Silyl Iminophosphoranes

While silyl iminophosphoranes of the type R3P=N-SiRJ can be obtained by the Kirsanov reactions such as (7.459), halogen derivatives can be obtained by reaction 

Silyl iminophosphoranes (N-silylphosphazenes) of the type R3P=NSiR3 (Chapter 9.5) undergo many interesting reactions. Compounds of this type appear to exist in equilibrium with dimers containing 5-coordinated trigonal bipyramidal Si atoms, and with cations based on 4-coordinated Si. 

2Ph3P=NSiMe3 -E 2PhPp4 [Ph3P=N-P(Ph)(F)-N=PPh3]+ PhPFj- -e 2Me3SiF (7.489) 

Me3P=NSiMe3 -E Me2SiF2 Me3P=NSiMe2F -e Me3SiF (7.490) 

Tris phosphazenyl phosphine is obtained by reaction of the methyl derivative with phosphorus trichloride (7.488), and with phenyltetrafluorophosphorane, a tetrahedral cation and an octahedral anion are produced (7.489). With dimethyldifluorosilane fluorination occurs (7.490), but with dimethyldichlorosilane a ring cation is formed (7.491), and with some alcohols the product is phosphinimine (7.461). 

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A recent communication is based on the nucleophilic substitution of N-silylated iminophosphoranes (Scheme 8), where activated chloro- (12) and nitro heterocycles (13) (triazines, pyrazines, and pyridines) are transformed into monosubstituted iminophosphoranes (14). Of special advantage are the mild reaction conditions and the preferential formation of monosubstituted... 

Die paarweise Substitution von Siliciumatomen in den Trisilylaminen (40) durch Al/P-Paare fiihrt theoretisch zu Verbindungen desTyps (41). Diese Formel macht diese zunachst hypothetischen Substanzen sofort als Metallalkylkomplexe der N-Silyl-iminophosphorane kenntlich. In diesem Sinne licBen sich die ersten Vertreter dieser Reihe auch tatsachlich dar-stellen 57> 128> ... 

Silylated iminophosphoranes of the type (42) have been shown to react with SO3 insertion of SO3 into the silazane bond occurs, to give (43). In the case of the bifunctional methylene(bisiminophosphorane) (44), silylated sulphuric acid splits off, and the phosphaza-sulphone (45) is formed. 

Short-chain varieties of silyl iminophosphoranes such as (7.494) can be made [13,14]. 

Fluorophosphoranes and halophosphines usually break Si-N linkages and replace them with P-N, without forming either Si-P or Si-N-P linkages (7.135,7.179,7.256,7.458,7.488,7.489). In the absence of these reagents, however, the grouping P = N-Si is relatively stable (7.490) and (7.529). Some reactions of silyl iminophosphoranes are given in Chapter 7.10. 

Silyl group migration has been observed in the reaction of silyl-substituted aminophosphanes to yield iminophosphoranes 44. A mechanism has been discussed (198, 201). 

Although boron is more accurately described as a metalloid rather than a metal, this section is concluded by two papers that describe the structures and bonding in several organoboron/organophosphorus compounds that display ylidic character. The X-ray structure of 9-borylanthracene (88) shows that only one of the diisopropylphosphine moieties is bonded to the boron in the solid state. However, H NMR evidence shows that an intramolecular bond-switching process takes place very rapidly in solution. The structures of a series of borabenzene adducts of phosphorus ylides, iminophosphoranes and tertiary phosphines have also been determined. Treatment of l-chloro-3,5-dimethyl-2-(trimethylsilyl)-l,2-dihydroborinine (89) with methylenetriphenylphosphorane (90) produces (triphenylphosphonio)methanide-3,5-dimethylborabenzene (91). However, if the reaction sequence is reversed and (90) is treated with (89), then (trimethylsilyl)(triphenylphosphonio)methanide-3,5-dimethylborabenzene (92) is obtained (Scheme 26). Treatment of an isomeric mixture of l-chloro(trimethyl-silyl)dihydroborinines (93) with N-(triphenylphosphoranylidene)aniline (94) produces iV-(triphenylphosphonio)anilide-borabenzene (95) (Scheme 27). Crystal structures of (91), (92) and (95) show that the P-C or P-N bonds are... 

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