DFT study and NBO analysis of the metallotropic shifts in cyclopentadienyl(trimethyl)silane, -germane and -stannane

Based on the optimized ground state geometries using B3LYP/3-21G, B3LYP/3-21G* and B3LYP/LANL2DZ* methods, the NBO analysis of donor-acceptor (bond-antibond) interactions revealed that the stabilization energies associated with the electronic delocalization from σC5-M bonding orbitals to π*C1C2 and π*C3C4 antibonding orbitals of cyclopentadienyl ring, increase from compounds 1 to 4. Also, the donor-acceptor interactions, as obtained from NBO analysis, could fairly explain the decrease of occupancies of σC5-M bonding orbital and the increase of occupancies of both πC1=C2* and πC3=C4* anti-bonding orbitals in cyclopentadienyl rings, from compounds 1 to 4. Therefore, the results suggest that in compounds 1-4, the metallotropic shifts are controlled by σ→π* energetic stabilizations, and also the increase of the σ→π* delocalization energy facilitates the M(CH3)3 group migration around cyclopentadienyl ring in these compounds.