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

2013-06-24T00:00:00Z (GMT) by Han-Gook Cho Lester Andrews
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.