The synthesis and metal coordination chemistry of a novel phosphine- and thiolate-substituted ferrocenediyl ligand

Article abstract of DOI:10.1021/om010783c

The synthesis and metal coordination chemistry of a phosphine- and thiolate-substituted ferrocenediyl ligand were discussed. Bridged dimeric species, with the thiolate S adopting a binucleating role were found to be observed for Pd(II) and Rh(I) metal centers while a mononuclear, square planar Ni(II) complex was formed on reaction of the ligand with [Ni-(TMEDA)Me₂]. It was found that the rhodium complexes with phosphorus-sulfur donor ligands showed excellent activities and stability as methanol carbonylation catalysts.

Full text of DOI:10.1021/om010783c

770
Organometallics 2002, 21, 770-772
Th e Syn th esis a n d Meta l Coor d in a tion Ch em istr y of a
Novel P h osp h in e- a n d Th iola te-Su bstitu ted
F er r ocen ed iyl Liga n d
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 August 28, 2001
Sch em e 1a
Summary: A novel, asymmetric 1,1′-disubstituted fer-
rocenediyl ligand featuring phosphine and thiolate sub-
stituents has been conveniently synthesized and struc-
turally characterized, and its coordination chemistry was
probed by reaction with late transition metal reagents.
Bridged dimeric species, with the thiolate S adopting a
binucleating role, are observed for Pd(II) and Rh(I) metal
centers, while a mononuclear, square planar Ni(II)
complex is formed on reaction of the ligand with [Ni-
(TMEDA)Me2].
The formation of asymmetric, multidentate ligands,
focusing on aspects of hemilability,1 has been of great
interest. In particular, ferrocenyl and ferrocenediyl
ligands are sought after due to their extensive coordina-
tion chemistry and applications within catalysis.2,3
While hemilabile P/S-,4 P/S,5 P/O,6,7 and N/O-8 ligand
systems are well-known and important in catalysis,
examples of analogous asymmetric 1,1′-substituted
ferrocenes9-14 are rare and those that are known are
* Corresponding author. Tel: 020 75945781. Fax: 020 75945804.
E-mail: n.long@ic.ac.uk.
(1) Bader, A.; Lindner, E. Coord. Chem. Rev. 1991, 108, 27.
(2) For a detailed literature review, see: Ferrocenes: Homogeneous
Catalysis-Organic Synthesis-Materials Science; Togni, A., Hayashi,
T., Eds.; VCH: Weinheim, Germany, 1995. Metallocenes; Togni, A.,
Haltermann, R. L., Eds.; Wiley-VCH: Weinheim, Germany, 1998.
(3) For a comprehensive overview of ferrocene and other metallocene
chemistry see: Long, N. J . Metallocenes: An Introduction to Sandwich
Complexes; Blackwell Science: Oxford, 1998.
a
Reagents and conditions: (i) n-BuLi, THF, -25 °C, 30 min;
0.5 S2Cl2, THF, rt, 16 h. (ii) 2 LiEt3BH, THF, rt, 30 min; 2
KPPh2, THF, rt, 20 h; H+. (iii) n-BuLi, toluene, rt, 2 h; trans-
[Pd(PhCN)2Cl2], toluene, 60 °C, 20 h. (iv) Ni(TMEDA)Me2,
MeCN, rt, 2 h. (v) n-BuLi, THF, rt, 0.5 h; [Rh(CO)2Cl]2, MeOH,
rt, 2 h.
(4) Dilworth, J . R.; Wheatley, N. Coord. Chem. Rev. 2000, 199, 89.
(5) For example: Perez-Lourido, P.; Romero, J .; Garcia-Vezquez, J .
A.; Sousa, A.; Zheng, Y.; Dilworth, J . R.; Zubieta, J . J . Chem. Soc.,
Dalton Trans. 2000, 769. Foreman, M. S. J .; Woollins, J . D. J . Chem.
