Ethylene/ethene protonated

Such J-mctals as Cu(I) [but not Cu(II)], form a variety of compounds with ethenes, for example [Cu(C2H4)(H20)2]C104 (from Cu, Cu2+, and C2H4) or Cu(C2H4)(bipy)+. It is necessary to mention that, of all the metals involved in biological systems, only copper reacts with ethylene [74b]. Such homoleptic alkene complexes can be useful intermediates for the synthesis of other complexes. The olefin complexes of the metals in high formal oxidation states are electron deficient and therefore inert toward electrophilic reagents. By contrast, the olefin complexes of the metals in low formal oxidation states are attacked by electrophiles such as protons at the electron-rich metal-carbon a-bonds [74c]. 

Scheme 8.67. The formation of ethene (ethylene, CH2=CH2) and diethyl ether (ethyl ether, (CH3CH2)20) from the reaction of ethanol (CH3CH2OH) with sulfuric acid (H2SO4). The reaction proceeds through the hydrogen sulfate ester of ethanol, which is apparently formed faster than the dehydration of the protonated ethanol can occur.

Scheme 9.133. A representation of the palladium(II) chloride-catalyzed oxidation of ethene (ethylene, CH2=CH2) to ethanal (acetaldehyde, CH3CHO), the Wacker process. Generally, a copper(II) catalyst (not shown) is also employed to effect the reoxidation of the palladium. Interestingly, it is probable that a 1,2-hydride shift occurs as the palladium is lost (rather than elimination to the corresponding enol and then rearrangement to the aldehyde) since nse of H20 (denterinm oxide) in place of its proton analogue (water, HaO) yields aldehyde in which there is no denterinm ( ) incorporation.

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