Molybdenum complexes iodides

The transformations discussed in Sects. 2.2-2.3 highlight several important features of the RCM process. Firstly, the compatibility of the ruthenium initiator 3 with a wide range of functional groups including epoxides, vinyl iodides, thia-zoles and alcohols is demonstrated. The versatility of 3 is further illustrated in Sect. 2.3, where it is used to effect RCM of polymer-bound substrates. Previously, the molybdenum complex 1 has been reported to be more sensitive than 3 [19]. Experiments reported here are consistent with this view (Sect. 2.2.3) [14b]. 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

In contrast to the unsuccessful early attempts to produce [W2(02CR)4], the heteronuclear compound [MoW(02CCMe3)4] was obtained by reacting a 3 1 mixture of W(CO)6 and vlo(CO)6 in refluxing dichlorobenzene.334 The heteronuclear complex was freed from Mo2(02CCMe3)4] by careful oxidation with I2. Structure analysis of MoW(02CCMe3)4]I-MeCN shows the expected idealized Dih symmetry with a short W—Mo separation of 2.194 A. The iodide ion is coordinated to the W atom and the MeCN molecule is coordinated to the molybdenum atom. 

Scheme 2.29 depicts two of the first examples of microwave-assisted carbonylation reactions7. In these reactions, the temperature controls the rate of the CO release. Thus, during heating at 150°C in sealed vessels, carbon monoxide was smoothly emitted from the molybdenum carbonyl complex into the reaction mixture (Fig. 2.1, Profile A). As a result, aryl iodides and bromides underwent efficient amino carbonylation with non-hindered, aliphatic, primary and secondary amines in only 15 min, using Herrmann s palladacycle as pre-catalyst7 (Scheme 2.29). In contrast, at a reaction temperature of 210°C, carbon monoxide was liberated almost instantaneously (Fig. 2.1, Profile B).

There are no routes yet to homoleptic metal isocyanide anions. If one considers the interesting products obtained from methyl iodide additions to molybdenum (43) and manganese (44) carbonyl isonitrile anions, negatively charged isocyanide complexes should have some interesting chemistry. Also, now that a simple route to [CpFe(CNR)2]2 complexes has been devised (45), the synthesis of the anion [CpFe(CNR)2] could provide a route to a range of products including heterometal-metal bonded systems. 

Bradfield and Stickland [40,41] determined molybdenum in plant tissue by its catalytic effect on the liberation of iodine from the reaction between potassium iodide and hydrogen peroxide. The detection limit is 0.003 pg/ml of molybdenum. Interference from iron and tungsten can be overcome by addition of ammonium fluoride, but for the greatest precision and accuracy a preliminary separation of molybdenum as its benzoin a-monoxime complex is recommended. 

Propynylnaphthalene 15 furnishes dinaphthylacetylene 20 in near quantitative yield. On the other hand, the Mori system performs somewhat less well if heteroatoms are present in the substrates, suggesting that the catalytic system is poisoned by the presence of the heteroatom through complexation and/or chelation of the active molybdenum center. Cyano groups and bromides/iodides inhibit the reactivity of the catalyst system. However, both propynylated phenols (16) and esters (17) give satisfactory dimerization results (21, 22). 

One of the chlorides in this complex can be exchanged for perchlorate on treatment of a solution of the complex in dichloromethane/acetonitrile with silver perchlorate2. Dicarbonyl(chloromethylidyne)[hydrotris(pyrazol-l-yl)borato]molybdenum(IV) reacted with sodium telluride in aqueous methanol to produce the anionic dicarhonyl[hydro-tris(pyrazol-l-yl)borato telluracarbonylmolybdate(0), which was isolated as the moderately air-stable tetraethylammonium salt. This salt reacted with methyl iodide in acetonitrile to form dicarbonyl[hydrotris(pyrazolo)borato](methyltelluromethylidyne) molybdenum(IV)3. 

Few monomeric d4 bisalkyne complexes with only monodentate ligands in the coordination sphere have been reported. The only molybdenum(II) complex in this category is Mo(PhC=CR)2(CO)(NCMe)I2 (R = Ph, Me), which was included in a reaction scheme illustrating products accessible from cleavage of the iodide bridges in dimeric [Mo(PhC=CR)(/r-I)-(I)(CO)(CNMe)]2 reagents (51). Efforts to convert Mo(RC=CR)(CO)-L2X2 complexes to bisalkyne derivatives were not successful (46). 

