Hang-gliding with ferrocenes: Unusual coordination chemistry of 1,1′-bis(mesitylthio)ferrocene

Article abstract of DOI:10.1021/om0004388

A sterically hindered ferrocene ligand system was synthesized for the analysis of its unusual modes of corrosion with late transition metal centers. The ferrocene ligand was formed by the addition of a toluene solution of dimesityl disulfide to a suspensi

Full text of DOI:10.1021/om0004388

Organometallics 2000, 19, 4425-4428
4425
Ha n g-glid in g w ith F er r ocen es: Un u su a l Coor d in a tion
Ch em istr y of 1,1′-Bis(m esitylth io)fer r ocen e
Vernon C. Gibson, Nicholas J . Long,* Andrew J . P. White,
Charlotte K. Williams, and David J . Williams
Department of Chemistry, Imperial College of Science, Technology and Medicine,
South Kensington, London, SW7 2AY U.K.
Received May 24, 2000
Summary: A rare C,S-cyclometalated PtIV complex is one
of a series of transition metal complexes formed by the
new redox-active and sterically hindered ligand 1,1′-bis-
(mesitylthio)ferrocene. Simple PdII and PtII chelate spe-
cies can be synthesized by less forcing reaction condi-
tions, in addition to a Re2(CO)6Br2 dinuclear species
featuring the ferrocene ligand adopting a binucleating
role and forming an unusual “quasi-closed” bridged
structure.
dination that it undergoes with late transition metal
centers.
The new 1,1′-bis(mesitylthio)ferrocene ligand 1 was
formed by the addition of a toluene solution of dimesityl
disulfide5 to a suspension of 1,1′-dilithioferrocene in
hexane under a N2 atmosphere. The mixture was stirred
at room temperature for 16 h, then after an aqueous
workup and column chromatography (neutral grade II
alumina, 9:1 hexane/CH2Cl2 eluent), a yellow micro-
crystalline solid was obtained in 65% yield. This syn-
thesis follows an approach similar to that used in the
formation of other 1,1′-disubstituted ferrocenediyl sul-
fides,6 although it had been suggested that bulky
substituents such as tert-butylthio could not be incor-
porated due to the steric crowding and subsequent lack
of reactivity (nucleophilic cleavage) of the disulfide
starting reagents. We believe that 1,1′-ferrocene-derived
sulfur ligands have great potential in coordination
chemistry.7 The ligand shows a fully reversible redox
couple (E1/2 ) 0.68 V vs Ag/AgCl), but to date, electro-
chemistry on the complexes has proved inconclusive due
to the large positive shift in redox potentials.
Ligand 1 was then reacted with labile transition
metal centers so as to explore its coordination chemistry
(Scheme 1). First, a slight excess of 1 and Re(CO)5Br
were stirred in refluxing THF. The reaction was moni-
tored by infrared spectroscopy and shown to be complete
after 20 h with the appearance of three strong bands
at 2022, 1923, and 1908 cm-1 in the CO stretching
region, consistent with a fac-LRe(CO)3Br structure.
However, rather than the simple bidentate, chelate
(L-L)Re(CO)3Br species, mass spectrometry, and an
X-ray crystal structure determination indicated that an
unusual Re2(CO)6Br2 dinuclear species 2 had been
formed, the first to involve a ferrocenediyl sulfur ligand.
The only other “quasi-closed bridged” dirhenium struc-
ture, namely, Re2(µ-OMe)2(CO)6(µ-dppf),8 features bridg-
ing dppf and methoxo ligands but is formed from the
dinuclear starting reagent Re2(CO)10. Our system uti-
lizes the mononuclear starting species, Re(CO)5Br, and
thus illustrates that due to the steric bulk of the ligand,
the simple mononuclear chelate species cannot form, a
Ferrocene-containing materials are currently under-
going something of a renaissance due to their increasing
role in the rapidly growing area of materials science.1
The substitution of ferrocenes by various donor het-
eroatoms has led to a series of chelating ligands that
have found wide application, e.g., incorporation of
phosphines for homogeneous catalysis in organic syn-
thesis, chiral phosphines for enantiomeric synthesis,
and amino alcohols for asymmetric catalysis.1,2 Another
currently very topical area is the search for well-defined,
single-site organotransition metal olefin polymerization
catalysts, with some of the most significant recent
developments occurring with late transition metal
systems.3 We decided to couple these areas and target
ligands so as to (i) create redox-active centers, either
within the backbone or as pendant groups, which would
offer an opportunity to change quite dramatically the
electronic environment of the active site, and (ii) intro-
duce bulky, sterically hindered substituents, which can
strongly influence the productivity and microstructure
of polyolefins.
