Coordination chemistry of the water-soluble ligand TPPTP and formation of a [Mo(CO)5(m-TPPTP)] monolayer on an alumina surface

Article abstract of DOI:10.1021/ic025862a

Phosphonate and phosphonic acid functionalized phosphine complexes of platinum(II) were prepared via direct reaction of the ligands with K₂PtCl₄ in water. Either cis or trans geometries were found depending on the nature of the ligand. The crystal structure of P(3-C₆H₄PO₃H₂) ₃·2H₂O (6b) (triclinic, P1, a = 8.3501(6) A, b = 10.1907(6) A, c = 14.6529(14) A, α = 94.177(6)°, β = 105.885(6)°, γ = 108.784(5)°, Z = 2) shows a layered arrangement of the phosphonic acid. The phosphonodiamide complex cis-[PtCl₂(P[4-C₆H₄PO{N (CH₃}₂}]₃)₂]· 3H₂O (10) was synthesized in 89% yield and hydrolyzed to the phosphonic acid complex using dilute HCl. Aqueous phase and silica gel supported catalytic phosphonylation of phenyl triflate using palladium phosphine complexes was achieved. A molybdenum complex, Mo(CO)₅{P(3-C₆H₄PO₃ H₂)₃} (11), was synthesized in situ and grafted to an alumina surface. XPS, RBS, and AFM studies confirm the formation of a monolayer of 11 on the alumina surface.

Full text of DOI:10.1021/ic025862a

Inorg. Chem. 2003, 42, 516−524
Coordination Chemistry of the Water-Soluble Ligand TPPTP and
Formation of a [Mo(CO)5(m-TPPTP)] Monolayer on an Alumina Surface
,†
Brandy A. Harper and D. Andrew Knight*
Department of Chemistry, Loyola UniVersity, 6363 St. Charles AVenue,
New Orleans, Louisiana 70118
Clifford George,§ Susan L. Brandow,‡ Walter J. Dressick,‡ Charles S. Dalcey,‡ and
Terence L. Schull‡,*
Center for Bio/Molecular Science and Engineering, Code 6950, and Laboratory for the Structure
of Matter, Code 6030, US NaVal Research Laboratory, 4555 OVerlook AVenue, SW,
Washington, D.C. 20375
Received July 10, 2002
Phosphonate and phosphonic acid functionalized phosphine complexes of platinum(II) were prepared via direct
reaction of the ligands with K PtCl4 in water. Either cis or trans geometries were found depending on the nature
2
of the ligand. The crystal structure of P(3-C H PO H ) ‚2H O (6b) (triclinic, P1h, a ) 8.3501(6) Å, b ) 10.1907(6)
6
4
3
2 3
2
Å, c ) 14.6529(14) Å, R ) 94.177(6)°, â ) 105.885(6)°, γ ) 108.784(5)°, Z ) 2) shows a layered arrangement
of the phosphonic acid. The phosphonodiamide complex cis-[PtCl2(P[4-C H PO{N(CH }2}]3)2]‚3H O (10) was
6
4
3
2
synthesized in 89% yield and hydrolyzed to the phosphonic acid complex using dilute HCl. Aqueous phase and
silica gel supported catalytic phosphonylation of phenyl triflate using palladium phosphine complexes was achieved.
A molybdenum complex, Mo(CO)5{P(3-C H PO H ) } (11), was synthesized in situ and grafted to an alumina
6
4
3 2 3
surface. XPS, RBS, and AFM studies confirm the formation of a monolayer of 11 on the alumina surface.
Introduction
present in compound 1 (Chart 1). This rhodium complex was
derived from the phosphine p-TPPMP (Na2[Ph2P(4-C6H4-
PO3)]‚1.5H2O) and was successfully applied in the biphasic
catalytic carbonylation of benzyl bromide.2 The presence of
the dianionic phosphonate moiety not only increases the
relative aqueous solubility, compared with sulfonate ana-
logues, but also increases the relative organophobicity. This
property can be exploited if leaching of the phosphine, or
phosphine-metal complex, into the organic phase of an
aqueous/organic biphasic solvent combination is undesirable.
A number of water-soluble phosphine-phosphonate ligands
have recently appeared in the literature.3
Phosphonic acid functionalized phosphine complexes of
transition metals are of general interest for a number of
reasons. First, the presence of the phosphonic acid group
renders the complexes water-soluble. This has allowed the
application of these, and related hydrophilic complexes, to
aqueous or biphasic homogeneous catalysis where separation
of catalyst from the reaction mixture is an issue, or where
the need for removal of an organic solvent from a chemical
process is desired.1 The water solubility is increased when
the phosphonic acid is in the anionic phosphonate form, as
* Correspondence may be addressed via given address or e-mail:
daknight@loyno.edu (D.A.K.); schull@nrl.navy.mil (T.L.S.).
† U. S. Navy-ASEE Summer Faculty.
In addition to desirable solubility characteristics, organo-
phosphonic acids are known to form layered di- and trivalent
metal phosphonates.4 If the phosphonic acid is derived from
a catalytically active metal complex, then an ordered,
supported catalyst may be formed which is expected to have
enhanced selectivity over the homogeneous form of the
‡ Center for Bio/Molecular Science and Engineering.
§ Laboratory for the Structure of Matter.
(1) For recent reviews of aqueous homogeneous catalysis see: (a) Cornils,
B. J. Mol. Catal. A: Chem. 1999, 143, 1. (b) Driessen-Ho¨lscher, B.
AdV. Catal. 1998, 42, 473. (c) Joo´, F.; Katho´, AÄ . J. Mol. Catal. A:
Chem. 1997, 116, 3. (d) Katti, K. V.; Gali, H. MGCN, Main Group
Chem. News 1999, 7, 21. (e) Aqueous Phase Organometallic Cataly-
sis: Concepts and Applications; Cornils, B., Herrmann, W. A., Eds.;
Wiley-VCH: Weinheim, 1998.
(2) Schull, T. L.; Fettinger, J. C.; Knight, D. A. Inorg. Chem. 1996, 35,
6717.
516 Inorganic Chemistry, Vol. 42, No. 2, 2003
10.1021/ic025862a CCC: $25.00 © 2003 American Chemical Society
Published on Web 12/28/2002

Coordination Chemistry of Water-Soluble TPPTP
Chart 1. Examples of Phosphine-Phosphonate Complexes as
Supported or Aqueous Phase Catalysts
The use of catalytically active supported complexes has not
been restricted to phosphonate-functionalized phosphines; for
example, Bujoli prepared a zirconium phosphonate-supported
manganese porphyrin complex which was active for olefin
epoxidation, although X-ray powder diffraction revealed the
absence of layering within the structure.7
The phosphonic acid group is particularly useful for
immobilizing molecules to oxide surfaces. Thus, monolayers
of redox-active ruthenium complexes functionalized with
8
-PO3H2 have been adsorbed to nanocrystalline TiO2 and
TiO2 modified ITO.9 Electronic coupling with the surface is
achieved allowing efficient light-induced charge separation,
and such systems show promise in the fabrication of devices
for the conversion of light to electricity. The clear advantage
of the phosphonic acid group over sulfonic and carboxylic
acids is the lack of desorption of the acid from the TiO2
surface over a wide pH range. Bujoli, Odobel, and Talham
recently reported the formation of organized monolayers of
phosphonic acid functionalized manganese porphyrins on
zirconium phosphonate Langmuir-Blodgett films.10 Silane
functionalized phosphines have been used to build up thin
films of organometallic complexes on surfaces such as silica,
glass, and quartz.11 To the best of our knowledge, phos-
phine-phosphonic acids have not been utilized for the
monolayer deposition of transition metal complexes onto
alumina surfaces.
