2ₛ + 2ₛ Reactions at Transition Metals

Citation

Steigerwald, Michael Louis (1984) 2ₛ + 2ₛ Reactions at Transition Metals. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/S0HZ-TF05. https://resolver.caltech.edu/CaltechETD:etd-01032007-142600

Abstract

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_s + 2_s reactions at M-H bonds. Those systems in which M can use d orbitals show lower barriers to the 2_s + 2_s reaction than those in which M cannot use d orbitals.

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_s + 2_s reactions which one unavailable to a simple olefin.

Studies concerning the importance of 2_s + 2_s reactivity in the organic chemistry of nickel, and in the Ziegler-Natta polymerization of simple olefins are presented.

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.

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