The synthesis of the cyclobutadiene dianion and cyclopentadiene dianion derivatives, as well as their application toward pyramidal clusters and multi-decker sandwiches, are discussed in this review. The preparation of both main group element and transition metal derivatives of the latter half-sandwich and sandwich complexes is presented, along with a discussion of their peculiar structural and bonding features.

Abstract

In this review, the current state of affairs in the application of tetrel cyclic polyene dianions, such as cyclobutadiene dianion and cyclopentadiene dianion, in the preparation of pyramidal clusters (pyramidanes) and multi-decker sandwiches is overviewed. The synthesis of both main group element and transition metal derivatives of the latter complexes is presented, along with a discussion of their peculiar structural and bonding features. The preference for either pyramidanes or sandwiches, depending on the nature of the central atom (main group element vs. transition metal), is also discussed.