Silicon complexes with cobalt

Silicon and germanium hydrides react with cobalt, manganese and rhenium carbonyls affording complexes having a silicon (or germanium)-metal bond. These reactions, described previously for inactive compounds have been used in the synthesis of optically active silyl and germyl-transition metals ... 

The cobalt-silicon complex is cleaved by LiAlH with inversion of configura-... 

While platinum and rhodium are predominantly used as efficient catalysts in the hydrosilylation and cobalt group complexes are used in the reactions of silicon compounds with carbon monooxide, in the last couple of years the chemistry of ruthenium complexes has progressed significantly and plays a crucial role in catalysis of these types of processes (e.g., dehydrogenative silylation, hydrosilylation and silylformylation of alkynes, carbonylation and carbocyclisation of silicon substrates). 

We must however keep in mind that some of the above reactions may not be simple reactions at the silicon atom, since transition metal complexes show multicenter reactivity (metal atom, ligands) as exemplified in the chemistry of triphenylgermyl-carbene complexes of cobalt carbonyl (253). Thus, displacements of a silyl ligand may result from a multistep process and a thorough examination of these reactions has to be made. An example can be drawn from molybdenum-germanium chemistry (247). As shown in Scheme 59, germanium is displaced from complex 167 by HO with retention of configuration. Actually,... 

Cartoni et al. [88] studied perspective of the use as stationary phases of n-nonyl- -diketonates of metals such as beryllium (m.p. 53°C), aluminium (m.p. 40°C), nickel (m.p. 48°C) and zinc (liquid at room temperature). These stationary phases show selective retention of alcohols. The retention increases from tertiary to primary alcohols. Alcohols are retained strongly on the beryllium and zinc chelates, but the greatest retention occurs on the nickel chelate. The high retention is due to the fact that the alcohols produce complexes with jS-diketonates of the above metals. Similar results were obtained with the use of di-2-ethylhexyl phosphates with zirconium, cobalt and thorium as stationary phases [89]. 6i et al. [153] used optically active copper(II) complexes as stationary phases for the separation of a-hydroxycarboxylic acid ester enantiomers. Schurig and Weber [158] used manganese(ll)—bis (3-heptafiuorobutyryl-li -camphorate) as a selective stationary phase for the resolution of racemic cycUc ethers by complexation GC. Picker and Sievers [157] proposed lanthanide metal chelates as selective complexing sorbents for GC. Suspensions of complexes in the liquid phase can also be used as stationary phases. Pecsok and Vary [90], for example, showed that suspensions of metal phthalocyanines (e.g., of iron) in a silicone fluid are able to react with volatile ligands. They were used for the separation of hexane-cyclohexane-pentanone and pentane-water-methanol mixtures. 

Trichloro(tripyridine)chromium(III), synthesis 36 Trichloro (tripyridine) molybdenum (III), synthesis 39 Potassium octacyanotungstate(IV) 2-hydrate, synthesis 40 Chlorine(CH )-labeled thionyl chloride, silicon tetrachloride, boron chloride, germanium(IV) chloride, and phosphorus-(III) chloride, synthesis 44 Unipositive halogen complexes, synthesis 46 Monopyridineiodine(I) chloride, synthesis 47 Tris(3-nitroacetylacetonato)cobalt(III), synthesis 55 Inner complexes of cobalt(III) with diethylenetriamine, synthesis 56... 

The anionic nature of pectin is yet another important aspect, which prevents the pol5mierization of organic silicon compounds. Thus pectin always makes crosslinked complexes with proteins under suitable conditions and act as a powerful chelator of allergens such as cobalt, nickel, copper (Table 8.1). 

Assay of beryllium metal and beryllium compounds is usually accomplished by titration. The sample is dissolved in sulfuric acid. Solution pH is adjusted to 8.5 using sodium hydroxide. The beryllium hydroxide precipitate is redissolved by addition of excess sodium fluoride. Liberated hydroxide is titrated with sulfuric acid. The beryllium content of the sample is calculated from the titration volume. Standards containing known beryllium concentrations must be analyzed along with the samples, as complexation of beryllium by fluoride is not quantitative. Titration rate and hold times are critical therefore use of an automatic titrator is recommended. Other fluoride-complexing elements such as aluminum, silicon, zirconium, hafnium, uranium, thorium, and rare earth elements must be absent, or must be corrected for if present in small amounts. Copper—beryllium and nickel—beryllium alloys can be analyzed by titration if the beryllium is first separated from copper, nickel, and cobalt by ammonium hydroxide precipitation (15,16). 

A series of complex silico-arsenides has been obtained 6 by melting metals with silicon and an excess of arsenic under a layer of molten cryolite and sodium chloride. The following have thus been prepared copper silico-arsenide, a grey crystalline brittle mass zinc silico-arsenide, which behaved as above with hydrochloric acid iron, cobalt and nickel siMco-arsenides, of composition M2SisAs4, similar in appearance to the copper compound. When platinum was treated in the same way, a hard white product of indefinite composition was obtained, almost insoluble in nitric acid. 

Again the ease of reaction depends very much on Q (P, As) and the substituents R1 and R63, 64l The preparation of a compound containing an optically active silicon center, trans-(+)-Pt(Pme2ph)2Cl[Si meph(l-naphthyl)], showed that these complexes are formed with retention of configuration at the silicon96. The stereochemical characteristics are also retained in the syntheses of cobalt carbonyls according to Eq. (9)210 ... 

The reaction between Sil4 and NaCo(CO)4 (equation 49) gives cobalt cluster (39) in which the silicon is coordinated to four cobalt atoms, the Si-Co(CO)3 distances averaging 2.218 A and the Si-Co(CO)4 distance being 2.288 The reaction of SiH4 with Co2(CO)g (equation 50) gives the spiro complex (40) in which the Si-Co distance averages 2.288 Similarly, the reaction between SiLt and NaM(CO)5 (M = Mn or Re) leads to tri- and tetra-substituted products (equation 51). ... 

With a platinum catalyst, methylviologen is undoubtedly a better electron transfer agent than macrobicyclic cobalt complexes. To the contrary, when colloidal RU2O3 (5 x IQ- moM i) deposited on silicon surface is employed as a catalyst, the rate of hydrogen production in the case of [Co(Clsar)]3+ cation is 55 pmolmin-h whereas for methylviologen it is 11 pmol min-i under the same experimental conditions. 

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