Infrared Spectra of Planar and Agostic-Like Bridged Scandium Methylidene Complexes Prepared in Reactions of Laser-Ablated Sc Atoms with Di-, Tri-, and Tetrahalomethanes

Abstract

Reactions of laser-ablated Sc metal atoms with di-, tri-, and tetrahalomethanes were carried out in excess argon during condensation, and the matrix infrared spectra of products were investigated. Scandium methylidenes are the primary products, and they have planar or bridged structures depending on the degree of halogen substitution in the precursor, whereas neither insertion nor methylidyne complexes were observed. Although these Sc methylidene complexes are not agostic as far as any C–H bonds are concerned, numerous bridged halogen agostic-like structures arise through electron donation from the halogen atom bonded to carbon to the scandium metal center. This bridged methylidene is in fact an intermediate between the methylidene and methylidyne complexes. The 3d14s2 electronic structure prevents scandium from generating higher oxidation state products, and the bond order of the methylidene C–Sc bond is approximately 1.5 or 1.0 for planar or bridged structures, respectively.