Recently, we described the preparation of a variety of tris-
substituted triphenylphosphine ligands bearing phosphonic
acid, phosphonate, or phosphonodiamide substituents on each
aromatic ring.3e We address here some of the key issues
associated with the use of these new ligands for catalytic
applications and as structural units for the fabrication of 2D/
3D surface-bound supramolecular architectures. In particular,
we demonstrate the ability to form phosphine coordinated
Pt or Mo complexes containing these ligands and confirm
the structure of the meta isomer of the free m-TPPTP ligand
by X-ray crystallography. Analogous palladium complexes,
prepared in situ, are shown to be effective catalysts for the
formation of C-P bonds in both homogeneous solution and
as heterogeneous species adsorbed to silica particles. In
addition, the ability to form monolayer films of complexes,
required for future studies of these species as heterogeneous
catalysts and building blocks for the formation of 2D/3D
supramolecular structures, is illustrated by the stepwise
synthesis and characterization of a molybdenum based mono-
TPPTP(H)6 complex monolayer on an Al2O3 surface.
catalyst, as well as to allow separation of catalyst from
organic reaction mixture, and subsequent recycle. The
concept itself is not particularly novel. In 1982, Dines and
co-workers at Occidental Research Corporation first reported
the in situ preparation of a layered material in which rhodium
complex 2 containing a coordinated phosphonate-function-
alized phosphine ligand was supported within a zirconium
phosphonate matrix.5 The supported catalyst was catalytically
active for the hydroformylation of propene to n- and i-butanal
without loss of activity when compared to RhCl(CO)(PPh)3,
although no modification of selectivity was achieved. More
recently, Villemin described the formation of a layered
zirconium phosphonate/phosphite containing a p-TPPMP
palladium complex 3 which is both active and selectiVe in
the Heck reaction between methyl acrylate and aryl iodides,
with no leaching of palladium from the phosphonate support.6
(3) (a) Kant, M.; Bischoff, S.; Siefken, R.; Gru¨ndemann, E.; Ko¨ckritz, A.
Eur. J. Org. Chem. 2001, 477. (b) Bischoff, S.; Kant, M. Catal. Today
2001, 66, 183. (c) Ma, X. B.; Fu, X. K.; Li, L. Q.; Chen, J. R.
Molecules 2001, 6, 390. (d) Villemin, D.; Nechab, B. J. Chem. Res.,
Synop. 2000, 429. (e) Dressick, W. J.; George, C.; Brandow, S. L.;
Schull, T. L.; Knight, D. A. J. Org. Chem. 2000, 65, 5059. (f) Schull,
T. L.; Olano, L. R.; Knight, D. A. Tetrahedron 2000, 7093. (g)
Eymery, F.; Burattin, P.; Mathey, F.; Savignac, P. Eur. J. Inorg. Chem.
2000, 2425. (h) Liek, C.; Machnitzki, P.; Nickel, T.; Schenk, S.;
Tepper, M.; Stelzer, O. Z. Naturforsch., B: Chem. Sci. 1999, 54, 1532.
(i) Machnitzki, P.; Nickel, T.; Stelzer, O.; Landgrafe, C. Eur. J. Inorg.
Chem. 1998, 1029. (j) Lelie`vre, S.; Mercier, F.; Mathey, F. J. Org.
Chem. 1996, 61, 3531. (k) Herring, A. M.; Steffey, B. D.; Miedaner,
A.; Wander, S. A.; DuBois, D. L. Inorg. Chem. 1995, 34, 1100. (l)
Ganguly, S.; Roundhill, D. M. Organometallics 1993, 12, 4825.
(4) See for example: (a) Clearfield, A. In Progress in Inorganic
Chemistry: Metal Phosphonate Chemistry; Karlin, K. D., Ed.; John
Wiley & Sons: New York, 1998; Vol. 47, p 271. (b) Alberti, G. In
ComprehensiVe Supramolecular Chemistry; Atwood, J. L., Davies, J.
E. D., MacNicol, D. D., Vogtle F., Lehn, J.-M., Eds.; Pergamon:
Oxford, 1996; Vol. 7, p 151.
(6) Villemin, D.; Jaffre`s, P.-A.; Nechab, B.; Courivaud, F. Tetrahedron
Lett. 1996, 38, 3905.
(7) Deniaud, D.; Schollorn, B.; Mansuy, D.; Rouxel, J.; Battioni, P.; Bujoli,
B. Chem. Mater. 1995, 7, 995.
(8) (a) Gillaizeau-Gauthier, I.; Odobel, F.; Alebbi, M.; Argazzi, R.; Costa,
E.; Bignozzi, C. A.; Qu, P.; Meyer, G. J. Inorg. Chem. 2001, 40, 6073.
(b) Pe´chy, P.; Rotzinger, F. P.; Nazeeruddin, M. K.; Kohle, O.;
Nazeeruddin, S. M.; Humphry-Baker, R.; Gra¨tzel, M. J. Chem. Soc.,
Chem. Commun. 1995, 65.
(9) Andersson, A.-M.; Isovitsch, R.; Miranda, D.; Wadhwa, S.; Schmehl,
R. H. J. Chem. Soc., Chem. Commun. 2000, 505.
(10) Ben´ıtez, I. O.; Bujoli, B.; Camus, L. J.; Lee, C. M.; Odobel, F.; Talham,
D. R. J. Am. Chem. Soc. 2002, 124, 4363.
(5) Lane, R. H.; Callahan, K. P.; Cooksey, R.; DiGiacomo, P. M.; Dines,
M. B.; Griffith, P. C. Presented at the Symposium on Immobilized
Homogeneous Catalysts, Kansas City, 1982.
(11) (a) Petrucci, M. G. L.; Kakkar, A. K. Chem. Mater. 1999, 11, 269.
(b) Petrucci, M. G. L.; Kakkar, A. K. Organometallics 1998, 17, 1798
and references therein.
Inorganic Chemistry, Vol. 42, No. 2, 2003 517

Harper et al.
Compound 6b (0.844 g, 1.57 mmol) was added as a solid in a single
portion with stirring. The reaction was stirred for 1 h, and the
solution was concentrated under oil-pump vacuum and ethanol
added. A solid formed which was collected by filtration and dried
under a stream of nitrogen to give 7b as a pure cream powder.
Experimental Section
General Data. All reactions were conducted under dry, pre-
purified N2 using standard Schlenk-line and catheter-tubing tech-
niques unless otherwise stated. IR spectra were recorded on Mattson
and Nicolet FT spectrometers. All H and 31P NMR spectra were
1
Yield 0.51 g. IR (KBr pellet): ν(P-OH) 2875 cm-1
.
31P{1H} NMR
recorded on Varian Inova 400, Bruker DRX 400, or Bruker AM-
300 spectrometers and referenced to internal or external tetra-
methylsilane (1H) and external H3PO4 (31P). GC/MS analyses were
performed on a Hewlett-Packard 6890 equipped with an HP-5 (5%)-
diphenyl-(95%)-dimethylpolysiloxane capillary column (30 m, 0.25
mm). The mass spectra under electron impact conditions (EI) were
recorded at 70 eV ionizing potential. High resolution ESI-MS
performed with an ABI QSTAR Pulsar QTOF mass spectrometer.
