Chemistry Reference
In-Depth Information
5
Fig. 12 Metal-ring and other chemical interactions in (
-C
5
H
5
)Mn(CO)
3
using the bond path
and the SF percentage descriptors; (a) the experimental molecular graph (bcps are shown in
red
,
rcps in
yellow
, and cage critical point in
green
); (b-f) source function percentage contributions
from atomic basins to the experimental electron density at different reference points (denoted by a
small yellow
sphere). These are (b) the Mn-C
2
bcp; (c) the C
2
-O bcp; (d) the Mn-C(Cp) bcp; (e)
the Mn-C(Cp) rcp; (f) the C-C bcp. Absolute source contributions less than 0.5% are not shown
(adapted from Figs. 2 and S23, with permission from [
83
], Copyright 2009, American Chemical
Society)
much alike to those found for terminal M-C(O) bonds in the dinuclear metal
carbonyls. The two bonded atoms yield about 68% of the bcp density and the
carbonyl O atom an additional 13%. As shown by Farrugia et al. [
72
], the large
contribution from the carbonyl O atom is not to be simply interpreted as a signal of
Mn-CO
p
back-bonding, since similar percentage source contributions are found
for the B-C bcp in the adduct H
3
B
back-bonding is possible.
In our view, this large SF contribution from the carbonyl O atom results from the
nonnegligible portion of the 3
s
HOMO lone pair orbital of CO lying into the O
basin ([
103
] and page 10061 of [
12
]) and the dominant role that such orbital plays in
the dative
CO where no B-C
p
bond to the metal [
103
].
When the rp is placed at the C-O bcp, the global contribution from the two
bonded atoms rises to about 98% (Fig.
12c
) as found for all other metal-carbonyls
thus far investigated. It is not just the sum which is transferable, but also the
separate contribution to this sum from the C and the O atoms, equal to about 41%
and 57%. The Mn-C
ring
bcps and the rcps pertaining to the three-membered rings
formed by the Mn and any two metal-bonded neighboring C atoms of the
s
-
hydrocarbyl ligand lie on an annulus of almost constant electron density and
p
