Reactions of Methane with Hafnium Atoms: CH2HfH2, Agostic Bonding, and (CH3)2HfH2

Laser-ablated hafnium atoms react with methane to form the methylidene complex CH 2 HfH 2 . The activation of a second CH 4 molecule forms (CH 3 ) 2 HfH 2 particularly on sample annealing. These molecules are identified from infrared spectra by isotopic substitution (CH 4, 13 CH 4, CD 4, CH 2 D 2 ) and comparison to DFT frequency calculations. The computed structure for singlet ground state CH 2 HfH 2 shows CH 2 and HfH 2 distortion and evidence for agostic bonding (angle H−C−Hf, 95.6°), which is more stable than the symmetrical nonagostic structure. The CHD HfHD isotopic molecules provide experimental evidence for agostic bonding distortion. In addition, changes within the absorptions of the CHD HfHD isotopic molecules on annealing the argon matrix to 20−26 K demonstrates facile interchange of the agostic bonding positions.