TGA was performed on a TA Instruments Hi-Res TGA 2950 under
N2 atmosphere.
Solvents were purified as follows: toluene (EM Science or
Aldrich), distilled from Na/benzophenone; acetonitrile (Baker),
distilled from CaH2; ether (Fisher), xylene (Aldrich), CDCl3
(Cambridge Isotope Laboratories), used as received. Silica gel
(Scientific Products, 230-400 mesh) was used as received.
Reagents and chemicals were obtained as follows: diethyl
phosphite (Strem), molybdenum hexacarbonyl (Strem), phenyl
triflate (Aldrich), sodium borohydride (W. H. Curtin), used as
received; potassium tetrachloroplatinate and sodium tetrachloro-
palladate (Johnson Matthey), used as received; triethylamine,
distilled from CaH2; cis-[PtCl2(PPh3)]2,12 P(4-C6H4PO3Na2)3 (p-
TPPTP, 4),3e P(3-C6H4PO3H2)3 (m-TPPTP(H)2, 6b),13 and P[4-C6H4-
PO{N(CH3}2}]3 (p-TPPTA, 8)3e were prepared according to the
literature procedures. P(4-C6H4PO3H2)3 (p-TPPTP(H)2, 6a) was
prepared according to the literature procedure3e and isolated as the
heptahydrate (determined from TGA analysis). Microanalyses are
not reported for metal complexes of ligands 4, 6a, and 6b because
of variable degrees of hydration or mixed counterions, and thus,
purity cannot be assessed. 31P NMR spectra for compounds 5, 7a,
and 7b are included in the Supporting Information.
1
(H2O): δ 14.0 (t, JPtP ) 3740 Hz, P), 16.1 (s, br, PO(OH)2). H
NMR (D2O): δ 7.73-7.01 (m, 24H, br, C6H4).
cis-[PtCl2(p-TPPTA)2]‚3H2O (9). A Schlenk flask was charged
with K2PtCl4 (0.50 g, 1.2 mmol), xylene (50 mL), and p-TPPTA
(8) (2.30 g, 3.46 mmol). The mixture was refluxed for 3 days and
then allowed to cool to room temperature. Then, an off-white solid
formed which was collected by filtration, washed with ether, and
dried under oil-pump vacuum to give 9 (1.76 g, 89%). Concentration
of the filtrate gave a small number of white crystals which have
been identified by single-crystal X-ray analysis as the phosphonium
salt HP[4-C6H4PO{N(CH3}2}]3OH.14 Anal. Calcd for C60H102
-
Cl2N12O9P8Pt: C, 43.69; H, 6.18. Found: C, 43.59; H, 6.13. 31P-
{1H} NMR (CDCl3): δ 15.6 (t, JPtP ) 3626 Hz, P), 29.0 (s,
1
P(O)(NMe2)2). H NMR (CDCl3): δ 7.70-7.29 (m, 24H, C6H4),
2.61 (d, JPH ) 10.1 Hz, CH3).
Aqueous Phase Palladium Catalyzed Coupling Reaction. The
following procedure is typical: A Schlenk tube was charged with
Na2PdCl4 (0.050 g, 0.170 mmol), 4 (0.500 g, 0.800 mmol), and
water (20 mL). The solution was sparged for 5 min with nitrogen.
Then, a solution of sodium borohydride (0.016 g, 0.423 mmol, 2.5
equiv) in water (2 mL) was added dropwise with stirring over a
period of 3 min. Once H2 evolution had ceased, the solution was
sparged with nitrogen for 3 min. A solution of phenyl triflate (0.769
g, 3.40 mmol), diethyl phosphite (0.563 g, 4.08 mmol), and
triethylamine (0.57 mL, 4.1 mmol) in degassed acetonitrile (2 mL)
was added to the reaction mixture. The solution was refluxed
overnight, allowed to cool to room temperature, and extracted with
ether (4 × 10 mL). The organic layer was washed with brine (4 ×
10 mL), dried over anhydrous sodium sulfate and the solvent
removed by evaporation to give crude diethyl phenylphosphonate.
Yield 0.565 g, 78%.
Synthesis of Mo(CO)5(m-TPPTP(H)6) (11). A Schlenk flask
was charged with a mixture of m-TPPTP(H6) (0.140 g, 0.260 mmol)
in ethanol (15 mL) and Mo(CO)6 (0.343 g, 0.130 mmol) in toluene
(15 mL). The reaction mixture was heated to approximately 100
°C in an oil bath. After 30 min, a golden yellow solution was
obtained. A check of the reaction mixture by 31P NMR showed no
free phosphine remaining, and nearly exclusive conversion to the
desired product. A small impurity peak was seen at 30.9 ppm (ca.
6%), along with a corresponding phosphonate peak at 13.2 ppm.
The solvent was removed under oil-pump vacuum to give an
orange-brown solid, which was used without further purification.
31P NMR: δ 40.7 (P), 13.8 (PO). ESI mass spectrum m/z: 738.8623
[M - H], calcd 738.8622.
trans-[PtCl2(p-TPPTP)2] (5). A Schlenk flask was charged with
K2PtCl4 (0.18 g, 0.43 mmol), water (15 mL), and a stir bar.
Compound 4 (0.545 g, 0.859 mmol) was added as a solid in a single
portion with stirring. The solution turned yellow and was stirred
for 5 h. The solvent was concentrated under oil-pump vacuum and
ethanol added. A yellow solid formed which was collected by
filtration and dried under a stream of nitrogen to give 5 as a pale
yellow amorphous solid contaminated with approximately 5% of
phosphine oxide. Crude yield 0.61 g. IR (KBr pellet): ν (P-O)
1081, 999 cm-1
.
31P{1H} NMR (D2O): δ 20.2 (t, JPtP ) 2519 Hz,
1
P), 10.9 (s, PO). H NMR (D2O): δ 7.91-6.99 (m, 24H, C6H4).
cis-[PtCl2{p-TPPTP(H)6}2] (7a). A Schlenk flask was charged
with K2PtCl4 (0.20 g, 0.48 mmol), water (15 mL), and a stir bar.
Compound 6a (0.48 g, 0.76 mmol, 1.6 equiv) was added as a solid
in a single portion with stirring. The reaction was stirred for 3 h,
and the solution was concentrated under oil-pump vacuum and
ethanol added. A solid formed which was collected by filtration
and dried under a stream of nitrogen to give 7a as a cream powder.
Silica Gel Supported Palladium Catalyzed Coupling Reaction.
A Schlenk flask was charged with Na2PdCl4, 6a, water (20 mL),
and sodium borohydride using the same procedure described
previously for the aqueous phase catalytic reaction using identical
amounts of reagents. The water was removed in vacuo, and then,
methanol (15 mL) was added. Silica gel (∼2 g) was added in a
single portion, and the mixture was refluxed for 30 min. The
resulting yellow solid was collected using filtration and washed
with ether. The solid was then dried in vacuo at 40 °C for 1 h. To
the dry solid was then added phenyl triflate (0.769 g, 3.40 mmol),
diethyl phosphite (0.563 g, 4.08 mmol), triethylamine (0.57 mL,
Yield 0.42 g. IR (KBr pellet): ν(P-OH) 2900 cm-1 31P{1H} NMR
.
(H2O): δ 14.8 (t, JPtP ) 3720 Hz, P), 14.0 (s, PO(OH)2). 1H NMR
(D2O): δ 7.83-7.21 (m, 24H, br, C6H4).
cis-[PtCl2{m-TPPTP(H)6}2] (7b). A Schlenk flask was charged
with K2PtCl4 (0.33 g, 0.79 mmol), water (20 mL), and a stir bar.
