Tuning Haptotropic Rearrangements of Arene–Chromium Complexes: Steric and Electronic Effects of Phosphorus Coligands

(η 6 ‐Arene)tricarbonylchromium 2 was synthesised by [3+2+1] benzannulation of the Fischer carbene complex 1 and converted to the thermodynamically more favorable regioisomer 3 by haptotropic metal migration. Photo‐induced ligand‐exchange reactions in both regioisomers with triphenylphosphine, triphenylphosphite, trimethylphosphine, and trimethylphosphite afforded dicarbonyl(phosphine or phosphite)arene complexes 4 – 11 . The regioisomers were separated by high‐performance liquid chromatography (HPLC), and kinetic analyses of the thermo‐induced haptotropic metal shift were performed with regioisomers 4 , 6 , 8 , and 10 . The kinetic parameters were compared with those obtained for the parent tricarbonyl complex 2 and were discussed in terms of the steric and electronic properties of the phosphorus ligands by applying a quantitative analysis of ligand effects (QALE). The molecular structures of regioisomeric PPh 3 and P(OPh) 3 complexes 4 / 5 and 6 / 7 as well as of P(OMe) 3 complex 10 have been established by single‐crystal X‐ray analysis.