The palladium(II)-induced oligomerization of acetylenes: an organometallic detective story

Abstract

One of the most fascinating chapters in organometallic chemistry concerns the interaction of transition-metal compounds with acetylenes. The number of different strange, unusual, and apparently unrelated types of molecules isolated from these reactions reminds one of the early days of organic natural product chemistry; the tale of the unravelling of their structures and of the elucidation of apparently tortuous mechanisms by which they are formed is reminiscent of a detective story. Clues abound, there are many red herrings, and the answer to the puzzle is seldom obvious even halfway through the problem.Interest in the general area was dramatically awakened by Reppe's discovery of the tetramerization of acetylene to cyclooctatetraene by a nickel catalyst.1 This was followed by extensive investigations of the structures of the multitude of complexes isolated from reactions of metal carbonyls and acetylenes, particularly by Hübel and his co-workers,2 and many others. These studies showed that a number of complex processes occur during such reactions, many involving polynuclear intermediates, and even today our understanding of that particular story is only

Frequency Effects in the Catalytic Oligomerization of Methane via Microwave Heating

“…Including a diluent in the feed will help prevent the coupling of intermediates to these products. [63][64][65][66]…”

Control of the β-Hydride Elimination Making Palladium-Catalyzed Coupling Reactions more Diversified

“…The main reason is that methods of quenching the carbon-palladium bond to regenerate the divalent palladium species are rare [11][12][13][14][15][16] and the carbon-palladium bond is easily quenched by b-hydride elimination or reductive elimination, which generates the Pd(0) species, making the catalytic cycle impossible. Thus, oxidizing agents are necessary to regenerate the divalent palladium catalyst [2].…”

Reactions of alkynes with molybdenum and tungsten bis(alkyne) complexes [M(SR)(CF3CCCF3)2(η5-C5H5)] (M = Mo, R = C6F5; M = W, R = C6H4Me-4): crystal and molecular structure of [Mo{η4-C(CF3)C(CF3)C(CO2Me)C(CO2Me)(SC6F5)}(CF3CCCF3)(η5-C5H5)] †

“…These were obtained on thermolysis of the η 3butadienyl complexes 8d, 8e in which the η 3 bonding mode (iii) (Table 2) of the butadienyl ligand is displayed. Structural studies of [W(SPr i ){η 5 7) Å], perhaps reflecting the 18-electron configuration in the former and the 16-electron configuration in the latter. It is therefore possible that sulfur-metal π donation provides a stabilising influence on the electronic unsaturation found in 7.…”