Tricyclic tin(IV) cages: Synthetic aspects and intriguing features of stannatranes and pseudostannatranes

Tin(IV) tricycles form a class of structurally unique and topologically attractive molecules with challenging synthetic attributes. Particularly, “stannatranes and pseudostannatranes” are one of the most intensively studied representatives of tin(IV) tricycles. In light of the recent research perspective, this review discuss the progress of stannatranes and pseudostannatranes over the past decades. Herein, stannatranes and pseudostannatranes are arranged into various groups based on their cage skeletons. The synthetic aspects of stannatranes are summarized for different categories of ligating systems viz. stannatranes with nitrilotriethanolate cage, aminotricarboxylate cage, and substituted nitrilotriethanolate cage. Likewise, detailed synthetic discussions of pseudostannatranes are presented in subsequent sections comprising [3.3.3.01,5], [4.3.3.01,5], [4.4.3.01,5] and [4.4.4.01,6] cages. Further, intriguing features of stannatranes and pseudostannatranes like variation of Sn-N transannular bond, oligomerization, extended exocyclic bonds, aqueous chemistry and unique spectroscopic aspects are explained with appropriate examples. Stannatranes possess interesting structural topologies and physical features, which can be tuned by controlling the rigidity/flexibility of the ligating system. The choice of rigid skeletons mitigates oligomerization effects and allows access to highly stable monomeric frameworks. The stability of such systems in aqueous systems facilitates the formation of new hydrolytic species and allows chemical reactivity of exocyclic bond to obtain new stannatranes.