Atoms and Two-Electron Donors

The interaction of metal atoms with monoalkenes has been investigated on both a spectroscopic and preparative scale. It appears that the primary interaction between a metal atom and an alkene at low temperature is the formation of a ir-complex. This may subsequently lead to a thermally stable 7r-alkene complex or to rearrangement products by hydrogen abstraction or reaction with another alkene moiety, depending on the electronic requirements of the metal and the particular alkene considered. 

Skell has examined the interaction of a wide range of metal vapors (Al, Ni, Pd, Pt, Cr, Zr, Dy, Er and Co) with propene at -196°C by subsequent deuterolysis of the cocondensates. No complexes were isolated, but it was assumed that D20 would label each metal-carbon bond present in the organometallic product. The deuterolysis of alumi-num-propene cocondensates was extensively studied, the products being mainly d2-propane, various isomeric d2-hexanes as well as some d°- and -propene. The formation of this would be rationalized in terms of the intermediate formation of 1,2-dialuminoalkanes, aluminocyclopro-panes, and aluminocyclopentanes (104, 110, 116), e.g., 

Similar results were obtained with erbium, dysprosium, and chromium vapors (104, 115). However, on deuterolysis, most transition metal cocondensates afforded mainly unlabeled propene with only two traces of propane and hexanes (104, 107, 110). The differing reactions of metal vapors with propene were interpreted in terms of a change in the r- and 7r-bonding propensities of the metal in the initial (unisolated) organometallic product on progressing along a period in the periodic table (110). 

The structure and properties of the initial nickel atom-propene complex has received detailed attention by Skell. The use of isotopically labeled propenes demonstrated that exchange occurs between the 1- and 3-positions but not between either the 1- and 2- or 2- and 3-positions (10)  

Similarly, condensation of a mixture of CsHe and C3D6 with nickel vapor resulted in isotopic scrambling. The intraligand isomerizations may be explained in terms of a 1,3-hydrogen shift via a nf-allyl nickel hydride complex in equilibrium with a ir-propene complex, e.g., 

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