Comproportionation compounds

Comproportionation Compounds with higher and lower oxidation states of one element react to a componnd with an oxidation state in between... 

A microwave-assisted three-component reaction has been used to prepare a series of 1,4-disubstituted-1,2,3-triazoles with complete control of regiose-lectivity by click chemistry , a fast and efficient approach to novel functionalized compounds using near perfect reactions [76]. In this user-friendly procedure for the copper(l) catalyzed 1,3-dipolar cycloaddition of azides and alkynes, irradiation of an alkyl halide, sodium azide, an alkyne and the Cu(l) catalyst, produced by the comproportionation of Cu(0) and Cu(ll), at 125 °C for 10-15 min, or at 75 °C for certain substrates, generated the organic azide in situ and gave the 1,4-disubstituted regioisomer 43 in 81-93% yield, with no contamination by the 1,5-regioisomer (Scheme 18). 

Suppose a compound, M, is observed to undergo two successive one-electron reduction steps (equation 5). The comproportionation constant Kc for reaction (6) is simply given by expression (7). At 298 K, with °, — E°2 = A ° expressed in mV, then expression (7) reduces to Kc = exp... 

Comproportionation of two nitrogen compounds to give a diazonium ion (top) or an acyl azide (bottom), respectively. 

Lead-acid, nickel-iron (Ni-Fe), nickel-cadmium (NiCd), and nickel-metal hydride (NiMH) batteries are the most important examples of batteries with aqueous electrolytes. In lead-acid batteries, the overall electrochemical reaction upon discharge consists of a comproportionation of Pb° and Pb4+ to Pb2+. All nickel-containing battery reactions are based on the same cathodic reduction of Ni3+ to Ni2+, but utilize different anodic reactions providing the electrons. Owing to toxicity and environmental concerns, the formerly widely used Cd°/Cd2+ couple (NiCd cells) has been almost entirely replaced by H/H+, with the hydrogen being stored in a special intermetallic compound (NiMH). 

With the tripod ligand np3 an entire series of compounds with tbp structures Ni(np3)X (X = Cl, Br, I, CN, CO, and H) can be prepared by reaction of nickel halides with the np3 ligand in the presence of borohydride, followed, if necessary, by metathesis with other X groups. The comproportionation of the Ni complex Ni2(CO)2(/i.-CO)(/i.-dppm)2 with NiG2(dppm)2 (dppm = Ph2PCH2PPh2) gives the iluxional A-frame compound (17-G-XIX).18... 

Complexes of palladium and platinum are accessible by the comproportionation of M° with M11 compounds,6 by reduction of M11 precursors,7 or by the judicious oxidation of M° complexes. The M1 products form metal-metal bonded dimers ... 

This compound and the similar YbO have salt-like (NaCl) structures and are genuine Ln" compounds, being insulators. Similar comproportionation methods using high pressures have been used to obtain SmO and NdO these are shiny conducting solids, probably containing Ln + ions. 

A frequently used indirect method involves cyclizable (cf. (7)) or other mechanistic probes which should provide evidence for free radical intermediates and thus for SET [19,37,59]. However, Newcomb and Curran have pointed out the pitfalls of such an approach especially if iodide precursors are used [17]. The supposedly radical-indicative reaction may come about albeit slower by a different, nonradical mechanism or the radical formation may occur via a secondary process which is not directly related to the first reaction step. A similar side-route can be made responsible for the appearance of stable radical compounds which may arise via a comproportionation reaction between non-reduced starting material and the doubly reduced species which can be formed from a hydro form (the normal product, Eq. (5)) and the usually strongly basic organometallic or hydridic reagents (Eq. (9)) [58]. The ability of strong bases to produce reduced radical species via complicated electron/proton transfer processes has been known for some time in the chemistry of quinones and quaternary salts [60,61]. 

Reactions of basic lithium compounds LiR or LiER with halides [19,37,59], pseudohalides [62] or unsaturated acceptors [63-65] were frequently reported to involve SET steps. The strongly basic character of such lithium compounds may, however, cause the observation of apparent one electron-reduced species such as ketyls or semiquinones via deprotonation of hydrolysis products and ensuing comproportionation reactions (Eq. (9)) [58]. 

The possible role of oxygen atom transfer in molybdenum enzyme catalysis was recognized in the early 1970s (190-194). In the ensuing years, a wealth of chemistry has established molybdenum as the premier exponent of such reactions (7, 195). Importantly, related dioxo-Mo(VI) and oxo-Mo(IV) complexes are interconverted by oxygen atom transfer reactions (Eq. (13)). These reactions are effected by reductants (X) such as tertiary alkyl and aryl compounds of the group 15 elements (especially phosphines) and oxidants (XO) such as S- and N-oxides. In many cases, however, the Mo(VI) and Mo(IV) compounds participate in a comproportionation reaction yielding dinuclear Mo(V) complexes (Eq. (15)). 

The GED structure determination of 3 showed a centrosymmetric molecule with a linear C—Mg—C center (4). On evaporation of 3, which is trimeric in benzene solution and probably polymeric in the crystalline state, dissociation into monomeric molecules occurs. The structure obtained is in accordance with the considerations in Section I,C. Important geometric parameters of the structure are the distances Mg—C (2.126 A) and C—C (1.541 A) and the angle Mg—C—C (118°). By fusion of3 and 2, the mixed crystalline compound 4 (m.p. 70-72°C) was obtained. The structure of this compound, which is stable toward comproportionation to... 

Allylstannanes rapidly undergo the Kocheshkov comproportionation reaction with SnCU, even at -50 °C. The initial product is apparently formed with allylic inversion, but further transmetallation may give other allylic isomers.35 The SnCl3 group which is formed enhances the electrophilic power of the allyl group. This has been exploited in aromatic allylation (equation 9-13),36 and transmetallations of this type provide the basis for some, but not all, of the examples of the catalysis of the allylation of carbonyl compounds by allylstannanes in the presence of Lewis acids37,38 (Section 9.1.3.4). 

The hydrides R2SnHX (X = e.g. halide, carboxylate, sulphonate, alkoxyl) can be formed by the comproportionation between diorganotin dihydrides, R2SnH2, and the compounds R2SnX2. 

Several different methods have been described to prepare doubly alkynylide-bridged dinuclear zirconocene(lll) compounds. The first approach reported was the comproportionation reaction between bis(alkynyl)metallocenes (M = Zr, Hf) and (butadiene)zirconocene, which has been utilized to prepare the examples summarized in Scheme 10.26 27 The solid-state structure of the representative example (MeC 5H 4 )2Zr(f I h ))2 22 was... 

Organic selenenic acids and their anhydrides are thermally unstable and readily disproportionate into the corresponding diselenides and seleninic acids (or their anhydrides) [15 a, 32]. Because this process is believed to be reversible, these selenium compounds can be generated in situ by the comproportionation, i.e. the reverse processes (going right to left in the following equations), and used directly without isolation (Scheme 15.10) [32-34]. 

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