Initial results on the ability of titanium and zirconium
complexes bearing the chelating dianionic 1,1′-ferrocene-
ditholate ligand to polymerize ethylene have recently
been communicated.4 In the course of this research
program, we have observed some remarkable coordina-
tion chemistry and herein report the formation of a new,
sterically hindered ferrocene ligand system and the
unexpected chemistry and the unusual modes of coor-
* Corresponding author. Tel: +44 020 75945781. Fax: +44 020
75945804. E-mail: n.long@ic.ac.uk. V.C.G. and D.J .W. are also corre-
sponding authors.
(1) For a detailed literature review see: Togni, A., Hayashi, T., Eds.
Ferrocenes: Homogeneous Catalysis-Organic Synthesis-Materials
Science; VCH: Weinheim, Germany, 1995. Togni, A., Halterman, R.
L., Eds. Metallocenes; Wiley-VCH: Weinheim, Germany, 1998.
(2) For a comprehensive overview of ferrocene and other metallocene
chemistry see: Long, N. J . In Metallocenes: An Introduction to
Sandwich Complexes; Blackwell Science: Oxford, U.K., 1998.
(3) For a recent review article see: Britsovek, G. J . P.; Gibson, V.
C.; Wass, D. F. Angew. Chem. 1999, 111, 448; Angew. Chem., Int. Ed.
1999, 38, 428.
(5) Wang, C. H. J . Am. Chem. Soc. 1957, 79, 1924.
(6) McCulloch, B.; Ward, D. L.; Woollins, J . D.; Brubaker, C. H., J r.
Organometallics 1985, 4, 1425.
(7) Herberhold, M.; J in, G.-X.; Rheingold, A. L. Angew. Chem. 1995,
107, 716; Angew. Chem., Int. Ed. Engl. 1995, 34, 656. Zurcher, S.;
Petrig, J .; Gramlich, V.; Worle, M.; Mensing, C.; von Arx, D.; Togni,
A. Organometallics 1999, 18, 3679.
(4) Gibson, V. C.; Long, N. J .; Martin, J .; Solan, G. A.; Stichbury, J .
C. J . Organomet. Chem. 1999, 590, 115.
(8) Yan, Y. K.; Chan, H. S. O.; Hor, T. S. A.; Tan, K.-L.; Liu, L.-K.;
Wen, Y.-S. J . Chem. Soc., Dalton Trans. 1992, 423.
10.1021/om0004388 CCC: $19.00 © 2000 American Chemical Society
Publication on Web 09/15/2000

4426 Organometallics, Vol. 19, No. 21, 2000
Notes
Sch em e 1a
F igu r e 1. Molecular structure of the Cs symmetric com-
plex 2. Selected bond lengths (Å) and angles (deg): Re-S
2.541(3), Re-Br(1) 2.6542(12), Re-Br(2) 2.6607(12),
Re-C(15) 1.920(14), Re-C(16) 1.91(2), Re-C(17) 1.85(2),
S-Re-Br(1) 89.35(8), S-Re-Br(2) 83.25(8), C(15)-Re-S
171.3(4), C(16)-Re-S 90.0(4), C(17)-Re-S 98.9(4), C(15)-
Re-Br(1) 89.7(5), C(16)-Re-Br(1) 177.0(5), C(17)-Re-Br-
(1) 94.6(5), C(17)-Re-Br(2) 177.1(5), C(16)-Re-Br(2)
a
93.5(5),
C(15)-Re-Br(2) 88.0(4),
Br(1)-Re-Br(2)
(i) Re(CO)5Br, THF, reflux, 20 h. (ii) Pd(PhCN)2Cl2,
83.47(4), C(15)-Re-C(16) 90.5(6), C(15)-Re-C(17)
89.8(6), C(16)-Re-C(17) 88.5(7), Re-Br(1)-Re′ 96.62(6),
Re-Br(2)-Re′ 96.31(6).
toluene, reflux, 20 h. (iii) Pt(PhCN)2Cl2, toluene, 60 °C, 16 h.
