Metallocycles rhodium

In contrast to the reaction of an i72-CS2-rhodium complex with dimethyl acetylenedicarboxylate which gives rise to a metallocycle,186 the iron complexes 103 are converted by activated acetylenes into air-sensitive carbene complexes 104. Decomposition of the latter in air provides an unusual synthetic route to substituted tetrathiofulvene derivatives (Scheme 121).187... 

Bicyclobutane derivatives react with rhodium complexes to give products which convincingly implicate metallocycles and metal-carbene species (72). 

Rhodium metallocycles reacted with freshly prepared amorphous tellurium in refluxing absolute xylene to give tellurophene derivatives3 s. 

Considerable information about the course of aldehyde decarbonylations has been gleaned from the decarbonylations of alk-4-enals. Pent-4-enals form cyclopentanones in high yield in decarbonylations catalyzed by [RhCl(PPh3)3], The major product from the decarbonylation of hex-4-enal is 2-methylcyclopentanone. As shown in Scheme 5, the cyclization reaction requires a vacant site on rhodium. The other products result from decarbonylation of the unsaturated acyl before cyclization can take place. In these cases, there is competition between addition of deuterium to C-1 of the alkenyl ligand or its addition to the alkene bond and the formation of an unstable metallocycle. ... 

Dioxo-l,3-diphenyl-4ff,10/7-[l]benzothieno[5,6-6][2]benzotellurophene Several g of powdered tellurium are dissolved in aqua regia, the solution is heated until all nitrogen oxides have been expelled, and is then diluted with water. A solution of sodium hydrogen sulfite is added to precipitate amorphous tellurium. The tellurium is filtered off, washed with water until the washings arc neutral, and then several times with ethanol. 50 ml of xylene are placed in a nitrogen-flushed, 250 ml flask fitted with a reflux condenser. 638 mg (5 mmol) of the moist, amorphous tellurium and 502 mg (0.5 mmol) of the rhodium metallocycle are added. The mixture is refluxed under nitrogen for 8 h while a spatula tip of tellurium is added every 2 h. The mixture is then filtered, and the filter is placed on a silica gel column which is eluted with 9/1 benzene/petroleum ether. The second yellow band is collected, the solvent is evaporated, and the residue is crystallized from benzene/ethanol yield 100 mg (38%) m.p. 248°. 

Yamazaki [51] has reviewed a number of stoichiometric cycloaddition reactions at the cobaltacyclopentadiene ring system that lead to a plethora of heterocycles. For example, five- and six-membered heterocycles containing nitrogen, sulfur, selenium, and phosphorus have been made accessible by this route (eq. (20)) [52]. The co-cyclization of substituted alkynes and isocyanates in the presence of a rhodium metallocycle gives 2-pyridones (eq. (21)) [53]. 

Rhodium(I) complexes of pyrazole, such as (81) have been studied by H and C NMR the boat conformation of the metallocycle was thus established <84JCPB25l>. Ruthenium(II) complexes of pyrazole, 3-methylpyrazole, 3,5-dimethylpyrazole, and indazole were described (x-ray crystallography and a careful H and C NMR study) in <90JCS(D)1463>. 

An alternative pattern for functionalization of quinoline-)V-oxides is observed with rhodium and iridium catalysis. The A -oxide functionality can direct the metal insertion to the 2-or the 8-position of the quinoline, and stable five-membered metallocycles can form after C-H insertion at the latter. As... 

The mechanism of this reaction is considered in Scheme 2.87 [3]. The metal-containing cyclopentene 2.260, formed from the initial vinylallenes 2.259 and rhodium catalyst, is probable the reaction intermediate. Next is the introduction monoyne 2.261 to the metallocycle 2.260 to... 

Me, R = R = R = H R = R = Me, R = R =H) (90JA2432, 9IJA559, 92JAI5I). The dienic group and the sulfur atom are planar but the rhodium atom is above the plane. A localized dienic structure is observed in the six-membered metallocycle. Complex 215 (X = H) formed in the corresponding photochemical reaction with thiophene appears unstable and gradually rearranges to 241... 

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