Methane and methyl halide activation by Sc atoms: Infrared spectra and DFT calculations for the CH3–ScX and CH2–ScHX complexes

Reactions of laser-ablated scandium atoms with methane and methyl halides have been done during condensation in excess argon, and matrix infrared spectra were recorded for the products. Scandium is as effective as titanium in producing insertion products (CH3–ScX, X = H, F, Cl, Br) and higher oxidation-state methylidene complexes (CH2–ScHX) following α-hydrogen migration. However, unlike the Group 4–6 metal complexes, the Group 3 methylidene complexes do not show agostic distortion, and the computed C–Sc bond lengths of the methylidene complexes are slightly shorter than those for the insertion products. This shows that carbon–transition metal bond lengths in the double bond range are needed to support the agostic interaction. The computed spin densities are consistent with weak C(p)–Sc(d) π-bonding in the methylidene complexes.