(12) Gillard. R. D.; Pilbrow, M. F. J. Chem. Soc., Dalton Trans. 1974,
2320.
(13) Schull, T. L.; Brandow, S. L.; Dressick, W. J. Tetrahedron Lett. 2001,
42, 5373.
(14) Details of this compound will be published elsewhere.
518 Inorganic Chemistry, Vol. 42, No. 2, 2003

Coordination Chemistry of Water-Soluble TPPTP
4.1 mmol), and toluene (30 mL). The reaction mixture was refluxed
overnight, allowed to cool to room temperature, and then analyzed
by GC. GC yield (diethyl phenylphosphonate) 84%.
correction to account for sample tilt followed by the application of
a median filter.
Rutherford Backscattering Spectroscopy. RBS was conducted
at 2.000 MeV using the Naval Research Laboratory’s 3 MeV
Pelletron on the 55° beamline. The experiments were performed
using a scattering angle of 165° and sample angles of both 15°
and 30°. In total, six measurements were made, a blank and sample
at 30° and two blanks and two samples at 15°. All the blanks and
samples gave reproducible results within experimental error.
X-ray Data Collection and Structure Refinement for P(3-
C6H4PO3H2)3‚2H2O (6b). A clear (0.41 × 0.17 × 0.05 mm3)
crystal was mounted on a thin glass rod for data collection on a
Bruker P4 automated four circle diffractometer using an incident
beam monochromator (λ ) 1.54178 Å). The unit cell parameters
were determined from 40 centered reflections in the range 9.3° e
2θ e 54.9°. A total of 3123 reflections were measured in the θ/2θ
Preparation of Aluminized Glass Substrate. A standard glass
microscope slide (1 in. × 3 in.) was prepared for deposition using
the RCA method:15 the substrate was immersed in a solution of
H2O/H2O2/NH4OH (5.0/2.0/1.0 by volume) at 75 °C for 10-15
min (to remove any organic contaminants). The substrate was then
rinsed with deionized water, immersed in H2O/H2O2/HCl (6.0/1.0/
1.0 by volume) at 75 °C for 10-15 min (to remove any heavy
metals), rinsed again with deionized water, and then dried under a
stream of N2. Then, a 150-200 nm thick layer of aluminum was
thermally evaporated onto the glass surface. Substrates not used
immediately upon removal from the evaporator were air plasma
cleaned (20 min, 200 mTorr, 100 W RF) before use.
Reflection-Absorption Infrared (RAIR).16 Analysis was
performed on a Nicolet Magna-IR System 750 Series II spectrom-
eter equipped with a liquid nitrogen-cooled MCT-A detector. The
aluminum-coated glass slides were taken directly from the thermal
evaporator and placed on a fixed 80° grazing angle sample holder
in the sample chamber. The sample chamber was purged with
nitrogen overnight. For each slide, a background spectrum was
collected (2000 scans, 2 cm-1 resolution). Once the background
spectrum was acquired, each slide was transported directly to a
nitrogen-purged trap and dip-coated with the desired solution.
Following immersion for the specified time, each slide was
removed, blown dry with filtered nitrogen, and carefully placed
back on the grazing angle stage in exactly the same position. The
sample chamber was again purged overnight, and the spectrum was
acquired (2000 scans, 2 cm-1 resolution). The background was
subtracted from the sample spectrum, using a multiplicative constant
to match the intensity of the water absorptions as closely as possible.
The resulting difference spectrum was then truncated to highlight
the 2200-750 cm-1 region, and automatic baseline correction was
applied.
IR Sample Preparation. The aluminized glass slide was
immersed in a methanolic solution of 11 (ca. 1 mM) for 4 h at
room temperature. The slide was removed and washed thoroughly
with methanol and dried under a stream of N2. Once the RAIR
spectra were acquired, the slides were stored in Fluoroware
containers under ambient conditions. As needed, the slides were
cut into sections approximately 1 cm2 for further analysis. This
was done on the benchtop under ambient conditions. Samples were
stored in glass vials under air.
X-ray Photoelectron Spectroscopy. Experiments were per-
formed on a Surface Science Instruments SSX-100 surface analysis
system, equipped with a monochromatic Al KR (1486.6 eV) source,
a hemispherical analyzer, and a position-sensitive detector. All
samples were analyzed at a 35° takeoff angle. The pressure in the
analysis chamber was typically between 1 × 10-9 and 5 × 10-9
Torr. Survey scans were taken to identify major elements present
on the surface. Chemical state information and surface concentra-
tions were derived from high-resolution scans of individual elements
measured with a pass energy of 100 eV. Measurements were
calibrated by assigning the C 1s binding energy as 284.5 eV.
Relative abundances were determined using the instrument back-
ground subtraction and peak-fitting software.
mode to 2θ
) 115°, -8 e h e 8, -10 e k e 10, -4 e l e
max
14, of which 2641 were observed with Fo > 4σ(Fo), Rint ) 0.015.
Three standards monitored every 100 reflections showed no decay
during data collection. Corrections were applied for Lorentz and
polarization effects. A face-indexed absorption correction was
applied, and max and min transmissions were 0.813 and 0.348,
respectively. The structure was solved by direct methods with the
aid of the program SHELXTL17 and refined with a full-matrix least-
squares17 on F2. The 322 parameters refined include the coordinates
and anisotropic thermal parameters for all non-hydrogen atoms.
Hydrogens were included using a riding model in which the
coordinate shifts of the carbons were applied to the attached
hydrogens, C-H ) 0.96 Å, and H angles idealized. One of the
PO3 groups was disordered, and the oxygens were refined in two
orientations with the occupancy required to sum to 1.0. The
occupancy ratio was ca. 9:1, and the lower occupancy oxygens were
refined with fixed isotropic thermal parameters. The final R values
were R1 ) 0.044, and wR2 ) 0.120 for I > 2σ(I), and R1 ) 0.048,
and wR2 ) 0.129 for all data; the goodness of fit parameter was
1.08. Final difference Fourier excursions were 0.42 and -0.48 e
Å-3. Tables of atomic coordinates, anisotropic thermal parameters,
and bond distances and angles are available as Supporting Informa-
tion.
Results and Discussion
Synthesis of Platinum Complexes. A variety of water-
soluble phosphine complexes of Pt(II) have been previously
prepared using a number of different methods. The direct
reaction of water-soluble phosphines with K2PtCl4 in water
has been used for the synthesis of cis-[PtCl2(PTA)2] (PTA
) 1,3,5-triaza-7-phosphaadamantane),18 cis- and trans-[PtCl2-
{Ph2P(CH2)nSO3M}2]19 (n ) 2, 3, 4; M ) Na, K), and cis-
[PtCl2(m-TPPTS)2].20 Addition of K2PtCl4 to aqueous solu-
tions of [PtCl2(PTA)2] or [PtCl2{Ph2P(CH2)nSO3M}2] resulted
in the formation of [PtL3Cl]+, that is, platinum analogues of
Wilkinson’s catalyst, presumably via a chloride-phosphine
exchange mechanism.18b An alternative procedure using a
(17) Sheldrick, G. M. SHELXTL97; University of Go¨ttingen: Germany,
1997.
(18) (a) Darensbourg, D. J.; Decuir, T. J.; Stafford, N. W.; Robertson, J.
