Investigation of agostic interaction through NBO analysis and its impact on β-hydride elimination and dehydrogenation: a DFT approach

Structural Characterization of β-Agostic Bonds in Pd-Catalyzed Polymerization

“…Agostic complexes are commonly assumed to be intermediates in catalytic reactions going through C–H activation and β-H elimination steps . Consequently, characterization of agostic bonds has attracted extensive interest. , Crystallography, including X-ray and neutron diffraction, serves as the key characterization method for agostic complexes. Among group 10 transition metals, single-crystal structures of Ni and Pt β-agostic complexes have been reported by us and others.…”

Quantum Crystallography and Complementary Bonding Analysis of Agostic Interactions in Titanium Amides

“…Some of the most commonly used criteria for the identification and characterization of the agostic bond involve: 1 ) geometry , elongation of the C−H bond, relatively short H⋅⋅⋅M distances (1.8–2.3 Å), small C−H⋅⋅⋅M angles (90–140°) and increasing C⋅⋅⋅M⋅⋅⋅H angles; [18] 2 ) IR vibrational spectroscopy , a red shift of the C−H stretching vibration [19] related to the C−H bond elongation/weakening and larger values of the C−H compliance constant; [20] 3 ) 1 H‐NMR spectroscopy , low 1 J CH value (50 to 100 Hz) and an upfield shift δ H relative to an uncoordinated CH group; [18,21] 4 ) electron density , a quantum theory of atoms in molecules (QTAIM [22] ) topological electron‐density pattern indicating the presence of a M⋅⋅⋅H interaction [23] as well as a region of local charge depletion at the metal ion core; [24,25] 5 ) bonding descriptors based on natural bond orbitals (NBO [26] ), electron localization and localizability functions (ELF, [27] ELI [28] ) or the non‐covalent interaction (NCI [29] ) index [30–33] …”

“…Some of the most commonly used criteria for the identification and characterization of the agostic bond involve: 1) geometry, elongation of the CÀ H bond, relatively short H•••M distances (1.8 -2.3 Å), small CÀ H•••M angles (90-140°) and increasing C•••M•••H angles; [18] 2) IR vibrational spectroscopy, a red shift of the CÀ H stretching vibration [19] related to the CÀ H bond elongation/weakening and larger values of the CÀ H compliance constant; [20] 3) 1 H-NMR spectroscopy, low 1 J CH value (50 to 100 Hz) and an upfield shift δ H relative to an uncoordinated CH group; [18,21] 4) electron density, a quantum theory of atoms in molecules (QTAIM [22] ) topological electron-density pattern indicating the presence of a M•••H interaction [23] as well as a region of local charge depletion at the metal ion core; [24,25] 5) bonding descriptors based on natural bond orbitals (NBO [26] ), electron localization and localizability functions (ELF, [27] ELI [28] ) or the non-covalent interaction (NCI [29] ) index. [30][31][32][33] From an experimental point of view, there are two major problems or challenges related to the above criteria: 1) All criteria depend critically on the hydrogen atom; and for all but the spectroscopic criteria, no reliable statement can be made without an accurate and precise localization of the hydrogen atom in the agostic bond from diffraction experiments. 2) Electrondensity related criteria of agostic interactions can be assessed through modelling of the experimental charge density based on high-resolution, low-temperature single-crystal X-ray diffraction experiments.…”