Square pyramidal-bridged butterfly interconversions

The facile interconversion between square pyramid and the pseudotvigomX bipyramid geometry (bridged butterfly) dominates the chemistry of Rii5C(CO)i5 and its derivatives. The square-pyramidal ruthenium cluster, Ru5C(CO)i5, is isolated in quantitative yield from the degradative carbonylation of Ru6C(CO)i7, which yields both the pentamer and Ru(CO)s.  

The kinetics of the reaction of Ru5C(CO)i5 with 21 P-donor nucleophiles, L, has been studied. The products from these reactions are not addition products but substitution products of formula Ru5C(CO)i4L. It was found that two different mechanisms are in operation during the substitution process, depending upon the 

The reverse isomerization, viz. I — II, occurs under photolytic conditions when I is embedded in a polymer film. A pseudovotation involving Ru-Ru bond cleavage is believed to bring about the rearrangement. The apparent conflict between the thermal and photolytic processes is probably a result of heterolytic and homolytic Ru-Ru bond fission brought about by the different initiation techniques. 

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