Low-valent metal compound

Reaction of Low-Valent Metal Compounds with Elemental Sulfur... 

Me proposed a new approach based on a different strategy to induce two electron transfer from a low valent metal compound to a water molecule leading to a hydrido-hydroxo-metal species (eq. 5). The nucleophilic attack of OH" on a coordinated CO is expected to... 

Otsuka and coworkers—addition of ligands to Pt and Rh complexes to facilitate water activation. Most researchers in the water-gas shift field focused their research primarily on the activation of CO through coordination that facilitated the nucleophilic attack by OH- or H20. In addition to this, Ostuka and coworkers28,40,47,55,56 added a new approach. It was based on a strategy that induces two-electron transfer from a low valent metal compound to a H20 molecule that leads to a hydrido-hydroxo-metal species, M + H20 <-> MH(OH). In so doing, they predicted that nucleophilic attack by the OH- on the coordinated CO would be more facile relative to the neutral H20 molecule. 

In practice this approach to the synthesis of compounds with dimetallacyclo-propane or -propene ring systems has been very successful. Complexes (1) - (12) are representative of those which have been readily prepared by reacting various low-valent metal compounds either with carbene-metal species, or with the carbyne complexes [w=CR( CO) 2(11-05 )] or [w=CR(Br)(CO) ]... 

REACTIONS OF LOW VALENT METAL COMPOUNDS WITH COMPLEXES CONTAINING METAL—METAL MULTIPLE BONDS. 

Low-valent metal compounds form Ge—M bonds in mild reactions with Hg agents. Thus (Et3Ge)2Hg gives Et3GeNi(PPh3)Cp- from (i -Cp)2Ni and (PhjP)2M inserts into Ge—Hg bonds forming a Ge—Hg—M—Ge chain ... 

As discussed in previous sections, direct reactions of low-valent metal compounds with O2 afford various metal-oxygen intermediates, including superoxo, peroxo, and high-valent metal-oxo species. However, with the exception of superoxides and dinuclear peroxides, alternative methods of generating these intermediates are more generally applicable, and often produce better results.15 16... 

Basically the same methods known from the synthesis of classical metal-silyl complexes can also be applied to the preparation of low valent Si compounds. The procedures given here are summarized with the focus on silylene complexes These are a) reactions of appropriate metal anions with halosilanes, which are the most important methods for the formation of M-Si bonds. Alternatively, silyl... 

Relatively few examples are known which utilize an oxidative addition reaction of metal hydrides to necessarily low valent silicon compounds. Seyfert s hexame-thylsilirane (31) could be used as a source of dimethylsilylene to perform an... 

Metal-induced reductive dimerization of carbonyl compounds is a useful synthetic method for the formation of vicinally functionalized carbon-carbon bonds. For stoichiometric reductive dimerizations, low-valent metals such as aluminum amalgam, titanium, vanadium, zinc, and samarium have been employed. Alternatively, ternary systems consisting of catalytic amounts of a metal salt or metal complex, a chlorosilane, and a stoichiometric co-reductant provide a catalytic method for the formation of pinacols based on reversible redox couples.2 The homocoupling of aldehydes is effected by vanadium or titanium catalysts in the presence of Me3SiCl and Zn or A1 to give the 1,2-diol derivatives high selectivity for the /-isomer is observed in the case of secondary aliphatic or aromatic aldehydes. 

Phosphinidenes [1] are low-valent organophosphorus compounds that have attracted attention since the early 1980s when they were first discovered [2]. They are known in two classifications, one being the six-electron singly substituted phosphorus species (A) and the other in which the phosphorus atom carries an additional ri -stabifizing group, typically, but not necessarily, a transition metal group (B). Much has been learned about the reactivities of the complexed phos-... 

The following chapter concerns another kind of low-valent organophosphorus compounds, namely phosphinidenes. Little is known about free phos-phinidenes in contrast to the corresponding transition metal complexes. Many new reagents have been generated exhibiting either electrophilic or nucleophilic properties. The reactivity of these carbene-like reagents is evaluated (K. hammer tsma). 

Two other publications on Ir (73 keV) Mossbauer spectroscopy of complex compounds of iridium have been reported by Williams et al. [291,292]. In their first article [291], they have shown that the additive model suggested by Bancroft [293] does not account satisfactorily for the partial isomer shift and partial quadrupole splitting in Ir(lll) complexes. Their second article [292] deals with four-coordinate formally lr(l) complexes. They observed, like other authors on similar low-valent iridium compounds [284], only small differences in the isomer shifts, which they attributed to the interaction between the metal-ligand bonds leading to compensation effects. Their interpretation is supported by changes in the NMR data of the phosphine ligands and in the frequency of the carbonyl stretching vibration. 

Ru, Os, and Ir carbene complexes have been prepared from reactions of anionic or low-valent metal complexes with some organic salts or neutral compounds with highly ionic bonds. Oxidative addition of halothiazole and -oxazole species to IrCl(CO)(PMe2Ph)2 affords Ir(III) complexes which on protonation yield cationic carbenes (69), e.g.,... 

Titanium-based reagents generated by the reduction of gem-dihalides with low-valent metal species are widely used for the alkylidenation of carbonyl compounds (Scheme 14.28). As in the case of methylidenation, the system gem-dibromide/TiCl4/Zn/TMEDA... 

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