Soc., Dalton Trans. 2000, 1533. Aucott, S. M.; Slawin, A. M. Z.;
Woollins, J . D. J . Chem. Soc., Dalton Trans. 2001, 2279.
(6) For example: Klabunde, U.; Ittel, S. D. J . Mol. Catal. 1987, 41,
123.
neutral in character. For asymmetric substitution around
ferrocenes, laborious, inefficient and nonfacile synthetic
routes are largely employed, but here, we describe the
first and convenient synthesis of a unique phosphine-
and thiolate- (P/S-) substituted ferrocenediyl ligand and
a preliminary study into its coordination chemistry.
(7) For example: Keim, W.; Appel, R.; Gruppe, S.; Knoch, F. Angew.
Chem., Int. Ed. Engl. 1987, 26, 1012.
(8) For example: Desjardins, S. Y.; Cavell, K. J .; Hoare, J . L.;
Skelton, B. W.; Sobolev, A. N.; White, A. H.; Keim, W.J . Organomet.
Chem. 1997, 544, 163.
(9) Dong, T. Y.; Chang, C.-K. J . Chin. Chem. Soc. 1998, 45, 577.
(10) Butler, I. R.; Griesbach, U.; Zanello, P.; Fontani, M.; Hibbs, D.;
Hursthouse, M. B.; Malik, K. L. M. A. J . Organomet. Chem. 1998, 565,
243. Butler, I. R.; Quayle, S. C. J . Organomet. Chem. 1998, 552, 63.
Butler, I. R.; Mussig, S.; Plath, M. Inorg. Chem. Commun. 1999, 2,
424.
(11) Deng, W.-P.; Hou, X.-L.; Dai, L.-X.; Yu, Y.-H.; Xia, W. Chem.
Commun. 2000, 285.
(12) Long, N. J .; Martin, J .; Opromolla, G.; White, A. J . P.; Williams,
D. J .; Zanello, P. J . Chem. Soc., Dalton Trans. 1999, 1981. (b) Gibson,
V. C.; Long, N. J .; White, A. J . P.; Williams, C. K.; Williams, D. J .
Chem. Commun. 2000, 2359.
The new, versatile precursor compound di[1′-bromo-
ferrocene]disulfide 1 was synthesized (see Experimental
Section) from 1,1′-dibromoferrocene,15 using 1 equiv of
n-butyllithium in a cooled THF solution, followed by
addition of freshly distilled sulfur dichloride (0.5 equiv).
After aqueous workup and column chromatography
(neutral grade II alumina, 20:80 CH2Cl2-hexane) and
washing with hexane the product was obtained in 30%
yield (Scheme 1). Although this sterically hindered
ligand probably has in its own right interesting but yet
to be explored coordination properties, it has here been
(13) Balavoine, G. A.; Daran, J .-C.; Iftiem, G.; Manoury, E.; Moveau-
Bossuet, C. J . Organomet. Chem. 1998, 567, 191.
(14) Adeleke, J . A.; Chen, Y.-W.; Liu, L.-K. Organometallics 1992,
11, 2443.
(15) Shafir, A.; Power, M. P.; Whitener, G. D.; Arnold, J . Organo-
metallics 2000, 19, 3978.
