On the surface reactivity of functionalized phosphinines on inorganic supports

Article abstract of DOI:10.1002/zaac.200900545

Phosphinines with pendant phenol or catechol functionalities and their gold(I) complexes were synthesised and characterised by spectroscopic data and in one case by a single-crystal X-ray diffraction study. Reactions of ligands or complexes with TiO₂

Full text of DOI:10.1002/zaac.200900545

ARTICLE
DOI: 10.1002/zaac.200900545
On the Surface Reactivity of Functionalized Phosphinines on Inorganic
Supports
Samith Komath Mallissery,[a] Martin Nieger,[b] and Dietrich Gudat*[a]
Keywords: Phosphinines; Titania; Silica; Immobilisation; NMR spectroscopy; Gold
Abstract. Phosphinines with pendant phenol or catechol functionali- was accompanied by complete degradation of the phosphinine moiety.
ties and their gold(I) complexes were synthesised and characterised by Base induced coupling with chloropropyl modified silica produced a
spectroscopic data and in one case by a single-crystal X-ray diffraction material that contained a mixture of several surface-bound phosphorus
study. Reactions of ligands or complexes with TiO2 or chloropropyl compounds. 31P MAS NMR studies revealed that approx. 40 % of the
modified hexagonal mesoporous silica were then studied with the aim ligand had retained its integrity whereas the remaining fraction had
to immobilise ligands or complexes on the carrier by covalent teth- been converted into further, not unambiguously identified structures.
ering. 31P MAS NMR studies revealed that immobilisation on TiO2
us to explore if the same approach allows also the anchoring
Introduction
Phosphinines (phosphabenzenes) were first prepared about
of phosphinines or their complexes, respectively. We report
here on the synthesis of tailored phosphinines with pendant
40 years ago [1] and have since then developed from labora-
phenol and catechol moieties, and their reactions with TiO2
tory curiosities into useful ligands that have found application
nanoparticles and surface modified mesoporous silica, respec-
in coordination chemistry and catalysis [2, 3], or for the stabili-
tively.
sation of metal nanoparticles [4]. Catalytic reactions with par-
ticipation of phosphinine ligands include hydroformylation,
Results and Discussion
amination, CC-coupling, with the diversity suggesting that
phosphinines may also belong to a set of privileged ligands
that can support a wide range of catalytic reactions. To the best
of our knowledge, all catalytic applications reported so far are
based on homogeneous reactions, and although attempts to im-
mobilise the catalysts in order to improve their separation and
recycling receive currently great attention [5, 6], no such at-
tempts with phosphinine ligands or their complexes have been
reported.
Owing to the stabilisation by π-aromaticity, phosphinines are
less prone to hydrolyse than other low coordinate phosphorus
compounds. Having recently elaborated Märkl’s original ap-
proach [1] into a modular synthesis of functional phosphinines,
Vogt and Müller showed that the phosphinine core tolerates a
variety of functional groups, including phenol and carboxylic
acid moieties [7]. The fact that catechol moieties have recently
been employed as anchoring group for the immobilisation of
phosphine complexes on inorganic supports [8, 9] stimulated
Considering that the previously reported immobilisation pro-
tocols [8, 9] require substrates with one or two adjacent freely
accessible phenolic OH-groups, we regarded 2,4,6-trisubsti-
tuted phosphinines like 1a–c as viable and readily accessible
target compounds (Scheme 1). As precursors, we prepared first
methoxy-substituted derivatives 2a–c from appropriately sub-
stituted chalcone and acetophenone building blocks by follow-
ing the protocol of Vogt and Müller [7]. Deprotection of the
phenolic OH-functionalities was accomplished by reaction
with BBr3 in CH2Cl2 [7] to give 1a–c as air sensitive, yellow-
ish powders in near quantitative yields. All phosphinines pre-
pared were sufficiently characterised by analytical and spectro-
scopic (1H, 13C, 31P NMR, MS) data.
In order to demonstrate the efficacy of phosphinines 1a–c
and 2a–c as ligands, we prepared gold complexes from the free
ligands and an equimolar amount of AuCl(tht) (tht = tetrahy-
drothiophene) in CH2Cl2 or thf, respectively. Gold(I) was cho-
sen since phosphinines form stable complexes with this metal
that are distinguished by a 1:1 metal-to-ligand ratio and are
not supported by additional ligands [10] and thus possibly min-
imise the chance of decomposition during subsequent immo-
bilisation. Model complexes 3a/b and 4a were isolated as pale
yellow solids in 90–95 % yield after precipitation with hexane
and identified by spectroscopic data and a single-crystal X-ray
diffraction study of 4a. The 31P NMR spectra are distinguished
by showing moderate negative coordination shifts (∆δ = –30
* Prof. Dr. D. Gudat
Fax: +49-711-685-64241
E-Mail: gudat@iac.uni-stuttgart.de
[a] Institut für Anorganische Chemie
Universität Stuttgart
Pfaffenwaldring 55
70550 Stuttgart, Germany
[b] Laboratory of Inorganic Chemistry
University of Helsinki
A. I. Virtasen aukio 1
Helsinki, Finland
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Z. Anorg. Allg. Chem. 2010, 636, 1354–1360

Surface Reactivity of Functionalized Phosphinines on Inorganic Supports
Figure 1. ORTEP-style representation showing two of the three crys-
tallographically independent molecules of 4a in the crystal (hydrogen
atoms omitted for clarity; displacement parameters drawn at 50 %
probability level). Selected bond lengths /Å and angles /° (values for
the second and third molecule given in brackets): P1A–Au1A 2.206(1)
[2.207(1), 2.212(1)], Au1A–Cl1A 2.277(1) [2.273(1), 2.278(1)], P1A–
Au1A–Cl1A 175.9(1) [177.0(1), 176.0(1)].
