Framework rearrangements fluxionality

The cyclic processes coupled with the framework rearrangement lead to total exchange of all the carbonyl ligands of the cluster in this final fluxional process. 

Reduction of the pentaalkyl-1,5-dicarba-closo-pentaboranes(5) 44 with elemental K opens the cluster and subsequent reaction with I2 enforces oxidative fusion of two C2B3 units to give a C4B6 cage (Scheme 3.2-36). The peralkylated hexaboraadamantane derivatives 70 (R = Me, Et X-ray structure analysis for R = Me [89]) rearrange irreversibly into the carboranes 71 with a wido-C4B6 framework [89] (X-ray structural analysis for R = Et [90]). The structure of the nido-C Bf, cluster is fluxional in solution [91]. 

Molecular Dynamics of H FeR CCO)-] and Related Mixed-Metal Clusters. Metal clusters have been shown to undergo a wide variety of fluxional processes in which carbonyls, hydrides, and even the metals themselves undergo rearrangement (25). Mixed-metal clusters are ideally suited for studies of fluxional processes because of the low symmetry which is inherent within their metal framework. In such clusters, the majority of... 

Most recent quantum chemical calculations involving [n]-ladderanes suggest a defect in the ladderane framework, in the form of an olefin pair, can result in fluxional molecnles named sigmatropic shiflamers." " " The fluxional natnre wonld stem from the ability of the olefin pair to travel across the defective ladderane framework via a series of Cope rearrangements (Fignre 12). Calcnlations predict the flnxionahty of the molecnles depends on the size of the framework. Specifically, [n]-ladderanes with n > 7 are expected to be fluxional at and above room temperatnre. 

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