SYNTHESIS, STRUCTURE AND CONFORMATION OF CIS-(MU-1,6-DIMETHYLHEPTALENE)BIS(TRICARBONYLIRON) AND ANS-(MU-1,6-DIMETHYLHEPTALENE)BIS(TRICARBONYLIRON)

The reaction of 1,6-dimethylheptalene (2) with Fe-2(CO)(9) affords two binuclear iron complexes 4a and 4b, each bearing two tricarbonyliron moieties, in trans and cis orientation, respectively. The reaction lea ds additionally to the formation of the monocomplexed compound 3. NMR studies indicate that the heptalene moiety of the new compounds is a p i-bond isomer of 2, and this is clearly attributable to steric factors . Single-crystal X-ray structure analyses of the metal complexes 4a an d 4b confirm that the Fe(CO)(3) fragments adopt trans and cis geometri es, respectively, with respect to the plane of the carbocycle. The rin g systems of the two isomers adopt different conformations in the soli d state. In the case of 4a, a hitherto unknown chair-like conformation is determined, whereas in complex 4b the ring system shows a twisted double boat conformation.