B.; Draper, J. D.; Reibenspies, J. H.; Katho´, AÄ .; Joo´, F. Inorg. Chem.
1997, 36, 4218. (b) Otto, S.; Roodt, A.; Purcell, W. Inorg. Chem.
Commun. 1998, 1, 415.
(19) Wedgewood, J. L.; Hunter, A. P.; Kresinski, R. A.; Platt, A. W. G.;
Stein, B. K. Inorg. Chim. Acta 1999, 290, 189.
(20) Herrmann, W. A.; Kellner, J.; Riepl, H. J. Organomet. Chem. 1990,
389, 103.
AFM Analysis. AFM tapping mode images were acquired under
air ambient conditions with a Nanoscope III AFM with a cantilever
tip radii of approximately 40 nm. Data processing consisted of a
(15) Kern, W. J. Electrochem. Soc. 1990, 137, 1887.
(16) Debe, M. K. Appl. Surf. Sci. 1982, 14, 40.
Inorganic Chemistry, Vol. 42, No. 2, 2003 519

Harper et al.
Scheme 1. Synthesis of Phosponate, Phosphonic Acid, and Phosphonodiamide Functionalized Phosphine Complexes of Platinum
biphasic ligand exchange reaction of [Pt(cod)2Cl2] with Ph2P-
(CH2)nSO3M resulted in the formation of the tris(phosphine)
platinum cation,19 which slowly converts to cis-[PtCl2{Ph2P-
(CH2)nSO3M}2] in solution.
phosphine ligand and associated Coulombic repulsion may
account for the preferred geometry in solution. These results
prompted us to return to the reaction of p-TPPMP with cis-
[PtCl2(PPh3)]2 under biphasic conditions (H2O/CH2Cl2), and
close inspection of the 31P NMR spectrum of the product in
CD3OD contained a doublet and triplet at 27.9 and 17.0 ppm,
respectively, (JPP ) 18.8 and 18.6, 3.6 Hz) with associated
195Pt satellites (JPtP ) 3620 and 2472 Hz), indicating
formation of [PtCl(p-TPPMP)3]Cl and the misassignment of
the resonances to cis and trans isomers of [PtCl2(p-TPPMP)2]
in the original report.2
We suspected that the lack of solubility of p-TPPTP (4)
in organic solvents would preclude any biphasic ligand
exchange reaction. When an aqueous solution of 4 was
rapidly stirred for 3 days, with either benzene or dichloro-
methane solutions of cis-[PtCl2(PPh3)]2, no platinum phos-
phine species in the aqueous phase were observed by NMR.
This is in contrast to the biphasic exchange reaction of
triphenylphosphine metal complexes with m-TPPTS19 or
p-TPPMP2 (TPPTS ) tris(sodium sulfonatophenyl)phos-
phane, TPPMP ) sodium phosphonatophenylphosphane),
which readily takes place under ambient conditions. Com-
bining a stoichiometric amount of 4 and K2PtCl4 in water
and monitoring the reaction by 31P NMR revealed that the
trans complex, trans-[PtCl2(p-TPPTP)2] (5), was formed
(Scheme 1).21 This was indicated by a peak in the spectrum
at 20.2 with corresponding 195Pt satellites (JPtP ) 2519 Hz).
A broad peak at 10.9 ppm is due to the uncoordinated
phosphonate group. No peaks corresponding to the presence
of a cis isomer or a tris(phosphine) species were present.
This behavior is quite different from the reaction of K2PtCl4
and m-TPPTS where the cis isomer is the sole product20 and
the recently described reaction of the ester phosphonate
ligand Ph2PC6H4P(O)(OEt)2 with PtCl2(PhCN)2 which gives
a 57/43 ratio of trans/cis PtCl2L2 isomers.22
The direct reaction of 1.6 equiv of phosphonic acid
functionalized phosphine ligand 6a and 1.6 equiv of 6b with
K2PtCl4 in water resulted in the formation of the new cis
complexes cis-[PtCl2(p-TPPTP(H)6)2] (7a) and cis-[PtCl2(m-
TPPTP(H)6)2] (7b), respectively (Scheme 1). No evidence
for coordination or reaction of the phosphonic acid group
was observed, and both complexes have the expected shifts
and coupling constants in the 31P NMR spectra (see
Experimental Section). In addition, a broad band due to the
free phosphonic acid OH groups was observed at approxi-
mately 2900 cm-1 in the IR spectra. Both complexes are
water soluble. When exactly 2 equiv of 6a was used, a
doublet and triplet in a 2:1 ratio, corresponding to the tris-
(phosphine) cation [PtCl(p-TPPTP(H)6)3]+ (8), appeared in
the 31P NMR spectrum at 22.7 and 12.2 ppm, respectively
(JP P ) 15 Hz, JP Pt ) 2462 Hz, JP Pt ) 3629 Hz). Complex
A
B
A
B
7a was also present in the solution, and no attempts were
made to separate these two species from the mixture. Similar
observations on the reaction of m-TPPTS with K2PtCl4 in
water at room temperature have recently been published by
Atwood.23 In this report, 1.5 equiv of phosphine ligand to
Pt gives exclusively the cis complex cis-[PtCl2(m-TPPTS)2],
and 2.0 equiv of ligand gives a 3/1 mixture of both cis-[PtCl2-
(m-TPPTS)2] and the tris complex [PtCl(p-TPPTS)3]Cl. In
Contrasting this behavior, a 2:1 mixture of cis- and trans-
[PtCl2(m-TPPTS)2] is formed when m-TPPTS is allowed to
react with Ziese’s salt, K[PtCl3(η2-C2H4)]H2O.20 We as yet
do not understand the anomalous behavior of p-TPPTP
although we speculate that the high anionic charge on the
(21) Minor impurities (<10%) were also observed which were attributed
to phosphine oxide (37 ppm) or unidentified species which could not
be assigned to simple PtCl2L2 or [PtClL3] complexes.
(22) Guerrero, G.; Mutin, P. H.; Dahan, F.; Vioux, A. J. Organomet. Chem.
2002, 649, 113.
(23) Francisco, L. W.; Moreno, D. A.; Atwood, J. D. Organometallics 2001,
20, 4237.
520 Inorganic Chemistry, Vol. 42, No. 2, 2003

Coordination Chemistry of Water-Soluble TPPTP
The grafting of phosphonic acids onto silica gel26 and
metal oxide27 surfaces has been previously reported; for
example, phenylphosphonic acid reacts covalently with the
surface hydroxy groups of silica gel to give a surface-bonded
mono ester. The general procedure involves stirring a slurry
of silica gel with the desired phosphonic acid in a polar
solvent such as 2-propanol, followed by collection of the
supported silica, with washing and drying. We were inter-
ested in assessing the catalytic activity of a supported
phosphine-phosphonic acid complex of palladium in the
C-P coupling reaction. Thus, the catalyst was prepared in
the manner described previously, and to a methanolic solution
of Pd(0) complex containing 6a as the ligand was added silica
gel in a single portion with stirring. The mixture was rapidly
stirred for 1 h, and the bright yellow silica gel was collected,
washed with ether, and dried in vacuo at 60 °C. Although
detailed measurements of palladium loading were not made,
the presence of the coordinated phosphonate ligand was
confirmed by direct observation of the characteristic PO3
bands in the IR spectrum at 1000-1080 cm-1. The supported
palladium complex is an effective catalyst for the coupling
of phenyl triflate with diethyl phosphite. Using toluene as a
solvent, a GC yield of 84% diethyl phenylphosphonate was
obtained from the reaction mixture (see Experimental Sec-
tion).