Scheme 1.
to –33) which are indicative of η1(P)-coordination of the phos-
phinine. The absence of splitting or line broadening effects
arising from J(197Au,31P) coupling is attributable to the high somewhat larger than in the case of 1a/NP-TiO2 (δ = –10), and
1
quadrupole moment of the metal nucleus which induces effect- comparison of the lineshapes observed in spectra of non rotat-
ive decoupling of both nuclei [10].
ing samples (Figure 2 b,d) revealed that the deshielding was
The single-crystal X-ray diffraction study reveals that crys- accompanied by a larger shielding anisotropy (although the
tals of 4a contain three crystallographically independent mo- line widths prevented the specific evaluation of individual
lecular complexes of composition LAuCl two of which are principal components of the shielding tensor, the observed
connected by
a weak Au···Cl interaction (Au1A–Cl1B spectra allowed to estimate the overall shielding anisotropy
3.387 Å) that is hardly shorter than the sum of van-der-Waals Ω = δ11–δ33 as < 55 ppm for 1a/NP-TiO2 and ≈170 ppm for
radii (Figure 1). The individual bond lengths and bond angles 3a/NP-TiO2). The amount of organic material deposited on the
in all three specimens show no significant deviations. The support corresponds on the basis of the analytical data to 23
metal atoms exhibit quasi-linear coordination (P–Au–Cl μmol·g–1 NP-TiO2 for the phosphinine 1a, or 53 and 48
175.9–177.0°). The Au–Cl (2.273–2.278 Å) and Au–P (2.206– μmol·g–1 NP-TiO2 for the complexes 3a/b, respectively (The
2.212 Å) bond lengths match those in bis(trimethylsilyl) phos- given loadings were derived from the analytically determined
phinine gold(I) chloride (Au–Cl 2.281(2) Å, Au–P 2.211(2) Å carbon content and were computed under the assumption that
[10]) and lie at the lower end of the ranges found for tertiary the intact ligand or complex had been deposited. Although this
phosphane complexes (Au–Cl 2.30 0.03 Å, Au–P is obviously not the case we reckon that the given figures allow
2.24 0.03 Å [11]; the short Au–P bond length is in accord at least a rough estimation of the amount of material depos-
with the different formal hybridisation of the phosphorus atom ited.). Even though the available data do not allow to decide
in phosphinines and phosphanes) [2].
if the phosphane ligands is bound to the surface by a covalent
Attempts towards immobilisation of the phosphinine 1a and bond or otherwise, the higher loading of the complex is signifi-
the gold complexes 3a/b on TiO2 nanoparticles (NP-TiO2) cant and points possibly to the presence of additional interac-
were carried out as described previously [8, 9] by stirring a tion of the chloride ligands with Lewis acidic sites on the sur-
suspension of the substrates and preheated NP-TiO2 in THF face.
for 24 h at ambient temperature, filtering off the supernatant
The observation of a single 31P NMR signal from the sur-
liquid, washing the solid residue with several portions of THF, face-bound species indicates that the immobilisation is clean
and drying in vacuo. The materials were then characterised by and produces no side products. However, comparison of the
elemental analyses and solid-state 31P NMR spectroscopy.
spectroscopic data with those of authentic samples of the phos-
The 31P CP-MAS NMR spectra of all materials displayed phinine 2a and complex 4a (Figure 3) indicates clearly that
each a single broad resonance (Δν1/2 = 0.8–3.1 kHz, Figure 2 the surface-bound species feature significantly lower isotropic
a,c) which suggested the presence of a single surface species chemical shifts and chemical shielding anisotropies [12] and
with a marked chemical shift dispersion. The isotropic chemi- exhibit thus no longer a phosphinine structure.
cal shifts in the two immobilised complexes 3a/NP-TiO2 (δ =
Although unambiguous structure elucidation was unfeasible,
28) and 3b/NP-TiO2 (δ = 27) were essentially identical and the 31P chemical shift and shielding anisotropy of 1a/NP-TiO2
Z. Anorg. Allg. Chem. 2010, 1354–1360
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S. Komath Mallissery, M. Nieger, D. Gudat
ARTICLE
NP-TiO2 which disclosed that the solid material contains both
phosphorus and gold with an atomic ratio P:Au of 0.92:1 that
comes quite close to the ideal value of 1:1.
Since the preceding experiments proved TiO2 to be not suita-
ble for the immobilisation of phosphinines, we decided to ex-
plore the use of alternative carrier materials. Silica seemed a
good choice as it provides a less acidic surface, and a number
of techniques allowing covalent tethering of a variety of func-
tional molecules, including phosphanes and their complexes,
under mild reaction conditions have been reported [5]. As the
synthesis of 1a–c had shown the feasibility of selective trans-
formations at the phenolic functionality under retention of the
phosphinine core, we reckoned that alkylation of the hydroxyl
group by a surface-bound haloalkyl moiety to give a phenol
ether should offer a viable approach to immobilise 1c. Hexago-
nal mesoporous silica (HMS) [13] was selected as carrier ma-
terial as its preparation is straightforward and does not require
strongly acidic conditions, the material can be readily function-
alized by treatment with chloropropyl triethoxysilane, and in-
corporation of the phosphinine into the porous material might
provide some additional protection against degradation of the
ligand during the immobilisation process.
