Copper carbonyl interaction

The central feature of the mechanism is the 3-cuprio(III) enolate Cpop, of an open, dimeric nature, as shown by comparison of theory with experimentation involving NMR and KIEs [80, 81]. This species serves as the direct precursor to the product (Scheme 10.5, top box). In this critical CPop complex, copper/olefin (soft/soft) and a lithium/carbonyl (hard/hard) interactions are present. The open complex may be formed directly, by way of an open cluster (bottom left of Scheme 10.5), or by complexation of a closed cluster with the enone (CPcl). Experiments have shown that the enone/lithium complex (top left of Scheme 10.11) is a deadend species [60, 74]. 

Fundamental studies by reflection angle infrared spectroscopy of the bonding of EME coupling agents to metal oxides reveal a significant shift in the carbonyl absorbance band when the coupling agent is applied as a very thin layer on a metal oxide. The shift is reproducible and the extent varies with the type of oxide. These results were obtained both by use of copper mirrors and from CuzO powder coated with very thin layers of model compounds. The compounds were not removable by isopropanol, a solvent for the bulk compound. The thiol absorbances of thin layers of model compounds were also found to decrease in relative intensity with time. This illustrates that a specific chemical interaction has occurred. 

Fig. 23. (CH3CN)2Cu2Ru6C(CO),6, 20 (50). The distorted octahedral Ru6C core is capped by two directly bonded copper atoms [Cu-Cu = 2.693(1) A], one on an Ru3 face, the second on the CuRu2 face so formed. The Ru-Ru distances range from 2.798(1) to 3.072(1) A (mean 2.89 A). Ru-Q.rtjrte distances range from 2.031(4) to 2.073(4) A (mean 2.05 A). There are thirteen terminal carbonyls, and three asymmetrically bridging Ru-Ru edges. No Cu-CO contacts are short enough to imply bonding interactions.

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