Chromium tricarbonyl complexes with biphenylene as η6 ligand:: synthesis, structure, dynamic behaviour in solid state and thermal η6,η6-haptotropic rearrangements.: Experimental (NMR) and theoretical (DFT) studies

The reaction of biphenylene (1) with Cr(CO)(3)Py-3/BF3.OEt2 at 25 degreesC gives a mixture of two known isomeric complexes: tricarbonyl(1-4,4a,8b-eta(6)-biphenylene)chromium (2) (yield 62%) and hexacarbonyl(mu-eta(6):eta(6)-biphenylene)bis-chromium (3) (yield 4%). Complexes 2 and 3 were separated by thin layer chromatography on silica and characterised by H-1 and C-13, as well as C-13 CP MAS-NMR. X-ray structure analysis for 3 proved trans-orientation of the chromium tricarbonyl groups. A novel regioselective method for the synthesis of (eta(6)-biphenylene)chromium tricarbonyl complexes bearing a substituent R (D (4), CH3 (5)) in position 1 of the coordinated ring was proposed. The kinetics of eta(6),eta(6)-inter-ring haptotropic rearrangement (IRHR) for 4 in inert, noncoordinating C6F6 was investigated by H-2-{H-1}-NMR spectroscopy' Density function theory (DFT) calculations for ground, intermediate and transition states were done and fitted well with experiment. (C) 2002 Elsevier Science B.V. All rights reserved.