Figure 2. Solid state 31P NMR spectra of 3a/NP-TiO2 (a,b) and 1a/
NP-TiO2 (c, d) recorded with cross polarisation for signal enhance-
ment. Spectra in traces (a) and (c) were recorded under MAS (νrot
=
8 kHz, spinning sidebands labelled with an asterisk) whereas traces (b)
and (d) show spectra of non-spinning samples.
Following the outlined scheme, HMS was first derivatised
by reaction with chloropropyl(triethoxy)silane in toluene. The
specific functionalisation was proven by 13C and 29Si CP-MAS
NMR studies. The 13C NMR spectrum (Figure 4) contains be-
side signals of the carbon atoms of the propyl chain at 6.1,
23.6 and 44.0 ppm two resonances (13.0, 56.6 ppm) arising
from an ethoxy group. The 29Si NMR spectrum (Figure 5) dis-
plays in addition to the signals of Q4, Q3 and Q2 groups in the
carrier material at –112.2, –102.8 and –93.5 ppm a resonance
at –53.2 ppm for the grafted organosilane species. These find-
ings suggest the predominance of a single surface species with
a constitution as shown in Figure 3, although the presence of
an additional unassigned 13C signal around 20 ppm indicates
the presence of another (minor) species of unknown structure.
Surface bound organosilane moieties which still contain resid-
ual OEt moieties were also found in other modified silica ma-
terials that had been prepared from triethoxysilane precursors
[14] whereas materials made from chloropropyl(trimethoxy)si-
lane were reported to contain only T3 and T2-type silicon at-
oms that carry no more alkoxy groups [15]. The observation
that the intensity of the signal of T2-groups relative to that of
the Qn-moieties in the bulk support is much lower than in other
modified silica materials [14, 15] suggests a rather low loading
of functional groups on the surface.
Figure 3. 31P CP MAS NMR spectra of 4a (top trace, νrot = 8 kHz,
δiso = 155) and 2a (bottom trace, νrot = 5 kHz, δiso = 188.0). Isotropic
chemical shifts are marked by asterisks. The fine structure of the lines
in the spectrum of 4a results from scalar and residual dipolar coupling
with the 197Au nucleus (I = 3/2).
are typical for a tertiary phosphane with a three coordinate
phosphorus atom. Regarding that phosphane derivatives are
easily accessible, e.g. via nucleophilic attack of the electro-
philic phosphorus centre in a phosphinine, or addition of vari-
ous XH-acidic compounds to the 6π-system [2], we consider
it likely that the phosphinine moiety cannot tolerate the acidic
environment on the TiO2 surface (the pH of a 4 % aqueous
dispersion is 3.5–4.5) and reacts during the immobilisation
process under uptake of a further ligand at the phosphorus
atom. Starting from this assumption, we assign the surface-
bound species in 3a/NP-TiO2 and 3b/NP-TiO2 to gold com-
plexes of the same phosphane species. This hypothesis is in
line with the observed increase in isotropic chemical shift and
Coupling of the phosphinine to the surface was carried out
by dropwise addition of a CH2Cl2 solution of 1c to a cooled
(–78 °C) suspension of the silica in a mixture of CH2Cl2/trieth-
ylamine. The mixture was then stirred overnight while warm-
ing to room temperature was allowed, and the modified silica
was isolated after work-up (see Experimental Section). At-
tempts to characterise the isolated material by 31P CP-MAS
NMR gave spectra with unsatisfactory signal-to-noise ratios
whereas much better results were obtained when the spectra
shielding anisotropy that is characteristic for many phosphane were recorded without cross polarisation under direct excita-
complexes, and also with the results of an XPS analysis of 3a/ tion of 31P nuclei (Figure 6). Large effects on signal intensities
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Surface Reactivity of Functionalized Phosphinines on Inorganic Supports
(δ =185.2) and a large shielding anisotropy and is assigned to
the desired covalently tethered phosphinine. The large line-
width (Δν1/2 ≈ 4 kHz) as compared to solid 2a (Figure 3,
Δν1/2 = 0.3 kHz) is attributed to the inhomogeneity of surface
environments. The remaining signals (δ = 43.0, 17.4, 3.8) ex-
hibit again smaller chemical shifts and shielding anisotropies
and are assigned to unidentified, presumably phosphine-type
side-products. Characterisation of the material by 13C MAS
NMR was unfeasible as the strong overlap of signals from
different surface species rendered the spectra uninterpretable
but 29Si MAS spectra gave no evidence that the material had
changed during the attachment process. As 31P NMR spectra
of the supernatant solution contained only the signal of unre-
acted 1c, it is clear that the degradation of the phosphinine
moiety occurs in the surface reaction; the available data do not
allow, however, to decide whether the reaction proceeds via
direct attack of surface functionalities on the electrophilic
phosphorus atom, or through a surface-induced intramolecular
attack by phenol or catechol functional groups.
Figure 4. 13C CP MAS NMR spectrum and molecular constitution of
the predominant surface species in chloropropyl modified HMS (νrot
=
8 kHz, contact time: 1.8 ms). The signals labelled a–c are attributable
to the carbon atoms in the propyl chain, and signals arising from the
ethoxy group are labelled with an askerisk.