10.1021/om010783c CCC: $22.00 © 2002 American Chemical Society
Publication on Web 01/19/2002

Notes
Organometallics, Vol. 21, No. 4, 2002 771
As an investigation into its coordination chemistry,
2 was deprotonated (using n-butyllithium), treated with
trans-[Pd(PhCN)2Cl2] in toluene, and stirred at room
temperature for 20 h. Following workup and crystal-
lization in CH2Cl2-hexane (1:1), 3 was isolated as a
brown microcrystalline powder in 64% yield, which
analyzes as a bridged dimer species, with a structure
seemingly analogous to the product formed with the
previously reported 1-thiolate, 1′-(mesitylthio)ferrocene
ligand;12b that is, for each ligand in the Pd dimer, the
thiolate S adopts a binucleating role. This role of
bridging thiolate has also been observed in other pal-
ladium complexes of P/S- ligands.19
To further probe its chemistry, 2 was treated with
dimethyl[tetramethylethylenediamine]nickel(II) in ac-
etonitrile (Scheme 1). After stirring at room temperature
for 2 h, an orange-pink precipitate was obtained, washed
(3 × 10 mL, acetonitrile), and dried in vacuo to give 4
in 46% yield. The microanalytical and NMR spectro-
scopic data indicate formation of a mononuclear Ni
complex in this case. We suggest that the complex has
a square planar structure due to its characteristic color
(tetrahedral Ni(II) complexes are usually blue or green)
and the lack of broadening in the NMR spectra (i.e.,
diamagnetic metal center). The 31P{1H} NMR shows one
peak at 29.92 ppm (shifted significantly downfield with
respect to 2 (-17.42 ppm)), and this is in the range for
F igu r e 1. Molecular structure of 2 (50% probability
ellipsoids). Selected bond lengths (Å) and angles (deg):
C(5)-S 1.761(7), P-C(10) 1.814(8), P-C(16) 1.850(4),
P-C(22) 1.852(3), C(10)-P-C(16) 101.0(2), C(10)-P-C(22)
102.7(3), C(16)-P-C(22) 99.7(2).
utilized to form 2, the first neutral-anionic P/S- fer-
rocene ligand. The S-S linkage in 1 was cleaved by
treatment with lithium triethylborohydride (2 equiv) in
THF. After 2 h, potassium diphenylphosphide (2 equiv)
was added, and the resulting suspension was stirred for
20 h at room temperature. Acidification was effected by
concentrated HCl (dropwise addition), and after extrac-
tion (diethyl ether), evaporation to dryness, and washing
1
nickel-chelating phosphines. H NMR shows that only
one isomer is formed, that with the acetonitrile ligand
trans to the phosphine. The spectrum shows the methyl
groups shifted upfield to -0.05 ppm (in the region for
nickel methyl complexes), and this signal is a doublet
due to phosphorus coupling. The C5H4 ring protons show
four pseudo triplets, and the acetonitrile methyl group
exhibits a singlet at 4.25 ppm (shifted downfield com-
pared to the resonance of free acetonitrile).
1
(cold pentane), 2 was isolated in 53% yield. H NMR
spectroscopy showed the asymmetrical substitution of
the cyclopentadienyl rings with the presence of signals
due to S-H, phenyl groups, and four pseudo triplets for
the C5H4 ring protons. Single-crystal X-ray analysis (see
Experimental Section) confirmed the structure of 2 to
be that shown in Figure 1. The two cyclopentadienyl
rings are almost perfectly eclipsed and are inclined by
less than 1° to each other. The C-S distance of 1.761(7)
Å is noticeably longer than that seen in other π-com-
plexed C5 and C6 S-H substituted ring systems (ca. 1.72
Å),16,17 there being no other structurally characterized
examples of ferrocenyl S-H compounds; the only slightly
similar structure to have been reported is a diphe-
nylphosphinyl benzenethiol species [2-(Ph2PO)-6-(Me3-
Si)C6H3SH].18 The angles at phosphorus are all signifi-
cantly reduced from tetrahedral, ranging between 99.7(2)
and 102.7(3) Å, the most “acute” angle being that
subtended by the two phenyl rings. The conformation
is stabilized by an intramolecular S-H‚‚‚π interaction
[H‚‚‚π 2.77 Å] to one (A) of the two phenyl rings.
Interestingly, this interaction is mirrored by an inter-
molecular C-H‚‚‚π contact from C(1)-H [H‚‚‚π 2.88 Å],
which approaches into the opposite face of ring A (the
two H‚‚‚π vectors are inclined by 177°). Ring B is
involved in an aromatic edge-to-face interaction
with ring A of a symmetry-related molecule (ring
centroid‚‚‚ring centroid 5.00 Å).
