Experimental and theoretical aspects of the haptotropic rearrangement of diiron and diruthenium carbonyl complexes bound to 4,6,8-trimethylazulene

摘要

The haptotropic rearrangement of dinuclear metal carbonyl species on the conjugate pi-ligand of (mu(2),eta(3):eta(5)-4,6,8-trimethylazulene)M-2(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 H-1 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; Delta S-double dagger = 7 +/- 1 cal K-1 mol(-1), Delta H-double dagger = 22 +/- 1 cal mol(-1), Delta G(373)(double dagger) = 25 +/- 1 cal mol(-1)), (4; Delta S-double dagger = 7 +/- 1 cal K-1 mol(-1), Delta H-double dagger = 25 +/- 1 cal mol(-1), Delta G(373)(double dagger) = 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 (ground state) to (transition state). Mechanistic consideration, in particular that of differences in transition states between the diiron and diruthenium complexes, is also described.