The haptotropic rearrangement of dinuclear metal carbonyl species on the conjugate π-ligand of (μ2,η3:η5- 4,6,8-trimethylazulene)M2(CO)5 [M = Fe (3) and Ru (4)] was investigated in detail both experimentally and theoretically. The complexes, 3 and 4, were synthesized and characterized by spectroscopy and crystallography. The spin saturation transfer technique of 1H NMR was used to measure the rate constant k of the haptotropic isomerization between the two enantiomers of 3 and 4, from which thermodynamic parameters were determined: (3; ΔS‡ = -7 ± 1 cal K-1 mol-1, ΔH‡ = 22 ± 1 cal mol-1, ΔG ‡373 = 25 ± 1 cal mol-1), (4; ΔS‡ = 7 ± 1 cal K-1 mol-1, ΔH‡ = 25 ± 1 cal mol-1, ΔG ‡373 = 23 ± 1 cal mol-1). DFT calculations (the B3LYP, B1B95 and PBE1PBE methods) were also carried out using the CEP-31G and cc-pVDZ as the basis set of the transition metal and other elements, respectively, by which both ground state and transition state structures were optimized for the haptotropic rearrangement of 3 and 4. The potential energy surface for these reactions suggests that the reaction involves the conversion of the coordination mode from μ2, η3,η5- (ground state) to μ2, η1,η5- (transition state). Mechanistic consideration, in particular that of differences in transition states between the diiron and diruthenium complexes, is also described.
All Science Journal Classification (ASJC) codes
- Inorganic Chemistry