(iv) Pt(PhCN)2Cl2, toluene, reflux, 20 h. (v) toluene, reflux, 10
h.
rearrangement must occur, and the unusual dinuclear
structure is the result.
reaction was observed on heating 1 and Re(CO)5Br in
toluene at 60 °C for 16 h. Alternatively, the steric bulk
of the mesityl groups could inhibit the ligand from
adopting a chelating geometry, as mononuclear rhenium
carbonyl species with ligands such as dppf and 1,1′-bis-
(methylthio)ferrocene are well-known.1
The X-ray analysis of 29 shows the bis(mesitylthio)-
ferrocene ligand to adopt a binucleating coordination
mode, bridging between the rhenium centers of a
Re2(CO)6(µ-Br)2 unit to form the Cs symmetric complex
illustrated in Figure 1. The geometry at rhenium is
distorted octahedral with cis angles in the range 83.25-
(8)-98.9(4)°. The rhenium coordination distances are
generally unexceptional, although the Re-S bond dis-
tance of 2.541(3) Å lies toward the high end of those
reported in the literature; the two Re-Br distances are
the same. The two mesityl ring systems (and the sulfur
lone pairs) are oriented syn, a geometry that is almost
certainly enforced by the steric bulk of the methyl
substituents. The only intramolecular interactions of
note are a pair of weak C-H‚‚‚π hydrogen bonds
between Cs-related methyl hydrogen atoms and their
adjacent substituted Cp rings (H‚‚‚π 2.75 Å). The
adoption by the bis(mesitylthio)ferrocene ligand of a
binucleating rather than a bidentate coordination mode
could be either a consequence of the initial formation
of the Re2(CO)8Br2 dinuclear species followed by dis-
placement of a pair of axial carbonyls and bis(mesit-
ylthio)ferrocene ligand coordination or that the THF
complex [{Re(CO)3(THF)(µ-Br)}2]10 is formed with sub-
sequent displacement of the THF molecules. Indeed, no
In contrast to the unexpected reaction with Re, a
bidentate coordination mode to a single metal center
was obtained by treatment of 1 with trans-Pd(PhCN)2Cl2
and trans-Pt(PhCN)2Cl2 but under different conditions
(Scheme 1). The Pd complex 3 was formed after 20 h
from refluxing toluene and isolated as a black powder
in ca. 40% yield. Its 1H NMR spectrum showed the
expected two “pseudo triplet” signals at 4.41 and 4.78
ppm for the cyclopentadienyl ring proton resonances
with slight downfield shifts of all the ligand resonances
due to coordination to the metal. The analogous Pt
complex 4, a yellow microcrystalline solid, was synthe-
sized in ca. 50% yield but under more mild conditions
(toluene, 60 °C, 16 h). However, employing the condi-
tions used to form the Pd species 3 (i.e., prolonged reflux
in toluene) from either 4 or directly from 1 and Pt-
(PhCN)2Cl2 gave, after column chromatography (neutral
grade II alumina, 2:3 CH2Cl2/hexane eluent), an orange
1
product in 41% yield. Observation of a complicated H
NMR spectrum suggested that the ligand had adopted
a different coordination mode, and this was confirmed
via the growth of small pale orange crystals, which were
shown by single-crystal X-ray analysis to be the unusual
cis-coordinated “hang-glider-like” complex 5 (Figure 2).11
In contrast to 2, the bis(mesitylthio)ferrocene ligand is
chelating rather than binucleating, adopting a unique
(9) Crystal data for 2: C34H30O6S2Br2Re2Fe, M ) 1186.8, orthor-
hombic, space group Pnma (no. 62), a ) 15.518(2), b ) 23.182(4), c )
10.227(2) Å, V ) 3679.2(9) Å3, Z ) 4 (the complex has crystallographic
Cs symmetry), Fc ) 2.143 g cm-3, µ(Mo KR) ) 92.8 cm-1, F(000) ) 2240,
T ) 293 K; yellow blocky needles, 0.27 × 0.14 × 0.09 mm, Siemens
P4/PC diffractometer, graphite-monochromated Mo KR radiation,
ω-scans, 3322 independent reflections. The structure was solved by
direct methods, and the non-hydrogen atoms were refined anisotropi-
cally using full matrix least-squares based on F2 to give R1 ) 0.049,
wR2 ) 0.072 for 1952 independent observed absorption corrected
reflections [|Fo| > 4σ(|Fo|), 2θ e 50°] and 218 parameters: CCDC
139099.
