Lewis base addition reactions with clusters

For example, opening of the cluster skeleton from closo to nido to arachno will accompany the addition of electron pairs, whether by reduction reactions or by addition of Lewis base molecules that do not dislodge other Lewis bases. Cluster closing is expected to accompany the removal of electron pairs, whether by oxidation or by loss of a substituent together with the electron pair by which it was formally bound to the cluster ... 

As mentioned above, addition of electron donors to electronic saturated species normally results in cluster degradation. However the presence of special multi-bridging substituents sometimes permits the addition of neutral Lewis bases without cluster degradation. Nonetheless the addition always implies the rupture of metal-metal bonds. The fragments remain, however, close by the bridging ligands. That is illustrated schematically for the reaction of the mixed-metal cluster MnFe2(CO)8Cp(//3-PR) with various electron donors in Fig. 2.57. 

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