Crystal Structure Analysis of P(3-C6H4PO3H2)3‚2H2O
(6b). Given our successful demonstration of heterogeneous
catalysis using the silica supported catalyst, we examined
the interaction of the m-TPPTP(H)6 ligand 6b with solid
supports further. Molecular modeling studies indicated that
the ideal arrangement of metal complexes of TPPTP in a
layered fashion on a planar surface would require the meta
isomer of the ligand to achieve optimum geometry. To
confirm this, we analyzed the structure of 6b in the solid
state using X-ray crystallography. Recrystallization of a
sample of 6b from HCl acidified water yielded single
colorless crystals of the phosphine dihydrate. The ORTEP
representation is shown in Figure 1, and crystallographic data
and selected bond distances and angles are listed in Tables
1 and 2. A comparison of the metric parameters of the
triarylphosphine subunit with those of triphenylphosphine28
revealed no remarkable or unexpected bond lengths or angles,
the phosphine phosphorus atom P(2) has a trigonal pyramidal
geometry, the P(2)-C distances are all virtually identical,
the mean P(2)-C distance is 1.832 Å, and the mean
C-P(2)-C angle is 102.4°. Very few crystal structures of
arylphosphonic acids have been reported in the literature
although, notably, the crystal structure of phenylphosphonic
acid was reported by Weakley in 1976.29 The structure of
PhP(O)(OH)2 is held together by a combination of both a
centrosymmetric dimer and continuous chain hydrogen
bonded motifs incorporating four carbon chains which result
in the formation of layered structure. The mean P(1)-C bond
Scheme 2. Aqueous Phase Coupling of Phenyl Triflate with
Diethylphosphite
the case of our phosphonic acid ligand 6a, the ratio of cis
bis(phosphine) complex to tris(phosphine) complex is re-
versed (1/3).
An alternative route to platinum complexes of TPPTP
involves coordination of triarylphosphine-phosphonodi-
amide ligand p-TPPTA (9) to platinum and subsequent post-
complexation ligand hydrolysis to give the desired p-TPPTP-
(H)6 complex 7a (Scheme 1). p-TPPTA was prepared from
red phosphorus, lithium, and N,N,N′,N′-tetramethyl-4-fluoro-
phenylphosphonodiamide according to the literature pro-
cedure3e and reacted with K2PtCl4 in refluxing xylene for 3
days. On cooling of the xylene solution, cis-[PtCl2(p-
TPPTA)2]‚3H2O (9) precipitated as a white solid which was
collected by filtration and characterized using NMR, IR, and
elemental analysis (see Experimental Section). The 31P NMR
spectrum of 10 shows the expected triplet at 15.6 with 195Pt
satellites (JPtP ) 3620 Hz). After concentration of the filtrate
following the isolation of 10, a very small amount of a
colorless, crystalline compound was collected and subse-
quently identified, using single-crystal X-ray crystallography,
as the phosphonium salt HP[4-C6H4PO{N(CH3}2}]3OH,
which presumably results from phosphine protonation due
to adventitious water.14
Aqueous Phase and Supported Catalysis. Water-soluble
palladium phosphine complexes are known to catalyze a wide
variety of coupling reactions in aqueous solution.1e We chose
the palladium(0) coupling of diethyl phosphite and phenyl
triflate to give diethyl phosphonate as a test case for p-TPPTP
under homogeneous and heterogeneous catalytic conditions.
While aryl iodides have previously been used as substrates
for the aqueous phase phosphonylation reaction,24 aryl
triflates have not been explored.25 The addition of 5 equiv
of 4 to a solution of sodium tetrachloropalladate in water at
room temperature resulted in the formation of a bright yellow
solution. To this was added sodium borohydride, triethyl-
amine, diethyl phosphite, and phenyl triflate. The mixture
was refluxed for 24 h, and following workup (see Experi-
mental Section), diethyl phenylphosphonate was obtained in
78% yield (Scheme 2). A notable increase in catalytic activity
was observed when a small amount of acetonitrile (∼10%)
was added as co-solvent. The role of the co-solvent is
unknown, but we suggest that it improves the solubility of
the substrate in the aqueous phase. Under biphasic conditions
using a 50/50 water/toluene or water/dichloromethane mix-
ture, no activity was observed. This is not too surprising as
p-TPPTP is particularly organophobic.
(24) (a) Casalnuovo, A. L.; Calabrese, J. C. J. Am. Chem. Soc. 1990, 112,
4324. (b) Harper, B. A.; Rainwater, J. C.; Birdwhistell, K.; Knight,
D. A. J. Chem. Educ. 2002, 79, 729.
(25) Aryl triflates have been previously used as substrates for Pd catalyzed
C-P bond formation in organic solvent. See: Petrakis, K. S.;
Nagabhushan, T. L. J. Am. Chem. Soc. 1987, 109, 2831.
(26) Lukes, I.; Borbaruah, M.; Quin, L. D. J. Am. Chem. Soc. 1994, 116,
1737.
(27) Gao, W.; Dickinson, L.; Grozinger, C.; Morin, F. G.; Reven, L.
Langmuir 1996, 12, 6429.
(28) Daly, J. J. J. Chem. Soc. 1964, 3799.
(29) Weakley, T. J. R. Acta Crystallogr. 1976, B32, 2889.
Inorganic Chemistry, Vol. 42, No. 2, 2003 521

Harper et al.
Table 2. Selected Bond Lengths [Å] and Angles [deg] for 6b
P(2)-C(1′′)
P(2)-C(1)
1.827(4)
1.835(4)
1.835(3)
1.484(3)
1.552(3)
1.554(3)
1.790(4)
1.512(3)
1.524(3)
1.558(3)
1.780(4)
1.514(3)
1.533(3)
1.536(3)
1.784(4)
99.48(15)
O(1′)-P(1′)-O(2′)
O(1′)-P(1′)-O(3′)
O(2′)-P(1′)-O(3′)
O(1′)-P(1′)-C(3′)
O(2′)-P(1′)-C(3′)
O(3′)-P(1′)-C(3′)
O(2")-P(1′′)-O(3′′)
O(2′′)-P(1′′)-O(1′′) 112.30(18)
O(3′′)-P(1′′)-O(1′′) 111.3(2)
O(2′′)-P(1′′)-C(3′′) 112.72(16)
O(3′′)-P(1′′)-C(3′′) 105.18(17)
O(1′′)-P(1′′)-C(3′′) 104.84(17)
112.51(16)
111.06(16)
106.76(15)
107.91(16)
109.68(16)
108.88(16)
110.17(16)
P(2)-C(1′)
P(1)-O(2)
P(1)-O(3)
P(1)-O(1)
P(1)-C(3)
P(1′)-O(1′)
P(1′)-O(2′)
P(1′)-O(3′)
P(1′)-C(3′)
P(1′′)-O(2′′)
P(1′′)-O(3′′)
P(1′′)-O(1′′)
P(1′′)-C(3′′)
C(1′′)-P(2)-C(1)
C(6)-C(1)-P(2)
C(2)-C(1)-P(2)
C(4)-C(3)-P(1)
C(2)-C(3)-P(1)
127.3(3)
114.2(3)
121.9(3)
119.2(3)
123.2(3)
117.8(3)
118.4(3)
123.0(3)
117.6(3)
124.6(3)
122.3(3)
118.5(3)
C(1′′)-P(2)-C(1′) 103.18(16) C(6′)-C(1′)-P(2)
C(1)-P(2)-C(1′)
O(2)-P(1)-O(3)
O(2)-P(1)-O(1)
O(3)-P(1)-O(1)
O(2)-P(1)-C(3)
O(3)-P(1)-C(3)
O(1)-P(1)-C(3)
104.66(15) C(2′)-C(1′)-P(2)
115.50(17) C(4′)-C(3′)-P(1′)
112.22(16) C(2′)-C(3′)-P(1′)
104.02(15) C(2′′)-C(1′′)-P(2)
108.84(16) C(6′′)-C(1′′)-P(2)
107.69(16) C(4′′)-C(3′′)-P(1′′)
108.24(15) C(2′′)-C(3′′)-P(1′′)
Figure 1. Structure of 6b drawn from experimental coordinates. Displace-
ment ellipsoids for non-hydrogen atoms are drawn at the 30% probability
level. The lower occupancy disorder of the PO3 group on C3′′ is not shown
for clarity.
