Stanley I. Goldberg
University of South Carolina Columbia, South Carolina
A Useful Metallocene Stereomodel
In the course of our studies of ferrocenecontaining systems, the need for a good stereomodel of the ferrocene nucleus arose. We tried to meet the need with such makeshift devices as models constructed out of stiff paper, but each device suffered from major drawbacks. We now feel that we have produced a highly useful and versatile ferrocene stereomodel, the basic design of which is equally applicable to metallocenes other than ferrocene itself. It was clear that any useful stereomodel of ferrocene would have to possess two features not found in commercial stereomodel sets. First, the model should reflect realistically the low energy barrier to independent rotation of each cyclopentadienyl ring about the central iron atom.' The second feature should be the ability of the model to allow the cyclopentadienyl rings to cant or tilt slightly about the central iron atom as they apparently do, for example, in l,l-(tetramethylethylene)-ferr~cene.~ These two important properties are met simply in the present design shown in the accompanying figure. The tube and rod connections from each of the two cyclopentadienyl rings to the central iron atom (a tight spring) allow the required independent rotation. The use of a tight spring to represent the central iron atom permits each of the cyclopentadienyl rings to be inclined to oblique orientations when necessary. The utility of these design features were further
' ROSENBI~UM, M.,. ~ N DWOODWARD, R. B., J . Am. Chem. Soe., 80, 5443 (1958).
= KINEHART,K. L.,
et al., J. Am. Chem. Soc., 82, 4111 (1860). DREIDING, A. S., H&. Chim. rlcla, 42, 1338 (1959). Itepresented in the U. S. by Swissco Instruments. Greenville. Illinois. DUNITZ, J. D., OXGEL,1,. E., :IND RICH,A., Acta Cryst., 9,373 (1956).
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enhanced by incorporating them into the general stereomodel concepts elaborated by Dreiding,a and by having the pieces shown in the figure so constructed that they correspond in both materials and scale to the presently available Dreiding stereomodel pieces offered by the W. Biichi Glasapparatefabrik of Flawil, Switzerland.4 To this end we enlisted the cooperation of the Biichi Company in the custom construction of the pieces. The bond distances, angles, and interring distance were based on the X-ray crystallographic d o terminations of Dunitz, Orgel, and Rich." There is an additional feature to the present model. One of the cyclopentadienyl rings is constructed with three of the five coplanar carbon-hydrogen bonds as rods and the remaining two as tubes. This arrangement is reversed in the second cyclopentadienyl ring in order to provide for a maximum flexibility in the assembly of complex ferrocene-containing systems.