Conclusions
The synthesis of phosphinines 1a–1c illustrates the stability
of the delocalised π-system against acidic phenol and redox
active catechol functional groups and thus emphasises the
functional group tolerance of this class of compounds. The
results of immobilisation studies show that the reactivity and
stability of these molecules is in principle sufficient to allow
their immobilisation by covalent tethering to an inorganic car-
rier. However, the observed degradation of ligands or com-
plexes during these reactions demonstrates also that immobili-
sation reaction imposes a great challenge to the stability of the
delocalised π-system which is not always met. Further efforts
to find a suitable carrier material and suitable reaction condi-
tions are therefore necessary in order to prepare well defined
materials that contain no decomposition products. It may be
envisaged that a similar degradation of the phosphinine moiety
as observed here may also affect other reactions (e.g. transfor-
mations with phosphinine-based catalysts) and may thus have
some impact on the mechanistic interpretation of these reac-
tions.
Figure 5. 29Si CP MAS NMR spectrum of chloropropyl modified
HMS (νrot: 9 kHz, contact time: 4 ms). Signals labelled Q2–Q4 arise
from the silicon nuclei in bulk HMS and the signal labelled T2 from
the surface bound organosilicon species.
in CP-MAS NMR spectra had also been detected for other
surface bound phosphane species, and arise presumably from
subtle differences in residual mobility or relaxation parameters
of the tethered ligands [16].
Experimental Section
General Remarks
All manipulations were carried out under argon using Schlenk tech-
niques. Solvents were dried prior to use by common procedures. Chal-
cone derivatives [17] and AuCl(tht) [18] were prepared as described.
Pyrogenic TiO2 nanoparticles (Degussa AEROXIDE TiO2 P25, pH of
4 % dispersion in H2O ≈ 3.5–4.5, specific surface 50 15 m2·g–1, avg.
particle size 21 nm) was commercially available and dried at 90 °C
for about 4 h prior to use. Solution NMR spectra were recorded with
a Bruker Avance 250 spectrometer (1H: 250.1 MHz, 13C: 62.8 MHz,
31P: 101.2 MHz) at 303 K and solid-state NMR spectra with a Bruker
Avance 400 spectrometer (13C: 100.5 MHz, 29Si: 79.49 MHz, 31P:
161.9 MHz) equipped with a 4 mm MAS probe. MAS experiments
Figure 6. Solution 31P{1H} NMR spectrum of 1c (top trace) and exper-
imental (middle trace) and simulated (bottom trace) solid state 31P{1H}
MAS NMR spectrum (νrot = 14 kHz) of 1c immobilised on chloropro-
pyl modified HMS. Spinning sidebands are denoted by asterisks.
Deconvolution of the measured spectrum reveals the pres-
ence of four distinguishable surface species. The main product
(41 % of the total spectral intensity) gives rise to a spinning
sideband system with the same isotropic chemical shift as 1c were performed using Standard ZrO2 rotors and spinning speeds be-
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S. Komath Mallissery, M. Nieger, D. Gudat
ARTICLE
tween 5 and 14 KHz. Cross polarization was applied using a ramp- gel was added. The solvent was evaporated and the residue subjected
shaped contact pulse and mixing times between 1.5 and 5ms unless to flash chromatography with petroleum ether/ethyl acetate (18.5:1.5)
noted. Chemical shifts were referenced to ext. TMS (1H,13C) or 85 % to give the phosphinine as pale yellow solid.
H3PO4 (Ξ = 40.480747, 31P). EI-MS: Varian MAT 711, 70eV. ESI-MS:
2-(3,4-Dimethoxyphenyl)-4,6-diphenylphosphinine 2a: Pale yellow
solid from the appropriate pyrylium salt (3.38 g, 7.2 mmol) and
tris(trimethylsilyl)phosphine (4.42 g, 18.1 mmol) in acetonitrile
(25 mL). Yield: 0.87 g (32 %); m.p. 147 °C. C25H21O2P1 (384.41):
calcd. C 78.11, H 5.51; found C 78.11, H 5.62. 31P{1H} NMR (C6D6):
Bruker Daltonics-microOTOF-Q. Elemental analysis: Perkin–Elmer
24000 CHN/O Analyser. Melting points were determined in sealed
capillaries.
1
δ = 182.3. H NMR (C6D6): δ = 3.41 (s, 3 H, OCH3), 3.44 (s, 3 H,
General Procedure for the Synthesis of Pyrylium Salts
3
OCH3), 6.60 (d, JHH = 8.2 Hz, 1 H), 7.18–7.36 (m, 8 H), 7.45–7.50
3
4
Tetrafluoroboric acid (52 % ethereal solution, 2 equiv.) was added
dropwise at 70 °C to a solution of the corresponding chalcone
(2 equiv.) and acetyl component (1 equiv.) in 1,2-dichloroethane
(50 mL). The reaction mixture was heated under reflux for 6 h, al-
lowed to cool to room temp. Addition of Et2O (approx. 150 mL) pro-
duced a precipitate, which was collected by filtration, washed with
Et2O, and dried in vacuo.
