Infrared Spectra of Manganese Insertion, Vinyl, and Cyclic Complexes Prepared in Reactions of Laser-Ablated Mn Atoms with Methane, Ethane, Ethyl Chloride, and 1,2-Dichloroethane

Manganese insertion, vinyl, and cyclic complexes are prepared in direct reactions of excited Mn atoms with CH₄, C₂H₆, C₂H₅Cl, and CH₂ClCH₂Cl, all with sextet ground states. The only organometallic product observed in the reaction with methane is CH₃–MnH. The analogous insertion product C₂H₅–MnH is observed with ethane, but hydrogen elimination is accompanied by generation of the vinyl product (CH₂CH–MnH). The unusual stabilities of metallacyclic over carbene products in the haloethane systems are in line with the previously observed group 4 metallacyclopropanes. NBO analyses reveal that the distinctively low metal d-orbital contribution to the C–M and M–H bonds is responsible for the linear backbones of CH₃–MnH and the group 12 metal analogues, which are similar to those of the Grignard reagents. Systematic NBO calculations for the first-row transition-metal CH₃–MH complexes show that a low metal d-contribution to the C–M and M–H bonds gives a linear molecular backbone and that increasing d-character in these bonds decreases the C–M–H angle. The stabilities of the half-filled and filled d-orbitals evidently make the group 7 and 12 metals similar to the group 2 metals. The tendency of increasing preference for higher oxidation state complexes with heavier members of the group is most dramatic for the group 7 metals Mn and Re.