Pentachloride pentavalent

There have apparently been no recent developments in reagents for desulphurizing sulphoxides that use pentavalent phosphorus compounds. Reagents that were reviewed in 1984 include phosphorus pentasulphide, thiophosphoryl bromide, Lawesson s reagent (1), and phosphorus pentachloride in the presence of a trap for CD ions. The traps used included an enamine or an N, JV-dialkylaniline. Presumably, the net effect of this reaction is to generate phosphorus trichloride in situ. The three thiophosphorus reagents obviously function because the P=S bond is some 150 kJ moD weaker than the P=0 bond . 

The pentavalent halides are the most stable, but even these can be prepared only in the dry way because of the readiness with which they undergo hydrolysis. The trichloride is obtained by reduction of the pentachloride with a powdered metal (lead, aluminium, zinc) the same process has also given a dichloride and perhaps a tetrachloride, but their formation awaits independent confirmation. The preparation of the chloroadi, HTasCl7.4H20, is of interest in that corresponding... 

Among die best known simple pentavalent tungsten compounds are the pentachloride, WOE. and the pentabromide, WBr . As is true of tungsten(IV), tungsten(V) forms complexes. 

A number of pentavalent trispyrazolylborate derivatives (see Tris(pyrazolyl)borates) have been reported, especially for niobium. Most of them are monomeric Tp MCl2X (X = O, NR) derivatives, jj and jj -pyrazolato (16) or 1,2,4-triazolato derivatives have been prepared as potential sources of nitrides for CVD. The reactions between dilithium l,4-diaza-l,3-diene and pentachlorides have been investigated. ... 

An alternative, reasonably satisfactory route to the pentachloride involves heating Pa206/C mixtures at 500°-600°C in a sealed tube containing carbon tetrachloride saturated with chlorine (47). It was this method of preparation which led to the characterization of the first pentavalent oxychloride, Pa20Cl8, the a-form of which is always produced together with the pentachloride under such conditions. The pentachloride is readily separated from Pa20Cl8 by vacuum sublimation at 180°-200°C. 

Formally, pentavalent neutral metallocorroles have been prepared by Murakami and coworkers.The first of these was the oxomolybdenum(V) corrole derivative 2.179. ° This complex was prepared by heating free-base corrole 2.82 with molybdenum pentachloride in oxygen-free decalin (Scheme 2.1.56). Alternatively, molybdenum hexacarbonyl (Mo(CO)e) could be used as the metal source. In both cases, oxidation to the oxomolybdenum complex 2.179 was believed to occur during workup (involving chromatography on neutral alumina followed by recrystallization). In this way, complex 2.179 was isolated in c. 40% yield. Similar yields of the oxochromium(V) complex 2.180 could be achieved via the reaction of 2.82 with anhydrous chromium(II) chloride in DMF. Here too, spontaneous oxidation during workup was used to afford the formally pentavalent oxo-complex 2.180. 

Phosphorus pentachloride probably cleaves As—C bonds by a related reaction involving formation of pentavalent intermediates (241, 242)... 

Sulfonyl chlorides are highly reactive derivatives of sulfonic acid and possess similar properties and reactivity to acid chlorides of carbo Q lates. The reaction with nucleophiles such as amines requires alkaline conditions (pH 9-10) and proceeds through the formation of an unstable pentavalent transition state (Scheme 1.10). Hydrolysis is a major competing reaction in water therefore the reaction with amines proceeds with better yield when done in organic solvents. Sulfonyl chlorides have played an important role in bioconjugation chemistry, since sulfonic acids can be easily converted into sulfonyl chlorides using thionyl chloride or phosphorus pentachloride in non-aqueous conditions. ... 

The pyramidal structure of phosphorus trichloride, PCI3 typifies trivalent phosphorus compounds, while tetrahedral phosphoryl chloride, POCI3, the ions PCIJ and PO together with trigonal bipyramidal phosphorus pentachloride, PCI5, typify the spatial arrangements adopted by pentavalent phosphorus compounds. The hexachloro-phosphate (hexachlorophosphoride) anion. 

The trihalides PnX3 are well established for all pnictogen/halogen combinations. The pentafluorides are known for P through Bi and the pentachlorides for P through Sb. The pentabromides and pentaiodides generally do not exist, at least not as molecular compounds. These facts provide a nice illustration of the decreasing stability of the pentavalent state from phosphorus downward. 

Information on the carbonyl chemistry of niobium and tantalum is, to date, very meager. The main difficulty appears to be the reduction of the usual pentavalent derivatives of these metals to the very low formal oxidation states of metal carbonyl derivatives. Nevertheless, the yellow anions [M(C0)6] (M = Nb, Ta) have been obtained by a method analogous to, but more difficult than, one of the preparations of the [VCCO) ]" anion. The method involves reduction of the pentachlorides with sodium metal in diglyme in the presence of high pressures of carbon monoxide (63). The niobium and tantalum derivatives are much more air-sensitive than the analogous vanadium derivative. The niobium derivative has not yet been obtained analytically pure (63). No chemistry of the [Nb(CO)J and the [Ta(CO)6] ions has been reported, even conversion to the neutral carbonyl derivatives [M(CO) (M = Nb or Ta = 1 or 2) or to the carbonyl hydride derivatives HM(CO)6 (M = Nb, Ta) still presenting unsolved problems. 

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