Tricarbonylchromium complexes of centro-polyindans. 2. Synthesis and structure of tricarbonylchromium mono-complexes and bis-complexes of 4b,5,9b,10-tetrahydroindeno[2,1-a]indene

The reaction of 4b,5,9b,10-tetrahydro[2,1 -a]indene, DIN, with Cr(CO)6 in Bu2O-THF (9:1) affords two mono-complexes with the inorganic unit bonded to the convex or to the concave side of the ligand, respectively. Prolonged reaction times cause the formation of two bis-complexes, bearing the two Cr(CO)3 units bonded both to the convex side of DIN in one case, and to the convex and to the concave side in the other. Steric factors seem important in the kinetic control of the stereochemistry of both the first and the second complexation reaction. Combined X-ray and NMR spectroscopic analyses indicate that coordination with two Cr(CO)3 groups at the convex side of DIN changes the structure of the ligand into a less bent and less favourable structure.