SYNTHESIS, STRUCTURE, AND REARRANGEMENTS OF NEW TRICARBONYLCHROMIUM COMPLEXES OF SUBSTITUTED HEPTALENES

Reactions of 1,2,5,6,8,10-hexamethylheptalene (1) and its bond isomer, 1,4,5,6,8,10-hexamethylheptalene (2), with tricarbonylchromium comple xes L(3)Cr(CO)(3) (L = NH3 and Py) have been investigated. Thermodynam ically less stable complex 1 exhibits higher reactivity with respect t o Py(3)Cr(CO)(3)/BF3 . Et(2)O under the conditions of Ofele's reaction than complex 2. At 10-30 degrees C, the Cr(CO)(3) group is coordinate d to the asymmetrically substituted ring, which is accomplished by the shift of double bonds in the ligand, to afford tricarbonyl-[1,4,5,6,8 ,10-hexamethyl-eta(6)-(10a, 1-5) heptalene]-chromium (6) as the only m ononuclear complex. Under more drastic conditions (Raush's reaction, 8 0 degrees C), 1 <-> 2 interconversion proceeds faster than the reactio n of individual bond isomers with coordinatively unsaturated ''hot'' p articles (solv)(n)Cr(CO)(3). In this case, all of the four possible is omeric mononuclear complexes (6-9) and two binuclear complexes (10 and 11) are formed. The structures of complexes 6-11 have been studied by NMR and mass spectrometry, the structure of 6 has been established by X-ray diffraction analysis. Heating a solution of 6 in octane at 115 degrees C results in the isomerization of 6 into complex 7 through the intracycle 1,2-shift of the Cr(CO)(3) group and also in its conversio n into complex 8, which is the first example of interring eta(6)-->eta (6)-haptotropic rearrangement in nonplanar seven-membered pi-systems.