(10) Storhoff, B. N.; Lewis, H. C. Synth. React. Inorg. Metal-Org.
Chem. 1974, 4, 467. Calderazzo, F.; Vitali, D. Coord. Chem. Rev. 1975,
16, 13. Calderazzo, F.; Vitali, D.; Poli, R.; Atwood, J . L.; Rogers, R. D.;
Cummings, J . M.; Bernal, I. J . Chem. Soc., Dalton Trans. 1981, 1004.

Notes
Organometallics, Vol. 19, No. 21, 2000 4427
tial of the system. These and other catalytic applications
will be the subject of future studies.
Exp er im en ta l Section
Gen er a l P r oced u r es. All preparations were carried out
using standard Schlenk techniques.13 All solvents were dis-
tilled over standard drying agents under nitrogen directly
before use, and all reactions were carried out under an
atmosphere of nitrogen. Alumina gel (neutral-grade II) was
used for chromatographic separations. All NMR spectra were
recorded using a Delta upgrade on a J EOL EX270 MHz
spectrometer operating at 250.1 MHz (1H). Chemical shifts are
reported in δ using CDCl3 (1H, δ 7.25 ppm) as the reference
for the spectra. Infrared spectra were recorded using NaCl
solution cells (CH2Cl2) using a Mattson Polaris Fourier Trans-
form IR spectrometer. Mass spectra were recorded using
positive FAB methods, on an Autospec Q mass spectrometer.
Microanalyses were carried out in the Department of Chem-
istry, University of North London.
Syn th esis of 1. 1,1′-Dilithioferrocene (0.64 g, 3.23 mmol)
was suspended in hexane (50 mL), and dimesityl disulfide (2.10
g, 7.00 mmol) in toluene (20 mL) was added to the suspension
and the mixture stirred for 16 h. Water (20 mL) was added,
the aqueous layer was extracted with dichloromethane (2 ×
10 mL), and the combined organic layers were dried (MgSO4)
and evaporated to dryness. The crude product was subjected
to column chromatography (activated neutral grade II alu-
mina, 1:9 CH2Cl2/hexane), which enabled the separation of 1
(1.03 g, 65%). Recrystallization of the yellow solid was carried
out by slow evaporation of a solution of hot hexane. Anal. Calcd
for C28H30S2Fe: C, 69.13, H, 6.22. Found: C, 69.15, H, 6.39.
1H NMR (270 MHz, CDCl3): δ 2.24 (s, 6H; CH3), 2.52 (s, 12H;
CH3), 4.17 (t, 4H; C5H4), 4.30 (t, 4H; C5H4), 6.88 (s, 4H; C6H2);
FAB (+ve) MS (CH2Cl2) m/z 486 (M)+, 336 (M - SMes)+.
Syn th esis of 2. A solution of 1 (0.12 g, 0.25 mmol) in THF
(5 mL) was added to a solution of Re(CO)5Br (0.09 g, 0.23
mmol) also in THF (15 mL) and the mixture heated to reflux
for 20 h. The solvent was removed in vacuo and the crude solid
washed with hot hexane (2 × 20 mL) to remove any unreacted
starting materials. Two-layer recrystallization from hexane/
CH2Cl2 resulted in the formation of an orange crystalline solid
(0.14 g, 46%). Anal. Calcd for C34H30O6S2Br2Re2Fe: C, 34.41,
H, 2.55. Found: C, 34.73, H, 2.60. 1H NMR (270 MHz,
CDCl3): δ 2.26 (s, 6H; CH3), 2.44 (s, 12H; CH3), 4.41 (t, 4H;
C5H4), 4.59 (t, 4H; C5H4), 6.86 (s, 4H; C6H2); IR (CH2Cl2) ν 2022,
1923, 1908 cm-1 (CdO); FAB (+ve) MS (CH2Cl2) m/z 1169 (M
- O)+.
