Atoms and Many-Electron Donors

The reaction of metal atoms with 1,5-cyclooctadiene (1,5-COD) offer special scope for forming new naked metal systems [Wilke (142)] i.e., complexes in which the ligands are readily displaced. The desire to explore these reactions was the impetus to developing the rotary solution reactor (81) which facilitates the reaction of metal atoms with slightly volatile or involatile ligands and, most important, aids the isolation of thermally unstable compounds (Tdec -60°C) in a pure state. 

The similar reaction with 1,3-COD affords only (C8H11)CrH(PF3)3. The molecular structure of this product has been shown by X-ray diffraction to be the T -cyclooctadienyl complex (140).  

It is of interest that the same product is obtained from both 1,3-COD and 1,5-COD with chromium atoms and PF3, as this compound contains the proposed ring-intermediate for the often observed interconversion of coordinated 1,3- and 1,5-COD (23, 86). With CO both the chromium-1,3-COD and -1,5-COD condensates afford the same product, 

The reactions of the Group VIII elements with 1,5-COD have been examined in detail and in each case a similar product is obtained  

Infrared spectroscopic studies have been particularly useful in demonstrating the generality of this reaction. The spectra of the films of the complexes, obtained by depositing each of the metal vapors and excess 1,5-COD on a cold window and pumping off the excess ligand at -70°C, are all extremely similar, i.e., the spectra of the new compounds of Fe, Co, and Pd are almost identical to the spectrum of Ni(COD)2 with its known tetrahedral structure (25). 

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