Oxidative addition reactions mercury

Periana et al. have reported a mercury system that catalyzes the partial oxidation of methane to methanol.81 Hg(II) is typically considered to be a soft electrophile and is known to initiate electrophilic substitution of protons from aromatic substrates. The catalytic reaction employs mercuric triflate in sulfuric acid, and a key step in the catalytic cycle is Hg(II)-mediated methane C—H activation. For methane C—H activation by Hg(II), an oxidative addition reaction pathway via the formation of Hg(IV) is unlikely. Thus, an electrophilic substitution pathway has been proposed, although differentiation between proton transfer to an uncoordinated anion versus intramolecular proton transfer to a coordinated anion (i.e., o-bond metathesis) has not been established. Hg(II)-based methane C H activation was confirmed by the observation of H/D exchange between CH4 and D2S04 (Equation 11.9). 

Oxidative addition reactions of mercury carboxylates [Hg(02CR)2] with cis-[Pt(C6H4CH2NMe2-o)a] afford novel stable aryl-platinum-mercury complexes (22) the corresponding rrans-platinum complex forms unstable Pt-H intermediates, which eliminate Hg to leave isomers of [Pt(CeH4CH2NMe2)2-... 

Complex [(CXI )Ir(/j,-pz)(/i,-SBu )(/j,-Ph2PCH2PPh2)Ir(CO)] reacts with iodine to form 202 (X = I) as the typical iridium(II)-iridium(II) symmetrical species [90ICA(178)179]. The terminal iodide ligands can be readily displaced in reactions with silversalts. Thus, 202 (X = I), upon reaction with silver nitrate, produces 202 (X = ONO2). Complex [(OC)Ir(/i,-pz )(/z-SBu )(/i-Ph2PCH2PPh2)Ir(CO)] reacts with mercury dichloride to form 203, traditionally interpreted as the product of oxidative addition to one iridium atom and simultaneous Lewis acid-base interaction with the other. The rhodium /i-pyrazolato derivative is prepared in a similar way. Unexpectedly, the iridium /z-pyrazolato analog in similar conditions produces mercury(I) chloride and forms the dinuclear complex 204. 

The chemistry of alkynes is dominated by electrophilic addition reactions, similar to those of alkenes. Alkynes react with HBr and HC1 to yield vinylic halides and with Br2 and Cl2 to yield 1,2-dihalides (vicinal dihalides). Alkynes can be hydrated by reaction with aqueous sulfuric acid in the presence of mercury(ll) catalyst. The reaction leads to an intermediate enol that immediately isomerizes to yield a ketone tautomer. Since the addition reaction occurs with Markovnikov regiochemistry, a methyl ketone is produced from a terminal alkyne. Alternatively, hydroboration/oxidation of a terminal alkyne yields an aldehyde. 

The major synthetic routes to transition metal silyls fall into four main classes (1) salt elimination, (2) the mercurial route, a modification of (1), (3) elimination of a covalent molecule (Hj, HHal, or RjNH), and (4) oxidative addition or elimination. Additionally, (5) there are syntheses from Si—M precursors. Reactions (1), (2), and (4), but not (3), have precedence in C—M chemistry. Insertion reactions of Si(II) species (silylenes) have not yet been used to form Si—M bonds, although work may be stimulated by recent reports of MejSi 147) and FjSi (185). A new development has been the use of a strained silicon heterocycle as starting material (Section II,E,4). 

An oxidative addition step is involved in the reaction between trans-(EtjP)2lr(CO)Cl and the mercurials Hg(MMe3)2 (M = Si, Ge) (141). 

In the oxidation of hydroxylamine by silver salts and mercurous salts, the nature of the reaction product apparently depends upon the extent to which catalysis participates in the total reaction. This is illustrated by some results obtained with mercurous nitrate as oxidizing agent. The reaction is strongly catalyzed by colloidal silver, and is likewise catalyzed by mercury. The reaction of 0.005 M mercurous nitrate with 0.04 M hydroxylamine at pH 4.85 proceeds rapidly without induction period. The mercury formed collects at the bottom of the vessel in the form of globules when no protective colloid is present, so the surface available for catalysis is small. Under these conditions the yield is largely nitrous oxide. Addition of colloidal silver accelerates the reaction and increases the yield of nitrogen. Some data are given in Table III. 

There are three important routes to the formation of the mercury-transition metal bond (a) displacement of halogen or pseudohalogen from mercury(II) salts with carbonyl metallate anions (b) reaction of a halo-phenylmercury compound with a transition metal hydride and (c) oxidative addition of a mercury halide to neutral zero valent metals.1 We report here the syntheses of three compounds containing three-centre, two-electron, mercury-ruthenium bonds utilizing trinuclear cluster anions and mercury(II) halides.2-4... 

Chalcogenolato complexes of mercury can be prepared by a variety of methods. Early preparations involve the reactions of thiols with mercury cyanide,1 the reaction of mercury salts with alkali chalcogenolates, electrochemical methods,2 and the oxidative addition of dichalcogenides to metallic mercury.3 The last method is very convenient for the preparation of complexes with sterically undemanding ligands, but becomes less facile as the... 

Iodine-Mercury(II) oxide, 149 Lithium diisopropylamide-Potassium /-butoxide, 164 Molybdenum carbonyl, 194 Phenyliodine(III) diacetate, 242 Sulfuryl chloride, 284 Conjugate addition reactions Michael reactions Alumina, 14... 

An additional cleanup step should be performed to remove sulfur using mercury or copper powder. Permanganate-sulfuric acid treatment is not recommended. Unlike PCBs, most pesticides are fully or partially oxidized by reaction withKMn04-H2S04. Treatment with concentrated H2S04 alone is not recommended, because pesticides such as dieldrin and endrin were found to be totally destroyed at 20 ng/mL and endrin aldehyde and endosulfan sulfate partially decomposed at 60 ng/mL concentrations, respectively, in the extract (Cavanaugh and Patnaik, 1995). 

In the majority of catalytic reactions discussed in this chapter it has been possible to rationalize the reaction mechanism on the basis of the spectroscopic or structural identification of reaction intermediates, kinetic studies, and model reactions. Most of the reactions involve steps already discussed in Chapter 21, such as oxidative addition, reductive elimination, and insertion reactions. One may note, however, that it is sometimes difficult to be sure that a reaction is indeed homogeneous and not catalyzed heterogeneously by a decomposition product, such as a metal colloid, or by the surface of the reaction vessel. Some tests have been devised, for example the addition of mercury would poison any catalysis by metallic platinum particles but would not affect platinum complexes in solution, and unsaturated polymers are hydrogenated only by homogeneous catalysts. 

When MejGeH is irradiated by a mercury lamp with Rh(CO)2Cp- ) (5 1 ratio in benzene in a sealed evacuated tube) about 50% (MejGe)2Rh(CO)Cp- / is recovered after 5d. Workup is by chromatography on alumina and sublimation. In contrast, heating the same system at 80°C for 5d gives only about 10% yield. Here, while the thermal reaction alone might be interpreted as an oxidative addition followed by CO loss [compare Eq. (e) in 5.8.4.2.2], the photolysis probably proceeds by initially forming Rh(CO)Cp- , and this intermediate may also be formed in the thermal reaction. 

Photolysis is a convenient route - to iron carbonyl derivatives using FefCO), and this route may be better than oxidative addition to Fej(CO),2. One illustration is the 1 1 reaction of FefCO), with (Me2GeH)20 under mercury lamp irradiation for 1 h. in pentane to produce ... 

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