The reaction of 2,3,5,6tetrakis(methylene)bicycle [2.2.2]octane (la) with Fez(CO), yields the two (q4-1,3diene)Fe(CO)3 isomers (2: exe; 3:endo) together with two bimetallic isomers (CIZH14)[Fe-(CO)3]2 (4:endo+xo; S:diexo). The reaction of la with RuB(CO)iZ yields the endo-(C1&14)Ru(CO)3 (6) and endo, exo-(C,,H,,)[Ru(CO),]z (7) complexes as the main products. The molecular structure of 3 has been determined by X-ray crystallography. The Fe(CO)J group is in the endo position with respect to the roof-shaped tetraene. The &and is bound through one diene group to two basal positions of a tetragonal pyramidal Fe(CO)9L, moiety. Hydrogen atom positions have been determined (final residual R = 0.029). The dimensions for the 1,3-butadieneirontricarbonyl system, as found in this and 41 other structures, are summarized and discussed statistically. In this study the weighted averages for all structures show the three C-C distances to be of equal length and the Fe-C (inner) distance to be shorter than the Fe-C (outer) distance. The deviations of H(Z) and H(E) atoms from the butadiene plane, as found in this and 6 other structures having an exocyclic unsubstituted 1,3diene group, are also discussed. Neither thermal epimerization of iron nor epimerization catalyzed by H+ were found for complexes 2 -7 whose structures in solution were deduced from their 'H and 13C NMR data on the basis of the known
structure of 3. been prepared for the first time in our laboratory [l-3] . z &I Z = CHs-CHs la Z=CH=CH lb ;:; Z=CHa lc PI z=o Id [31 la-d These roof-shaped molecules have two homoconjugated s&s-butadiene groups and can be attacked by metal carbonyls on their exo or endo faces, thus leading to mixtures of exo and endo-M(C0)3-diene complexes [4]. We report in this study the results of the reaction of la with iron and ruthenium carbonyls as well as the crystal structure of the endo-(C&#e(CO) 3 complex (3) and a statistical comparison of the dimensions of the 1,3_butadieneirontricarbonyl system in 42 structures. Reaction of la with Fe and Ru Carbonyls Upon treatment with yields the expected exo-
8