Table 1. Summary of Crystallographic Data for 6b
empirical formula
C22H12O11P4
532.19
213(2)
1.54178
triclinic
P1h
fw
Table 3. Hydrogen Bonds for 6b [Å and deg]
temp, K
wavelength, Å
cryst syst
space group
unit cell dimensions
a, Å
D-H
(Å)
H‚‚‚‚A
(Å)
D‚‚‚‚A D-H‚‚‚‚A
D-H‚‚‚‚A
(Å)
(deg)
O(1S)-H(1SA)‚‚‚O(2′′)#1a 0.985(10) 1.653(13) 2.632(4)
0.991(10) 1.580(14) 2.561(4)
172(4)
170(5)
130(4)
173(7)
139(6)
O(1S)-H(1SB)‚‚‚O(2′)#2
8.3501(6)
10.1907(6)
b, Å
c, Å
O(1S)-H(1SB)‚‚‚O(1′A)#2 0.991(10) 1.74(5)
O(2S)-H(2SB)‚‚‚O(2′A)#3 0.980(11) 1.74(3)
2.49(3)
2.72(3)
2.931(6)
14.6529(14)
94.177(6)
R, deg
O(2S)-H(2SB)‚‚‚O(3′)#3
0.980(11) 2.12(5)
â, deg
105.885(6)
a Symmetry transformations used to generate equivalent atoms: #1 -x,
-y + 1, -z + 1; #2 -x, -y + 1, -z; #3 -x + 1, -y + 2, -z + 1.
γ, deg
108.784(5)
V, Å3
1117.50(15) Å3
2
Z
d
calcd, g/cm3
1.582
abs coeff, mm-1
F(000)
3.668
544
cryst size, mm3
θ
0.41 × 0.17 × 0.05
3.19-57.49
index ranges
-8 e h e 8,
-10 e k e 10,
-4 e l e 14
3123
reflns collected
indep reflns
completeness to θ ) 57.49°
abs correction
2884 [R(int) ) 0.0146]
94.2%
integration
max and min transm
refinement method
data/restraints/params
GOF on F2
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak and hole, e Å-3
0.8126 and 0.3840
full-matrix least-squares on F2
2884/13/322
1.079
R1 ) 0.0441, wR2 ) 0.1201
R1 ) 0.0484, wR2 ) 0.1295
0.424 and -0.479
length of 1.785 Å in P(3-C6H4PO3H2)3‚2H2O is slightly
longer than 1.773(5) Å found in phenylphosphonic acid. The
two long P(1)-O bonds (mean value 1.543 Å) and one short
P(1)-O bond (mean value 1.503 Å) fall into the expected
range. The phosphonic acid phosphorus atom, P(1), is
tetrahedral with a mean X-P-X angle of 109.4°. Two water
molecules of solvation are present in the unit cell which are
hydrogen bonded to the PO3H2 groups. Hydrogen bond
distances are listed in Table 3.
Figure 2. Molecular drawing of 6b showing layered structure of crystal
lattice. View is approximately along the a axis.
the phosphonic acid layer. Presumably, weak van der Waals’
forces are responsible for holding the organic layers together,
similar to those proposed for layered metal organophospho-
nates.4
It is clear that P(3-C6H4PO3H2)3‚2H2O also has a layered
structure in the solid state, as shown in Figure 2, with the
organic triphenylphosphine groups forming one layer, and
the phosphonic acid groups forming a second layer. The
water molecules form a hydrogen bonded network within
Formation of Mo(CO)5{P(3-C6H4PO3H2)3} and Surface
Grafting to Alumina. To further study the nature of the
supported phosphonate ligand, we investigated the attachment
of phosphonate functionalized phosphine complexes to planar
Al2O3 by IR. The careful choice of a molybdenum carbonyl
522 Inorganic Chemistry, Vol. 42, No. 2, 2003

Coordination Chemistry of Water-Soluble TPPTP
derivative was made because of the intense and characteristic
CO stretching frequencies which are sensitive to the metal
complex environment and the well-known ability of metal
carbonyls to undergo ligand substitution reactions. In addi-
tion, the stepwise formation of group VI metal carbonyl
phosphine complexes is well-known, and the molybdenum
phosphine stoichiometry is more readily controlled and easier
to study than that of platinum and palladium derivatives. The
reaction of 6b with an excess of Mo(CO)6 in refluxing
ethanol/toluene resulted in the formation of yellow Mo(CO)5-
{P(3-C6H4PO3H2)3} (11) as shown by IR and 31P NMR
spectroscopies. Analogous sulfonated phosphine complexes
[M(CO)5(m-TPPTS)] (M ) Mo, W) have been previously
studied by Darensbourg and also provided us with useful
spectral data for comparison.30,31 The IR spectrum of 11,
2
recorded as a KBr pellet, contained the expected A1 , E, and
A1 bands in the carbonyl region at 2074, 1990, and 1935
Figure 3. Comparison of the RAIR spectrum of surface-adsorbed Mo-
(CO)5{P(3-C6H4PO3H2)3} on alumina with the transmission IR spectrum
of the complex prepared as a KBr pellet. Absorbances are normalized for
comparison purposes.
1
cm-1, consistent with the formation of a monophosphine
adduct (cf. Mo(CO)5(PPh3),32 2073, 1984, 1952 cm-1; and
Mo(CO)5(m-TPPTS),30 2075, 1955, 1941 cm-1). Although
water is clearly present in the spectrum, the degree of
hydration remains unknown. The phosphonic acid P-OH
absorption was observed as a broad band at 3412 cm-1. The
31P NMR spectrum of 11 recorded in methanol showed peaks
at 41.1 and 14.2 ppm corresponding to coordinated phosphine
and uncoordinated phosphonic acid groups, respectively. No
evidence for the formation of a bis(phosphine) complex was
observed in solution by 31P NMR. We were interested to
know whether complex 11 could be deposited as a monolayer
onto the surface of an oxide such as alumina via direct
attachment of the phosphonic acid group. Because alumina
is transparent in the carbonyl region of the IR spectrum, it
proved to be a useful substrate for binding the phosphonic
acid complex and observing any possible chemical changes
occurring at the molybdenum center. A glass 3 in. × 1 in.
microscope slide was vapor deposited with 150-200 nm of
aluminum substrate, plasma cleaned, and air oxidized. The
slide was subsequently immersed in a 1 mM methanolic
solution of 11 for 4 h, washed exhaustively with methanol,
and dried under a stream of filtered nitrogen. A reflection-
absorption infrared (RAIR) spectrum of the surface-grafted
phosphine complex was recorded, and the spectrum indicated
little change in the metal carbonyl absorption frequencies
compared to the spectrum recorded as a KBr disk, suggesting
that the carbonyl groups are not interacting with the alumina
surface (Figure 3).
