An unusual example ofendo-stereoselectivity in the ligand exchange reactions of rhodium(i)diethylene derivatives withpara-semiquinoid ligands
摘要:
The ligand exchange reactions of [(C2H4)(2)Rh(acac)] in benzene and [(C2H4)(2)RhCl](2) in CH2Cl2 with 4-methyl-4-trichloromethyl-2,5-cyclohexadiene-1-one occur with 100% exo-stereoselectivity. The similar process with 4-methyl-4-trichloromethyl-1-(4,4-dimethyl-2,6-dioxocyclohexylidene)-2,5-cyclohexadiene (trienedione) is strictly exo-stereospecific only if [(C2H4)(2)Rh(acac)] in benzene is used, while in the case of [(C2H4)(2)RhCl](2) in CH2Cl2, it proceeds with an endo-stereoselectivity of 43%. An explanation for these facts has been suggested that assumes that the metal atom initially attacks the central double bond in the trienedione, which is removed from the area of main steric hindrance. The subsequent metallotropic rearrangement of the resulting ethylene-triene intermediate gives rise to the final eta(4)-coordinated pi-diene structures.
Redox troponization of (η5-cyclopentadienyl)(η4-4-menthyl-4-exo-trichloromethylcyclohexa-2,5-dien-1-one)rhodium as a novel approach to the synthesis of metal-coordinated nonbenzenoid aromatics of the tropone seriesas a novel approach to the synthesis of metal-coordinated nonbenzenoid aromatics of the tropone series
作者:V. A. Nikanorov、T. V. Storozhev、S. G. Novikov、S. V. Sergeev、D. V. Zverev
DOI:10.1007/bf02503503
日期:1998.6
possibility of redox troponization of a gem-polyhalomethylated semiquinoid system, π-coordinated to a metal atom, was shown in relation to the reaction of (η5-cyclopentadienyl)(η4-4-menthyl-4-exo-trichloromethylcyclohexa-2,5-dien-1-one)rhodium with Pd(PPh3)4. The reaction occurs with retention of the metal coordination affording a sevenmembered organometallic derivative of the nonbenzoid aromatic series, namely