(m, 2 H), 7.71–7.74 (m, 2 H), 8.11 (dd, JHP = 5.9, JHH = 1.1 Hz, 1
H), 8.21 (dd, 3JHP = 5.8, 4JHH = 1.21 Hz, 1 H). 13C{1H} NMR (C6D6):
3
δ = 55.47 (OCH3), 55.50 (OCH3), 112.0 (d, JCP = 13.4 Hz), 112.6,
120.1 (d, 3JCP = 13.4 Hz), 125.5, 127.9, 127.97, 128.05, 128.13, 128.3,
2
129.02 (2 C), 129.05 (2 C), 129.1, 131.4 (d, JCP = 11.3 Hz, C3/5),
2
2
131.6 (d, JCP = 11.3 Hz, C3/5), 136.5 (d, JCP = 24.7 Hz, C-i of Ph),
3
2
142.7 (d, JCP = 3.2 Hz, C4), 143.7 (d, JCP1 = 24.5 Hz, C-i of Ph),
3
144.3 (d, JCP = 13.9 Hz), 150.5, 171.9 (d, JCP = 52.5 Hz, C2/C6),
1
2-(3,4-Dimethoxyphenyl)-4,6-diphenyl-pyrylium
tetrafluorobo-
172.1 (d, JCP = 52.1, C2/C6). MS (EI, 70eV): m/e (%) = 384.1 (100)
[M+].
rate: Orange solid from benzylidene acetophenone (12.96 g,
62.3 mmol), 3,4-dimethoxyacetophenone (5.61 g, 31.2 mmol) and
ethereal HBF4 (10.2 g of 52 % solution, 62.3 mmol). Yield: 8.2 g
(58 %); m.p. 248 °C. C251H21O3B1F4 (456.25): calcd. C 65.81, H 4.64;
found C 65.81, H 4.32. H NMR (250 MHz, CD3COCD3): δ = 4.03
(s, 3 H, OCH3), 4.04 (s, 3 H, OCH3), 7.35 (d, JHH = 8.7 Hz, 1 H),
4-(2,3-Dimethoxyphenyl)-2,6-diphenylphosphinine 2b: Pale yellow
solid from the appropriate pyrylium salt (4.98 g, 10.92 mmol) and
tris(trimethylsilyl)phosphine (5.47 g, 21.84 mmol). Yield: 0.9 g
(22 %); m.p. 112 °C. C25H21O2P1 (384.41): calcd. C 78.11, H 5.51;
1
found C 77.12, H 5.76. 31P{1H} NMR (C6D6): δ = 184.3. H NMR
7.72–7.86 (m, 5 H), 8.06 (d, JHH = 2.1 Hz, 1 H), 8.32 (dd, JHH
=
8.5 Hz, 2.3 Hz, 1 H), 8.44–8.48 (m, 2 H), 8.54–8.58 (m, 2 H), 8.97
(d, JHH = 1.6 Hz, 1 H), 9.00 (d, JHH = 1.6 Hz, 1 H). 13C{1H} NMR
(250 MHz, CD3COCD3): δ = 56.76, 56.81, 111.9, 113.4, 115.0, 115.6,
122.3, 125.5, 129.3 (2 C), 130.4 (2 C), 130.4, 130.8 (2 C), 130.) (2
C), 134.2, 135.6 (2 C), 151.4, 157.4, 166.1, 170.5, 172.2. MS (ESI):
m/e (%) = 369.15 (100) [M+–BF4].
(C6D6): δ = 3.36 (s, 3 H, OCH3), 3.53 (s, 3 H, OCH3), 6.61 (m, 1 H),
6.97 (d, JHH = 5.0 Hz, 2 H), 7.10–7.24 (m, 6 H), 7.71–7.73 (m, 4 H),
3
8.25 (d, JHP = 5.9 Hz, 2 H). 13C{1H} NMR (C6D6): δ = 55.6, 60.1,
4
112.8, 123.0 (d, JCP = 2.0, 124.1, 127.7, 127.96, 128.01 (3 C), 128.1,
2
3
129.0 (4 C), 133.7 (d, JCP = 12.1 Hz, C3/C5, 2 C), 137.1 (d, JCP
=
3
2
2.7 Hz, C4), 141.4 (d, JCP = 14.3 Hz), 143.6 (d, JCP = 24.3 Hz, C-α
4
1
of Ph, 2 C), 147.4 (d, JCP = 1.6 Hz), 153.7, 170.9 (d, JCP = 52.4 Hz,
C2/C6, 2 C). MS (EI = 70eV): m/e (%) = 384.1 (100) [M+].
2,6-Diphenyl-4-(2,3-dimethoxyphenyl)-pyrylium
tetrafluorobo-
rate: Dark orange solid from 2,3-dimethoxybenzylidene acetophenone
(10.53 g, 38.8 mmol), acetophenone (2.33 g, 19.4 mmol) and ethereal
HBF4 (6.37 g of 52 % solution, 38.8 mmol). Yield: 4.9 g (55 %); m.p.
183 °C. C25H21O3B1F4 (456.25): calcd. C 65.81, H 4.64; found C
2-(3-Methoxyphenyl)-4,6-diphenylphosphinine 2c: Pale yellow solid
from the appropriate pyrylium salt (4.05 g, 9.5 mmol) and tris(trimeth-
ylsilyl)phosphine (4.75 g, 19.0 mmol). Yield: 1.2 g (35 %); m.p.
121 °C. Spectroscopic data were identical with those reported in the
literature [7].
1
64.42, H 4.52. H NMR (250 MHz, CD3COCD3): δ = 3.95 (s, 3 H,
OCH3), 4.02 (s, 3 H, OCH3), 7.40 (d, JHH = 8.0 Hz, 1 H), 7.49 (dd,
JHH = 8.1 Hz, 1.4 Hz, 1 H), 7.62 (dd, JHH = 7.8 Hz, 1.6 Hz, 1 H),
7.78–7.93 (m, 7 H), 8.56–8.61 (m, 5 H). 13C{1H} NMR (250 MHz,
CD3COCD3): δ = 56.9, 62.3, 119.51 (2 C), 119.54 (2 C), 123.4, 126.1,
129.1, 129.6 (4 C), 130.3, 131.0 (4 C), 136.1 (2 C), 149.7, 154.5,
167.0, 171.7 (2 C). MS (ESI): m/e (%) = 369.15 (100) [M+–BF4].
