Pentacarbonyl methoxy

In an analogous reaction, Wulff isolated54 the free vinylketene 41 in good yield from the reaction of pentacarbonyl[methoxy(2,6-dimethylphenyl) car-beneJchromium(O) with trimethylsilylacetylene. The -stereochemistry of the product was found to be unchanged even after heating to 200°C for 24 h.54... 

In 1979, Rudler ef al. reported another example of the presence of a vinylidene complex during the reaction of pentacarbonyl[methoxy(methyl)carbene] tungsten 5 with MeLi followed by acidification with TFA [4]. It was proposed that the vinylidene complex 7 was generated by deprotonation of the a-proton of the carbene complex followed by elimination of methoxide and reaction with the dimethylcarbene complex 8, the addition-elimination product of MeLi with the starting carbene complex, to give the dinuclear complex 6 (Scheme 5.2). 

Scheme 5.2 The reaction of pentacarbonyl[methoxy(methyl)] carbenejtungsten with MeLi followed by TFA.

Pentacarbonyl(methoxyphenylmethylene)tungsten(0), [Pentacarbonyl[methoxy(phenyl)carbene] tungsten(O)]... 

A reaction between pentacarbonyl[methoxy(2,6-dimethoxyphenyl) methylene]chromium(0) and pent-4-yn-l-ol provides direct access to the functionalized tetrahydropyran-2-one 1005 the best yield is obtained via thermal heating of the two starting materials in THF (Equation 395) <2000TL9323>. 

Charge the first flame dried and argon flushed two-necked flask with pentacarbonyl-(methoxy(4-pentenyl)carbene)chromium(0). 

The first X-ray crystal structure determination, carried out by Mills in cooperation with us 31) on pentacarbonyl[methoxy (phenyl) carbene ]-chromium(0), confirmed our originally postulated bonding concept. According to this concept, the carbene carbon atom is sp1 hybridized. It should therefore possess an empty p-orbital and be electron-deficient. 

Fig. 2. The structure of pentacarbonyl [methoxy(phenyl)carbene]chromium (0) bond lengths in angstroms.

Fig. 4. Reactions of pentacarbonyl[methoxy(methyl)carbene]chromium(0) with tertiary phosphines.

Naturally, reactions are especially interesting to us if the products obtained are not readily accessible by the methods of classic organic chemistry but are easily preparable with our complexes. We found one such example upon treatment of pentacarbonyl[methoxy(aryl)carbene]chrom-ium(O) complexes with oxygen, sulfur, or selenium (76). In this way one obtains conveniently the corresponding methyl esters of arylcarboxylic acids and the O-methyl esters of arylthio- as well as arylselenocarboxylic acids this seems to us to be synthetically useful in the last two cases ... 

Fig. 6. Hypothesis concerning the course of the reaction during the treatment of pentacarbonyl[methoxy(phenyl)carbene]chromium(0) with JV-vinyl-2-pyrrolidones under a CO pressure of 150 atm.

As mentioned earlier, the carbene ligand in our complexes shows nucleophilic character with respect to the metal fragment. Therefore, we decided to combine it with an electrophilic carbene. For this purpose we treated pentacarbonyl[methoxy(phenyl)carbene]chromium(0) with phenyl(tri-chloromethyl) mercury (85). Compounds of this kind have been studied intensively by Seyferth et al. (86) and are known as a source of dihalogeno-carbenes. The carbene complex reacted with the carbenoid compound at... 

It was also of interest to us how changes in the organic residue of the carbyne ligand influence the stability and the behavior of carbyne complexes. Hence, we treated with boron tribromide a series of pentacarbonyl-[methoxy (aryl) carbene tungsten (0) complexes which were substituted at... 

K. H. Dotz, Synthesis of the Naphthol Skeleton from Pentacarbonyl[methoxy(phenyl)-carbene]chromium(0) and Tolane, Angew. Chem. Int. Ed. Engl. 14, 644-645 (1975). 

Methylation of(CO)5W[C(OH)Me] with CH Nj [MejOjCBFJ or MeOSO F and of [(C0),WC(0)Me]- with H20/CH2N2 HjO/CMejOJCBFJ MeOSOjF or CHjI finally gives pentacarbonyl[methoxy(methyl)carbene]-tungsten ... 

Dotz, K. H. Synthesis of the naphthol skeleton from pentacarbonyl[methoxy(phenyl)carbene]chromium(0) and tolan. Angew. Chem. 1975, 87, 672-673. 

The reaction of pentacarbonyl[methoxy(phenyl)carbene]chromium(0) with vinyl ethers gives 1-methoxy-l-phenylethene as the main product. If these substrates are allowed to react in the presence of carbon monoxide under pressure, the corresponding cyclopropanes are formed in good yield. 

Procedure A A solution of pentacarbonyl[methoxy(cyclopropyl)carbene]chromium(0) (0.276 g, 100 mmol) and an alkene (2.00 mmol) in THE (20 mL) was added dropwise via a syringe pump over a period of 5 h to refluxing THE (tOOmL) under N2. 

Pentacarbonyl[methoxy(phenyl)carbene]chromium(0) reacts regioselectively across the 4,5-double bond of electrophilic conjugated dienes. The reactions run at a much slower rate than those with electrophilic alkenes, e.g. formation of 6, 7 and 8-10. The diastereomer with the methoxy group cis to the olefinic moiety is largely favored (85 15). Double adducts are only formed as minor side products, but they become the major product in the case of (E,E)-7V,iV-dimethylhexadienamide. ... 

Aza-l,3-dienes are cyclopropanated by pentacarbonyl[methoxy(phenyl)carbene]chromi-um(0) to give fra/M-cyciopropaneimines stereoselectively.71... 

The not very stable VHb decomposes to the corresponding cyclopropane. In the same way pentacarbonyl (methoxy p-tolyl)carbenetungsten reacts with allylamine to give complex VIII (no interaction of the double bond with the metal), which decomposes to... 

In MeOD solutions, in the presence of catalytic amounts of sodium methanolate, pentacarbonyl[methoxy(methyl)carbene]chromium(0) exchanges all hydrogen atoms of the methyl group for deuterium. Analogous molybdenum and tungsten complexes react in the same manner. 

In an interesting and novel organometallic approach to monocyclic and bicyclic p-lactam synthesis, it has been shown that pentacarbonyl(methoxy-methyl)chromium complexes will add to imines under sunlight irradiation (Scheme 38). ... 

Another route to vinylcarbene C-glycosides is based on a TiCl4-assisted aldol condensation of pentacarbonyl[(methoxy)methylcarbene]chromium (229) and formyl glycosides 230-232. This reaction is trans-selective and affords sugar carbene complexes 233-235 in good yields (Scheme 11.53) [111]. 

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