Rhodium(I) complexes with phosphorus-sulfur donor
ligands have shown excellent activities and stability as
methanol carbonylation catalysts.20 This was a motiva-
tion for the reaction of the lithium salt of 2 with
tetracarbonyldichlorodirhodium(I) in methanol, which
resulted in the formation of a yellow, sulfide-bridged
dimeric species (5), analogous to 3, in excellent yield.
The 1H NMR spectrum shows two pseudo triplets in the
ferrocenyl region (3.89 and 4.37 ppm) along with a
multiplet at 4.43 ppm, due to two pairs of overlapping
pseudo triplets, and in the phenyl region, there are
downfield shifted (from the ligand) multiplets at 7.43
and 8.04 ppm. The 31P{1H} NMR spectrum shows a
doublet at 36.60 ppm due to coupling of the phosphorus
with rhodium. The coupling constant is 165 Hz, which
is in good agreement with other ferrocenyl phosphine
rhodium(I) complexes.21 The IR spectrum shows a single
strong band at 1972 cm-1 in the CO-stretching region,
21
indicating terminal (and no bridging) CO ligands in
5 and further reinforces the assignment of bridging
thiolates in both 5 and 3.
(19) Brugat, N.; Polo, A.; Alvarez-Larena, A.; Piniella, J . F.; Real,
J . Inorg. Chem. 1999, 38, 4829. Hauptman, E.; Fagan, P. J .; Marshall,
W. Organometallics 1999, 18, 2061. Cao, R.; Hong, M.; J iang, F.; Kang,
B.; Xie, X.; Liu, H. Polyhedron 1996, 15, 2661.
(20) Dilworth, J . R.; Miller, J . R.; Wheatley, N.; Baker, M.; Sunley,
J . G. J . Chem. Soc., Chem. Commun. 1995, 1579.
(16) Sunkel, K.; Blum, A. Chem. Ber. 1992, 125, 1605.
(17) Fukuzawa, S.; Kato, H.; Ohtaguchi, M.; Hayashi, Y.; Yamazaki,
H. J . Chem. Soc., Perkin Trans. 1997, 1, 3059.
(18) Perez-Lourido, P.; Garcia-Vazquez, J . A.; Romero, J .; Sousa, A.;
Block, E.; Maresca, K. P.; Zubieta, J . Inorg. Chem. 1999, 38, 538.
(21) Hor, T. S. A.; Neo, S. P.; Tan, C. S.; Mak, T. C. W.; Leung, K.
W. P.; Wang, R.-J . Inorg. Chem. 1992, 31, 4510.

772 Organometallics, Vol. 21, No. 4, 2002
Notes
(2H, t, C5H4), 4.08 (2H, t, C5H4), 4.22 (2H, t, C5H4), 4.38 (2H,
t, C5H4), 7.31 (10H, m, C6H5). MS: m/z 402 (M+), 218 (M -
PPh2+).
From the results described above, we expect this novel
ferrocenediyl ligand system, and its subsequent ana-
logues (i.e., O/S-, N/S-), to display diverse coordination
chemistry and to support metal environments relevant
to a number of homogeneous catalytic processes.
3. 2 (0.15 g, 0.37 mmol) was dissolved in toluene (30 mL),
n-butyllithium (0.15 mL of a 2.5 M solution in hexane, 0.37
mmol) was added, and the solution was stirred for 2 h. After
this time, the solution had turned dark red and was cloudy.
THF (10 mL) was added to aid dissolution, and the solution
was added to bis(benzonitrile)palladium(II) dichloride (0.14 g,
0.37 mmol) dissolved in toluene (40 mL) at 60 °C. The solution
was stirred at this temperature for 20 h. The solvent was
removed, and the residue washed with hexane (3 × 50 mL)
and precipitated from a CH2Cl2 solution by layering with
hexane. 3 was isolated as a brown microcrystalline powder
(0.26 g, 0.24 mmol, 64%). Anal. Calcd for C44H36S2P2Fe2Pd2-
Cl2: C 48.65, H 3.34. Found: C 48.51, H 3.20. 31P{1H} NMR
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.22 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. Deactivated alumina gel (neutral
grade II, 3% H2O) was used for chromatographic separations.
