2ₛ + 2ₛ Reactions at Transition Metals
<p>A study of the suprafacial 2 + 2 reaction at transition metal centers is presented. It is demonstrated that this reaction is allowed and proceeds with a low activation energy if the reacting transition metal-to-substituent bond is covalent, nonpolar, and has a large component at transition...
| Summary: | <p>A study of the suprafacial 2 + 2 reaction at transition metal centers is presented. It is demonstrated that this reaction is allowed and proceeds with a low activation energy if the reacting transition metal-to-substituent bond is covalent, nonpolar, and has a large component at transition nickel d-orbital character. These chains are evinced by examination of 2<sub>s</sub> + 2<sub>s</sub> reactions at M-H bonds. Those systems in which M can use d orbitals show lower barriers to the 2<sub>s</sub> + 2<sub>s</sub> reaction than those in which M cannot use d orbitals.</p>
<p>The importance of the electronic structure of the metal-to-substituent bond is highlighted by a study of dichorotitanacyclopropane. This molecule, being a metallacyclopropane, can undergo 2<sub>s</sub> + 2<sub>s</sub> reactions which one unavailable to a simple olefin.</p>
<p>Studies concerning the importance of 2<sub>s</sub> + 2<sub>s</sub> reactivity in the organic chemistry of nickel, and in the Ziegler-Natta polymerization of simple olefins are presented.</p>
<p>It is suggested that the principle of maximum bonding (the Woodward-Hoffmann rules) implies the conservation of transition metal covalency in low-energy catalytic cycles.</p> |
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