F igu r e 2. Molecular structure of the Cs symmetric “hang-
glider-like” complex 5. Selected bond lengths (Å) and angles
(deg): Pt-Cl(1) 2.308(2), Pt-Cl(2) 2.340(2), Pt-S
2.4249(13), Pt-C(1) 2.058(6), C(1)-Pt-C(1′) 92.6(4), C(1)-
Pt-Cl(1) 85.4(2), C(1)-Pt-Cl(2) 91.2(2), Cl(1)-Pt-Cl(2)
175.14(7), C(1′)-Pt-S 177.3(2), C(1)-Pt-S 84.8(2), Cl(1)-
Pt-S 95.13(4), Cl(2)-Pt-S 88.06(5), S-Pt-S′ 97.75(6),
Pt-C(1)-Ar 112.8(4).
tetradentate coordination mode through deprotonation
of two of the methyl substituents to form a pair of CH2-
CCSPt chelate rings. The complex has crystallographic
Cs symmetry, and the ferrocene unit adopts an eclipsed
conformation, which is also observed in 2. The geometry
at platinum is distorted octahedral with cis angles in
the range 84.8(2)-97.75(6)°. The Pt-S [2.425(1) Å] and
Pt-C [2.058(6) Å] distances are typical of octahedral
PtIV species. Both of the five-membered chelate rings
are folded, the platinum atom lying 0.62 Å out of the
C3S plane. The combined effect of these two folds is to
create a 141° dihedral angle between the two mesityl
“wings” of the complex. In common with 1, there is a
weak intramolecular C-H‚‚‚π interaction between one
of the hydrogen atoms of each of a pair of methyl groups
and their proximal C5H4 rings (H‚‚‚π 2.92 Å). The only
intermolecular packing interaction of note is a π-stack-
ing of adjacent mesityl ring systems to form a continu-
ous sinusoidal motif (centroid‚‚‚centroid and mean
interplanar separations of 3.71, 3.53 Å).
This cyclometalation reaction, featuring sulfur (and
also ferrocene ligands) on Pt is, so far as we are aware,
unique. The only other similar example is a C,P-
cyclometalated compound of PtII formed from trans-Pt-
(PhCN)2Cl2 and tri-o-tolylphosphine, which on oxidative
addition of halogens gives neutral C,P-cyclometalated
PtIV species.12 The driving force for our reaction comes
from the conversion of PtII to PtIV and, perhaps, a
disproportionation reaction to also generate Pt0, in
addition to the steric bulk of the mesityl substituents;
it is interesting to note that there is no evidence for any
cyclometalated products from the reactions with Pd.
This important reaction highlights a novel platinum
C-H activation system carrying a redox-tunable ligand
which may be exploited to optimize the catalytic poten-
Syn th esis of 3. A solution of 1 (0.2 g, 0.40 mmol) in toluene
(60 mL) was added to dichlorobis(benzonitrile)palladium(II)
(0.15 g, 0.40 mmol) also in toluene (60 mL). The solution
darkened immediately and was stirred at room temperature
for 20 h. A black precipitate was filtered off and the filtrate
evaporated to dryness and washed with hot hexane (5 × 10
mL). Two-layer recrystallization (CH2Cl2/hexane) of the crude
solid gave a dark brown microcrystalline solid (0.11 g, 40%).
Anal. Calcd for C30H34S2FePdCl6: C, 43.22, H, 4.08. Found:
1
C, 42.93, H, 3.95. H NMR (270 MHz, CDCl3): δ 2.21 (s, 6H;
CH3), 2.84 (s, 12H; CH3), 4.41 (t, 4H; C5H4), 4.78 (t, 4H; C5H4),
6.88 (s, 4H; C6H2); FAB (+ve) MS (CH2Cl2) m/z 663 (M)+, 627
(M - Cl)+, 592 (M - 2Cl)+.