All NMR spectra were recorded using a Delta upgrade on a
J EOL EX270 MHz spectrometer operating at 270.1 MHz (1H),
67.9 MHz (13C{1H}), and 101.3 MHz (31P{1H}). Chemical shifts
(δ) are reported in ppm using CDCl3 (1H, 7.25 ppm, 13C{1H}
77.0 ppm) as the reference, while 31P{1H} spectra were
referenced to H3PO4. Infrared spectra were recorded using
NaCl solution cells (CH2Cl2) using a Mattson Polaris Fourier
Transform IR spectrometer. Mass spectra were recorded using
positive FAB methods, on an Autospec Q mass spectrometer.
Microanalyses were carried out at SACS, University of North
London.
1
δ (CDCl3): 27.31. H NMR δ (CDCl3): 3.94 (2H, t, C5H4), 4.25
(2H, t, C5H4), 4.33 (2H, t, C5H4), 4.42 (2H, t, C5H4), 7.41 (6H,
m, C6H5), 7.88 (4H, m, C6H5). MS: m/z 1051 (M - Cl+), 1015
(M - 2Cl+), 909 (M - 2Cl - Pd+).
4. 2 (0.15 g, 0.37 mmol) in acetonitrile (20 mL) was added
to a solution of dimethyl[tetramethylethylenediamine]nickel-
(II) (0.08 g, 0.37 mmol) in acetonitrile (20 mL). The solution
darkened and an orange solid precipitated. The reaction was
stirred for 2 h, and the pink-orange product was filtered,
washed with acetonitrile (3 × 10 mL), and dried in vacuo (0.09
g, 0.17 mmol, 46%). Anal. Calcd for C25H24FeNNiPS: C 58.14,
H 4.65. Found: C 58.28, H 4.64. 31P{1H} NMR δ (C6D6): 29.92.
1H NMR δH (C6D6): -0.05 (3H, d, CH3, 3J PH 8 Hz), 3.78 (2H, t,
C5H4), 3.92 (2H, t, C5H4), 4.11 (2H, t, C5H4), 4.25 (3H, s,
CNCH3), 4.63 (2H, t, C5H4), 7.06 (6H, m, C6H5), 8.22 (4H, m,
C6H5). MS: m/z 475 (M - MeCN+), 460 (M - MeCN - Me+),
401 (M - MeCN - Me - Ni - H+).
Syn th eses: 1. 1,1′-Dibromoferrocene (2.00 g, 5.74 mmol)
was dissolved in dry, oxygen-free THF (35 mL) and cooled to
-25 °C. N-Butyllithium (3.40 mL, 5.44 mmol) was added and
the solution maintained at -25 °C for 30 min. Freshly distilled
sulfur dichloride (0.22 mL, 2.72 mmol) was then added at -25
°C, and the solution was allowed to warm to room temperature
and stirred for 16 h. The solvent was removed and the residue
suspended in CH2Cl2. Water was added, and the layers were
separated. The aqueous layer was extracted with CH2Cl2, and
the combined organic fractions were dried (MgSO4) and
evaporated to an orange oil. Column chromatography (neutral
grade II alumina, 20:80 CH2Cl2-hexane) enabled separation
of the product in the second fraction. This fraction was
evaporated to dryness and washed several times with hexane
(100 mL) until no traces of impurity were seen in the 1H NMR
of the compound, and 1 was isolated as a yellow solid (0.50 g,
0.85 mmol, 30%). Anal. Calcd for C20H16S2Br2Fe2: C 40.58, H
5. 2 (0.16 g, 0.39 mmol) was dissolved in THF (10 mL) and
n-butyllithium (0.24 mL, 0.39 mmol, 1.6 M solution in hexanes)
added. The solution was stirred for 30 min at room tempera-
ture and the solvent removed in vacuo. The residue was
redissolved in THF (10 mL) and added to a solution of [Rh-
(CO)2Cl]2 (0.08 g, 0.193 mmol) dissolved in methanol (30 mL).