General Procedure for the Synthesis of Hydroxy-Functional-
ized Phosphinines
The appropriate methoxy phosphinine (1 equiv.) was dissolved in di-
chloromethane. BBr3 in CH2Cl2 (5 equiv.) was added dropwise at –
78 °C. The reaction mixture was warmed to room temp. and stirred
for about 24 h. Afterwards, it was poured into cooled degassed water
and stirred for 30 min. The organic layer was separated and dried with
MgSO4. The crude mixture was then subjected to flash chromatogra-
phy (silica gel, hexane/ethyl acetate 50:50) to obtain the desired prod-
uct.
2-(3-Methoxyphenyl)-4,6-diphenyl-pyrylium
tetrafluoroborate:
Yellow solid from benzylidene acetophenone (9.09 g, 43.7 mmol), 3-
methoxyacetophenone (3.27 g, 21.8 mmol) and tetrafluroboric acid
(7.17 g of 52 % ethereal solution, 43.7 mmol). Yield: 5.6 g (60 %);
m.p. 182 °C. Spectroscopic data are identical with those reported in
the literature [13].
2-(3,4-Dihydroxyphenyl)-4,6-diphenylphosphine 1a: from 2a
(0.84 g, 2.2 mmol) and BBr3 (11 mL 1 m soln in CH2Cl2, 11 mmol).
Yield: 500 mg (63 %); m.p. 192 °C. C23H17O2P1 (356.36): calcd. C
General Procedure for the Synthesis of Methoxy-Functional-
ized Phosphinines 2a–2c
The pyrylium salt (1 equiv.) was dissolved in acetonitrile, and tris(tri- 77.52, H 4.81; found C 77.70, H 5.55. 31P{1H} NMR (CD2Cl2): δ =
1
methylsilyl)phosphine (2 equiv.) was added dropwise at room temp. 181.1. H NMR(CD2Cl2): δ = 5.85 (br. s, 2 H, OH), 6.85 (d, JHH
=
The dark coloured solution was heated to 80 °C for 5 h. Formation of 8.3 Hz, 1 H), 7.21 (m, 1 H), 7.32 (m, 1 H), 7.44–7.56 (m, 6 H), 7.71–
the product was confirmed by 31P NMR spectroscopy. After cooling 7.78 (m, 4 H), 8.16 (dd, JHH = 1.2, JHP = 9.1 Hz, 1 H), 8.02 (m, 1
4
3
to room temperature, the solvent was removed under vacuum. The H). 13C{1H} NMR (CD2Cl2): δ = 114.9 (d, JCP = 13.1 Hz), 116.2
3
residue was dissolved in CH2Cl2 and an appropriate amount of silica (2C), 120.5 (d, 3JCP = 13.1 Hz), 127.9, 128.1 (2 C), 128.1, 128.3, 129.3
1358
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© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 1354–1360

Surface Reactivity of Functionalized Phosphinines on Inorganic Supports
2
2
(2 C), 129.4, 131.4 (d, JCP = 11.9 Hz, C3/C5), 131.6 (d, JCP
=
=
3a: from 1a (100 mg, 0.28 mmol) and AuCl(tht) (90 mg, 0.28 mmol).
12.2 Hz, C3/C5), 136.7 (d, 2JCP = 24.8 Hz, C-α of Ph), 142.5 (d, 3JCP
Yield: 150 mg (91 %); m.p. 202 °C. C23H17O2P1Cl1Au1 (588.78):
3.3 Hz, C4), 143.6 (d, JCP = 24.4 Hz, C-α of Ph), 144.4, 144.6 (2 C), calcd. C 46.92, H 2.91; found C 47.84, H 3.53. 31P{1H} NMR
2
4
1
1
3
144.8 (d, JCP = 2.1 Hz), 171.2 (d, JCP = 51.7 Hz, C2/C6), 171.6 (d, (CD2Cl2): δ = 152.40. H NMR (CD2Cl2): δ = 6.88 (dd, JHH = 0.8,
1JCP = 51.2 Hz, C2/C6). MS (EI, 70eV): m/e (%) = 356.1 (100) [M+]. 4JHP = 8.2 Hz, 1 H), 7.18 (dt, JHH = 2.2, JHP = 8.1 Hz, 1 H), 7.28–
4
3
7.35 (m, 1 H), 7.41–7.57 (m, 6 H), 7.77–7.88 (m, 4 H), 8.44 (dd,
3
4
4JHH = 1.6, JHP = 22.4 Hz, 1 H, H at C3/C5), 8.52 (dd, JHH = 1.6,
4-(2,3-dihydroxyphenyl)-2,6-diphenylphosphinine 1b: from 2b
(700 mg, 1.8 mmol) and BBr3 (9 mL 1 m soln in CH2Cl2, 9 mmol).
Yield: 400 mg (62 %); m.p. 165 °C. C23H17O2P1 (356.36) with ethyl
acetate: C 72.96, H 5.67; found C 72.43, H 5.00. 31P{1H} NMR
(CD2Cl2): δ = 185.3. 1H NMR(CD2Cl2): δ = 4.85 (br., 2 H, OH), 6.58–
3JHP = 22.4 Hz, 1 H, H at C3/C5).
3b: from 1b (100 mg, 0.28 mmol) and AuCl(tht) (90 mg, 0.28 mmol).
Yield: 0.16 g (97 %); m.p. 208 °C. C23H17O2P1Cl1Au1 (588.78): calcd.
