Simulating the Agostic Interaction in Electron-deficient (16-e) Group (VI) ML6 Complexes: [M(CO)5(C(Me)OMe)] (2+) (M = Cr, Mo, and W) as Models
A large number of theoretical studies have focused on understanding the molecular features of the agostic interaction in various kinds of molecular environments. However, there is a lack of electronic structure information about the agostic interaction in electron-deficient group (VI)ML6 organometallic complexes. In this simulation study, a unique case of an intramolecular stabilizing interaction has been discovered and evaluated. A geometric analysis revealed that beta-(C-H) and alpha-(C-C) can occupy the seventh and eighth coordination sites in the title Fischer carbene complexes as agostic interactions, which allows classifying the carbene as a η3 ligand in these cases. This theory was supported by the relative energies of the conformers and an NBO analysis. Both C2-C1 (σ) and C2-H1 (σ) were found to interact with the antibonding orbital of M-C6 (σ*), therefore these interactions are classified as σ→σ*. These two simultaneous interactions have significant impact on the carbene characteristics; the structure, the atomic charges, infrared stretching vibrations (C-H, C-C, and C-O), and the 1H and the 13C-NMR chemical shifts. From a fundamental organic-organometallic chemistry point of view, this is a new addition to the orbital interaction theory and to group (VI) chemistry.
Keywords: DFT, agostic interaction, NBO analysis, NPA charges, IR, GIAO-NMR