Syn th esis of 4. A solution of 1 (0.12 g, 0.25 mmol) in
toluene (30 mL) was added to dichlorobis(benzonitrile)plati-
num(II) (0.11 g, 0.23 mmol) also in toluene (30 mL). The
solution was heated to 60 °C and stirred for 16 h. The yellow
precipitate formed was filtered off, washed with hot hexane
(11) Crystal data for 5: C28H28S2Cl2FePt, M ) 750.5, orthorhombic,
space group Pnma (no. 62), a ) 12.492(1), b ) 20.637(1), c ) 10.089(1)
Å, V ) 2600.9(4) Å3, Z ) 4 (the complex has crystallographic Cs
symmetry), Fc ) 1.916 g cm-3, µ(Cu KR) ) 178.9 cm-1, F(000) ) 1464,
T ) 293 K; pale orange rhombs, 0.11 × 0.10 × 0.07 mm, Siemens P4/
RA diffractometer, graphite-monochromated Cu KR radiation, ω-scans,
2235 independent reflections. The structure was solved by direct
methods, and the non-hydrogen atoms were refined anisotropically
(12) Fornies, J .; Martin, A.; Navarro, R.; Sicilia, V.; Villarroya, P.
Organometallics 1996, 15, 1826.
(13) Errington, R. J . In Advanced Practical Inorganic and Metalor-
ganic Chemistry; Blackie: London, 1997.
using full matrix least-squares based on F2 to give R1 ) 0.033, wR2
)
0.073 for 1942 independent observed absorption corrected reflections
[|Fo| > 4σ(|Fo|), 2θ e 128°] and 161 parameters: CCDC 139100.

4428 Organometallics, Vol. 19, No. 21, 2000
Notes
(4 × 10 mL), and recrystallized (CH2Cl2/hexane) (0.09 g, 50%).
Anal. Calcd for C28H30S2FePtCl2: C, 44.69, H, 4.02. Found: C,
44.79, H, 3.97. 1H NMR (270 MHz, CDCl3): δ 2.22 (s, 6H; CH3),
2.83 (s, 12H; CH3), 4.40 (t, 4H; C5H4), 4.79 (t, 4H; C5H4), 6.86
(s, 4H; C6H2); FAB (+ve) MS (CH2Cl2) m/z 753 (M)+, 715 (M -
Cl)+, 680 (M - 2Cl)+.
Syn th esis of 5. (Method iv) 1 (0.12 g, 0.25 mmol) was added
to a toluene (30 mL) solution of dichlorobis(benzonitrile)-
platinum(II) (0.11 g, 0.23 mmol). The reaction mixture was
stirred, heated to reflux for 20 h, and then filtered to remove
a black precipitate. The resulting dark brown solution was
evaporated to dryness and the crude brown solid washed with
hot hexane (4 × 10 mL). Further purification was achieved
by column chromatography (neutral grade II alumina, 2:3 CH2-
Cl2/hexane eluent), which resulted in the isolation of an orange
microcrystalline solid (0.07 g, 41%). Anal. Calcd for C28H28S2-
Cl2FePt‚0.5CH2Cl2: C, 42.43, H, 3.56. Found: C, 42.27, H,
3.52. 1H NMR (270 MHz, CDCl3): δ 1.84 (s, 6H; CH3), 2.28 (s,
6H; CH3), 3.98 (d, 2H; CH2), 4.14 (m, 2H; C5H4), 4.30 (m, 2H;
C5H4), 4.58 (d, 2H; CH2), 4.91 (m, 2H; C5H4), 5.13 (m, 2H;
C5H4), 6.70 (s, 2H; C6H2), 6.99 (s, 2H; C6H2); FAB (+ve) MS
(CH2Cl2) m/z 750 (M)+.
Ack n ow led gm en t. This research was supported by
the EPSRC, and J ohnson Matthey plc is thanked for
the loan of platinum salts.
Su p p or tin g In for m a tion Ava ila ble: Details about the
X-ray crystal structures including ORTEP diagrams, tables
of crystal data and structure refinement, atomic coordinates,
bond lengths and angles, and isotropic and anisotropic dis-
placement parameters for 2 and 5. This material is available
free of charge via the Internet at http://pubs.acs.org.
OM0004388