1998 cm-1 is gradually transformed to a pair of superim-
posable quartets centered at 2031 cm-1. The shift is ascribed
to the interaction of the carbonyl oxygen atoms with Lewis
acidic sites on the alumina surface. The absence of such
interactions for 11 adsorbed to alumina indicates that the
Mo(CO)5 kernal is well separated from the alumina surface
by the m-TPPTP(H)6 spacer ligand. Such behavior is
consistent with the crystal structure of 6b and a surface
binding model involving interaction of each of the three
2-
PO3 groups with the alumina in a tripodal binding
configuration.34
Surface Analysis of Mo(CO)5{P(3-C6H4PO3H2)3} on
Alumina. To further understand the nature of the molybde-
num phosphine complex on the surface of alumina and to
unambiguously show the presence of monolayers of 11, XPS,
Rutherford backscattering spectrometry (RBS), and AFM
measurements were made. A survey scan of a 600 µm2 area
of the samples by XPS showed that carbon, phosphorus, and
molybdenum were present on the aluminum/aluminum oxide
surface. Integration of the C 1s and P 2p peaks gave a C/P
ratio of 4.7/1. The calculated C/P ratio for Mo(CO)5{P(3-
C6H4PO3H2)3} is 5.75/1. However, analysis at the Mo 3d
energy level showed two molybdenum containing species
present on the surface, with an approximate ratio of 70/30,
thought to be Mo(CO)5{P(3-C6H4PO3H2)3} and molybdenum
oxide resulting from oxidative degradation of the Mo(0)
complex. If 30% of the CO ligands were lost due to
decomposition, the expected C/P ratio would be closer to 4.
Thus, a C/P ratio between 4 and 5.75 is in reasonable
agreement with the expected results.
Previous workers have observed substantial differences in
the IR carbonyl stretching frequencies of the solid state
molecular species compared to alumina supported complexes.
The adsorption of Mo(CO)6 onto partially de-hydroxylated
γ-alumina resulted in significant spectral changes in the
carbonyl region of the IR spectrum compared to the gas phase
spectrum of the complex33 The single strong absorption at
The major fraction of molybdenum species had binding
energies of 233.8 eV (3d3/2) and 230.7 eV (3d5/2). This can
be compared with [Mo(CO)5(PPh3)] which is reported to have
(30) Darensbourg, D. J.; Bischoff, C. J. Inorg. Chem. 1993, 32, 47.
(31) Darensbourg, D. J.; Bischoff, C. J.; Reibenspies, J. H. Inorg. Chem.
1991, 30, 1144.
(32) Poilblanc, R.; Bigorgne, M. Bull. Soc. Chim. Fr. 1962, 1301.
(33) Reddy, K. P.; Brown, T. L. J. Am. Chem. Soc. 1995, 117, 2845.
(34) Similar observations were made when using the para isomer. Control
experiments involving immersion of aluminized slides into ethanolic
solutions of Mo(CO)5(PPh3) and Mo(CO)5(solvate) and recording
RAIR spectra show no adsorption of these species to the surface and
clearly implicate the phosphonic acid group in surface adsorption.
Inorganic Chemistry, Vol. 42, No. 2, 2003 523

Harper et al.
3d3/2 and 3d5/2 binding energies of 230.8 and 227.6 eV35 and
for elemental molybdenum (231.1 and 227.8 eV).36 The
minor fraction had 3d3/2 and 3d5/2 binding energies at 235.4
and 238.4 eV, respectively, as compared to the values
reported for native films of molybdenum oxide (232.7 eV,
235.8 eV, presumably as MoO2/MoO3).36 It is not clear why
the binding energies are consistently high for the molybde-
num 3d spectrum although it does not appear to be related
to sample charging, as the C 1s binding energy was actually
1 eV too low, and the adjusted binding energies for Al/Al2O3
2p electrons (72.1 and 74.6 eV) are in reasonable agreement
with the expected values (72.7 and 74.7 eV).3b
To calculate the estimated density of a monolayer of Mo-
(CO)5{P(3-C6H4PO3H2)3}, a molecular model was con-
structed37 in which the phosphonate groups were assumed
to be oriented toward the surface. In this configuration, the
molecule was projected on the surface as a circle approxi-
mately 9 Å in diameter, and from this estimate, a molecular
area of 2.03 × 10-15 cm2 was calculated, giving a maximum
surface coverage for a monolayer on a flat surface of
approximately 4.93 × 1014 molecules/cm2. The actual surface
coverage was determined by Rutherford backscattering
spectrometry. The integrated area under the Mo edge was
448 counts, corresponding to approximately 5.0 × 1014
atoms/cm2 (5%. This value is consistent with full monolayer
coverage by the molybdenum complex but does not rule out
the formation of crystallites or patches of multilayer cover-
age.
deviation in surface area from an atomically flat surface was
calculated to be 2.65%. This is less than the experimental
error for RBS measurements, so surface roughness was
ignored when estimating the RBS value expected for
monolayer coverage.
Surfaces exposed to a solution of Mo(CO)5{P(3-C6H4-
PO3H2)3} exhibited no significant morphological differences
from the control sample over scan areas ranging from 1 to
100 µm2. High-resolution scans exhibited no evidence of
crystalline deposition on the substrate surface, and there was
no evidence of multilayer domains. This further supports the
RBS measurements indicating that monolayer coverage of
the molybdenum complex exists.
In conclusion, new water-soluble complexes of phosphonic
acid substituted phosphines have been prepared and char-
acterized, and we have demonstrated application of a
palladium complex in aqueous phase and supported C-P
bond formation. A crystal structure of m-TPPTP(H)6 revealed
the presence of a layered structure in the solid state and an
ideal molecular geometry for building a monolayer of a metal
phosphine complex on a planar surface. We have also shown
that a phosphonic acid functionalized phosphine can act as
suitable supporting ligand for a metal carbonyl monolayer
on the surface of alumina.
Acknowledgment. We would like to thank the Office of
Naval Research under the Naval Research Core Program and
Loyola University New Orleans for partial support of this
work, and the ASEE for a Summer Faculty Research
Fellowship (to D.A.K.). The authors are grateful to Dr. David
L. Knies, NRL Surface Modification Branch, Code 6370,
for the RBS analyses.
To address this issue, atomic force microscopy of the
surface was carried out. AFM images of aluminum coated
control samples showed a homogeneous pebble-grained
morphology with an average surface roughness (rms) of 12.7
nm over a 25 µm2 area (5 µm × 5 µm scan area). The
Supporting Information Available: 31P NMR spectra for
complexes 5, 7a, 7b, and 8. XPS and RBS data for 11 on alumina.
X-ray crystal files for 6b in CIF format. This material is available
free of charge via the Internet at http://pubs.acs.org.
(35) Hughes, W. B.; Baldwin, B. A. Inorg. Chem. 1974, 13, 1531.
(36) Crist, B. V. Handbook of Monochromatic XPS Spectra: The Elements
and NatiVe Oxides; John Wiley and Sons: West Sussex, England,
2000.
(37) Chem3D Ultra V. 6.0; CambridgeSoft.com: Cambridge, MA, 2000.
IC025862A
524 Inorganic Chemistry, Vol. 42, No. 2, 2003