This is believed to occiu- by intercalation of the positively charged phenanthridinium iinit, and it is noted that this occurs 50 times more effectively at the electron-rich C and G bases than at the AT sites. Ligand 46 was prepared by reaction of the acid chloride form of the pendant 61) to the molybdenum tricarbonyl complex of cyclen (62). The monosubstituted cyclen was then reacted with 3 moles of (R)-or (S)-JV-(2-chloroethanoyl)-2-phenylethylamine (61). Quartemization was achieved by reaction of methyl iodide with the Eu(III) complex (61). 

Hexacarbonylchromium(O) is readily attacked by chlorine giving CrCb, CO, and COCI2. Bromine and iodine do not attack Cr(CO)6 to any substantial extent at room temperature. The chromium tricarbonyl arene complexes, Cr(CO)3( -arene), are readily oxidized at room temperature by I2 to give Cris this is a conveitient preparative method for the anhydrous iodide. Although the oxidation of the tricarbonyl arene derivatives of chrontium with I2 does not show evidence of intermediate carbonyl complexes in oxidation states >0, the corresponding molybdenum(O) compounds give a series of carbonyl iodides of molybdenum(II), for example, the ionic [Mo(CO)3 ( ) -arene)]I. 

The rearrangement of a tungsten carbonyl-complexed 7-phosphanorbomadiene to its 7-phosphatricyclo[3.2.0 ]hept-2-ene complex has been analysed by ab initio MO calculations, and it has been shown that the reactions of molybdenum and tungsten metallates of the type [CpM(CO)2CNR] with methyl iodide yield methyl complexes of the composition [CpM(CO)2(CNR)], which subsequently rearrange to / -iminoacyls and / -l-azaallyls depending on the nature of the metal, the isocyanide R substituent, and the solvent used. ... 

Cr(VI). In acting as catalysts, these substances fonn complexes or peroxides, though complex formation in itself is not sufficient to produce catalysis. In basic solution, catalysts involve substances that are easily oxidized and reduced, such as Fe(II), Co(II), and Cu(II). As an example, Svehla and Erdey determined traces of molybdenum through its catalytic effect on the overall hydrogen peroxide-iodide reaction,... 

Many of these complexes were purified by chromatography. The pure compounds are sensitive towards atmospheric oxygen. The bare tellurium atoms in these complexes can be protonated alkylated with methyl iodide, methyl lithium triethyloxonium tetrafluoroborate or methyl trifluoromethylsulfonate and reacted with diazoalkanes to produce complexes with coordinated telluroformaldehyde or telluroacetone. The anion [O = MoTeJ combined with dimethyl acetylenedicarboxylate to produce a tellurolate-containing molybdenum compound ... 

In early patents by Halcon, molybdenum carbonyls are claimed to be active catalysts in the presence of nickel and iodide [23]. Iridium complexes are also reported to be active in the carbonylation of olefins, in the presence of other halogen [24] or other promoting co-catalysts such as phosphines, arsines, and stibines [25]. The formation of diethyl ketone and polyketones is frequently observed. Iridium catalysts are in general less active than comparable rhodium systems. Since the water-gas shift reaction becomes dominant at higher temperatures, attempts to compensate for the lack of activity by increasing the reaction temperature have been unsuccessful. 

A large number of styrenic monomers have been investigated in metal-catalyzed radical polymerizations. Polymerization of styrene (M-19) can be controlled with copper,28,84,85 152 176 ruthenium,57 60 62 66 86,205 iron,71 75 rhodium,86 140 rhenium,141 and molybdenum catalysts.144 The polymerizations have actively been studied with the copper-based systems, among which precisely controlled molecular weights and very narrow MWDs (MJMn =1.1) were obtained in a homogeneous system consisting of 1-13 (X = Br), CuBr, and L-3 in the bulk at 130 °C.85 Similar well-controlled polymerizations are feasible with several ruthenium (Ru-5)60 and iron (Fe-2,72 Fe-3,73 and Fe-471) complexes in conjunction with a bromide or iodide initiator. Even a chloride initiator (1-25, X = Cl) can afford narrow MWDs (MJMn =1.1) when coupled... 

The manganate ion is not reduced by bromide ion but is reduced slowly by iodide ion and quickly by vanadyl(IV) or hexacyano-ferrate(II) ions. When the latter two ions are used as reductants, especially with the potassium complex, green products are obtained rapidly and in high yield. The green species is unstable in solution and is apparently in equilibrium with the reactants. With potassium salts, the solubility of the product is low, and the reaction is driven to completion. Potentiometric titrations show that a one-electron reduction occurs to produce the green species, which has been characterized by analysis and optical and e.s.r. spectroscopy. It is a mixed-valence species similar to the heteropoly blues of molybdenum and tungsten. E.s.r. spectra suggest that the extra electron is fairly well trapped on a specific vanadium atom, and the complex is therefore a class II mixed-valence species.8... 

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