C 46.92, H 2.91; found C 47.97, H 3.43. 31P{1H} NMR (CD2Cl2): δ =
6.81 (m, 4 H), 7.18–7.23 (m, 5 H), 7.65–7.68 (m, 4 H), 8.08 (d, 3JHP
=
1
3
5.7 Hz, 2 H). 13C{1H} NMR (CD2Cl2): δ = 115.1, 121.0 (2 C), 122.4,
153.17. H NMR (CD2Cl2): δ = 6.74–6.86 (m, 2 H), 6.93 (dd, JHH
=
1.6, 4JHP = 7.2 Hz, 1 H), 7.45–7.57 (m, 6 H), 7.84–7.88 (m, 4 H), 8.57
127.5 (2 C), 127.9 (2 C), 128.1 (2 C), 128.7, 129.2 (2 C), 133.4 (d,
3
3JCP = 12.1 Hz, C3/C5, 2 C), 140.3 (d, JCP = 13.9 Hz), 141.5 (d,
3
(d, JHP = 22.7 Hz, 2 H, H at C3/C5). MS (ESI): m/e (%) = 587.02
(100) [M+–H].
3JCP = 1.8 Hz, C4), 143.6 (d, JCP = 24.1 Hz, C-α of Ph, 2 C), 144.7
2
1
(2 C), 171.9 (d, JCP = 52.8 Hz, C2/C6, 2 C). MS (EI, 70eV): m/e
1a/NP-TiO2: Phosphinine 1a (150 mg, 0.25 mmol) was dissolved in
CH2Cl2 (20 mL). The solution was added to a suspension of TiO2
(1.00 g) in CH2Cl2. The suspension was stirred for 24 h. Afterwards
the solid was filtered off, washed with CH2Cl2 (3 × 20mL), and dried
under vacuum.
(%) = 356.1 (100) [M+].
2-(3-Hydroxyphenyl)-4,6-diphenylphosphinine
1c: from
2c
(700 mg, 2.0 mmol) and BBr3 (9.9 mL 1 m soln in CH2Cl2,
9.9 mmol). Yield: 410 mg (61 %); m.p. 183 °C. C23H17O1P1 (340.36):
calcd. C 81.17, H 5.46; found C 81.33, H 5.32. 31P{1H} NMR
(CD2Cl2): δ = 184.2. 1H NMR (CD2Cl2): δ = 3.96 (br., 1 H, OH), 6.58
(m, 1 H), 6.98 (m, 1 H), 7.05 (m, 1 H), 7.12–7.28 (m, 7 H), 7.39–7.45
3a/NP-TiO2 and 3b/NP-TiO2): A solution of the phosphinine com-
plex 3a (or 3b) (150 mg, 0.25 mmol) in thf (20 mL) was added to
TiO2 (1.00 g). The suspension was stirred for 24 h. Afterwards the
solid was filtered off, washed with thf (3 × 20 mL), and dried under
vacuum for 8 h.
(m, 2 H), 7.64–7.69 (m, 2 H), 8.08 (d, JHP = 5.8 Hz, 2 H). 13C{1H}
3
3
4
NMR (CD2Cl2): δ = 114.7 (d, JCP = 12.7 Hz), 115.0 (d, JCP
=
2.1 Hz), 120.1 (d, 3JCP = 13.3 Hz), 127.91, 127.94, 128.0 (2 C), 128.1,
129.0 (4 C), 130.0, 131.8 (d, JCP = 10.2 Hz, C3/C5), 132.0 (d, 3JCP
=
=
=
3
Chloropropyl-modified HMS: A mixture of calcined HMS (3.00 g)
in anhydrous toluene (50 mL) and (3-chloropropyl)triethoxysilane
(2.16 g, 9.0 mmol) was heated under reflux for 24 h. The solid was
filtered off, washed with toluene (3 × 50 mL), and dried under vacuum
at 80 °C for 8 h.
3
2
10.2 Hz, C3/C5), 142.4 (d, JCP = 3.2 Hz, C4), 143.6 (d, JCP
3
2
24.1 Hz, C-α of Ph), 144.2 (d, JCP = 13.6 Hz), 145.0 (d, JCP
1
24.6 Hz, C-α of Ph), 156.7 (2C), 171.6 (d, JCP = 52.3 Hz, C2/C6),
1
171.9 (d, JCP = 52.5 Hz, C2/C6). MS (EI, 70eV): m/e (%) = 339.09
(100) [M+–H].
Immobilisation of 1c on chloropropyl-HMS: Triethylamine (0.89 g,
8.8 mmol) was added to a suspension of chloropropyl-HMS (0.85 g)
in toluene (7 mL). The mixture was cooled to –78 °C, and a solution
of 1c (300 mg, 0.88 mmol) in CH2Cl2 (5 mL) was added dropwise.
The suspension was allowed to warm slowly to room temp. while stir-
ring was continued for 24 h. Afterwards the solid was filtered off,
washed successively with toluene (3 × 20 mL) and CH2Cl2 (3 ×
20 mL), and dried under vacuum for about 8 h.
General Procedure for the Synthesis of Phosphinine Com-
plexes
The phosphinine (1 equiv.) and AuCl(tht) (1 equiv.) were weighed in-
side a glove box. Freshly distilled CH2Cl2 (for 4a) or thf (for 3a/b)
was then added and the mixture stirred for 15 min. Completion of the
reaction was checked by 31P NMR spectroscopy. Reduction of the vol-
ume in vacuo followed by hexane precipitation afforded the complexes
as pale yellow solids.