There was an immediate precipitation of a yellow powder, and
the suspension was stirred at room temperature for 2 h. The
supernatant liquid was removed by filtration and 5 washed
with hexane (3 × 20 mL) and dried in vacuo (0.18 g, 88%).
Anal. Calcd for C46H36Fe2O2P2S2Rh2: C 51.91, H 3.41. Found:
C 51.56, H 2.94. 31P{1H} NMR δ (CDCl3): 36.60 (d, 1J Rh-P 165
Hz). 1Η ΝΜR δ (CDCl3): 3.89 (4H, t, C5H4), 4.37 (4H, t, C5H4),
4.43 (8H, m, C5H4), 7.43 (12H, m, C6H5), 8.04 (8H, m, C6H5).
MS: m/z (THF) 604 (RhL(CO)THF+), 575 (M - CO+), 523 (M
1
2.72. Found: C 40.72, H 2.70. H NMR δ (CDCl3): 4.08 (2H,
t, C5H4), 4.32 (4H, m, C5H4), 4.39 (2H, t, C5H4). MS: m/z 592
(M+), 295 (C10H8SBrFe+).
2. 1 (2.00 g, 4.16 mmol) was dissolved in THF (40 mL),
lithium triethylborohydride (9.61 mL, 9 mmol) was added, and
the solution was stirred at room temperature for 2 h. The
solvent was removed and the residue redissolved in THF (40
mL). Potassium diphenylphosphide (21.0 mL, 10.4 mmol) was
added, and the solution immediately became cloudy. The
reaction was stirred for 20 h at room temperature, and the
solvent was then removed. The residue was extracted with
diethyl ether (3 × 100 mL), and 1% aqueous KOH solution
(200 mL) was added to the diethyl ether solution by cannula.
The solution was vigorously stirred, and the aqueous layer was
removed and acidified by dropwise addition of concentrated
hydrochloric acid. Once the thiol had formed, it precipitated
as a yellow solid. The solid was extracted with diethyl ether
(3 × 50 mL), dried (Na2SO4), and evaporated to give an orange
solid. The crude product was washed with pentane at 0 °C (3
× 20 mL), enabling isolation of 2 as a yellow solid (1.70 g, 4.24
mmol, 51%). Cooling a pentane solution of the ligand grew
- THF+). IR (CH2Cl2): νCO 1972 cm-1
.
Cr ysta l Da ta for 2: C22H19PSFe, M ) 402.3, monoclinic,
P21/c (no. 14), a ) 8.708(4) Å, b ) 17.125(5) Å, c ) 13.134(4)
Å, â ) 107.53(5)°, V ) 1867.5(11) Å3, Z ) 4, Dc ) 1.431 g cm-3
,
µ(Mo KR) ) 10.1 cm-1, T ) 193 K, yellow plates; 3070
independent measured reflections, F2 refinement, R1 ) 0.066,
wR2 ) 0.148, 1857 independent observed absorption corrected
reflections [|Fo| > 4σ(|Fo|), 2θ e 50°], 206 parameters. CCDC
177081.
Ack n ow led gm en t. We acknowledge financial sup-
port from the EPSRC, and J ohnson Matthey plc are
thanked for the loan of the palladium and rhodium 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 This material is available free of
charge via the Internet at http://pubs.acs.org.
crystals suitable for X-ray diffraction. Anal. Calcd for C22H19
-
SPFe: C 65.69, H 4.76. Found: C 65.74, H 4.75. 31P{1H} NMR
1
δ (CDCl3): -17.42. H NMR δ (CDCl3) 2.76 (1H, S, SH), 4.04
(22) Errington, R. J . Advanced Practical Inorganic and Metalorganic
Chemistry; Blackie: London, 1997.
OM010783C