Prototropic and metallotropic migration of isolobal fragments on indol rings. Theoretical study and NBO analysis

Abstract

Molecular structures, energies, NBO analysis and sigmatropic behaviour of 1-Indenyl(dihydro)borane (1) and 1-Indenyl-threecarbonylcobalt(I) (2) were investigated using DFT and ab initio molecular orbital methods. In these compounds BH₂ and Co(CO)₃ fragments areisolobal. The Results of calculations using B₃LYP, HF and MP2methods [Basis set 6-311+G**] showed that -BH₂ and -Co(CO)₃ had similar behaviour in sigmatropic shifts. Prototropic shifts in compounds 1 and 2 have similar mechanisms too. Results showed that metallotrotropic shift is faster than Prototrpic shift in compounds 1 and 2. The activation energies (Ea) of Prototropic shift in compounds 1 and 2 are 18.83 and 17.38 kcal.mol^-1. These energies are higher than -BH₂ shifts in compound 1 (10.11 kcal.mol^-1) or migration of -Co(CO)₃ fragment in compound 2 (12.39 kcal.mol^-1)_. Lower amount of activation energy in borotropic shift and cobalt`s fragment shift show that rotation of boron and cobalt on the indol ring can happen in the ambient temperature. Calculation results revealed that migration of proton and Co(CO)₃ was carried out via suprafacial[1,2]-sigmatropic mechanism while -BH₂ shift took place via antrafacial [1,3]-rearangment.