metal-organic compounds
threne FeCp hexafluoridophosphate gave rise to a mixture of
both in-fold and out-of-fold isomers, as found in a crystal-
lographic study of the reaction products (Hendsbee et al.,
2009). The only previously reported out-of-fold thianthrene
complex was obtained, along with its in-fold isomer, in a
different reaction, a photolytic demetallation of a mixture
containing cis- and trans-di(ꢀ5-Cp)(ꢀ6,ꢀ6-thianthrene)(iron)2
bis(hexafluoridophosphate)s, which were prepared in a ligand-
exchange reaction (see Abboud et al., 1990).
Two phenoxathiin complexes which were obtained using a
double nucleophilic substitution reaction have been reported
in the literature to date. Both (phenoxathiin)FeCpPF6 (Lynch
et al., 1986) and [(5a,6,7,8,9,9a-ꢀ)-1,4-benzoxathiino[3,2-b]-
pyridine]FeCpPF6 (Sutherland et al., 1988) contain, in the
solid state, only out-of-fold FeCp moieties. In both complexes,
the FeCp moiety is located outside the shallow heterocycle
fold, with hinge angles of 178.7 (1) and 176.8 (1)ꢀ for the
phenoxathiin and azaphenoxathiin complexes, respectively.
The hinge angle for the free phenoxathiin molecule was
reported as 138ꢀ (Hosoya, 1966) and as 147.8ꢀ (Fitzgerald et
al., 1991; 223 K). This angle has yet to be reported for the
uncoordinated azaphenoxathiin molecule. It appears then that
FeCp complexation flattens the phenoxathiin skeleton. In this
study, it was found that the FeCp moiety is located inside the
phenoxathiin 10,10-dioxide fold, with a hinge angle of
169.9 (2)ꢀ between the two peripheral benzene rings. Thus,
oxidation of the S atom in the central ring appears to coun-
teract the effect of FeCp complexation, causing more
pronounced folding of the heterocycle molecule and appar-
ently converting the FeCp-out-of-fold isomer into the FeCp-
in-fold one. For free phenoxathiin 10,10-dioxide, we found the
hinge angle to be 171.49 (6)ꢀ, which means that when this
molecule is coordinated to FeCp it is slightly more folded. This
is the first confirmed example, and only the second case in
which FeCp coordination appears to increase folding of the
tricyclic heterocycle molecule. In the earlier case, this effect
was observed in the structure of a methylthianthrene molecule
carrying a methyl group in an uncoordinated benzene ring.
The structure of the free heterocycle, 2-methylthianthrene, has
not yet been reported, so the folding angle of a parent
thianthrene molecule was used for comparison (Simonsen et
al., 1985). A similar effect was reported for a structurally
related thioxanthene molecule, with a methylene group
replacing the O atom in the central ring. Literature reports
indicate that oxidation of the S atom to a dioxide results in
slightly more pronounced folding of the molecule. For thiox-
anthene, the hinge angle was reported as 135.3 (1)ꢀ (Gillean et
al., 1973), while for thioxanthene 10,10-dioxide this angle was
133.9ꢀ (Chu & Chung, 1974).
Figure 2
The free heterocycle, (II), showing the atom-labelling scheme. Displace-
ment ellipsoids are drawn at the 50% probability level. H atoms have
been omitted for clarity.
the two Fe—C(quaternary) distances are the longest of all six
distances (Lynch et al., 1986; Sutherland et al., 1988).
The C—C distances in the coordinated ring of phenoxathiin
10,10-dioxide appear to be the same length as those in the
uncoordinated ring, with the average distances being 1.401 (6)
and 1.387 (6) A, respectively. The C—S bonds extending from
both the coordinated and uncoordinated ring C atoms to the
bridging S atom are similar in length [1.757 (4) and
˚
˚
1.743 (4) A, respectively]. The C—O distances, however, are
quite different, as the bond extending from the bridging O
atom to the C atom of the coordinated ring is significantly
shorter than the C—O bond extending towards the uncoor-
dinated ring [1.361 (5) and 1.393 (5) A, respectively]. Both
these observations agree with earlier findings for phenoxathiin
and azaphenoxathiin complexes (Lynch et al., 1986; Suther-
´
land et al., 1988) and for dibenzodioxin complexes (Piorko et
al., 1994, 1995; Hendsbee et al., 2010).
The C—C bonds in the rings of the free heterocycle,
phenoxathiin 10,10-dioxide, (II), have similar average lengths
˚
˚
[1.385 (2) and 1.387 (2) A] and are similar in length to the C—
C bonds in the uncoordinated ring of complex (I). The S—C
bond lengths from the bridging S atom to the benzene ring C
atoms in the uncoordinated heterocycle are similar
[1.7471 (16) and 1.7481 (18) A] to those found in the complex.
The C—O distances in the free heterocycle are 1.369 (2) and
˚
1.371 (2) A, more similar to the length of the C—O bond
extending towards the coordinated ring of the FeCp complex
˚
[1.361 (5) A] rather than that extending towards the uncoor-
˚
˚
dinated ring of the FeCp complex [1.393 (5) A].
A double nucleophilic aromatic substitution reaction
yielding tricyclic heterocycle complexes may result in the
formation of FeCp-in-fold, FeCp-out-of-fold or both isomeric
molecules of the nonplanar tricyclic heterocycle in the solid
state. Examples of all three cases may be found in the litera-
ture, and all reports provide crystallographic data supporting
this statement. The earlier studies of the synthesis and struc-
ture of dibenzodioxin and thianthrene FeCp complexes
suggested that only FeCp-in-fold molecules are formed in such
a reaction. This conclusion was based on the results of several
crystallographic studies (Simonsen et al., 1985; Abboud et al.,
We suggest that both the increased folding and the location
of the FeCp moiety inside the fold may be requirements for
minimizing the interaction of S-bonded O atoms with Fe in a
complex. In this apparently favoured in-fold isomer, the
distance from Fe to the proximal O atom will be longer than
the analogous distance in the out-of-fold molecule. With a
relatively small hinge angle in the starting phenoxathiin mol-
ecule, thermal flipping of this molecule during oxidation,
´
1990; Christie et al., 1994; Piorko et al., 1994, 1995). Recently,
we reported that a double nucleophilic substitution reaction
leading to the formation of (1,2,3,4,4a,10a-ꢀ)-1-methylthian-
ꢁ
m352 Hendsbee et al. [Fe(C5H5)(C12H8O3S)]PF6 and C12H8O3S
Acta Cryst. (2011). C67, m351–m354
Hendsbee, Arthur D.
