Low-valent compounds

Common reducing agents are hydrogen in the presence of metallic or complex catalysts (e.g. Ni, Pd, Pt, Ru, Rh), hydrides (e.g. alanes, boranes, LIAIH, NaBHJ, reducing metals (e.g. Li, Na, Mg, Ca, Zn), and low-valent compounds of nitrogen (e.g. NjHj, NjHJ, phosphorus (e.g. triethyl phosphite, triphenyiphosphine), and sulfur (e.g. HO-CHj-SOjNa = SFS, sodium dithionite = Na S O. ... 

The methodology of heteroatom-directed lithiation has been applied to the synthesis of a variety of organochalcogen compounds, including unstable, low-valent compounds (Section 15.6). ° The Se N interactions in the diselenide 15.4 activate the Se-Se bond toward insertion of a sulfur atom or a methylene group to give the derivatives 15.21a,... 

The synthetic potential of silicon substituents in organic and organometallic chemistry has by far not been fully exploited, which is evidenced by the numerous contributions in this chapter. This is examplified for the description of the silyl group as a substituent and as a functional group in carbene and carbenoid chemistry, for the function of the trimethylsilyl substituent in the synthesis of low-valent compounds containing elements ofgroup 15 andfor the influence of a supersilyl ligand to a phosphorous center. 

The Trimethylsilyl Substituent in the Synthese of Low-valent Compounds 173 Five Membered Phosphorus Containing Heterocycles... 

The starting point for most molybdenum-based carbonyl chemistry is the white crystalline air stable hexacarbonyl [Mo(CO)6], which is commercially available. Low valent compounds that are derived from this starting material tend to give products that obey the Effective Atomic Number Rule (EAN Rule). Since Mo° has a d configuration, six two-electron ligands are required to obey the EAN rule. 

A convenient preparation of Cr(bipy)3(0104)2 has been published (380) and methods of examining spectra of low valent compounds in general have been discussed (349). In contrast to the iron(II) system, spin pairing occurs on the chromium(II) cation on addition of the second molecule of bipyridyl, thus [Cr(bipy)2(H20)2](C104)2 is low spin (178). 

Low-valent compounds of other early transition metals were shown to be elfective reagents for the pinacol coupling. Zirconium,... 

All low-valent compounds and low-valent-like reactive systems considered in this report are highly reactive and in particular extremely air and moisture sensitive (some even react with dinitrogen—see Section 2.3.4) and are best handled in an inert-atmosphere dry box or on a vacuum line by the usual Schlenk techniques. 

The Co chemical shifts of Co(lll) complexes are clearly grouped together according to the identity of the donor atom. In Table 15 selected (5( Co) have been reported. In view of the large line-widths found, often large variations in shift values have been found. Small anisotropy has been found in the low-valent compounds [Co2(CO)g] and [Co(CO)4X] where X is MnlCOs) as also in [Co(NH3)5(CN)]Cl2, [Co(NH3)4(C03)]Br, whereas... 

The more strongly the trans influence comes to the fore, the shorter are the remaining rhenitim-carbon distances. The latter ones may then even be much shorter (e.g., 214-223 pm in compound 7a Fig. 7) than in low-valent compounds containing exclusively ir-acceptor ligands such as carbon monoxide (e.g.,230 pm,average, in (n "C5H4SiMe3)Re(CO)3, Table I). 

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