(Phenalene)chromium Tricarbonyl Complexes. Synthesis, Structure, and Thermal Rearrangements

Abstract

The reaction of phenalene with Cr(CO)3Py3/BF3·OEt2 gives a mixture of two isomeric complexes: tricarbonyl(6a,7−9,9a,9b-η6-phenalene)chromium (1) and tricarbonyl (3a,4−6,6a,9b-η6-phenalene) chromium (2). Deprotonation of the mixture of 1 and 2 followed by the treatment with MeI, 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 °C leads for 5 to deuterium label redistribution over the positions 1-exo, 1-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.