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
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Abstract
Manganese
insertion, vinyl, and cyclic complexes are prepared in
direct reactions of excited Mn atoms with CH<sub>4</sub>, C<sub>2</sub>H<sub>6</sub>, C<sub>2</sub>H<sub>5</sub>Cl, and CH<sub>2</sub>ClCH<sub>2</sub>Cl, all with sextet ground states. The only organometallic
product observed in the reaction with methane is CH<sub>3</sub>–MnH.
The analogous insertion product C<sub>2</sub>H<sub>5</sub>–MnH
is observed with ethane, but hydrogen elimination is accompanied by
generation of the vinyl product (CH<sub>2</sub>CH–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 CH<sub>3</sub>–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
CH<sub>3</sub>–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