Metals pentavalent, complexes

Phosphoms haUdes and metals or metal salts form addition complexes. Some typical compounds are PCl iSbCl and PCl iAlCl. The trivalent complexes contain metal—phosphoms bonds. The pentavalent complexes involve rearrangements to produce assembles of tetrahedral PX cations and various anions. 

Figure 65. Structural variety in tri-, tetra-, and pentavalent metal(loid) complexes of aliphatic diols.

Oxidation of trifluorophosphine by halogens is well known (282) and although corresponding reactions with alkyl or aryl fluorophosphines have received only little attention, it has become apparent that oxidation to the pentavalent phosphorus fluorides can be brought about by a wide variety of reagents. In certain cases the reducing property of the fluoro-phosphine has been utilized in the synthesis of zero-valent transition metal fluorophosphine complexes (Section IX). 

Trivalent and pentavalent phosphorus halides will form addition complexes with metals or metal salts. While the trivalent complexes contain metal-phosphorus bonds (Chapter 8), the pentavalent complexes involve rearrangements to produce ionised assemblies of tetrahedral PX4 cations and various complex anions. 

Rhenium Halides and Halide Complexes. Rhenium reacts with chlorine at ca 600°C to produce rheniumpentachloride [39368-69-9], Re2Cl2Q, a volatile species that is dimeric via bridging hahde groups. Rhenium reacts with elemental bromine in a similar fashion, but the metal is unreactive toward iodine. The compounds ReCl, ReBr [36753-03-4], and Rel [59301-47-2] can be prepared by careful evaporation of a solution of HReO and HX. Substantiation in a modem laboratory would be desirable. Lower oxidation state hahdes (Re X ) are also prepared from the pentavalent or tetravalent compounds by thermal decomposition or chemical reduction. 

Physical properties of binary or ternary Ru/Ir based mixed oxides with valve metal additions is still a field which deserves further research. The complexity of this matter has been demonstrated by Triggs [49] on (Ru,Ti)Ox who has shown, using XPS and other techniques (UPS, Mossbauer, Absorption, Conductivity), that Ru in TiOz (Ti rich phase) adopts different valence states depending on the environment. Possible donors or acceptors are compensated by Ru in the respective valence state. Trivalent donors are compensated by Ru5+, pentavalent acceptors will be compensated by Ru3+ or even Ru2+. In pure TiOz ruthenium adopts the tetravalent state. The surface composition of the titanium rich phase (2% Ru) was found to be identical to the nominal composition. 

Figure 9. Simplified model of the (111) surface of the corundum-type structure, (a) A view of the surface from a direction slightly shifted from <111>. Only metal ions of the zeroth, first, and second layers are shown, (b) A section of the surface along the arrows depicted in part a. Hexagonally close-packed oxide ion layers are shown with lines. Surface protons are not shown, (c) A divalent Co-57 or pentavalent Sb-119 ion on the zeroth metal ion layer, (d) Aquo or hydroxyl complex of divalent Co-57 or pentavalent Sb-119 hydrogen-bonded to the surface oxide ion layers of hematite.

In decomposition reactions of dimethyl-metal complexes of palladium(II) and nickel (II) one finds the formation of only traces of methane [49] which may also attributed to an a-elimination process. In regard to the valence state, note that, formally, the alkylidene ligand is considered as a neutral ligand and therefore, in the tantalum-alkylidene complex in Fig. 4.29, tantalum is trivalent. The electronic structure of the alkylidene is of course reminiscent of the corresponding oxide CpTa(Cl)20, which we would definitely call pentavalent. All that matters is that there should be a sufficient number of electrons for the multiple bonds which we draw. 

While they form few complexes with simple amines, the pentavalent metals form important M(NR2)xX5 compounds. The M(NMe2)5 compounds, obtained by reaction of MC15 with LiNMe2, have been greatly studied and used for synthesis of other compounds. They are mononuclear in the gas phase with apparently square pyramidal geometry30 but in the solid Ta(NMe2)5 is tbp while Nb(NMe2)5 approaches an sp structure. Mixed species can be obtained by reactions such as... 

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. 

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