Single Crystal X-ray Diffraction Study of 4a
Bruker-Nonius Kappa-CCD diffractometer at 123(2) K using Mo-Kα
radiation (λ = 0.71073 Å). Direct Methods (SHELXS-97 [19]) were
used for structure solution and full-matrix least-squares refinement on
F2 (SHELXL-97 [19]). Hydrogen atoms were localised by difference
Fourier synthesis and refined using a riding model.
4a: from 2a (110 mg, 0.36 mmol) and AuCl(tht) (110 mg, 0.36 mmol)
in CH2Cl2 (5 mL). Yield: 110 mg (96 %); m.p. 142 °C.
C25H21O2P1Cl1Au1 (616.83): calcd. C 44.50, H 3.30; found C 44.47,
1
H 3.21. 31P{1H} NMR (CD2Cl2): δ = 152.39. H NMR (CD2Cl2): δ =
4
3.93 (s, 3 H), 3.99 (s, 3 H), 7.05 (d, JHP = 8.0 Hz, 1 H), 7.36 (dt,
3
4JHP = 8.2, JHH = 2.1 Hz, 1 H), 7.41–7.42 (m, 1 H), 7.49–7.59 (m, 6
4a: yellow-orange crystals, C25H21AuClO2P, M = 616.80, crystal size
3
H), 7.70–7.74 (m, 2 H), 7.78–7.83 (m, 2 H), 8.40 (dd, JHP = 22.7,
¯
0.30 × 0.20 × 0.15 mm, triclinic, space group P1 (No. 2): a =
4JHH = 1.7 Hz, H at C3/C5, 1 H), 8.49 (dd, 3JHP = 22.7, 4JHH = 1.7 Hz,
11.376(1) Å, b = 14.232(2) Å, c = 21.024(2) Å, α = 101.68(1) °, β =
98.86(1) °, γ = 92.83(1)°, V = 3282.2(6) Å3, Z = 6, ρ(calcd) = 1.872
Mg·m–3, F(000) = 1788, μ = 6.94 mm–1, 63463 reflexes (2θmax = 55°),
14992 unique [Rint = 0.035], semiempirical absorption correction from
equivalents, max. and min. transmission 0.4305 and 0.2368, 817 pa-
rameters, 0 restraints, R1 [I > 2σ(I)) = 0.023, wR2 (all data) = 0.046,
GooF = 1.07, largest diff. peak and hole 0.777 and –1.230 e·Å–3.
H at C3/C5, 1 H). 13C{1H} NMR (CD2Cl2): δ = 55.1, 55.3, 111.07,
3
4
111.10, 111.13, 120.1 (d, JCP = 12.7 Hz), 126.9 (d, JCP = 3.3 Hz),
127.6 (d, 3JCP = 11.6 Hz), 128.0 (d, 4JCP = 1.1 Hz), 128.4 (4 C), 128.5
(d, 4JCP = 2.1 Hz), 130.4 (d, 3JCP = 12.3 Hz), 135.0 (d, 2JCP = 10.1 Hz,
2
2
C3/C5), 135.2 (d, JCP = 10.6 Hz, C3/C5), 138.0 (d, JCP = 12.0 Hz),
2
3
139.8 (d, JCP = 5.7 Hz), 142.8 (d, JCP = 26.2 Hz, C4), 149.0, 149.9
4
1
1
(d, JCP = 2.2 Hz), 158.8 (d, JCP = 36.1 Hz, C2/C6), 158.8 (d, JCP
=
36.1 Hz, C2/C6). MS (EI, 70eV): m/e (%) = 616.0 (100) [M+], 384.1 Crystallographic data (excluding structure factors) for the structure re-
(50) [M+–AuCl].
ported in this work have been deposited with the Cambridge Crystallo-
Z. Anorg. Allg. Chem. 2010, 1354–1360
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 1359

S. Komath Mallissery, M. Nieger, D. Gudat
ARTICLE
de Jong, C. A. van Walree, R. J. M. Klein Gebbink, G. van Ko-
ten, Adv. Synth. Catal. 2007, 349, 2619–2630; Y. Yang, B. Beele,
J. Blümel, J. Am. Chem. Soc. 2008, 130, 3771–3773.
graphic Data Centre as supplementary publication no. CCDC-756491.
Copies of the data can be obtained free of charge on application to
The Director, CCDC, 12 Union Road, Cambridge DB2 1EZ, UK (Fax:
+44-1223-336-033; E-Mail: deposit@ccdc.cam.ac.uk).
[6] F. R. Hartley, Supported Metal Complexes (Eds.: R. Ugo, B. R.
James), D. Reidel, Dordrecht, Holland, 1985 and literature cited
therein; An overview on state-of-the-art techniques is given in
J. A. Gladysz, Chem. Rev. 2002, 102, 3215.
Acknowledgement
[7] C. Müller, L. G. Lopez, H. Kooijman, A. L. Spek, D. Vogt, Tetra-
hedron Lett. 2006, 47, 2017–2020; C. Müller, D. Wasserberg,
J. J. M. Weemers, E. A. Pidko, S. Hoffmann, M. Lutz, A. L.
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Financial support by the Deutsche Forschungsgemeinschaft (Graduate
College 448 “Modern NMR Methods in Material Science”; scholarship
for S.K.M.) is gratefully acknowledged. M.N. also thanks the Finnish
Academy.
[8] N. T. Lucas, J. M. Hook, A. M. McDonagh, S. B. Colbran, Eur.
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Received: December 2, 2009
Published Online: March 8, 2010
1360
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© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 1354–1360