Exohedral metallofullerenes have recently attracted much attention concerning the effects of metal coordination on the chemical and physical properties of C 60 . [1] Most approaches to forming metal complexes have been based on metal ± C 60 pcomplex chemistry, which has resulted in h 2 -C 60 , m-h 2 ,h 2 -C 60 , and m 3 -h 2 ,h 2 ,h 2 -C 60 ligands in monometallic (for most metals), [2] bimetallic (Re 2 , Ru 2 , Ir 2 ), [3] and metal cluster complexes (Ru 3 , Os 3 , Ru 5 C, Ru 6 C, PtRu 5 C), [4,5] respectively. Metal clusters can potentially accommodate all these C 60 bonding modes, but the interaction of C 60 with cluster frameworks has been, thus far, dominated by the face-capping cyclohexatriene-like bonding mode, m 3 -h 2 ,h 2 ,h 2 -C 60 . The mh 2 ,h 2 -C 60 bonding mode has never been observed on a cluster framework, although it has been postulated as an intermediate for the transformation of [Os 3 (CO) 11 (h 2 -C 60 )] to [Os 3 -(CO) 9 (m 3 -h 2 ,h 2 ,h 2 -C 60 )] by loss of carbonyl ligands. [5c] The interconversion among the three kinds of the C 60 ligands remains to be established in the area of C 60 ± metal cluster chemistry. We have recently observed the elusive m-h 2 ,h 2 -C 60 bonding mode on an Os 5 C cluster framework, and furthermore demonstrated that the two C 60 bonding modes m-h 2 ,h 2 and m 3 -h 2 ,h 2 ,h 2 are interconvertible.
Reaction of [Os 5 C(CO) 12 (PPh 3 )(NCMe) 2 ] with C 60 in refluxing ClC 6 H 5 produced a mixture of 1 and 2 (see the [Os 5 C(CO) 11 (PPh 3 )(m 3 -h 2 ,h 2 ,h 2 -C 60 )] 1 [Os 5 C(CO) 12 (PPh 3 )(m-h 2 ,h 2 -C 60 )] 2
Experimental Section). The conversion of 1 into 2 could be effected by heating a solution of 1 in ClC 6 H 5 at 80 8C under 1 atm of carbon monoxide. Upon thermolysis at 132 8C, 2 was cleanly reconverted into 1 by loss of a carbonyl ligand (Scheme 1). The solid-state structure of 1 is isomorphous to that of the ruthenium analogue [Ru 5 C(CO) 11 (PPh 3 )(m 3 -h 2 ,h 2 ,h 2 -C 60 )]. [4b] The structure of 2 (Figure 1) reveals a very intriguing feature excellent, which is unusual for such reactions. The stepwise procedure allows the highest ee values to be obtained together with high chemical yields. [23] These results show the wide scope of such aldol reactions, with certain limitations for bulky and/or conjugated aldehydes (results not optimized). The use of bulkier trialkylsilyloxyfurans slightly improved the d.r.; further optimization studies are in progress. Furthermore these findings may provide some evidence for amplification of ee values of biomolecules (by chemical reactions) in the chemical origins of life. Indeed, conditions for aldol reactions may have been found in prebiotic systems. More experiments are nevertheless needed to set a mathematical model for such a mechanism. [24] Such a process could also be involved in other asymmetric reactions. [23,25,26]