Tricarbonylchromium complexes of centropolyindans .4. Physicochemical and structural characterization of anti-Cr(CO)(3)-4b,9,9a,10-tetrahydroindeno[1,2-a]indene, syn-Cr(CO)(3)-4b,9,9a,10-tetrahydroindeno[1,2-a]indene and syn,anti-[Cr(CO)(3)](2)-4b,9,9a,10-tetrahydroindeno[1,2-a]indene

The reaction of 4b,9,9a,10-tetrahydroindeno[1,2-a]indene, B, with Cr(CO)(6) in boiling mixtures of Bu2O and tetrahydrofuran (THF) (9: 1) affords two mono-complexes, one of which bears the Cr(CO)(3) group bonded to the convex side of the ligand (anti complex, B1) and the other inorganic unit to the concave side of B (syn complex, B2), After prolonged reaction times, two bis-complexes were isolated, the first having one Cr(CO)(3) group bonded to the convex side of B and the other to the concave side (syn,anti bis-complex, B3), and the second having both of the inorganic groups bonded to the convex side of B (anti,anti bis-complex, B4), The results of X-ray structural analysis support the hypothesis that the stereochemistry of the first and the second metallation reaction are related to the conformation of the ligand as induced by the steric interactions between aliphatic hydrogen atoms, The results confirm the existence of weak bonding interactions between oxygen atoms of the syn-Cr(CO)(3) carbonyl groups with vicinal benzene rings bearing an anti-Cr(CO)(3) group as well as methylene protons.