(Phenalene)chromium tricarbonyl complexes. Synthesis, structure, and thermal rearrangements

The reaction of phenalene with Cr(CO)(3)Py-3/BF3. OEt2 gives a mixture of two isomeric complexes: tricarbonyl(6a,7-9,9a,9b-eta(6)-phenalene)ch (1) and tricarbonyl (3a,4-6,6a,9b-eta(6)-phenalene) chromium (2). Deprotonation of the mixture of 1 and 2 followed by the treatment with Mel, n-BuI, or D2O results in the formation of 1-exo-R-(1) complexes 3-5 ((3) R = Me, (4) R = n-Bu, (5) R = D). The molecular geometry of the complex 3 was characterized by a single-crystal X-ray diffraction study. Heating of 5 and 3 in toluene or C6F6 at temperatures 90-110 degrees C leads for 5 to deuterium label redistribution over the positions l-exo, I-endo; and 3 by means of sigmatropic shifts of exo- and endo-hydrogens in nonaromatic ring and inter-ring migrations of chromium tricarbonyl group, whereas for 3 the methyl label distributes over the positions 1-exo and 3 via the same processes resulting in the formation of structurally similar isomeric complexes 6-8 (6 = 1-exo-methyl-(2); 7 = 3-methyl-(2); 8 = 3-methyl-(1)), respectively, through the same processes as for isomerization of 5, excluding exo-hydrogen migrations. The mechanisms of these rearrangements are discussed.