim-ethylsilyl)phosphanes with elemental sulfur in toluene (Equation 40).53 These 6z,s(silyl esters) can be readily converted into the parent trithiophosphinic acid by a very slow, controlled reaction with water or methanol.53... 

Dilithiated primary phosphanes could only be isolated in a reproducible crystalline form if the lithiation of the phosphane with BuLi (ratio of 1 2) in toluene was carried out in the presence of a trace amount of LiOH (3). This is evident by the respective transformation of the silylphosphanes 1, which furnished, depending on the steric demand of the silyl group, a dodecameric or a octameric associate (Scheme 1). Thus, reaction of la with BuLi in the molar ratio of 1 2 led to the globular, Li20-filled cluster 5a, whereas metalation of the bulkier substituted phosphane lb gave the Li20-filled octamer 5b. 

In contrast, the same reaction between the bulkily substituted silyl-(fluorosilyl)phosphane le with NaN(SiMe3)2 underwent, surprisingly, a different, course (Scheme 2). Its transformation in the molar ratio of 1 1 in toluene as solvent furnished the dimer 13, whereas Id can only be completely converted to 13 if 2 molar equiv sodium amide have been employed, because of the initial formation of heteroaggregate intermediates (26). Excess of sodium amide has been recovered by... 

Hydrolysis of 14 gives the secondary silyl(fluorosilyl)phosphane le, with evolution of H2. 

Treatment of propyne iminium triflate 258 with silylated phosphorus nucleophiles such as Me3SiPPhR affords (3-morpholinoallenyl)phosphanes 259 in high yield (Scheme 8.69) [150]. 

When phosphaalkynes are exposed to bis- and tris(diazo) compounds, bis- or tris(l,2,4-diazaphosphol-5-yl) compounds are formed that may be further converted into a variety of novel heterocyclic systems. For example, bis- and tris[diazo(tri-methylsilyl)methyl]phosphanes 237 and 240 afforded bis- and tris(diazaphospho-lyl)phosphanes 238 and 241 after cycloaddition with terf-butylphosphaacetylene followed by a subsequent 1,5-silyl shift (Scheme 8.56) (300). Reaction with electrophilic halides at the Wsilyl functions allows the introduction of a heteroatom bridge between the diazaphosphole ring leading to polycyclic ring systems such as 239 and 242. 

The most convenient substrates for fluorination with tetrafluoro(phenyl)-25-phosphane are silyl ethers of alcohols 7.13 17 The trimethylsilylation of alcohols with chlorotrimethylsilane in the presence of pyridine is generally quantitative. 

In contrast to substitution reactions of lithium salts of OMCTS with fluoroboranes, -phosphanes and -silanes no mono- or disubstituted OMCTS with a triorganylsilyl group is known. According to chemical experiments, the anion of the OMCTS contracts in reactions with Me3SiCl and forms a silyl-substituted six-membered-ring isomer 20,31,56 58,60 (Scheme 29). 

The inverted process, however, of transforming 1,6-diphosphahexa-1,5-diene b into 3,4-diphosphahexadiene or divinyl diphosphane proceeds under very mild conditions [Eq. (51)]. The diphosphide, prepared from succinylchloride and phenylbis(trimethylsilyl)phosphane between —70 and — 80°C, rearranges after silyl migration above 0°C, forming the spectroscopically detectable 1,6-diphosphahexadiene intermediate, and finally ending up with the divinyl diphosphane via a [3.3] sigmatropic bond shift (101). 

The conversion of silyl ethers into fluorides may serve as an indirect method for the conversion of hydroxy compounds into fluorides, but in some cases the silyl ethers are not formed from the corresponding alcohols and then a step is saved by direct conversion into the fluorides. Two classes of fluorinating reagents have been used so far to transform silyl ethers into fluorides these are nuoro-A -phosphanes, which were used first, and fluoro-/, -suIfanes. 

The ability of fluoro-2 -phosphanes to transform silyl ethers into fluorides was first observed during a study of the reactions of phosphorus pentafluoride and its derivatives R PF5 (n = 1, 2, 3 R = hydrocarbon group) with trimethylsilyl ethers. Subsequently, this reaction was proposed as a new method for the preparation of C-F compounds from silyl ethers or silicic acid esters with fluoro-A -phosphanes. Pentafluorophenyl-substituted fluoro-A -phos-phanes were found to react similarily, Other workers found that tctrafluoro(phenyl)-A -phos-phane. which was chosen as the most convenient reagent with regard to reactivity and stability, gave considerable amounts of elimination products, especially with primary and cyclic alcohols. Good yields of fluorinated products are obtained when stable carbocations can be formed at the site of substitution, such as in tertiary alcohols, but 2-phcnylethanol. benzyl alcohol and diphcnylmethanol, on the other hand, give only poor yields of fluorinated products ethers and polymers are the main products. ... 

The mechanism of the formation of organic fluorides from silyl etliers and fluoro-/. -phosphanes has been studied in some detail for tetrafluoro(phcnyl)-A -phosphane. The first step, which is usually quantitative at low temperatures, is the formation of an intermediate alkoxyfluoro-A -phosphane 1 and fluorotrimethylsilanc. 

However, silyl ethers with very strong electron-withdrawing substituents, such as trichloro-methyl or trifluoromethyl, in the -position give stable alkoxyfluoro-A -phosphanes, which cannot be cleaved to the fluorinated products. ... 

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